Before Installing Rooftop Solar: Key Questions to Ask First

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Rooftop solar quotes often arrive as one headline figure, but that number only makes sense when you understand what sits behind it: panel wattage, efficiency and warranty terms. This guide uses insights from A1 SolarStore, a solar equipment supplier that has shipped more than 100 megawatts of panels since 2017.

With the federal homeowner credit no longer available for systems placed in service after the end of 2025, the equipment itself matters more than ever in the decision. If you are considering home solar, the first things to sort out are panel type, the spec sheet, system sizing based on your electric bill, and the roof and permitting process.

Which Panel Types Belong on a Roof, and Which Ones Do Not

Nearly every solar panel made today uses monocrystalline silicon. Germany’s Fraunhofer ISE says 690 of the 706 gigawatts produced worldwide are mono-Si. Polycrystalline panels, the older blue-speckled style, have largely disappeared from the market.

Type	Share of production	Panel efficiency	Typical use
Monocrystalline silicon	About 98% (690 of 706 gigawatts)	Commercial silicon panels range from 18.9% to 24.8%, averaging 22.7% (Q4 2024)	Residential rooftops and most other projects
Thin-film CdTe	About 2% (16 gigawatts, First Solar only)	Rose from 15.6% to almost 20% over a decade	Almost entirely utility-scale systems
Polycrystalline	Essentially no new production	No current benchmark	Rarely sold new

Within the monocrystalline category, the cell design is another useful question. Fraunhofer ISE puts n-type wafers, which underpin TOPCon and heterojunction cells, at 86% of production, replacing older PERC designs. Thin-film cadmium telluride (CdTe) is used almost entirely in utility-scale projects, according to the Department of Energy, so for a rooftop system, monocrystalline is the practical choice.

How to Read a Spec Sheet Without an Engineering Degree

Five datasheet entries deserve special attention. The reference points below come from the National Renewable Energy Laboratory (NREL, renamed the National Laboratory of the Rockies, or NLR, in December 2025), the Department of Energy and manufacturer datasheets.

Spec	What it tells you	A useful reference point
Rated power	Output under laboratory test conditions	400W, the panel size in NREL’s cost benchmark
Solar panel efficiency	Share of sunlight turned into electricity; most important when roof space is tight	20.4% in the same benchmark; the DOE cites 20% to 22% for industrially produced panels
Degradation	Output lost each year	Median of 0.4% to 0.5% a year for the first mainstream models in NLR’s 2025 field study
Product warranty	Coverage for defects and workmanship	Recent datasheets from several major manufacturers list 12 to 25 years
Power warranty	Guaranteed output over time	Commonly 25 to 30 years

One important detail: a 400W rating is measured in the lab at a cell temperature of 77 F. The DOE notes that cells lose voltage as they heat up, so a hot summer roof will produce less than the label implies.

How Many Panels a Home Actually Needs

Begin with your own utility bills, not a salesperson’s estimate. The Energy Information Administration says the average U.S. home bought 863 kilowatt-hours per month in 2024, or about 10,356 a year. Sizing a system also requires a capacity factor, meaning the share of a panel’s rated output it delivers over a year; the table below uses NREL’s 2025 range.

Step	What to do	Worked example
1	Add up 12 months of usage from your bills	10,356 kWh a year (EIA’s 863 a month in 2024, times 12)
2	Choose a capacity factor for your region	NREL’s range is 11.7% to 18.3%; 15% as a middle case
3	Divide usage by capacity factor × 8,760, the hours in a year	10,356 kWh ÷ (0.15 × 8,760 h) = about 7.9 kW
4	Divide by the panel rating	7.9 kW ÷ 400 W = about 20 panels

Sun exposure changes the answer. At the sunny end of NREL’s range, 18.3%, the same home would need about 6.5 kW, or 16 panels. At the low end, 11.7%, it would need about 10.1 kW, or 25 panels. If an electric vehicle is in your future, the DOE recommends accounting for that before choosing a system size.

