Quick answer
Solar Production is the amount of electricity a solar system generates over a period, measured in kilowatt-hours (kWh) and usually quoted per year.
It depends on system size, local sunlight, roof direction and angle, shade, heat and equipment losses. NLR's free PVWatts model estimates 10,179 kWh a year for a 7 kW south-facing array in Charleston, SC.
Quick facts
The key facts about solar production, with sources:
- Unit
- Kilowatt-hours (kWh), AC, per month or year
- Standard estimating tool
- NLR PVWatts (free, address-based) 1
- Example: 7 kW, Charleston, SC
- 10,179 kWh/year (PVWatts, inputs below) 2
- Example: 7 kW, Atlanta, GA
- 9,812 kWh/year (same inputs) 2
- US small-scale PV, 2025
- About 93 billion kWh 3
- Not the same as
- Wattage (power, in W) or capacity (size, in kW)
Key takeaways
- Production is energy, counted in kWh. It is what your utility bill measures, so it is the number that saves you money.
- A 7 kW south-facing roof system in Charleston models at about 10,179 kWh a year. Atlanta is close at 9,812 kWh.
- Production swings by season. In Charleston, December makes about 58% of what May makes.
- Roof direction matters more than most people think. Facing east or west cut the Charleston model by about 13%.
- Judge a system on 12 months of output, not one bad week, and compare it with the installer's estimate.
What solar production means in plain terms
Production is how much electricity your panels make over time. It is counted in kilowatt-hours, the same unit on your power bill. One kWh runs a 1,000-watt microwave for one hour.
It helps to keep three words apart. Wattage is the power of one panel in a lab test. System size, in kW, is all the panel watts added up. Production is the energy those panels actually make in real sun, over a day, month or year.
Installers usually quote production for the first year, in AC kWh. AC means the power has passed through the inverter and is ready for your home. That is the number to compare with your yearly usage.
Production adds up fast across the country. The EIA reports that small-scale grid-connected PV systems, mostly on rooftops, made about 93 billion kWh in 2025. That is up from about 18.8 billion kWh in 2016 3.
Where production comes from
How production is estimated before you buy
Nobody can measure a system before it exists, so installers model it. The DOE points homeowners to PVWatts, a free tool from NLR (formerly NREL). It estimates the energy any grid-connected system will make at any address.
PVWatts takes a few inputs. You give it system size in kW, panel type, mount type, tilt, direction (called azimuth) and a loss figure. It pairs those with a typical weather year for your spot. PVWatts version 8 uses 2020 typical-year weather from the National Solar Radiation Database where that data exists.
The result is a month-by-month and yearly kWh estimate. Installers often use paid design software that also maps shade on your roof. Either way, the logic is the same: size, sun, angle and losses.
A real estimate: 7 kW in Charleston and Atlanta
We ran NLR's PVWatts version 8 on 7 October 2026 for two cities with the same inputs: 7 kW DC, standard module, fixed roof mount, 20° tilt, due south (180°), 14% system losses, and the PVWatts defaults of a 1.2 DC-to-AC ratio and 96% inverter efficiency 2.
| Result | Charleston, SC (32.78, −79.93) | Atlanta, GA (33.75, −84.39) |
|---|---|---|
| Annual AC production | 10,179 kWh | 9,812 kWh |
| Per kW installed | about 1,454 kWh | about 1,402 kWh |
| Best month | May, 1,038 kWh | May, 1,007 kWh |
| Weakest month | December, 598 kWh | December, 608 kWh |
| Capacity factor | 16.6% | 16.0% |
Charleston's winter months fall to roughly 60% of May. That swing is why a bill is not flat after solar. Your own result will differ with roof, shade and equipment.
Month by month, 7 kW in Charleston
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 710 | 751 | 889 | 943 | 1,038 | 962 | 971 | 902 | 849 | 832 | 734 | 598 |
How roof direction changes production
| Roof faces | Azimuth | Yearly kWh | Versus south |
|---|---|---|---|
| South | 180° | 10,179 | — |
| Southeast | 135° | 9,803 | about 4% less |
| Southwest | 225° | 9,792 | about 4% less |
| East | 90° | 8,883 | about 13% less |
| West | 270° | 8,869 | about 13% less |
| North | 0° | 7,325 | about 28% less |
The main things that move the number
- Size. Production scales almost in step with kW installed. Double the panels, roughly double the kWh.
- Direction. See the table above and our page on panel orientation.
- Angle. In the same Charleston model, lying flat (0°) gave 9,148 kWh and a 10° tilt gave 9,797 kWh, against 10,179 kWh at 20°. See panel tilt.
- Shade. Our runs used a 14% allowance for all system losses combined. A heavily shaded roof can lose more than that from shade alone. See solar shading.
- Heat and age. Hot cells make less power, and output declines slowly over the years. See panel degradation.
