Model your electric bill, solar system, battery and payback using current California utility data — with the assumptions, rates and official sources shown behind every result. No sign-up.
Whole-house sizing
Updated August 6, 2026 · based on NREL PVWatts Los Angeles production data · by Cali Energy
Can solar power a whole house in California? For annual energy, yes. A home using about 9,000 kWh a year needs roughly a 5.3 kW system — about 14 panels at 400 W — to offset 100% of its electricity, if the roof and shading allow. Running the house overnight or through an outage is a separate battery question, not a bigger array.
✓ Built on NREL PVWatts Los Angeles production (~1,700 kWh per kW-year) — not a guess. See every figure it uses ↓
Offsetting your yearly use (not a backup calculator).
Assumptions: LA modeled production ~1,700 kWh per kW per year (NREL-based); 400 W modules; bill converted at ~35¢/kWh (a very rough conversion — fixed charges and time-of-use rates distort it, so prefer entering annual kWh from your last 12 bills). Planning estimate for annual offset, not a quote; real design depends on roof orientation, tilt and shading. Battery/backup sizing is separate.
The rates and figures this calculator usestap to verify
The tool sizes a system to your annual usage using Los Angeles production and a 400 W panel — here is every number it uses, with the production figure linked to its source.
| Energy per kW installed, per year | ~1,700 kWh |
| Basis | Fixed roof-mount, standard system losses |
| Panel wattage | 400 W |
| Bill → usage (only in $ mode) | ~$0.35 / kWh (rough) |
| Annual use | yearly kWh, or monthly bill ÷ $0.35 × 12 |
| Minimum modeled size | annual ÷ 1,700 |
| Panels | modeled kW × 1000 ÷ 400, rounded up |
| Installed size (kW DC) | panels × 0.4 |
Production is NREL PVWatts modeling for Los Angeles — the coast runs a little lower and hot inland a little higher. This offsets annual energy; running the home after sunset or through an outage is a battery-sizing question, not a larger array. The $0.35/kWh bill conversion is rough (fixed charges and time-of-use rates distort it) — enter annual kWh from your last 12 bills for accuracy.
Example results you can reproduce
Each row enters a yearly-kWh figure with 400 W panels — enter the same value above to reproduce it.
| Annual use | Modeled minimum | Rounded system |
|---|---|---|
| 6,000 kWh | 3.5 kW | 9 panels · 3.6 kW DC |
| 9,000 kWh | 5.3 kW | 14 panels · 5.6 kW DC |
| 12,000 kWh | 7.1 kW | 18 panels · 7.2 kW DC |
How this calculator works
It takes your annual usage — entered directly in kWh, or estimated from a monthly bill at ~$0.35/kWh — and divides by Los Angeles production of about 1,700 kWh per kW of panels each year (NREL PVWatts) to get the minimum modeled size. Dividing by 400 W and rounding up gives the panel count, and those whole panels come to a slightly larger installed size (panels × 0.4 kW) — both are shown so the kW and panel count always agree. Because it works from your annual total, the answer already accounts for your air conditioning and every other load across the year. These are Cali Energy planning calculations, not a stamped design.
How to read your result
You get your annual use, the minimum modeled size in kW that offsets it, and the practical system once that’s rounded to whole panels (panel count and installed kW DC). “Offsetting your use” means producing as many kWh over a year as you consume — it does not mean the panels power the house directly at every moment. At night you draw from the grid (or a battery) and bank credit by day.
What moves the result the most
Your annual usage drives it almost entirely, followed by whether your roof has the space and sun for the full system. Bigger, all-electric or EV-charging homes need proportionally more; a smaller, gas-heated home needs less. Local sun matters too — the same house needs a slightly larger array on a shaded or north-facing roof.
Common questions
What do I need to use this calculator?
Your annual electricity use in kWh (add up the last 12 bills, or read it off an annual summary), or a typical monthly bill in dollars. Entering kWh is far more accurate than the bill estimate.
Can solar really cover 100% of my house?
On an annual basis, yes — if your roof has enough unshaded space for the system size shown. Over a year the panels can produce as many kWh as you use; the grid or a battery covers the times they don’t.
Will it run my house at night or in a blackout?
Not on its own. Offsetting annual energy and keeping power during an outage are different problems — backup is a battery sized to the loads you need and for how long. A battery isn’t required just to offset your yearly use.
Does the estimate include my air conditioning?
Yes. Because it sizes to your annual kWh, everything you used across the year — summer AC included — is already in the total.
Should I size bigger for an EV or future electrification?
If you plan to add an EV, a heat pump or an induction range, size to your expected future usage, not just last year’s. Add the extra annual kWh to your input before reading the system size.
Is my roof big enough for the system it shows?
Roughly 20 sq ft of usable roof per 400 W panel — so a 14-panel system needs about 280 sq ft of clear, well-oriented roof. Setbacks, vents and shade reduce what’s usable.
Is this a quote?
No — it’s a planning estimate from NREL production data. A real design depends on your roof planes, orientation, shading and equipment, and your rate plan (LADWP vs SCE) changes the economics.
Sources
- EIA — Electric Power Annual, Table 2.8 (residential sales & customers)
- DOE — Homeowner's Guide to Going Solar (sizing)
- NREL — PVWatts (production per kW)
Estimates only, not a quote. Assumptions, rates, incentives and program rules can change — confirm current details with your utility, the program administrator or a licensed professional.
Read the full guide →