Home solar questions, answered

Payback here is the installed price divided by one year of bill savings. It uses EnergySage's average price per watt in each state, our PVWatts estimate of what 1 kW of south-facing panels makes there, and EIA's average home electricity price. It assumes every kWh the panels make is worth the full retail rate, which is only true if you use it all yourself or your utility credits exports at full price.

The Department of Energy lists what drives your own number: how much electricity you use, the size of the system, whether you buy or lease, how much sun your roof gets, your utility's rates and how much it pays for the extra power you send back. State and utility rebates, where they exist, shorten payback; DSIRE lists them.

Panels also lose a little output each year (see how long panels last, below), which stretches payback slightly.

EnergySage gives two reasons a battery-free system shuts off. Solar output changes minute by minute, which the grid smooths out but your home's wiring and appliances could not handle alone. And the main one: line-worker safety. Solar inverters keep checking that the grid is up and shut the panels' output down when they cannot detect it.

Home batteries usually cannot run a whole house, so installers ask which circuits to back up and put them on a critical loads panel. A smart electric panel lets you change that later.

The Department of Energy describes storage as a way to use solar power when it is needed most, regardless of whether it's sunny at the time: at night, after dinner, or when the power goes out.

At that price, one 13.5 kWh battery is about $15,255. The IRS's Residential Clean Energy Credit listed battery storage technology of at least 3 kWh as a qualified expense, and is not available for property placed in service after December 31, 2025.

Because output swings this much by season, solar calculators and installers size a system on its yearly total.

The same study found the rate depends on climate, with panels degrading more slowly in cooler places, and that it did not differ much between module technologies.

For the arithmetic: losing 0.75% a year compounds to about 93% of the original output after 10 years and about 80% after 30. The study measured larger, non-home systems; home systems were not part of it.

The Department of Energy suggests checking whether net metering is available in your service area, which system sizes and customer types qualify, the rates, and how the bill credits work.

DSIRE lists net metering and other solar policies by state.

Panel counts assume 400 W panels on an unshaded, south-facing roof at a 20 degree tilt, the same assumptions as our solar calculator.

• Utah (HB 340): Signed March 2025; in effect since May 7, 2025.
• Maine (LD 1730): Signed April 6, 2026 (Public Law 2025, c. 644).
• Virginia (HB 395 / SB 250): Signed April 22, 2026; takes effect January 1, 2027.
• Colorado (HB26-1007): Signed May 7, 2026; in effect since August 12, 2026.
• Maryland (HB 1532): Signed May 12, 2026 (Chapter 353); in effect since July 1, 2026.
• Connecticut (HB 5340): Signed June 4, 2026 (Public Act 26-127); in effect since October 1, 2026.
• Vermont (S.202): Signed June 16, 2026 (Act 149); in effect since July 1, 2026.
• New Hampshire (SB 540): Signed July 2, 2026 (Chapter 262); takes effect January 1, 2027.
• New Jersey (S2368 / A4836): Signed September 1, 2026; the governor's office says it takes effect March 1, 2027.
• California (SB 868): Signed September 30, 2026 (Chapter 985); takes effect January 1, 2027.
• New York (S8512C / A9111C): pending.

Each law sets its own rules on size, certification, notice to the utility and whether exported power earns credit. Our plug-in solar guide summarizes each one and links to the bill.