Solar + battery calculator
How much solar does your bill need?
Pick your utility and slide to your monthly bill. You'll see a system size, panel count, battery size and savings range, and every number the math uses is listed below it.
Checked . Sources linked in the text.
By the Golden Hour Energy editorial team. How we research and check our guides
Your bill already holds the answer to how big a solar system you need. Divide the dollars by your utility's price per kWh and you have your usage. Divide a year of usage by what one kilowatt of panels makes in Southern California and you have a system size. The calculator below does that, then sizes a battery for the 4 to 9 p.m. peak.
Your estimate
System size
4.5 kW
Panels
about 10
430 W each
Yearly use
7,413 kWh
Roof space, about
220 sq ft
Estimated bill savings
$105 to $170 a month
About $1,260 to $2,040 a year, with a right-sized battery.
Battery: about 6.7 kWh of your daily use likely falls from 4 to 9 p.m. That points to one 13.5-kWh-class battery.
Check my actual homeEstimate, not a quote. Real pricing comes from a licensed installer after a site review.
How the math works
Nothing here is hidden. These are the exact steps and numbers the calculator uses, so you can check them against your own bill or an installer's proposal.
- Bill to usage. A summer bill runs above your yearly average, so it's scaled down by 15%. A winter bill is scaled up by 10%. The result is divided by your utility's average price per kWh: 34.4¢ for SCE (SCE, June 2026) and 46.4¢ for SDG&E (SDG&E, April 2026). LADWP uses 30¢, the middle of its tiers.
- Usage to system size. Twelve months of usage divided by 1,650 kWh, our rule of thumb for what one kW of well-placed panels makes in a year in Southern California. NREL's (now NLR) PVWatts calculator will give you a figure for your exact address and roof angle.
- Size to panels. System watts divided by 430 W, a common residential panel size today.
- Savings. A share of your average bill, which differs by utility and drops with shade. Fixed charges and evening use you can't shift keep it from reaching 100%.
- Battery. We assume about 33% of a day's use falls between 4 and 9 p.m., then round up to batteries of about 13.5 kWh, the usable size of a Tesla Powerwall 3 (Tesla).
| Topic | SCE | SDG&E | LADWP |
|---|---|---|---|
| Price per kWh used | 34.4¢ avg | 46.4¢ avg | about 30¢ (tiered) |
| Billing for exports | NEM 3.0 | NEM 3.0 | LADWP net metering |
| Battery suggested | Yes | Yes | Optional, for backup |
| Yearly output per kW | 1,650 kWh | 1,650 kWh | 1,650 kWh |
What the calculator can't see
It doesn't know which way your roof faces, how steep it is, what's shading it at 3 p.m. in December, or whether you're about to add an EV or a heat pump. Those change the answer more than any rate does. If the numbers look worth it, our guide to how many solar panels you need goes deeper on each of them.
It also doesn't price the system. Battery prices alone vary widely: EnergySage puts the average California home battery at about $13,500 installed before incentives (EnergySage).