NEM 3.0 Calculator: California Net Billing Savings With and Without a Battery

A NEM 3.0 calculator estimates California solar savings when solar you use at home offsets your import price but exports earn much lower avoided-cost credits. With the defaults, 9,000 kWh of solar saves about $1,728 a year alone and $2,749 with a 13.5 kWh battery, against roughly $3,600 for the same system under the old NEM 2.0.

How to use the NEM 3.0 calculator

1. Yearly solar output. From your installer's proposal. Default 9,000 kWh.
2. Yearly electricity use. 12 months of kWh from your utility account. Default 9,000 kWh.
3. Solar used directly without a battery. Commonly 25% to 45% for California homes. Default 35%.
4. Average price of power you buy. Your time-of-use rate, weighted toward evening peak hours. Default 40¢ per kWh.
5. Average credit for exports. Export values change by hour and month; most midday exports earn only a few cents. Default 8¢.
6. Battery size (0 for none). Default 13.5 kWh.
7. Advanced: Days the battery fully cycles (300) and Round-trip efficiency (90%).

The results show yearly savings with the battery, solar only, the extra savings from the battery and a rough NEM 2.0 comparison, with a bar chart of all three. A 25-year schedule (rates rising 3% a year, panels losing 0.5% a year) gives yearly and running totals for solar only and with the battery, downloadable as CSV. The scenario table compares no battery, 13.5 kWh and 27 kWh.

How the calculation works

Direct self-use   = min(output × self-use %, use)
Exports, no batt  = output − direct self-use
Stored per year   = min(battery kWh × 90% usable × cycle days, exports)
Battery output    = min(stored × round-trip efficiency, use not yet covered)
Solar only        = direct self-use × import price + exports × export credit
With battery      = direct self-use × import price + battery output × import price
                    + (exports − energy stored) × export credit
NEM 2.0 (rough)   = min(output, use) × import price

Assumptions that match the code:

• 90% of the battery size is usable in the model, on top of round-trip losses.
• The battery charges only from solar that would otherwise be exported, and its output offsets power you would buy at the average import price.
• Yearly averages for prices; no hourly export values or ACC Plus adder.
• No fixed charge and no non-bypassable charges.
• The schedule grows savings by 3% a year and trims them by 0.5% a year for panel aging.

Worked example

Default inputs: 9,000 kWh output and use, 35% self-use, 40¢ import, 8¢ export, 13.5 kWh battery, 300 cycle days, 90% round trip.

• Direct self-use: 3,150 kWh × $0.40 = $1,260. Exports: 5,850 kWh × $0.08 = $468.
• Yearly savings, solar only: $1,728.
• Battery: 13.5 × 0.9 × 300 = 3,645 kWh stored, 3,281 kWh delivered.
• Yearly savings with battery: $2,749; extra savings from the battery: $1,021.
• Same system under old NEM 2.0 (rough): $3,600.
• Over 25 years the schedule totals about $58,910 for solar only and $93,704 with the battery.

Doubling the battery adds less the second time, because there is less excess solar and less evening use left to shift.

Second example, a smaller system on a larger home: 7,500 kWh output, 10,000 kWh use, 30% self-use, 36¢ import, 5¢ export, 13.5 kWh battery.

• Solar only: $1,073 a year. With battery: $2,071, so the battery adds $999.
• Rough NEM 2.0 value: $2,700. Over 25 years: about $36,563 solar only and $70,611 with the battery.

What your result means

The gap between solar-only and NEM 2.0 shows how much the export rule costs you. The battery line shows how much of that gap storage can win back. Compare the battery's extra savings with its price using the time of use battery savings calculator, and read our California NEM 3.0 guide and are solar batteries worth it.

Rules that change the answer

• Eligibility. The Net Billing Tariff covers PG&E, SCE and SDG&E applications on or after April 15, 2023 (CPUC D.22-12-056 (opens in a new tab)). Legacy NEM customers keep their tariff for 20 years from interconnection.
• Export values are hourly avoided-cost values, locked for nine years for early enrollees (CPUC (opens in a new tab)).
• ACC Plus adder. Locked for nine years: PG&E $0.022 per kWh (CARE $0.090), SCE $0.040 (CARE $0.093), SDG&E $0. The adder for new enrollees falls 20% a year and reaches zero after five years.
• Fixed charge. About $24.15 a month for most customers; SCE and SDG&E began billing it in late 2025 and PG&E in March 2026 (PG&E (opens in a new tab)).
• Annual true-up remains, with monthly billing.
• Federal credit. As of October 2026, the 25D credit does not apply to systems completed after December 31, 2025. See our federal solar tax credit guide and the net metering calculator for other states.

Common mistakes

• Using retail as the export credit.
• Using the off-peak rate as the import price when most of your purchases fall in the evening peak.
• Assuming 365 full battery cycles; winter and cloudy days cycle less.
• Oversizing solar for 100% offset, which mostly adds low-value exports.
• Forgetting the fixed charge when estimating your new bill.

Limits of this calculator

This is an educational estimate using yearly averages. It does not model hourly export values, seasonal rate differences, the ACC Plus adder, the fixed charge, non-bypassable charges or battery exports at peak. Ask installers for an hourly bill simulation under your actual rate and export schedule before you sign.