NREL Style Guide Full Text

---

508 compliance

As a leading, respected national laboratory, NREL must ensure that its publications and content are accessible to all people. Specifically, we must ensure that everything is “508 compliant.”

What It Means

In 1998, Congress amended the Rehabilitation Act of 1972 to require federal agencies to make their electronic and information technology accessible to people with disabilities. For example, individuals using assistive technology (such as JAWS, a computer screen reader program) can read a document that is 508 compliant.

What It Involves

All graphs, graphics, animations, fact sheets, and so on must be accessible. Further, videos, animations, and audio files must be 508 compliant. These media types require text versions.

Working with a communications representative will ensure that your content goes through the proper process and is 508 compliant before publishing.

**Don’t Forget To Add Alt Text!**

A key part of ensuring 508 compliance involves adding alt text for every figure and photo in technical reports, fact sheets, articles, web pages, social media, and so on. Alt text provides a semantic meaning or description of the image. It can also be read by search engines. 

Keep It Simple

Imagine if, instead of reading a document, you had to listen to it being read to you. By keeping this in mind, you can write alt text that is clear and descriptive. To help, see the following examples of alt text—one for a photo and one for an illustration. For more complicated figures or graphs, try to provide a high-level overview of what is being shown (versus describing every detail).

Alt text: Eagle flying out of a cage with wind turbines in the background.

Alt text: Illustration of spar-buoy, barge, and tension-line floating offshore wind turbines in the ocean, with foundations anchoring them to the seabed.

For more information on accessibility and alt text, review NREL’s Communication Standards.

Subjects:  Government Terms, Publication Formatting, Publication Policies and Services

---

a and an

Use "a" before any acronym or word that begins with a consonant sound. Use "an" before any acronym or word that begins with a vowel sound. An acronym is pronounced as a word (for example, a HEPA filter); an initialism is pronounced as its letters (for example, an NGO). The first sound of the word or letters indicates whether to use "a" or "an." Examples: a light-water reactor, an LWR; a Human Resources Office memo, an HRO memo; a nongovernmental organization, an NGO; a National Renewable Energy Laboratory subcontract, an NREL subcontract.

Subject:  Grammar and Usage

---

abbreviations and acronyms

Subjects:  Data and Measurement, Writing Style

---

abstracts

An abstract usually accompanies a journal article or conference paper. It is an important indexing and research tool. Abstracts are usually 200 to 250 words in length and the content summarizes and highlights the major points of the journal article, conference paper, or report. It may also include a brief description of the purpose, scope, and methods used to reach the conclusions.

Some journals and conferences ask that you submit an abstract that briefly describes the paper’s purpose and contents before your submission is accepted. Check with the journal or conference sponsor for guidance on abstract requirements such as length.

Abstracts for NREL Publications

The U.S. Department of Energy’s Office of Scientific and Technical Information requires an abstract of 200 words or fewer for its citation record posting. This abstract is also typically included in the metadata of the final publication PDF and should briefly describe the context, purpose, and nature of the work and summarize major results or conclusions.

Subject:  Publication Formatting

---

academic degrees

Avoid the use of academic degrees unless it's absolutely necessary to establish credentials. If so, use the following abbreviations with periods included after a name and set them off with commas: Ph.D., B.A., M.A., and LL.D. Use them only on first reference. Also, use an apostrophe in bachelor's degree, a master's, etc., but there is no possessive in Bachelor of Arts or Master of Science, for example.

When possible, avoid using Dr. before the names of individuals who hold doctoral degrees, such as Ph.D. Instead, when necessary or appropriate, write out the name of the person’s degree.

The academic subject of the degree should be lowercase, except for proper nouns.

Subject:  Writing Style

---

acknowledgments

You may acknowledge the reviews, funding, and other assistance of individuals and groups in NREL technical reports and papers. Acknowledgments can go in a preface or foreword in a technical report, or they can be on a separate page if they are extensive. They also often follow the main text in professional journal articles. Journals usually contain examples or instructions for authors.

Subject:  Publication Formatting

---

active voice and passive voice

Try to write more active-voice sentences than passive-voice sentences. In other words, the subject of most of your sentences should be the "actor" or "agent" (who did it?) rather than the thing "acted upon."

Research shows that active voice helps even highly educated readers absorb information more quickly. Passive voice is no longer considered to be more scholarly or scientific than active voice. Active voice also lends clarity and vigor to technical writing. But sometimes passive voice is appropriate, especially when it's more important to emphasize what was done than who did it. Passive voice can add variety to your writing, too. See also personal pronouns.  

Subject:  Writing Style

---

addresses

Use U.S. Postal Service abbreviations (such as CO for Colorado and DC for District of Columbia) for states in bibliographies, references, and full addresses (those that include streets or post office boxes).

In text, when you refer to a state with a city or by itself (for example, "The state energy office is stepping up solar retrofit activities in Massachusetts."), spell out the name of the state in full, except for the District of Columbia (D.C.). See also states and countries.

Subject:  Geography

---

affect and effect

"Affect" is usually a verb, and "effect" is usually a noun.

affect (verb):

effect (noun):

These words can be confusing because "affect" can sometimes be a noun (when it denotes an emotion), and "effect" can be a verb (when it means "to bring about").

Subject:  Grammar and Usage

---

air conditioning

"Air conditioning" is two words when used as a noun and hyphenated when used as an adjective. 

Subject:  Writing Style

---

air-source heat pump

Subject:  Technology-Related Terms

---

Alliance for Sustainable Energy, the Alliance

The Alliance for Sustainable Energy LLC, equally owned and governed by Midwest Research Institute and Battelle, is the manager and operator of NREL (effective Oct. 1, 2008).

The appropriate term on second and subsequent references is "Alliance" as opposed to the acronym "ASE." Because many companies and groups have ASE as their acronym, this usage will help distinguish the Alliance. Also, because it is used as a proper second reference and not a generic term, the Alliance will remain capitalized for that usage.

Subject:  Government Terms

---

American Recovery and Reinvestment Act of 2009

After spelling out the full name on first reference, you may use "Recovery Act" in subsequent references instead of the acronym "ARRA." But when using "Recovery Act," do not identify it in parentheses after the full name like you would with the acronym.

Subject:  Government Terms

---

ampersands

Ampersands can be used in acronyms, left navigation, right navigation, and in a website's top banner (but not in the heading). Ampersands can also be used as the official name of a company or initiative, for example, PG&E or Leadership in Energy & Environmental Design. Do not use "&" to mean "and" in other situations.

Subject:  Writing Style

---

appendices

You can include detailed background or technical information, derivations, equations, or data tables in one or more appendices. Large, detailed tables are often placed in an appendix. If you have more than one appendix, title them with letters (Appendix A, B, C, etc.). If you have only one appendix, title it "Appendix" rather than "Appendix A." Name figures and tables in appendices so they reflect the title (Figure A-1, Table B-2, etc.). In the case of only one appendix, use the “A-1” convention for figures and tables. 

Subject:  Publication Formatting

---

assure, ensure, and insure

"Assure" means to make sure or give confidence. "Ensure" means to guarantee. "Insure" means to provide or obtain insurance.

Subject:  Grammar and Usage

---

author-date citations

This is the preferred style for NREL reports and papers. Do not use a comma between the author's last name and the year: (Smith 2000). See also references.

Subjects:  Publication Formatting, Writing Style

---

bandgap

"Bandgap" is one word.

Subject:  Technology-Related Terms

---

baseload

"Baseload" is one word when used as a noun or adjective.

Subject:  Technology-Related Terms

---

because and since

"Because" indicates a cause-and-effect relationship. "Since" indicates a time relationship.