Where production shows up: quote, app and bill
On a proposal, look for "estimated annual production" or "year-one production" in kWh. Good proposals also show a monthly chart and name the tool that made it. Some show an "offset", which is production divided by your yearly usage.
In your monitoring app, you will see daily, monthly and lifetime kWh. DOE guidance says the installer should give you a monthly and yearly estimate and access to real-time data, so you can compare the two 5.
On your utility bill, you will not see total production. The meter sees only what flows in and out. Power your home uses as it is made never reaches the meter. Our guide to your first bill after solar walks through the lines.
What knowing your production gives you, and its limits
Why the number helps
- It lets you size a system to your real usage.
- It lets you compare quotes on the energy they deliver, not just on panel count.
- It gives you a baseline to spot faults later.
- With your rate, it turns into a savings estimate.
What it cannot tell you
- It is a model of a typical year. Real years run higher or lower.
- It does not say when the power is made, which matters on time-of-use rates.
- It does not say what each exported kWh is worth. That depends on your utility.
- Estimates that skip a shade survey can run too high.
Limits: why one year differs from the model
PVWatts and design tools use a typical weather year. Any single year can be cloudier or sunnier. So a few percent above or below the estimate is not a fault.
Production also does not tell you value. A kWh used at home saves the full retail rate. A kWh sent to the grid earns whatever your utility pays for exports, which may be much lower. Our guide to net metering, net billing and buyback explains the difference.
How production links to cost, lifespan and warranty
We do not quote dollar prices here. Production is the bridge between what you pay and what you save. See solar cost for current figures.
- Cost per kWh, not per panel. Two systems at the same price can differ in yearly kWh. More kWh for the same price means a better deal.
- Output fades slowly. Panel power warranties state the yearly loss. One current data sheet allows no more than 0.33% a year after year one 6.
- Long life. DOE guidance says major parts typically carry 25-year warranties and the system should produce for at least 30 years 5.
- Production guarantees. Some leases and contracts promise a minimum kWh. Read exactly what is paid if output falls short.
- Payback. Yearly kWh times your rate drives payback. Try the payback calculator.
How to check production against a quote
- Find the annual kWh estimate on the proposal and the tool that produced it.
- Run your address in PVWatts with the quoted size, tilt and direction, and the 14% default losses.
- If the quote is more than about 10% higher than your run, ask what loss and shading assumptions explain the gap.
- After installation, compare 12 months of monitoring with the estimate, not a single month.
The 10% threshold is our rule of thumb for starting a conversation, not an industry standard.
Keeping production on track
DOE guidance says a roof system has no moving parts and should need no routine maintenance. Rain usually cleans the panels well enough. Dust from a long dry spell has little effect.
Your job is to watch the app. Look at each month against the same month last year. Snow on a low-pitch roof may sit for days; DOE says you may clear it with a long-handled snow rake from the ground. Never climb onto the roof.
Sources: [5]
Warning signs of low production: when to call a pro
Call your installer for any of these. Our underproduction guide covers the common causes.
- The app shows zero on a sunny day. See monitoring shows zero.
- One panel or string reads far below the others.
- A month runs well below the same month last year, with no new shade.
- Twelve months of output fall clearly short of the estimate.
- An inverter shows a fault light or error code.
Safety
Do not open the inverter or touch panel wiring to find a fault. Panels make power whenever light hits them. A licensed installer should do all testing.
Rules that shape what your production is worth
No law sets how much a system must produce. Rules shape what each kWh is worth and how big the system can be.
Your state sets net metering policy, and your utility's tariff sets the credit rate and size cap.
The DOE advises checking with your utility, since net metering depends on state and utility practice 4.
In South Carolina, Act 62 of 2019 moved customers who applied after 1 June 2021 onto Solar Choice metering tariffs rather than legacy net metering 7.
Duke Energy Carolinas' Rider RSC nets usage within each time-of-use period monthly and credits any net excess at $0.0419 per kWh (Rider RSC, effective 1 January 2026) 8.
Production and credits in SC, GA and VA
South Carolina customers who applied after 1 June 2021 are on Solar Choice tariffs, so self-used and exported production are valued differently 7.
Duke Energy Carolinas caps residential systems at 20 kW AC 8. Georgia Power limits residential renewable facilities to 10 kW 9.
Virginia allows residential net metering up to 25 kW on investor-owned utilities 10.
Solar production compared with related terms
| Term | What it measures | Unit |
|---|---|---|
| Solar production | Energy made over a period | kWh |
| Panel wattage | Peak power of one panel in a lab test | W |
| Capacity factor | Production as a share of nonstop full power | % |
| Peak sun hours | Daily sunlight as hours of full-strength sun | hours/day |
| Irradiance | Strength of sunlight at one moment | W/m² |
Common misconceptions about solar production
- Myth Panels make nothing on cloudy days.
