Net metering or a battery?
Once your panels are generating more than the house is using, that surplus has to go somewhere. There are exactly two destinations: the grid, or a battery. Which one you should build around is decided almost entirely by the rules your utility sets, not by the technology.
The three export regimes
| Regime | What you get for an exported unit | What it means for you |
|---|---|---|
| Full net metering | The same as you pay to import | The grid is a free, lossless, infinite battery. A battery adds almost nothing financially. |
| Net billing / feed-in | A fraction — often 25–60% of retail | Self-consumption is worth more than export. Storage starts to make sense. |
| Zero export | Nothing, and you may be required to block it | Every surplus unit is wasted unless you store it. Storage is the only option. |
Find out which one applies to you before you design anything. The answer is on your utility's website under "net metering", "distributed generation" or "prosumer" rules, and it changes the correct system design completely.
Why net metering is so hard to beat
Under true net metering, the grid behaves like a battery with perfect round-trip efficiency, unlimited capacity, no capital cost, no degradation and no maintenance. Nothing you can buy competes with that.
A battery under full net metering is bought for one reason only: to keep the lights on in an outage. That is a real and legitimate reason. It is just not a financial one, and you should not let anyone sell it to you as an investment when it is insurance.
The arithmetic when export is worth less
This is where most people now are, because utilities worldwide have been retreating from full net metering.
Say you import at 55 a unit and export at 27. Every unit you divert from export into your own evening consumption earns you the difference: 28 a unit. That spread is the entire financial return of the battery.
A 10 kWh battery cycled 300 times a year at 80% utilisation shifts about 2,400 kWh. At a spread of 28 that is 67,200 a year. If the battery cost 320,000, simple payback is 4.8 years — against a warranty that might run ten. That works, but only just, and only because the spread is wide and the cycling is heavy.
Now halve the spread to 14 and the payback doubles to 9.5 years, which is most of the warranty. Halve the cycling because your surplus is small and it fails outright. The battery case is fragile in a way the panel case is not.
Why panels nearly always beat batteries on return
Panels have no moving parts, degrade at well under 1% a year, carry 25-year warranties and generate new energy. Batteries wear out by being used, carry warranties around half as long, and do not generate anything — they only move energy in time, losing 6–20% of it in the process.
Spend a fixed budget on panels and you buy generation for 25 years. Spend it on storage and you buy a time-shift for ten. Unless export is worth very little or your grid is unreliable, the panels win.
The order that usually makes sense: panels first, up to the limit your roof and export rules support. Then, if outages are a real problem, a battery sized for the loads you genuinely cannot lose.
The case where a battery clearly wins
All of the above is about money. If your grid fails regularly, the comparison is not battery versus net metering — it is battery versus diesel generator, and that changes everything.
A generator has a low purchase price and a brutal running cost: fuel at every outage, oil changes, filters, noise, fumes, and someone who has to go and start it. A battery has a high purchase price and a running cost near zero, because the panels refill it for free.
Work out what you currently spend on fuel in a year. In places with heavy load-shedding that figure alone often pays for a battery inside three to four years — before counting a single unit of tariff saving. If you are replacing a generator rather than supplementing a reliable grid, the battery case is strong and gets stronger every time fuel prices move.
Hidden costs on both sides
- Net metering is not always free to join. A bidirectional meter, an application fee, a licensed installer's certification and sometimes an upgraded connection all cost money up front.
- Export caps. Many utilities cap exported credit at your annual consumption, or reset unused credit to zero each year. Oversizing your array past your own use can mean generating units nobody will pay you for.
- The rules change. Export rates have been cut in market after market, usually with existing customers grandfathered for a period. Model what your payback looks like if the export rate halves in year five. If the system only works at today's rate, it is fragile.
- Batteries need a hybrid inverter. Retrofitting storage to a plain grid-tied system usually means replacing the inverter too. Buying a hybrid on day one costs a little more and keeps the option open.
- Backed-up circuits are not the whole house. Most installs put a subset of circuits on the battery. Decide which ones early — it affects the wiring, not just the battery size.
A decision table
| Your situation | Build this |
|---|---|
| Reliable grid, full net metering | Panels only, sized to your annual consumption |
| Reliable grid, export worth under half of retail | Panels, plus a modest battery if the spread is wide and you will cycle it daily |
| Reliable grid, zero export allowed | Panels sized to daytime load, plus a battery for the surplus |
| Frequent outages, currently running a generator | Panels plus a battery. Compare against fuel, not against tariff |
| No grid connection at all | Off-grid design with multi-day autonomy — a different exercise entirely |
Test it on your own numbers
The calculator lets you run both cases directly. Set the battery to "None" and note the payback, then switch it to "Backup for essentials" and watch what happens. Adjust the export rate in the advanced panel to match what your utility actually pays, and the self-consumption percentage to match how much of your generation you use as it is made.
Then do the thing almost nobody does: halve the export rate and run it again. If the system still makes sense, you have a robust investment. If it collapses, you have an investment that depends on a policy staying put.