Subject:  Grammar and Usage

---

bibliography

A bibliography, which is different from a reference list, is a list of works that are related to your subject or publication but not cited, either by author or by number, in the text. Alphabetize works in bibliographies according to the last name of the first author. You may use NREL's reference style in listing the works if you don't have other guidelines (e.g., from a journal). Some bibliographies are titled "For Further Reading." Compile your in-text citations of literature and other sources in a list of references.

Subject:  Publication Formatting

---

black start

When used as a noun, “black start” is two words. Hyphenate “black-start” when it is used as a modifier. Avoid using as a verb if possible.

Subject:  Technology-Related Terms

---

BOS

BOS stands for balance of systems (not system).

Subject:  Technology-Related Terms

---

British thermal units

The abbreviation for "British thermal unit" is Btu. "Btu" is used for both singular and plural cases.

Subject:  Data and Measurement

---

bullets

Bullets are printed to the left of items in a list. You must have at least two items in a bulleted list.

Report Formatting
In text, the first level of bullet is indented 0.25 in., and text begins at the 0.5-in. mark. This level is bulleted with a solid dot. Second-level bullets are open dots, and third-level bullets are em dashes (—). Each subsequent level of bullet is sequentially indented 0.5 in. In lists with items that are more than one line, each bulleted item is followed by a 6-pt. space. 

On the Web 
For web content (and for PowerPoint slidesand figures), terminal punctuation for a bulleted list is optional when there is no lead-in sentence. Use best judgmentand remember that consistency is key. When formatting bullets on the web, there should be a space between the text above the bullets and the first bullet. To facilitate scanning, consider adding a blank line between each bulleted item when the bulleted text is long. Do not use bullets with lists of links.

Subject:  Publication Formatting

---

capitalization

1. Proper Nouns

Capitalize proper names. These include the names of government programs, official projects, formal groups, organizations, companies, titles when they precede a name (use lowercase in titles that follow the name), specific geographic areas or features, and ethnic groups.

When referring to NREL, "National Renewable Energy Laboratory" is capitalized, but "the lab," "the laboratory," and "national laboratories" are not.

One exception to this rule is companies and products with stylized lowercase or "camel cap" names (e.g., eBay, iPhone). In these cases, use the company’s or product’s preferred capitalization.

2. Figure Captions, Table Titles, and Section Headings

Figure captions: Capitalize only the first word and proper nouns in figure captions. No period needed (unless there are multiple full sentences).

Table titles and section headings: Capitalize the main words of table titles and headings and subheadings, including the second word in a hyphenated term (e.g., "PV Program Five-Year Plan"). No period needed.

Do not capitalize:

• Articles (e.g., "a," "an," and "the") unless they begin the title or heading
• Conjunctions of three or fewer letters (e.g., "and," "or," "nor," "yet," "so," and "but")
• Prepositions of three or fewer letters (e.g., "for," "of," "on," and "up").

Do capitalize:

• Conjunctions (e.g., "than") and prepositions of four or more letters (e.g., “from,” “with,” “above,” “after,” “down,” “inside,” “over,” and “into”)
  
• "To" as an infinitive (but lowercase as a preposition, e.g., “Scientists Travel to Chile To Engage Utilities”)
• Verbs, including "is" and "are."
  

For journal/conference submissions or other non-NREL publications, follow the style recommended by the professional society or publisher.

3. Titles

Capitalize titles when they precede the person's name. Lowercase titles and names of groups when they follow the name.

4. Trade Names

Capitalize trade or brand names, and include a trademark, copyright, or other symbol only when it's an Alliance-registered trademark. Include the symbol the first time you use the trade name in body text (not in a title, acronym list, or section header); thereafter, you may omit the symbol. Also use superscript for trademark symbols. See the trademark symbols entry for a list of Alliance trademarks.

5. Taxonomic Names

When writing about botanical and zoological divisions, capitalize the names of all divisions higher than species: genera, families, orders, classes, and phyla. Italicize genera, species, and varieties.

After you first mention them (and spell them out), you can abbreviate most generic names followed by species names.

See also captions, fiscal year, geographic regions, headings and subheadings, states and countries, and tables.

Subjects:  Grammar and Usage, Writing Style

---

captions

Each substantive photo and image should be accompanied by a caption. Capitalize the first word in a caption and use lowercase thereafter, except for proper nouns and capitalized abbreviations. You don't need a period at the end of a caption unless there is additional text below the caption such as a figure note or the caption includes multiple complete sentences.

For information about figure captions, see figures.

See also  photo, image, and video credits.

Subject:  Publication Formatting

---

chemical terms

Do not use a hyphen in most chemical expressions, even when the terms are used as modifiers.

Use a hyphen after prefixes when that's the standard for certain chemical formulas.

Use a hyphen to indicate mixtures or combinations.

Subject:  Technology-Related Terms

---

citations

See references and citations for guidance on author-date and numbered citations.

Subject:  Publication Formatting

---

cleantech

"Cleantech" is spelled as one word. It is not hyphenated, and the "t" is not capitalized. The word "cleantech" is typically used in reference to investments in sustainable technologies, including renewable energy and energy efficiency. Don't use as a shortened form of "clean technology" in other references.

Subject:  Technology-Related Terms

---

close-spaced sublimation

The term is "close-spaced sublimation," not "closed-space sublimation."

Subject:  Technology-Related Terms

---

cogeneration

Subject:  Technology-Related Terms

---

colons

Colons formally introduce a list or series, a question, or an amplification.

When the colon is followed by a complete sentence, capitalize the first letter of the first word after the colon.

Colons also often separate the parts of a ratio.

However, commas, not colons, usually follow words such as "that is," "namely," and "for example." You don't need a colon after a verb or preposition that precedes or introduces a list ("includes," "to," "with," "between," etc.). Use a colon when a noun (such as "the following") introduces a list in the text.

Subject:  Punctuation

---

commas

1. When To Use Commas

Use a comma to separate items in a series, including the next-to-last word in the series.

Use a comma to separate the parts of a compound sentence linked by a coordinating conjunction (such as "and," "but," "or," and "nor") when each part has its own subject and verb (unless they're very short).

Use commas to set off nonessential or nonrestrictive (parenthetical) words, phrases, and clauses from the rest of the sentence. In other words, the commas signal that the information between them is something extra and not essential to the meaning of the sentence.

Use commas to enclose the name of a state when it follows a city and a year when it follows the month and day.

2. When Not To Use Commas

Do not use a comma to separate compound subjects or compound verbs.

Do not use commas to set off words or phrases that are restrictive (i.e., essential to the meaning of a sentence).

See also which and that.

Subject:  Punctuation

---

compose and comprise

"Composed of" is correct; "comprised of" is incorrect. See the examples below.

Subject:  Grammar and Usage

---

concentrating solar power

Concentrating solar power (CSP) captures the sun’s heat and uses the thermal energy to produce electricity (e.g., via a steam turbine).
Subject:  Technology-Related Terms

---

Congress and congressional

Capitalize "U.S. Congress" and "Congress" when referring to the U.S. Senate and House of Representatives. Lowercase "congressional" unless it is part of a proper name.

Subject:  Government Terms

---

contents

See table of contents. For a list of all the content a report may include, see  report contents.

Subject:  Publication Formatting

---

contiguous United States, continental United States, and CONUS

"Contiguous" means sharing a common border; "continental" means belonging to a continent. In its strictest sense, “contiguous United States” refers to the lower 48 states in North America (including the District of Columbia), and "continental United States" refers to 49 states (including Alaska and the District of Columbia). However, the terms are often confused and used inconsistently. Best to specify the meaning on first use of the phrase.

Follow the acronym rules if using CONUS, but specify which states the phrase covers on first mention.

