No government agency publishes what a home solar system or battery costs to install at your address, and no two homes save the same amount. So every Leaf & Watt cost page shows its work, every payback runs on numbers you can change, and every rule is quoted from its source with the date we read it. This page sets out how each part works and where its limits are.
How we estimate costs
Cost pages work in three layers: published estimates side by side, a build-up from parts you can check, and an explanation of why the numbers differ.
1. Published estimates, side by side
Each cost page opens with named published figures. For each we give the figure, the date it was published or read, and what it measures: prices owners reported paying for installed systems, a modelled benchmark for one defined system, or an average of quotes on a marketplace. We label these “published estimates”. Our main sources are Lawrence Berkeley National Laboratory’s distributed solar and storage data, the National Laboratory of the Rockies’ cost benchmarks and Annual Technology Baseline, Wood Mackenzie and SEIA’s market reports, and EnergySage’s marketplace data. EnergySage is a commercial quote marketplace, and we say so when we cite it.
We never average these into one number. Two figures that measure different things don’t make a truer third figure when you blend them; they just hide what each one means.
2. A worked build-up
Next, we build the cost from its parts:
- Equipment: quantities from the system size, with specifications from the maker’s datasheet and a dated price from a named maker or retailer where one is published.
- Labor: hours times the BLS median hourly wage for the trade, times an employer-cost uplift for benefits and payroll taxes.
- Permits and interconnection: the fee where a city, county or utility publishes it, or a labelled example.
- Overhead and profit: a percentage on top, shown as its own line.
The arithmetic is on the page, and the calculators let you change the inputs. A quote for your own roof is a better number than ours; the build-up helps you see what that quote should cover.
3. Why the numbers differ
Finally, we explain what each source includes or leaves out: roof work, an electrical panel upgrade, permits and interconnection, how much of the house a battery backs up, the region, and whether the price was paid in cash or wrapped into a loan. That is usually where a large gap comes from.
Here is an example. EnergySage puts its national average at $2.60 per watt, an average of quotes on its marketplace before incentives (read 4 November 2026). Lawrence Berkeley National Laboratory’s August 2026 data update looks at prices owners reported for systems installed in 2025, and finds that the median price charged by each of the top 100 residential installers ran from $2.4 to $6.3 per watt. It also reports that loan-financed systems were priced considerably higher than cash purchases. A quote average and a spread of prices actually paid answer different questions, so we show both.
How we price labor
The wage. We use the national median hourly wage for the trade from the Bureau of Labor Statistics, May 2025 data, released in May 2026. For solar photovoltaic installers that is $25.55 an hour; for electricians, $30.38. A median is the wage half of workers earn more than and half less than. It covers employees only, not the self-employed, and it is a wage, not what an installer charges you.
The employer-cost uplift. An employer pays more than the wage. In June 2026, construction employers paid on average $51.96 an hour in total compensation for every $36.13 in wages (BLS Employer Costs for Employee Compensation). So we multiply the wage by 1.44 to cover benefits and payroll taxes. This is an average across the construction industry, not the cost for any one trade or company. BLS has said that, starting with data published in March 2027, it will remove workers’ compensation costs from these figures. When we move to that data, we will say so.
The hours. We found no free public source that says how long a home solar or battery installation takes. So labor hours on every page are marked “our assumption”, with a sentence on how we got there, and the calculator lets you change them.
Overhead and profit
An installer’s price also covers design, sales, permits and paperwork, insurance, vehicles, warranty service and a margin. Our default is 20% on top of equipment and labor, marked “our assumption”, and you can set your own figure. The 20% follows the insurance convention of 10% overhead plus 10% profit, which FEMA’s flood insurance program has called the typical charge where a general contractor coordinates several trades. That is a claims convention, not a measured solar margin. Solar quotes often carry more: Lawrence Berkeley National Laboratory puts soft costs and other balance-of-system costs at about 80% of the median installed price in 2025, so our build-up can come in below real quotes, and we say so on the page when it does.
A worked example
Here is the arithmetic with round, made-up inputs, so you can follow it. Say a job needs $10,000 of equipment, 40 hours of installer time, 8 hours of electrician time and a $500 permit and interconnection fee.
| Line | Working | Amount |
|---|---|---|
| Equipment | Example figure | $10,000.00 |
| Installer labor | 40 hours (example) × $25.55 BLS median × 1.44 = 40 × $36.79 | $1,471.60 |
| Electrician labor | 8 hours (example) × $30.38 BLS median × 1.44 = 8 × $43.75 | $350.00 |
| Subtotal | $10,000.00 + $1,471.60 + $350.00 | $11,821.60 |
| Overhead and profit | 20% (our assumption) × $11,821.60 | $2,364.32 |
| Permit and interconnection | Example figure | $500.00 |
| Estimate | $14,685.92 |
On a real page, the equipment line lists each item with its quantity, specification, source and date, and the hours line explains the assumption.
How we work out payback, with no tax credit
The 30% homeowner credit under 25D “shall not apply with respect to any expenditures made after December 31, 2025” (26 USC 25D(h)), and an expenditure counts as made when installation is completed (25D(e)(8)). The IRS FAQ adds that paying in 2025 does not help if installation was completed later. So every payback figure on Leaf & Watt leaves the credit out. The IRS credit page still mentions a phase-out in 2033; the statute is what applies, and we cite the statute.