- Reality They make less, but output follows the light that gets through, so cloudy days still add some kWh.
- Myth A system makes the same every month.
- Reality The Charleston model ranges from 598 kWh in December to 1,038 kWh in May.
- Myth East and west roofs are useless.
- Reality In our Charleston model they made about 87% of a south roof.
- Myth My bill shows all my production.
- Reality The meter sees only imports and exports. Power used as it is made never shows up there.
When production matters to you
Use these rules when you plan or check a system:
- If you are comparing quotes, compare yearly kWh for the price, not panel count.
- If a quote has no monthly estimate, ask for one and the tool used.
- If your exports earn less than retail, size production closer to what you use.
- If output drops against last year, call the installer before the warranty runs out.
- Next step: size a system with the system size calculator, then estimate savings with the savings calculator.
Questions about solar production
How many kWh does a solar panel produce per day?
It depends on wattage and location. In our Charleston model, 7 kW made 10,179 kWh a year, about 4 kWh per kW per day on average.
A 440 W panel would average roughly 1.75 kWh a day there. It would make more in May and less in December. Run your own address in PVWatts for your number.
Do solar panels produce electricity on cloudy days?
Yes, but less. Output follows the sunlight reaching the panel, so a heavy overcast day can produce a small share of a clear day. Thin cloud costs less. Over a year, typical-year weather files used by PVWatts already include cloudy days, so the yearly estimate accounts for them.
How accurate is PVWatts?
It is a model built on typical-year weather, so any single year can be higher or lower. It is best used to compare designs and to check a quote, not as a guarantee.
It does not map shade on your roof, so you enter shade as part of the loss figure. Installer software with a shade survey can be more precise.
Is solar production the same as capacity?
No. Capacity is the system's size in kW, the sum of the panel ratings. Production is the energy it makes in kWh over time. Capacity factor links the two: it is production divided by what the system would make at full power every hour of the year.
How much does a 7 kW solar system produce?
About 9,800 to 10,200 kWh a year in the Southeast, if it faces south with little shade. Our PVWatts runs gave 10,179 kWh in Charleston and 9,812 kWh in Atlanta, at a 20° tilt with 14% losses. A shaded, east-facing or west-facing roof would make less.
Which month does solar produce the most?
In the Southeast, usually late spring. Our Charleston and Atlanta models both peaked in May. Summer days are longer, but heat lowers panel output and summer storms add cloud. December is the weakest month, at about 58% of May in Charleston and 60% in Atlanta.
Why is my solar producing less than estimated?
Common reasons are new shade, a faulty panel or inverter, dirt in a long dry spell, or an estimate that was too high to begin with. Weather also varies year to year. Compare 12 months against the estimate. If you are clearly short, ask the installer to check the system and the original shade assumptions.
Does solar production go down over time?
Yes, slowly. Panels lose a small share of output each year, and the power warranty states the most they may lose. One current data sheet allows no more than 0.33% a year after the first year. DOE guidance says a system should keep producing for at least 30 years.
How do I see how much my panels are producing?
Use the monitoring app or web portal your installer set up. DOE guidance says installers should give you access to real-time production data and a monthly and yearly estimate to compare against. Your utility bill alone will not show total production, because the meter only sees power flowing in and out.
Sources
- NLR (formerly NREL), PVWatts V8 API documentation, retrieved .
- PVWatts V8 API runs by HyreSolar, 7 October 2026 (7 kW, standard module, roof mount, tilt 20°, losses 14%, azimuth as stated, NSRDB PSM V3 TMY), retrieved .
- US EIA, Solar explained: Photovoltaics and electricity, retrieved .
- US DOE Solar Energy Technologies Office, Homeowner’s Guide to Going Solar, retrieved .
- US DOE Weatherization Assistance Program, Solar Frequently Asked Questions, retrieved .
- Qcells, Q.TRON BLACK (Q.TRON BLK S-G3R.12+/BFG 435–450) data sheet, 2025-08 Rev04, retrieved .
- South Carolina Code Title 58 Ch. 40 (Act 62 of 2019, customer-generators), retrieved .
- Duke Energy Carolinas (SC), Rider RSC Residential Solar Choice, retrieved .
- Georgia Power, Behind-the-Meter Interconnection Summary for Residential Customers (rev. 15 Aug 2025), retrieved .
- Code of Virginia §56-594 (net energy metering), retrieved .
Expert review
Written by the HyreSolar Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Production figures are direct outputs of PVWatts V8 API runs on 7 October 2026 with every input listed; per-kW, daily and percentage figures divide those outputs. National totals are from the EIA.
Monitoring, maintenance and lifespan guidance is from the DOE Weatherization solar FAQ. SC tariff facts are from sc-local/facts.js and the Duke rider; GA and VA caps from the Georgia Power summary and Va. Code §56-594.
Suggest a correction. We fix errors and say what changed.