Subject:  Writing Style

---

cooperative research and development agreement

Use lowercase for "cooperative research and development agreement" because it's not a proper noun. On second reference, you can use the acronym "CRADA."

Subject:  Government Terms

---

coproduction

Subject:  Technology-Related Terms

---

CPV

CPV (concentrating photovoltaics) uses lenses to intensify the sunlight striking PV cells, which enhances the cells' electricity production.

Subject:  Technology-Related Terms

---

criterion, datum, memorandum, phenomenon, and their plurals

"Criterion" is a singular noun (one criterion), and "criteria" is the plural (two or more criteria). "Data" is the plural of "datum." The plural of "memorandum" can be either "memoranda" or "memorandums." "Phenomenon" is singular, and "phenomena" is plural.

Subjects:  Data and Measurement, Grammar and Usage

---

cyber

Follow the general rule for prefixes and do not use a hyphen:

Exceptions: Cyber Monday (n.) and cyber (adj.) as a separate modifier, e.g., cyber shopping and cyber liability insurance.

See the Associated Press Stylebook for more guidelines.

Subjects:  Websites, Writing Style

---

dashes

Use dashes (often called "long dashes" or "em dashes") to enclose and set off parenthetical (nonessential but often illustrative) information in a sentence. Also use dashes to set off a list of items separated by commas. Do not add spaces around the dash.

Use an em dash to signal that an important point is going to be made or that a change in the construction of the sentence follows.

You can usually use commas, colons, and semicolons in place of dashes, but dashes add special emphasis.

Use shorter dashes known as "en dashes" (rather than a hyphen or em dash) to indicate a range or to substitute for the word "to."

In date spans, do not use "from" in conjunction with an en dash (e.g., "from Jan. 16–Feb. 3"). The correct form is "from Jan. 16 to Feb. 3" or "Jan. 16–Feb. 3."

Do not use an en dash (or hyphen) to mean "and"; the word "between" is followed by the word "and" (not "to"): between 25 and 30.

Subject:  Punctuation

---

data in tables

Place a zero to the left of the decimal in any number less than 1 in text and tables (e.g., 0.5, 0.039). Align columns of data vertically on the decimals. When the units of measurement for the data are different, alignment is not necessary (but be sure to specify the units).

Subject:  Data and Measurement

---

dataset

“Dataset” is spelled as one word.

Subject:  Data and Measurement

---

decision maker

Subject:  Writing Style

---

degree symbol

Do not include a space before or after the degree symbol.

Repeat the degree symbol in ranges.

Express kelvins as K rather than as °K; leave a space before the K.

Subject:  Data and Measurement

---

dish/engine systems

Use a slash rather than a hyphen.

Subject:  Technology-Related Terms

---

dollars

Express thousands of dollars using a comma.

Express millions and billions of dollars this way.

Do not use a hyphen to join a number and words such as “million” or “billion,” even when used as a unit modifier.

In technical reports and papers, use a dollar sign to express costs less than $1.

Subject:  Data and Measurement

---

"e-" terms

Email is acceptable in all references for "electronic mail." Use a hyphen with other e- terms: e-book, e-business, e-commerce, e-fuel. 

Subject:  Writing Style

---

ellipses

When you want to leave out part of text material you are quoting, use ellipsis marks (three dots with a space on each side) to indicate the omission.

If the words before the ellipses form a grammatically correct sentence, put a period at the end of the sentence and follow it by ellipses. In most cases, however, you don't have to use ellipses at the beginning or end of quotes, just within them. When you add a word or words to the quote, to make it clear, enclose the added word or words in brackets to show that it is not part of the original quotation.

When you quote whole paragraphs but omit text between any two of them, center three asterisks, with spaces between them (* * *), between the paragraphs quoted. See also quotation marks.

Subject:  Punctuation

---

energy efficient

Subject:  Punctuation

---

ENERGY STAR

ENERGY STAR is always in capitals. Use ENERGY STAR^® the first time it is used on a page; thereafter, use ENERGY STAR. The ® should be superscript, and there's no space between the ® and ENERGY STAR.

Subject:  Government Terms

---

enhanced geothermal system

The preferred term is "enhanced geothermal system." It is also sometimes referred to as an "engineered geothermal system."

Subject:  Technology-Related Terms

---

equations

Make sure that all the terms in your equations are defined and used consistently both in the text and in subsequent equations, figures, and tables.

Subject:  Data and Measurement

---

etc.

Because it's vague, use "etc." (et cetera) sparingly. Don't add it to the end of a list beginning with "for example," or the abbreviation "e.g.," because each word in your list is an example of your subject or topic, but "etc." is not, so you don't need it.

Subject:  Writing Style

---

executive summary

If you include a summary in a report, place it before the table of contents page. If your report is brief, a summary is not usually necessary. If your report is long, or if you think some readers will want one, you can include an executive summary.

An executive summary can be up to 5% to 10% of the length of your paper. It should be written so that it can be read independently of the full report, as executive summaries are frequently published as a separate document. Its content should include a brief statement of the problem or proposal covered in the report, background information, concise analysis, and the main conclusions. Furthermore, it should be written in plain language, where technical language is defined or examples/further context are provided, making it easy for nontechnical readers to understand.

Subject:  Publication Formatting

---

exergy

Subject:  Technology-Related Terms

---

federal

Use a capital letter with "federal" for corporate or governmental bodies that use the word as part of their formal names.

Use lowercase when the word is used to distinguish something from state, county, city, etc. entities.

Subject:  Government Terms

---

figures

Figures can include line drawings, graphs, charts, diagrams, schematics, flowcharts, illustrations, and photographs. Be sure that computer-generated figures are clear and readable, so they can be reproduced easily. Make sure the data in your figures correspond to the data in your text and tables.

Number figures in a simple sequence (e.g., Figure 1, Figure 2). In long reports, papers, or book chapters, you may include section or chapter numbers in the figure numbers (e.g., Figure 1-1, Figure 1-2, Figure 2-1, and so on).

Use 10-pt. Arial bold for captions. The caption is centered under the illustration. For data charts and graphs, use 9-pt. Arial for source lines below the figure. See also captions.

Figure 1. Renewables as a percentage of total installed capacity worldwide

No period is needed after a caption if it is an incomplete sentence (see Figure 1 above). If one or more full sentences follow the incomplete sentence (as a continuing caption or subcaption), each caption (including the opening incomplete sentence) should have a period. Don’t bold subcaptions. See Figure 2-1 below for an example.

As required, appropriate credit and Image Gallery information should be provided for figure images. See photo and image credits. Place credit information after the caption.

Subject:  Publication Formatting

---

first-person pronouns

See personal pronouns.

Subjects:  Grammar and Usage, Writing Style

---

fiscal year

Spell out "fiscal year" (e.g., Fiscal Year 2024) the first time you use it; after that, you can abbreviate it using two capitals followed by a space before the full year (e.g., FY 2024). FY24 may be used to save space in charts and graphs. On the web, always spell out fiscal year.

Subject:  Dates

---

fonts

Use Times New Roman for the text of NREL technical papers and reports. Use Arial for figures, tables, and headings.

Subject:  Publication Formatting

---

footnotes

You can use footnotes to place detailed explanatory or supplementary information at the bottom of a page; use in-text references to cite others' works. Use superscript numerals for footnote numbering. You can also place explanations, details, contradictions, and examples in the text rather than in footnotes. Footnote numbers are printed outside commas and periods but inside colons, semicolons, and dashes.

Mark the footnotes to tables in NREL reports with superscript letters: ^a, ^b, ^c, etc.

Subject:  Publication Formatting

---

foreword

The foreword to a book or formal report contains introductory remarks written, and usually signed, by someone other than the author or authors. Brief introductory remarks written by authors are contained in a preface.

