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Solar Grid Export Optimizer

Maximize solar self-consumption vs grid export. Model NEM 3.0, high export rates, or TOU arbitrage — see how battery storage shifts the economics and optimal battery sizing.

Solar system and load profile
kW
kWh/day
kWh
Rate structure
$/kWh
$/kWh
$/kWh
$/kWh
Grid export optimization results
Self-consumption: 17% without battery → 47% with battery
Self-consumption % (no battery)17%
Self-consumption % (with battery)47%
Daily export kWh (no battery)33.2 kWh/day (lost value at low export rate)
Daily export kWh (with battery)21.1 kWh/day
Daily grid import (no battery)27.2 kWh/day
Daily grid import (with battery)15.7 kWh/day
Annual bill (no battery)$2,174/yr
Annual bill (with battery)$1,068/yr
Annual savings vs no solar (no battery)$1,233/yr
Annual savings vs no solar (with battery)$2,339/yr
Additional annual value from battery$1,106/yr
Value of each additional kWh of battery$75.56/kWh battery/yr
Optimal battery size for evening load21.0 kWh
Break-even battery size (at $900/kWh)12 kWh
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How to Use This Calculator

Enter your solar system and load profile

Start with your solar system size and daily production. Then select your load profile — this is critical. An evening-heavy home (family cooking, entertainment, AC after work) uses most electricity when solar isn't producing. A daytime-heavy home (work-from-home, heavy AC during day) uses electricity while solar is producing. Your load profile determines how much solar goes to self-consumption vs. grid export.

Set your rate structure

The gap between export rate and retail rate is the key economic driver. Under NEM 1.0/2.0, export credited at full retail rate — self-consumption wasn't critical. Under NEM 3.0 in California, export is credited at 3-8¢ while retail rates are 28-55¢ — a 5-10x gap that makes batteries financially essential. Enable TOU to model time-of-use rates where peak hours (4-9pm) have much higher rates — batteries that shift solar to peak hours dramatically improve savings.

Read the results

The calculator shows self-consumption percentage with and without battery, export and import quantities, annual bill comparison, battery added value, and optimal battery sizing for your load profile. The break-even battery size shows when additional battery capacity stops paying for itself.

The Formula

Daily Load = Daily Production × 0.85 (typical home near grid parity) Daytime Direct Consumption = min(Daytime Load, Solar Production) Excess Solar = max(0, Production − Daytime Load) Battery Charge = min(Battery kWh × 0.9, Excess Solar) Evening Import (no battery) = Evening Load Evening Import (with battery) = max(0, Evening Load − Battery Discharge) Self-Consumption % = (Production − Export) ÷ Production × 100 Annual Bill = Import × Rate − Export × Export Rate Marginal Battery Value = (Retail Rate − Export Rate) × 0.9 × 365 per kWh/yr

The optimizer assumes solar production is concentrated in the 8am-4pm window. Load profile determines what fraction of daily consumption occurs in each period. The marginal battery value formula captures the economic benefit of shifting one kWh from low-value export to high-value self-consumption — this is the fundamental NEM 3.0 economics driver.

Example

The Garcias — NEM 3.0 California, 8 kW solar, evening-heavy usage

The Garcias have an 8 kW solar system in San Diego producing 40 kWh/day. They're on NEM 3.0 with a 5¢/kWh export rate, $0.28/kWh retail rate, and TOU peak rate of $0.45/kWh from 4-9pm. They're deciding whether to add a 13.5 kWh Powerwall.

Solar8 kW, 40 kWh/day
Load profileEvening-heavy
Export rate$0.05/kWh (NEM 3.0)
Retail rate$0.28/kWh
TOU peak rate$0.45/kWh (4-9pm)

Result

Self-consumption (no battery)~24% — most solar exported at 5¢
Self-consumption (with battery)~78% — battery captures daytime solar
Annual savings without battery~$800/yr
Annual savings with battery~$2,400/yr
Battery added annual value~$1,600/yr
Break-even battery size~39 kWh at $900/kWh cost

Under NEM 3.0, the Garcias' 8 kW solar system is almost worthless without a battery — exporting 76% of production at 5¢ while buying evening power at $0.28-0.45. Adding the Powerwall triples their annual savings from $800 to $2,400. The battery pays for itself in approximately 8 years while also providing backup power.

FAQ

NEM 3.0 (Net Billing Tariff) is California's solar interconnection policy effective April 2023. Under NEM 1.0 and 2.0, exported solar was credited at the full retail rate — self-consumption didn't matter economically. Under NEM 3.0, exported solar is credited at the "Avoided Cost Calculator" rate — roughly 3-8¢/kWh — while retail rates are 28-55¢/kWh. This 5-10x gap means a solar system without battery storage earns very little from its excess production. Batteries retain that value by storing the solar for later self-consumption instead of selling it cheap.
Solar panels produce electricity from roughly 8am to 4pm. An evening-heavy household uses most energy from 5-10pm. Without a battery, excess daytime solar gets exported to the grid (at low NEM 3.0 rates), and evening consumption gets drawn from the grid (at high TOU peak rates). A battery stores daytime solar excess and discharges it during the evening peak — converting cheap exported energy into avoided expensive grid purchases. A 13.5 kWh battery can typically shift 10-12 kWh per day, covering most of a typical family's evening load.
The break-even battery size is the capacity at which adding more battery stops paying for itself. Each kWh of battery storage shifts (Retail Rate - Export Rate) × 365 of value per year. At $900/kWh installed cost and a $0.23/kWh spread, each kWh of battery earns $84/year, paying back in ~11 years. When the rate spread is small (full retail NEM 2.0), battery value drops and break-even size shrinks. When the spread is large (NEM 3.0, high TOU rates), every kWh of battery capacity is highly valuable.
Yes — the optimal solar size under NEM 3.0 is smaller and paired with larger batteries, compared to NEM 2.0 where bigger solar always meant more savings. Under NEM 3.0, oversized solar produces large amounts of cheap-credit export. The goal shifts from "maximize production" to "maximize self-consumption." A system sized to cover 80-90% of your self-consumable load (what you can use plus store) is typically optimal. Adding more solar beyond what you can self-consume has diminishing returns under low export rates.
TOU rates create arbitrage opportunities: charge battery when rates are low (solar daytime or off-peak overnight) and discharge when rates are high (peak 4-9pm). A battery on a $0.45/kWh peak / $0.14/kWh off-peak TOU schedule captures $0.31/kWh of arbitrage per cycle. With one cycle per day and 90% round-trip efficiency, that's $102/kWh battery/year — enough to pay back a $900/kWh battery in under 9 years, ignoring the solar self-consumption benefit. Most modern battery inverters have scheduling features to optimize charge/discharge timing.

Related Calculators

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🔋 Battery Arbitrage Calculator
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🕐 Time-of-Use Calculator
Optimize solar and battery for time-of-use rate schedules.
💰 Solar Savings Calculator
Estimate annual electricity bill savings from your solar system.

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