What Still Affects Solar Costs After the 30% Credit Disappears

The IRS says the residential clean energy credit covered 30% of qualified costs for property installed from 2022 through 2025, and that it is not available for property placed in service after December 31, 2025. That means the discount no longer factors into the math for new purchases, whether paid in cash or financed.

As a benchmark, NREL’s first-quarter 2025 estimate for an 8kW rooftop system using 400W panels at 20.4% efficiency is $2.78 per watt at its minimum sustainable price and $2.95 at its modeled market price, in 2024 dollars and before storage. On an 8kW system, that works out to roughly $22,200 to $23,600 installed.

Four items still shape what a homeowner pays:

Equipment price per watt, the cost that can be compared line by line across quotes.
State and local incentives and utility programs, which vary by location and should be confirmed with a tax professional before signing.
Net metering and interconnection rules, which determine the value of exported electricity.
Financing terms, if the system is not paid for in cash.

Roof, Permits and Paperwork: The Unseen Part of the Job

According to the DOE, the installation itself takes only a few days. Permits and inspections can stretch from weeks to months, and the roof determines whether the project can begin at all.

Stage	What to know
Roof	Age and structure matter. Whoever inspects it, whether installer, roofer or structural engineer, must confirm it can support the load. If the roof is near the end of its life, replacing it and adding panels in one project may cost less.
Sun exposure	Orientation and shading determine how much the roof can produce. Online tools use satellite imagery for a first estimate; an installer visit provides a more detailed one.
Permits and inspections	Local rules determine which permits and inspections apply. Expect weeks to months.
Installation	A few days.

Your installer handles the permit package, so ask early which equipment documents the local office wants to see.

What to Resolve Before You Sign Anything

Incentives change, but two basics remain constant. Price per watt allows fair comparisons between panels of different sizes, so a 400W panel and a 450W panel can be judged on equal footing. Documentation also matters, because installers and permit offices need the specifications in writing.

Suppliers differ on that point. A1 SolarStore, for example, ships full documentation with every order, so the paperwork is ready before anyone steps onto the roof.

Before reviewing the next quote, make sure you know your annual kilowatt-hours, your region’s capacity factor, the panel’s efficiency and power warranty, and the installed price per watt.

A Second Look at System Size

Whatever company supplies the equipment, ask for the datasheet, warranty terms and production estimate before paying anything. A1 SolarStore also offers in-house engineering help for first-time buyers who want to check system size before ordering, so the panel count comes from an engineer’s review rather than a rough guess.

Questions Homeowners Ask Most Often

Are Solar Panels Still Worth It Without the Federal Credit?

That depends on how much power you use, local electricity prices, how much sun your roof receives and what the system costs. NREL’s PVWatts calculator can estimate the output of a grid-connected system; compare that estimate with your bills and the quoted price per watt. NREL’s Annual Technology Baseline assumes a 30-year life for a residential system.

How Long Do Solar Panels Last?

Output declines gradually rather than stopping altogether, though not every model ages the same way: in NLR’s 2025 study of 16 module types, four lost more than 1% a year. Using 25 years, the shorter end of today’s warranty range, two benchmark degradation rates produce the following results:

Annual degradation	Source	Output remaining after 25 years
0.5%	NLR field data, upper end for mainstream models	About 88%
0.7%	NREL 2025 baseline	About 84%

Can a Home With an HOA Still Have Solar Panels?

In most cases, yes. The DOE says homeowners can install panels on a home governed by a homeowners association, although a request is usually required. Many states have solar access laws that prevent HOAs from unreasonably blocking solar, but those rules vary, so check the law in your area and read the HOA guidelines before ordering equipment.

Does Solar Make It Harder to Sell a Home?

Usually not if the system is owned outright. The DOE’s homeowner guide says purchasing a solar system will likely raise a home’s value. Third-party-owned systems, such as leased ones, are different: the guide says their overall effect on sale price and time on the market is mostly neutral, though they can add some complexity to the transaction.