Subject:  Publication Formatting

---

fractions

Use words instead of numerals for simple fractions in text.

Write out complex fractions with numerals separated by a solidus.

Display complex, built-up fractions by centering them vertically between two parts of a paragraph.

Place a zero to the left of the decimal in fractions less than 1.

See also equations.

Subject:  Data and Measurement

---

front matter and back matter

NREL reports can include front and back matter in the following order:

Front Matter

1. Title page
2. Disclaimer
3. Foreword
   
4. Preface
   
5. Acknowledgments
   
6. Nomenclature
   
7. Executive summary
   
8. Table of contents
   
9. Lists of figures and tables

Back Matter

1. Glossary
   
2. Reference list
   
3. Bibliography
   
4. Appendices

Paginate front matter with small Roman numerals (i, ii, iii) rather than Arabic numbers. Count the title page as page i, but don't print the number on it. All technical reports should contain a title page, a disclaimer, and a table of contents. Many outreach publications, such as DOE/NREL program overviews, contain only a contents list and brief acknowledgments in the front matter.

Subject:  Publication Formatting

---

geofluid

Subject:  Technology-Related Terms

---

geographic information system

Do not capitalize "geographic information system" unless used as part of a proper noun. It's also "geographic," not "geographical." Our acronym style guidelines apply as well.

Subject:  Writing Style

---

geographic regions

Don't capitalize words that describe general areas of the country or areas of a state.

Capitalize directional words when they designate specific or widely known regions; if in doubt, use lowercase.

Subject:  Geography

---

geopressured geothermal resource

Subject:  Technology-Related Terms

---

Geothermal Electric Technology Evaluation Model

Subject:  Technology-Related Terms

---

geothermal heat pump

Subject:  Technology-Related Terms

---

glossary and nomenclature

If you use many mathematical or Greek symbols or technical terms in your report or paper, consider defining them in a glossary or nomenclature. Arrange the list alphabetically, and group Greek letters and definitions alphabetically in a separate list. Nomenclatures are usually in the front of a report, before the contents page. Glossaries usually go in the back, before the references.

Subject:  Publication Formatting

---

Google Earth and Google Maps

When using satellite images from Google Earth and terrain images from Google Maps, include attribution to Google, which is included in Google images with copyright notices such as "© 2009 Google, Map Data © 2009 Tele Atlas." The Google logo and attribution text can be removed if they are added elsewhere within the image content.

In print, if attribution cannot be placed on the image or map, separate attribution text must be provided directly adjacent to it.

In video, attribution must appear on-screen for the duration of the time the map or image is shown; including attribution in end credits only does not suffice.

If the Google Earth image is altered (e.g., text or graphics are added), the image is legal only if Google Earth software is used to make the alteration and correct attribution is included. Any other alteration of the image using any other software is strictly prohibited.

Derivative works cannot be created. For example, NREL cannot combine multiple static map images to show a larger map.

Subject:  Publication Policies and Services

---

headings and subheadings

Here is a standard format for six levels of report subheadings:

You can number headings and subheadings (e.g., 1.0, 1.1, 1.2, 2.0) if that will help readers with a long report. Print text in 12-point Times New Roman.

Subject:  Publication Formatting

---

heat mining

Subject:  Technology-Related Terms

---

high-performance computing

“High-performance computing” should be hyphenated. The abbreviation HPC can be used to refer to high-performance computing but should not be used to mean high-performance computer. However, the term "supercomputer" may be used in place of high-performance computer.

Subjects:  Punctuation, Technology-Related Terms

---

hybrid electric vehicle

This phrase contains no hyphens.

Subject:  Technology-Related Terms

---

hyphens, compound words, and unit modifiers

Hyphenation rules can be intimidating, but remember that the ultimate goal is to provide as much clarity and consistency as possible. If you can’t find the proper hyphenation in this style guide, consult the AP Stylebook, followed by Merriam-Webster.

1. Verb Phrases: Verb, Noun, and Adjective Forms

Verb phrases that contain an adverb (e.g., build up, set up, start up, and break down) are usually written as two words. The noun and adjective forms of these words are usually one word, although there are exceptions.

2. Compound Words Containing Prefixes and Suffixes

In most cases, you don't need a hyphen between prefixes or suffixes and the root words.

Exceptions: 
Sometimes hyphens are needed when the root word begins with the same letter that the prefix ends in.

Use a hyphen between prefixes and proper nouns (but not common nouns) or dates whether they're used as nouns or modifiers.

Use two hyphens when adding a prefix to a word that already contains a prefix, even when there is no hyphen after the prefix in the original word.

Finally, these prefixes usually require a hyphen: "ex," "self," and "quasi."

3. Unit Modifiers With and Without Hyphens

Use a hyphen to indicate that words have been combined into a unit modifier, which is a descriptive expression composed of two or more words that form one new meaning. For example, in the term "flat-plate collector," "flat-plate" is the unit modifier. Here are some examples of unit modifiers that usually include hyphens:

To see how adding the hyphen can prevent confusion, consider these examples:

In the first example, the scientists might seem to have tested a defect; in the second example, it's clear that they tested a gas.

You don't need a hyphen in common unit modifiers that are not ambiguous or confusing.

Don't use a hyphen when both words of a unit modifier are capitalized.

Leave out the hyphens if you rewrite a sentence so the words in the unit modifier come after the noun they describe

Don't use a hyphen with a unit modifier containing an adverb ending in "-ly."

Don’t use a hyphen with two-word Latin phrases when the phrases are used as modifiers.

When you use numbers in unit modifiers, retain all the necessary hyphens. However, do not use a hyphen to join a number and words such as “million” or “billion.”

Or rewrite the sentence to omit the hyphens.

Use suspended hyphens when your compound modifier is interrupted by another word, such as part of a list.

Suspended hyphens can also be used for different prefixes on the same root word (micro- and mesoscale), but the preferred style is to write out each word fully (microscale and mesoscale). Use your best judgment, considering both the context and audience.

4. Common Hyphenated Terms

Certain words and phrases are always hyphenated, regardless of context. Examples include:

Subject:  Grammar and Usage

---

III-V solar cell

This term refers to a cell composed of semiconducting materials from Group III (e.g., gallium) and Group V (e.g., arsenic) elements of the periodic table.

Subject:  Technology-Related Terms

---

Inc. and LLC

Official company names can use the abbreviation “Inc.” or the initialism “LLC” without first defining these terms. Do not use commas around either term. 

Subject:  Writing Style

---

inclusive language

Subject:  Grammar and Usage

---

initialisms

An initialism is similar to an acronym, but it is pronounced by its letters. 

Use a small s (no apostrophe) for plurals of most initialisms (e.g., PUCs and CFCs, not PUC's or CFC's).

Avoid the use of initialisms unless they are used extensively in a document. In short reports, spell out initialisms that are used fewer than five times. In long reports, spell out initialisms that are used fewer than 10 times. If initialisms are used, spell them out on first use, and put the initialism in parentheses after the full name.

To avoid confusion, try not to use too many in any sentence or paragraph. Include a glossary or list of acronyms if your publication contains a lot of them.

On the Web
The above guidelines apply to web content as well. However, if you use an initialism, spell it out or define it the first time you use it on each webpage. On the web, spell out initialisms that are used fewer than three times.

Subject:  Writing Style

---

International and Non-English Speaking Audiences

If your audience is international, consider following an international style guide such as the United Nations Editorial Manual. If your text is in English, consider using British English. Use plain language. Keep sentences short. Write in active voice when possible. Avoid idioms and colloquialisms. Be aware of differences in style for currencies, dates, units, and addresses.