Payback is simple cash payback: the number of years until your savings add up to the price after any state, city or utility rebate you enter, with no interest or discounting. Savings in the first year are the solar you use at home times your rate, plus the solar you export times your export credit, minus upkeep. Each year after, savings change by your rate rise and by the panels’ slow loss of output. With a battery, we add what it saves by shifting your own solar into the hours you would otherwise buy power, after its round-trip losses, plus any program payment you enter, for the battery’s life only.
In the default example of our solar payback calculator, a $23,100 system with $982.64 of first-year savings after upkeep, growing 1.78% a year, pays back in about 19.8 years. Every input that drives that answer is shown, dated and editable.
Leases and power purchase agreements are different. The company that owns the system may be able to claim a business credit under 48E, but you can’t. Our lease pages compare what you would pay over the term with buying, on your own payment and escalator, and show the provider’s possible credit as a separate note. Whether any of its value reaches you depends on the contract, so ask the provider in writing.
Where rates come from
Calculators ask for your own rate, from your bill. Until you change it, they use a stated default: the state’s average residential price from the Energy Information Administration. For January to August 2026 the US average was 18.19 cents per kWh (EIA Electric Power Monthly, released 23 October 2026). That is average revenue across all charges and all utilities in a state, not your tariff rate, and a time-of-use or tiered rate can differ a lot from it.
Export credits, net metering terms and time-of-use periods come from the utility’s own tariff or the state commission’s order, read by hand, because no national database covers them well. For example, our payback calculator’s default export credit, $0.05554 per kWh, is from Arizona Public Service’s RCP rate rider. Your utility’s tariff sets your rates and credits.
Where production figures come from
Solar output figures come from runs of PVWatts version 8, the National Laboratory of the Rockies’ free model, and we record the inputs for every run: location, system size, panel type, tilt, direction and losses. For example, PVWatts estimates about 1,420 kWh a year per kW of panels in Houston, for a south-facing roof at a 20° tilt with 14.08% losses (run 4 November 2026). Your roof’s direction, tilt and shade change this, so the calculators let you enter your installer’s figure or your own PVWatts run. We never invent a production figure.
Battery capacity, power, round-trip efficiency and warranty terms come only from makers’ current US datasheets and warranty documents. Makers measure efficiency and surge power in different ways, so we say how each figure was measured, and write “not stated” where a maker gives none.
How rules and programs are checked and dated
Every tax rule, export rate, state law and battery program a page uses goes first into a rules register, with its primary source, the date we read it and one of three labels:
- Confirmed: we read the statute, tariff, order or official program page and checked the wording.
- Partly confirmed: we saw the primary source only in part, or it supports only part of the claim. The page says what is missing.
- Unconfirmed: only a news report, a seller or nothing. We do not state it as fact: we leave it out, or say plainly that it is unconfirmed.
Rules that move fast are rechecked every month: California, Virginia, Nevada, North Carolina and Illinois, state battery programs and plug-in solar laws. Everything else in the register is rechecked at least every three months, and sooner when we learn of a change. Program pages often change without notice, so before you sign anything, confirm the current terms with the utility or the state agency.
The cost register
Every shared figure, such as a wage, the uplift, a published estimate, a state’s average rate or a battery specification, goes into one cost register before a page uses it. For each figure the register records the value, the source and its link, the date we read it and what it measures. Pages draw from the register, so the same figure shows the same way everywhere, and a change is made in one place.
Government data are rechecked when the source publishes a new release: EIA prices monthly, the BLS uplift quarterly and BLS wages yearly. Marketplace prices and makers’ datasheets are rechecked about once a month. A page shows an updated date only when its content really changed.
What we don’t use, and why
- The ended 25D credit. It is not in any payback figure for a system installed in 2026 or later.
- Sellers’ savings claims as fact. An installer’s or lease company’s savings estimate is reported as their claim, not as ours.
- Code limits we haven’t read. Fire-code text such as NFPA 855 sits behind a sign-in, so we quote no limit from it unless we have read it in a primary source.
- Figures we can’t trace. If we can’t find where a number came from or what it measures, we leave it out or say plainly that it is unconfirmed.
What an estimate can’t know
- Your roof. Direction, tilt, shade, age and condition change both the price and the output. A roof near the end of its life may need replacing first.
- Your electrical panel. Some homes need a panel or service upgrade before solar or a battery can connect.
- Your rate plan and export credit. These set most of the savings, and they vary by utility and can change over the life of a system.
- Your contract. Escalators, buyout terms, warranties and who claims any credit are in the paperwork, not in a national average.
- Permits and interconnection. Fees, inspections and approval times vary by city, county and utility. The local building department and the utility decide what the job needs.
So our numbers are estimates, not quotes, and never a verdict on whether a price is right or a system is worth it for you. Use them to ask better questions. Your utility, your state or a tax professional decides what applies, and a licensed installer prices the real job. Our editorial policy covers how pages are checked, and our disclaimer sets out the limits. If a figure looks wrong, please tell us.