How this calculator works
Two identical solar systems on identical houses can save very different amounts of money. The panels aren’t the difference. The compensation scheme is, because it decides what an exported kilowatt-hour is worth. This calculator runs the same household through every common scheme, month by month, and shows the annual bill under each.
Your annual solar production is spread over the year with a typical seasonal pattern for your climate, and your consumption with a pattern that matches your home (flat, lighting-driven, electric heating or air conditioning). Each month, a share of production is used directly in the house; the rest is exported, and the shortfall is imported. Four sets of rules are then applied:
- Net metering: exports and imports are netted kWh for kWh. Surplus kWh are banked and rolled over, paid out monthly, or forfeited, and the bank is settled once a year at the true-up date. Non-nettable network charges, if any, are billed on every imported kWh.
- Net billing: each exported kWh earns a money credit at the export rate. The credit can reduce energy charges but not the fixed fee. Unused credit rolls over, expires monthly, or is paid at year end.
- Feed-in (net export): imports are paid at the retail price and exports are paid separately at the feed-in price.
- Gross feed-in (optional): all production is sold at a fixed tariff and all consumption is bought from the grid.
The formulas
Net metering: billable_m = import_m − export_m − bank_(m−1) bill_m = fixed + import_m × p × nn% + max(0, billable_m) × p × (1 − nn%) bank_m = max(0, −billable_m) → leftover × true-up rate at year end Net billing: bill_m = fixed + max(0, import_m × p − export_m × p_export − credit_(m−1)) Feed-in: bill_m = fixed + import_m × p − export_m × p_FiT
Worked example: 5,000 kWh home with 5,000 kWh of solar
The defaults model a home using 5,000 kWh a year with a system producing the same amount, in a south-east European climate. 30% of production (1,500 kWh) is used directly; 3,500 kWh are exported and 3,500 kWh imported. Electricity costs €0.25/kWh plus €8 a month, so without solar the bill is about €1,346.
- Net metering cuts the bill to about €176, saving €1,170. The kWh bank builds from April, peaks at about 920 kWh in September and still holds 381 kWh at a January true-up, which are paid out at only €0.04/kWh.
- Net billing at €0.08 per exported kWh leaves a bill of €691, a saving of €655.
- Feed-in at €0.06/kWh leaves €761 and saves €585.
The self-consumed 1,500 kWh are worth €375 in every scheme. The whole difference comes from the exported 3,500 kWh, valued at about €0.23 under net metering against €0.06–0.08 otherwise. Moving the netting year to start in April (advanced option) lets the summer bank cover the following winter: the saving rises to about €1,250.
How to read the results
- Value per exported kWh should drive your decisions on system size and batteries. Close to the retail price? Export freely. A quarter of it? Push self-consumption as high as you can.
- NM credit forfeited above zero means the system is larger than your annual use, or the true-up month strands credit.
- The monthly chart shows imports, exports and the net-metering bank. A bank that is still large at the true-up date is wasted value.
Typical values
| Scheme (examples) | Export value | Typical saving per solar kWh |
|---|---|---|
| Full retail net metering (many US states, historic EU schemes) | 100% of retail energy price | 0.9–1.0 × retail |
| Net metering, network fees not netted | 50–70% of retail | 0.6–0.8 × retail |
| Net billing at wholesale/avoided cost | 20–40% of retail | 0.35–0.6 × retail |
| Net-export feed-in tariff | 10–35% of retail | 0.3–0.55 × retail |
| No payment for exports | 0 | equals self-consumed share only |
Tips
- Read the tariff sheet carefully. Netting interval, rollover rules, true-up date, minimum bills and whether taxes apply to credits are often decisive.
- Size close to annual use under net metering; extra kWh earn only the true-up rate.
- Under net billing or feed-in, raise self-consumption: shift dishwasher, laundry, water heating and EV charging to midday, or test a battery.
- Get a realistic production figure from the solar panel calculator and a realistic self-consumption share from the battery calculator’s hourly simulation (with no battery set).
- Check grandfathering. Many regions lock existing systems into the old scheme for 10–20 years when rules change.
Limitations
The model works in monthly steps with a fixed self-consumption share; real self-consumption varies with weather and routine, so results can differ by a few percent from hourly analysis. Time-of-use prices, demand charges, export limits, taxes on credits and minimum-bill rules aren’t modelled separately. Approximate them through the price, fixed charge and non-nettable share. Seasonal production shapes are typical for each climate band, not specific to your roof.
Method & assumptions
Annual production and consumption are spread over the months with typical shapes. Each month: self-consumed = min(production × direct share, consumption); import = consumption − self-consumed; export = production − self-consumed.
Net metering: billable kWh = import − export − banked credit; positive → billed at the nettable price, negative → banked, paid or forfeited per your rule; leftover bank in December is paid at the true-up rate. Net billing: credit = export × export price + carried credit; bill = fixed + max(0, import × price − credit). Feed-in: bill = import × price + fixed − export × feed-in price. Savings are against the same household with no solar.
Frequently asked questions
What is the difference between net metering and net billing?
How does a net metering true-up work?
Is it better to have net metering or a feed-in tariff?
Should I size my solar system bigger than my usage under net metering?
Does a battery make sense with net metering?
What are non-nettable charges?
Sources & references
Embed this calculator
Free for blogs, installers, schools and NGOs. Copy the code below; it updates itself automatically.