Solar Surplus Calculator - How Much Energy You Export and What It Earns

Solar surplus and why self-consumption decides your savings

A 10 kW residential system in the US produces roughly 13,000-15,000 kWh per year, but the average home consumes only 10,500 kWh. The gap between production and consumption is your surplus - and how your utility compensates that surplus determines whether solar saves you $800 or $2,200 per year. Under true 1:1 net metering, every exported kWh earns full retail value, so the self-consumption percentage barely matters. Under net billing or avoided-cost policies, exported energy earns $0.03-$0.08/kWh instead of $0.15-$0.35 retail. That gap is where thousands of dollars disappear.

How to use this calculator - step by step

Annual solar production (kWh) - enter the total kWh your system generates per year. Check your inverter monitoring app or use the Solar Production Calculator to estimate based on system size and location.
Annual electricity consumption (kWh) - find this on your utility bill (12-month total). The US average is about 10,500 kWh. Homes with EVs or heat pumps use 14,000-18,000 kWh.
Self-consumption (%) - what share of production you consume while the panels are generating. Without battery: 25-40%. With battery: 60-80%. With battery and EV: 80-95%.
Billing policy - select how your utility credits surplus. Net metering 1:1 gives full retail credit. Net billing pays a separate (lower) export rate.
Electricity rate ($/kWh) - your effective rate from the utility including energy, delivery, and fees.
Export rate ($/kWh) - for net billing or direct sale only. Typically $0.03-$0.08/kWh. Leave at 0 for net metering (auto-calculated at retail).
Read the results - the calculator shows your annual savings split between self-consumed energy and exported surplus, your remaining grid bill, and practical tips for increasing self-consumption.

Self-consumption impact on annual savings

This table shows how self-consumption percentage affects savings for a 10 kW system producing 14,000 kWh/year, with $0.18/kWh retail rate and $0.05/kWh export rate (net billing).

Self-consumption	Self-used (kWh)	Exported (kWh)	Savings from self-use	Export income	Total savings
25%	3,500	10,500	$630	$525	$1,155
40%	5,600	8,400	$1,008	$420	$1,428
60%	8,400	5,600	$1,512	$280	$1,792
80%	11,200	2,800	$2,016	$140	$2,156
100%	14,000	0	$2,520	$0	$2,520

Net metering vs. net billing - what the policy means for your wallet

Policy	Export credit	Self-consumption matters?	States / trend
Net metering 1:1	Full retail rate	Not much	Declining - many states phasing out
Net metering (reduced)	50-80% of retail	Moderate	Growing - transitional policies
Net billing	$0.03-$0.08/kWh	Critical	California NEM 3.0, Hawaii, Nevada
Direct sale	Wholesale rate	Critical	Commercial systems, PURPA

Real-world examples

Arizona family, net metering 1:1
12,000 kWh produced, 10,000 kWh consumed, 35% self-consumption, $0.14/kWh retail
Savings: $1,400/year - surplus credited at retail up to consumption

California couple, NEM 3.0
15,000 kWh produced, 9,000 kWh consumed, 30% self-consumption, $0.35/kWh retail, $0.05 export
Savings: $2,100/year - high retail rate offsets low export value

Texas homeowner, no net metering
14,000 kWh produced, 12,000 kWh consumed, 25% self-consumption, $0.13/kWh retail, $0.03 export
Savings: $771/year - low self-use + low export = minimal savings

New York with battery
10,000 kWh produced, 11,000 kWh consumed, 75% self-consumption, $0.22/kWh retail, $0.06 export
Savings: $1,800/year - battery shifts surplus to evening use

Colorado EV owner
16,000 kWh produced, 16,000 kWh consumed, 60% self-consumption, $0.15/kWh retail, $0.04 export
Savings: $1,696/year - high consumption absorbs most production

Frequently asked questions

What is a good self-consumption rate for solar?

Without a battery, 30-40% is typical for a household that is empty during the day. Shifting loads to midday (laundry, dishwasher, water heater timers, EV charging) can push it to 40-50%. Adding a home battery raises self-consumption to 60-80%. Off-grid systems with large battery banks can reach 90-100%.

How much does net metering 1:1 save compared to net billing?

For a system exporting 8,000 kWh/year: under 1:1 net metering at $0.18/kWh retail, you earn $1,440 in credits. Under net billing at $0.05/kWh, you earn $400. That is a $1,040 annual difference. This is exactly why self-consumption becomes critical under net billing - every kWh you consume yourself is worth 3-4 times more than one you export.

Does oversizing a solar system make sense under net billing?

Under net billing, excess production earns a low export rate, so oversizing gives diminishing returns. A system sized to cover 80-100% of consumption with high self-consumption is usually more cost-effective than a larger system that exports heavily. The exception is if you plan to add an EV or heat pump soon - then sizing for future consumption makes sense.

What happens to my surplus credits at the end of the year?

Under most net metering policies, unused credits roll over month to month. At the annual true-up (usually in April), the utility either pays out remaining credits at avoided-cost rate ($0.02-$0.04/kWh), resets them to zero, or carries them forward indefinitely. The true-up rules vary by state and utility. Check your specific tariff.

Can I sell surplus directly to neighbors or the wholesale market?

Peer-to-peer solar trading is legal in a few pilot programs but not widely available. Selling directly to the wholesale market requires a PURPA qualifying facility contract and is typically only practical for commercial-scale systems (100+ kW). Most residential owners are limited to their utility's net metering or net billing program. Community solar programs offer an alternative where you share production with neighbors.

How does time-of-use (TOU) pricing affect surplus value?

Under TOU rates, electricity costs more during peak hours (usually 4-9 PM) and less during off-peak. Solar panels produce most during midday (off-peak under TOU). This means exported surplus earns the lower off-peak rate, reducing its value. A battery lets you store midday surplus and discharge during peak hours, earning the higher TOU rate. In California, TOU can make a $500-$800/year difference compared to flat-rate billing.

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