If you choose to translate content and are trying to reach a wider audience, select a standard dialect of Arabic, Chinese, an Indian language, or Spanish. Your NREL communications representative can help you choose both the appropriate translation for your audience and a contractor to provide the translation. If you translate content, have it reviewed by a person fluent in that language. NREL has a list of bilingual staff members who can help read, write, and translate many languages. Your NREL communications representative can provide you that list.

Subject:  Writing Style

---

internet

Lowercase "internet," except for the specific phrase "Internet of Things" (abbreviated IoT).

Subjects:  Websites, Writing Style

---

introduction

Introductions usually contain background information on the research being reported, the general nature and context of the work, and its results (the "big picture"). Earlier related work can also be described.

Subject:  Publication Formatting

---

inverters

Inverters convert direct current to alternating current.

Subject:  Technology-Related Terms

---

italics

1. Using Italics for Emphasis

Use italics (sparingly) to emphasize a word or phrase or bring attention to it.

2. Using Italics for Foreign Words and Phrases

Italicize such foreign words and phrases as terra incognita, in vivo, and inter alia; however, if the word or phrase is commonly used in your field (e.g., in situ, et al., ad hoc, ab initio), you may omit the italics.

3. Using Italics for Hyphenated Prefixes

Italicize hyphenated prefixes (such as cis-, trans-, o-, m-, and p-) to chemical formulas.

4. Using Italics To Cite Published Documents

Use italics for the names of books, journals, newspapers, magazines, and reports.

In print, the titles of journal and magazine articles are listed in regular roman type within quotation marks. On the web, omit the quotation marks.

5. Using Italics in Taxonomic Names

Unless you're discussing a genus in a general way, use italics to refer to specific genera, species, and varieties.

Subject:  Writing Style

---

it's and its

Even though "it's" has an apostrophe, it isn't a possessive pronoun. "It's" is a contraction, a short form of two words, like "isn't." "It's" always means "it is." "Its" is the possessive form of "it." Like "his," "hers," and "ours," the possessive "its" never needs an apostrophe.

Subject:  Grammar and Usage

---

Kalina cycle

Subject:  Technology-Related Terms

---

kilowatt (kW)

Subject:  Data and Measurement

---

kilowatt-hour (kWh)

Subject:  Data and Measurement

---

laboratory and lab

Only capitalize "laboratory" or "lab" when used with a laboratory's full name. Lowercase in all other references.

Subject:  Writing Style

---

life cycle

Subject:  Writing Style

---

lightbulb

"Lightbulb" is spelled as one word.

Subject:  Writing Style

---

lists

You can use bulleted or numbered lists in NREL publications or web pages. Here's an example of a numbered list:

You can also list a few items or procedures in paragraph format and number them (1) one, (2) two, (3) three, etc. See bullets for more formatting information.

On the Web

All of the above guidelines apply to the web. When formatting lists on the web, there should be a blank line between the text above the list and the first item listed. To facilitate scanning, consider adding a blank line between each listed item when the text for each one is long.

Subject:  Publication Formatting

---

lithology

Subject:  Technology-Related Terms

---

logos

Please visit the NREL Brand Lab for guidance on the proper use of the NREL logo, a library of downloadable logo files, and guidance on NREL branding.

---

low-e

Subject:  Technology-Related Terms

---

mathematical symbols

Leave a space on either side of mathematical symbols used as operation signs.

The solidus (a/b) or division sign is an exception. Do not leave a space between numerals and the symbols for degrees, dollars, and percent (32°, $100, 17%). (However, leave a space between numerals and symbols of measurement such as cm and Å.) Do not leave a space between symbols such as >, <, and ≥ and the numeral unless they are the operation signs in an equation.

Subject:  Data and Measurement

---

megawatt (MW)

Subject:  Data and Measurement

---

megawatt-hour (MWh)

Subject:  Data and Measurement

---

metric conversions

For quick online conversions of English units of measurement to metric units, see the Digital Dutch WWW Unit Converter website or IFP Reference Conversions on the French Property website.

Subject:  Data and Measurement

---

microgrid

"Microgrid" is spelled as one word.

Subject:  Writing Style

---

microseismic events

Subject:  Technology-Related Terms

---

misplaced modifiers

Modifiers in the wrong place can make a sentence confusing.

In this example, it isn't clear who or what identified the correct material. This might be better: After identifying the correct material, we conducted the 5-minute test procedure.

What, or who, was lost—the manuscript, the woman, or the reader? Try to keep modifiers as close as possible to the people and things they describe. Strunk and White, authors of The Elements of Style, say this: "Modifiers should come, if possible, next to the word they modify." This is especially true for sentences containing introductory prepositional phrases or clauses followed by a comma.

Subject:  Grammar and Usage

---

months and years

Capitalize the months in all uses. When a month is used with a specific date, abbreviate only Jan., Feb., Aug., Sept., Oct., Nov., and Dec. (Jan. 9, 2008). Also abbreviate these months in tables; however, omit the period. Spell out months when used alone or just with the year, and omit commas when the month and year appear together (October 2001).

Use a lowercase s (no apostrophe) to show the plural of a decade expressed with numerals (e.g., the 1990s).

Subject:  Dates

---

multijunction solar cell

This term is preferred over "tandem solar cell."

Subject:  Technology-Related Terms

---

multiplication symbols

Be as consistent as possible in using multiplication symbols in your paper or report. As appropriate, choose one symbol (× or ·), or omit the symbol and use proximity or parentheses: ab, (ab) (cd), etc.

Subject:  Data and Measurement

---

nation

Always use lowercase for the word "nation" when referring to the United States.

Subject:  Writing Style

---

net zero

When used as a noun, “net zero” is two words. It is also two words when referencing the Net Zero Labs program. Hyphenate “net-zero” when it is used as a modifier.

Subjects:  Government Terms, Technology-Related Terms, Writing Style

---

nonattainment

Spell as one word. Don't hyphenate.

Subject:  Writing Style

---

noncondensable gases

Subject:  Technology-Related Terms

---

nonrestrictive phrases and clauses

A nonrestrictive phrase or clause is one that adds information but is not essential to the meaning of the sentence.

Nonrestrictive or nonessential phrases and clauses are enclosed between two commas when the phrase or clause is within a sentence, and they usually begin with "which" rather than "that." See also restrictive phrases and clauses and which and that.

Subject:  Grammar and Usage

---

non-SI (English) units of measurement

Use non-SI (Systeme International d'Unites) or nonmetric units of measurement (English or Imperial units) instead of metric units only when they are the industry standard. Otherwise, state metric units first, followed by English equivalents in parentheses.

Subject:  Data and Measurement

---

noun and adjective strings

Try not to string too many nouns and adjectives together in a sentence. An "agency personnel communications interface display" could also be called a "display of the communications of the agency's personnel." Better yet, it could just be called the "staff bulletin board."

Subjects:  Grammar and Usage, Writing Style

---

nouns

To give your writing more flow and vigor, try changing some of the nouns (especially those ending in -tion and -ment) to verbs (e.g., determine, complete, accomplish, achieve, measure, convert, characterize, combine) and other parts of speech. Doing this will move your readers along more quickly and make it easier for them to understand your text. In these examples, we changed some of the nouns in the first sentences to verbs and other parts of speech.

Which sentences were easiest to read and understand?

Subject:  Grammar and Usage

---

NREL attribution statement

The NREL attribution statement, which recognizes NREL's affiliation with the U.S. Department of Energy and the Alliance for Sustainable Energy, is required on all NREL publications. In addition, note that a period is used on the "sentence" version of the statement.

Subjects:  Government Terms, Technology-Related Terms

---

numbers

1. Units of Measurement and Mathematical Expressions

Use numerals with units of measurement and time.

With units of time, you can spell out numbers less than 10 if you do so consistently (this applies mainly to outreach products rather than technical reports and papers).

Use numerals to imply arithmetical values or manipulation.

Express measurement errors as:

Leave a space between the number and the unit of measurement (0.2 nm) and put spaces around the operation sign. When the measurement error appears by itself, omit the space between the sign and the number.

2. Aligning Numbers

Align numbers that share a common unit of measurement on the decimals in columns of tables. Put a zero before the decimal in numbers smaller than one.

If all the numbers in a column do not share the same unit of measurement, you may center the numbers in the column and specify the unit of measurement.

3. Fractions and Decimals

You can spell out and hyphenate simple fractions (this is preferred in text) or express them, like more complex fractions, in numerals with a solidus.

Use a hyphen to separate the integral and fractional parts of a mixed number, or convert the fraction to a decimal.

For numbers of 1 million or more, use the numeral (and a decimal, if necessary) and the words million, billion, etc.

4. Precision and Numbers

Measurement uncertainty analysis calls for precision in measurements to a significant digit to the right of a decimal point, such as two or three digits (hundredths or thousandths). If you're not absolutely sure, check with an expert before changing the number of digits to the right of the decimal, or rounding the numbers. See also standard errors.

5. Punctuating Numbers

Use a comma to separate groups of three digits in numbers.

6. Ranges of Numbers

To show ranges, use an en dash (which is a little shorter than an em or long dash) with no spaces. Alternatively, if you write out a range, make sure you use the word "to" when you use "of" or "from" before the range. To express a range between some number and another number, always use the word "and" (not "to") with the word "between."

Note that some symbols, such as ° and %, are repeated in a range.

7. Scientific Notation

Express multiples of SI (metric) units in powers of 10 with the appropriate prefixes and technical abbreviations.

Use standard scientific notation to express very small and very large numbers.

Avoid using M to mean "thousands" and MM to mean "millions"; use a capital M for "mega," or millions, as in MW for "megawatts."

8. Spelling out Numbers

Except with units of measurement and time (in technical reports), spell out numbers less than 10.

Spell out all numbers at the beginning of a sentence.

In general, spell out numbers at the beginning of a bulleted item, but use best judgment depending on the context (e.g., a list of sentence fragments using numbers with many digits).

When a sentence contains one or more numbers greater than nine that are related to a smaller number, use numerals for all of them.

Spell out the first of two adjacent numbers unless the first one requires three or more words.

See also fractions.

Subject:  Data and Measurement

---

over and under

In cases involving quantity, use "more than" rather than "over," and use "fewer than" or "less than" rather than "under." In cases involving temperature, use "higher than" or "lower than" or "warmer than" or "cooler than." In cases involving weight, use "heavier than" or "lighter than."

Subject:  Grammar and Usage

---

pagination

Paginate the front matter of NREL reports with lowercase Roman numerals, up through the lists of figures and tables. The title page is usually page "i," although that number isn't printed on the page. Paginate the main body of your report with Arabic numerals. You may insert a blank page before Page 1 to make sure it will be a right-hand (odd-numbered) page, but don't insert blank pages after that. All subsequent sections can begin on the left or on the right, as they fall. Center the page numbers on each page.

If you include appendices at the end, you may continue to paginate them sequentially with numerals or use A-1, A-2, A-3, B-1, B-2, and so on, for the page numbers.

Subject:  Publication Formatting

---

parallelism

Use parallel construction in sentences as well as in lists. Express all similar sentence elements (subjects, verbs, verbals, objects) in a similar way.

Subject:  Grammar and Usage

---

parentheses

Use parentheses as appropriate for explanatory material in text and as shown in the examples that follow.

1. Parentheses in Equations

In equations, use parentheses, brackets, and braces in this sequence (which may be repeated as needed).

2. Parentheses with Measurements

Use parentheses around English measurements that follow SI (metric) measurements.

3. Parentheses in Citations

When you use parentheses in text, such as for author-date references or for parenthetical (added) information, place a comma after the parentheses rather than before them.

4. Nested Parentheses in Text

In body copy, use parentheses, brackets, and braces in this sequence, which may be repeated as needed: ([{ }]).

Subject:  Punctuation

---

percent, %, and percentage

Use the symbol % with numerals; use the word "percent" when you spell out numbers at the beginning of a sentence. To determine whether "percent" or % is singular or plural, look at the noun following it. If the next noun is a plural, use a plural verb; if it's singular, use a singular verb.

When there is no number, use the word "percentage," unless people in your field use a different terminology, such as "percent difference."

Subject:  Data and Measurement

---

periods

Periods are used in some abbreviations (e.g., i.e., a.m., p.m.) and not in others (ac, dc, rpm). Most acronyms do not have periods. When you end a sentence with "etc." (although this is seldom necessary) or another abbreviation that includes a period, do not add another one.

Subject:  Punctuation

---

personal pronouns

First-person pronouns may be used in technical communications when appropriate, and some scientific and technical associations (such as the American Institute of Physics) encourage technical writers to do so. Common first-person pronouns include "we," "our," and "us." Personal pronouns can prevent confusion by clearly and concisely showing who performed an experiment or procedure.

Which of the following two sentences is easier to read and understand quickly?

See also active voice and passive voice.

Subject:  Grammar and Usage

---

phone numbers

Do not use parentheses around area codes in phone numbers. Parentheses previously were used to set off the three-digit code in a phone number because it wasn't always necessary when dialing the number. However, they are required in most instances now.

Use hyphens to separate the digits in phone numbers.

Subject:  Geography

---

photo, image, and video credits

If you use a photo, image, or video from the NREL Image Gallery, an NREL staff member, or a paid or external source, you must provide appropriate credit. See the entries on captions and sources for more information, as well as the copyrighted material page on the publishing site.

For Publications

For the Web

For photos, images, and video on the web, include the credit after the caption and italicize it.

Use "from" for external sources and "by" for NREL sources. Do not use "courtesy of."

Don't include image numbers in the credit. Instead, the photo image file name should include the image number so it can be easily located in the Image Gallery if needed.

Subject:  Publication Formatting

---

photovoltaics and photovoltaic

"Photovoltaics" is a singular noun. "Photovoltaic" is an adjective. The acronym PV can be a noun or an adjective, but do not pluralize it.

Subject:  Technology-Related Terms

---

policymaker

"Policymaker" and "policymaking" are both spelled as one word.

Subject:  Writing Style

---

preface

Brief introductory remarks and acknowledgments go in the report's preface. The preface comes after the title page and disclaimer page. (See front matter.) A preface written by someone other than the authors of the report is usually called a "foreword."

Subject:  Publication Formatting

---

prefixes

See hyphens, compound words, and unit modifiers and scientific notation.

Subject:  Grammar and Usage

---

pressure

Use the standard SI unit for pressure or stress, which is the pascal (Pa) or the bar. Non-SI units include psi (pounds per square inch), millimeters of mercury, torr, and atmospheres, and they are still in relatively widespread use.

Subject:  Data and Measurement

---

principal and principle

"Principal" often means "chief" or "main," such as the principal investigator in a research project or the principal of a high school. "Principle" often refers to a belief, value, or rule.

Subject:  Grammar and Usage

---

quotation marks

Use quotation marks for direct quotes and the titles of articles, papers, and book chapters. In print, use "curly" or "fancy" quotation marks; on the web, use "straight" quotation marks. 

Place commas (and periods) inside quotation marks; place semicolons, question marks, dashes, and exclamation points outside quotation marks unless they're part of the quotation.

Use single quotation marks to indicate a quotation within material that is already enclosed in double quotation marks.

When quotations are longer than two or three lines of text, begin them on the next line and indent them on each side (block quotations). You do not need quotation marks around block quotations, and you can use standard double quotation marks for quotes within block quotations. In in-text quotations, place reference numbers, superscripts, and author-date citations outside quotation marks (but before the final punctuation of a sentence). Place them after the final punctuation of the last sentence in a block quotation.

Subject:  Punctuation

---

race and ethnicity

As a laboratory that strives for diversity of perspectives and inclusivity, our word choices, style, and tone must be carefully considered, particularly when it comes to topics related to race and ethnicity.

Capitalize Black when referring to African Americans or, more broadly, in any racial, ethnic, or cultural sense; do not capitalize white. Do not use the terms “Black(s)” or “white(s)” as singular or stand-alone nouns referring to a person or people. In the plural form, “Black people,” “white people,” “Black scientists,” and “white scientists” are preferable when clearly relevant.

Capitalize “Indigenous” in reference to original inhabitants of a place, aligning with long-standing capitalization of other racial and ethnic identifiers such as Latino, Asian American, and Native American. (Note that no hyphen is used in dual heritage terms such as “Asian American” and “Mexican American.”) Capitalize “Elder” when referring to a Tribal or religious leader, but lowercase it when used to identify someone by age or when used generally.

The terms “Tribal” and “Tribe” should be capitalized, even when they are not part of an entity’s official name. Capitalize the word “nation” when part of a formal name.

In Alaska, the Indigenous groups are collectively known as Alaska Natives. Both “American Indians” and “Native Americans” are acceptable terms when referring to two or more people of different Tribal affiliations. “First Nation” is the preferred term for native Tribes in Canada. “Indian” is used to describe the peoples and cultures of the South Asian nation of India and should not be used as shorthand for American Indians, unless that is how a particular group prefers to be referenced.

For additional details, refer to the AP Stylebook's race-related coverage.

Subject:  Grammar and Usage

---

Rankine cycle

Subject:  Technology-Related Terms

---

ratios

In general, use a colon to indicate a ratio.

However, some industries (such as the American automotive industry) use a solidus to express a ratio.

Subject:  Data and Measurement

---

references and citations

Subject:  Publication Formatting

---

renewable energy certificate

Don't capitalize "renewable energy certificate." It's not a proper noun. Also, this is the term preferred over "renewable energy credit" or "green tags."

Subject:  Government Terms

---

renewable portfolio standard

Only capitalize "renewable portfolio standard" when a state name precedes it.

Subjects:  Government Terms, Technology-Related Terms

---

report contents

Report contents may include (in order):

1. A report cover
2. A title page
3. A disclaimer
4. A foreword
5. A preface
6. Acknowledgments
7. A nomenclature, list of abbreviations, or list of acronyms
8. An executive summary
9. A table of contents
10. A list of figures
11. A list of tables
12. Body text
13. A glossary
14. references
15. A bibliography
16. Appendices.

See also front matter and back matter.

Subject:  Publication Formatting

---

report covers

NREL uses standard covers for most technical reports and papers and subcontract reports. Covers contain the laboratory's name, address, and logo as well as an NREL report number and date of publication. You may spell out an author's first name with or without a middle initial or use initials for the first and middle name.

Subject:  Publication Formatting

---

Research Support Facility

Use "Research Support Facility" (RSF), regardless of which phase or wing is cited.

Subject:  Government Terms

---

restrictive phrases and clauses

Do not use commas around restrictive phrases and clauses. They are essential to the meaning of the sentence, in contrast to nonrestrictive phrases and clauses, which simply add information that is not essential.

See also which and that.

Subject:  Grammar and Usage

---

rheology

Subject:  Technology-Related Terms

---

scientific notation

Standard scientific notation represents a number as a factor multiplied by a power of 10; 3,560,000 is expressed as 3.56 × 10⁶. This is useful for very large and very small numbers, especially in non-SI units. You can also use certain standard prefixes, many of which are listed here with their abbreviations.

We recommend choosing a prefix that permits the numerical value to fall between 0.1 and 1,000 (62 kW rather than 62,000 W).

Subject:  Data and Measurement

---

semicolons

Semicolons indicate a stronger or more important break in the flow of words than the break indicated by a comma. Use a semicolon in compound sentences that are NOT linked by a conjunction (such as "and," "but," "or," "nor," and "yet"). Place a semicolon before conjunctive adverbs (such as "however," "hence," "therefore," "nevertheless," and "consequently") in most complex sentences containing two or more clauses. When a sentence contains items in a series, you may use a semicolon between the items if one or more of the items contains commas.

1. Using Semicolons in Compound Sentences without Conjunctions

When clauses in a sentence are closely related in meaning, a semicolon is an appropriate dividing punctuation mark. Note that the words "and," "but," "or," and "nor" do not follow semicolons.

2. Using Semicolons with Conjunctive Adverbs

"Yet" and "so" are usually preceded by commas in a complex sentence. But use a semicolon before such conjunctive adverbs as "then," "however," "thus," "therefore," "hence," "accordingly," "moreover," "nevertheless," "consequently," "besides," "indeed," and "subsequently"; place a comma after the adverb.

Use a semicolon before "i.e." ("that is") and "e.g." ("for example") and a comma after them when a clause (with a subject and verb) follows them; use a comma when a phrase or list follows.

3. Using Semicolons in a Series

When items in a series contain internal punctuation (e.g., commas) or are very long, you can separate them with semicolons. In those cases, a conjunction can follow the last semicolon.

Subject:  Punctuation

---

SI (metric) system

NREL follows national policies and those of scientific societies by using the SI (Systeme International d'Unites, International System of Units) or metric system in expressing technical measurements. English units may follow metric ones or may be used alone in special cases, when that is appropriate for a publication's audience. See also the National Institute of Standards and Technology.

Subject:  Data and Measurement

---

slash (solidus)

The solidus (or slash, slant, shilling mark, or virgule) is a versatile symbol that has mathematical as well as textual functions.

1. Using a Solidus in Fractions

Use a solidus to express a quotient in text when you do not need to use a displayed equation.

Use a solidus in superscript and subscript fractions.

2. Using a Solidus in Text

In text, use a solidus to indicate some junctions, interfaces, and components.

With abbreviated units of measurement, the solidus stands for "per."

But spell out "per" when you spell out the units of measurement.

Subjects:  Data and Measurement, Punctuation

---

Smart Grid and smart grid

Use capital letters for "Smart Grid" when referring to the overall goal or concept and lowercase letters for "smart grid" when referring to current implementations or when used as an adjective.

Subject:  Technology-Related Terms

---

solar cell interfaces

Use a slash rather than a hyphen to designate solar cell interfaces or layers.

Subject:  Technology-Related Terms

---

solar conversion efficiency

Define in outreach publications as "the percentage of sunlight striking a solar cell that is converted into electricity." A definition is often unnecessary in technical publications.

Subject:  Technology-Related Terms

---

solar electricity

This term is interchangeable with "photovoltaic power," "PV power," or "PV electricity."

Subject:  Technology-Related Terms

---

sources

Include the sources of all figures and tables that were originally published by others, especially those outside NREL. If figures or tables come from a copyrighted publication, you may need permission to reproduce them. Add the source at the end of a figure caption or in a note following a table.

Write out the source in full, as in the example, if it is not in your reference list or bibliography. If it is in the reference list, use one of these styles.

Subjects:  Publication Formatting, Publication Policies and Services

---

spaces

Use only one space between a period and the beginning of the next sentence.

Subject:  Publication Formatting

---

spelling

If you can't find a word or phrase in this style guide, consult the following reference guides in this order: (1) The Associated Press Stylebook and (2) Merriam-Webster's Collegiate Dictionary, Eleventh Edition.

For spelling out numbers, see numbers.

Subject:  Grammar and Usage

---

standard errors

Express standard measurement errors as shown below.

Subject:  Data and Measurement

---

state implementation plan

Capitalize "state implementation plan" only when a state or organization name precedes it.

Subject:  Government Terms

---

states and countries

1. States

In text, consistently spell out states' names rather than using U.S. Postal Service abbreviations.

You may use D.C. for the District of Columbia in text, in both formal and informal publications. When you include addresses or state names in full addresses (containing streets and cities), contact lists, reference lists, and bibliographies, however, you may use the following abbreviations:

2. Countries

Do not abbreviate the names of countries (including the United States) when they are used as nouns. Use "U.S." as the adjective form.

Subject:  Geography

---

statistical terms

When referring to statistical or graphical terms, use a hyphen but no italics. Also, do not use capital letters.

Subject:  Data and Measurement

---

subcaptions

Print captions to figures and photos in a bold font. Subcaptions are supplementary information that follows a period after the main caption. Subcaptions are not printed in bold.

But follow the publisher's guidelines for journal articles and conference papers.

Subject:  Publication Formatting

---

systems integrator

The correct term is "systems integrator," not "system integrator."

Subject:  Technology-Related Terms

---

table of contents

A table of contents is required in most technical reports. In NREL reports, the table of contents follows the rest of the front matter. Lists of figures and tables follow the contents page(s). Each main section of the report is listed in the table of contents with the page it begins on; some authors also like to list subsections. Nothing that comes before the table of contents (front matter) is listed, but references, bibliography, and appendices (back matter) are listed. Publications for general audiences probably should include a contents list if the publication is more than 10 pages long.

Subject:  Publication Formatting

---

tables

In small or average-sized tables, place a horizontal line (as wide as the table) under the title, under the column headings, and below the table (between the table and sources or notes, if any). Delete vertical lines and extra horizontal lines. If the table is very large, shading every other line with a light color or inserting horizontal lines every three or four rows can help readers locate data.

Number tables in simple sequence or by section in long reports (Table 1, Table 2 or Table 1-1, Table 1-2, and so on). Center the table title (in title case) over the table (unlike a figure caption, which is sentence case and goes under the figure) and print the title in 10-pt. Arial bold; supplementary material in the title is not in bold. If possible, print tables in Arial, rather than Times New Roman. Define abbreviations in notes to the table if they are not obvious. Table notes are denoted by lowercase superscript letters (a, b, c) rather than footnote numbers or asterisks.

Subject:  Publication Formatting

---

taxonomic names

See capitalization and italics.

Subject:  Writing Style

---

technical abbreviations

Unless your profession, technical field, or scientific discipline specifies something different, use the abbreviations in NREL's list of technical abbreviations or the National Institute of Science and Technology's Guide.

Subjects:  Data and Measurement, Technology-Related Terms

---

techno-economic

Hyphenate. Don't spell as one word.

Subject:  Technology-Related Terms

---

temperature

Use a degree symbol (°) with temperatures expressed in the Celsius and Fahrenheit scales but not with kelvins (just use K). Don't leave a space between the number and the letter for °C and °F, but leave a space between the number and K.

Subject:  Data and Measurement

---

that and which

See which and that.

Subject:  Grammar and Usage

---

time

Subject:  Grammar and Usage

---

title page

Most NREL technical reports contain a standard title page inside the cover.

Subject:  Publication Formatting

---

trademark symbols

Subject:  Government Terms

---

translations

See International and Non-English Speaking Audiences.

---

U.S. Department of Energy

This is the preferred term for printed and outreach materials. When spelling it out, "U.S." should precede "Department of Energy" to distinguish it from other state and international departments. However, "U.S." should not be included with the acronym "DOE." Do not include "the" before "DOE."

On first reference, "Energy Department" may be used in communications to the press.

If the possessive is used with the term, the apostrophe should go after "U.S. Department of Energy" and with the "DOE" acronym as well. However, if you can write it in a way that avoids use of the possessive, that is preferred.

Subject:  Government Terms

---

unit modifiers

See hyphens, compound words, and unit modifiers.

Subject:  Grammar and Usage

---

United Kingdom and U.K.

Spell out "United Kingdom" when it is used as a noun. The abbreviation "U.K." is acceptable when it is used as an adjective.

Subject:  Writing Style

---

United States and U.S.

Spell out "United States" when it is used as a noun. The abbreviation "U.S." is acceptable when it is used as an adjective.

Subject:  Writing Style

---

units of measurement

Use numerals with units of measurement and time in technical papers and reports, even when the number is less than 10. In some outreach publications, you may spell out numbers less than 10, especially with units of time.

Except with $, °, and %, leave a space between the numeral and the unit. Include a hyphen between a numeral and an abbreviated unit when the value is used as an adjective. 

Avoid nonstandard abbreviations such as sec or cc, and instead use standard abbreviations such as s and cm³. Unless your profession, technical field, or scientific discipline specifies something different, use the abbreviations in NREL's list of technical abbreviations or the National Institute of Standards and Technology (NIST) guide.

Use a center dot to indicate multiplication of units (such as N∙m for Newton-meters), and use a slash or negative exponent to indicate division. For example, 344 meters per second can be written as 344 m·s⁻¹ or 344 m/s.

Format variables in italic type and units in roman type:

Do not mix information with unit symbols or names:

Avoid mixing symbols and names; for example, use kg/m instead of kilogram/m.

When expressing a range, repeat the unit symbol if it is closed-up with the numeral ($, °, %):

Refer to the NIST style conventions checklist for additional style tips and examples.

Subject:  Data and Measurement

---

URLs

Uniform resource locators, or URLs, are essentially web addresses.

On websites, URLs should be embedded in text.

In print, URLs should not be embedded in text. If a URL extends beyond one line of text, add a break at a solidus. Also, in general, you do not need to include the http:// prefix on most URLs. But test it before removing it. Shorten URLs as much as possible (e.g., remove unnecessary trailing such as /index.html) while ensuring functionality.

Subjects:  Websites, Writing Style

---

watt

Subject:  Data and Measurement

---

web terms

The following words are lowercase:

• web
• webpage
• webcast
• webinar
• webmaster
• website.

"World Wide Web" is a proper noun and should be capitalized.

Subjects:  Websites, Writing Style

---

website content

For website content guidance, see Content and Writing for NREL.gov. We use the NREL Style Guide in conjunction with these guidelines and standards. Some specific NREL style guidelines, which are different from print style, for the web include:

Abbreviations and acronyms

Ampersands

Bullets

Fiscal year

Initialisms

Lists

Photo credit

URLs.

Subjects:  Websites, Writing Style

---

which and that

Standard American English uses "which" is a thing for nonrestrictive or nondefining phrases and clauses and "that" for restrictive or defining phrases and clauses. The word "which" usually signals the approach of added, nonessential information. When a phrase or clause is not essential to the meaning of a sentence, use the relative pronoun "which" and enclose the phrase or clause in commas. See also nonrestrictive phrases and clauses and  restrictive phrases and clauses.

When a phrase or clause is essential to the meaning of a sentence (that is, the sentence would not make much sense without it), use "that" and leave out the commas.

Subject:  Grammar and Usage

---

work-for-others agreement

Use lowercase for "work-for-others agreement" because it's not a proper noun. The acronym "WFO" refers only to work for others; therefore, when using the acronym, "WFO agreement" is correct.

Subject:  Government Terms

---

zero

For numbers less than one, place a zero before the decimal.

Subject:  Data and Measurement

---

zero energy building

Use the term to indicate an energy-efficient building where, on a source energy basis, the actual annual delivered energy is less than or equal to the on-site renewable exported energy. Similar terms include zero energy campus, zero energy portfolio, and zero energy community.

Subject:  Technology-Related Terms

---