Does storing solar pay on its own?

It depends on the gap between the import and export price. In Zorowatt's illustrative Romanian farm, a battery storing surplus at a gap of €0.12 per kWh pays back in about 32 years on its own; with a peak to shave, a connection limit or a grant, the case changes.

Is a bigger battery always better for solar?

No. Above the typical daily surplus, extra kWh fill only on the sunniest days. The year's simulation shows where the next kWh stops paying.

What if my export is capped?

Then surplus above the cap is lost unless it is used or stored, and the battery's value per stored kWh rises to the full import price after losses. The study needs the cap and when it applies.

Does stored solar avoid taxes?

In the Netherlands, energy charged from the site's own solar avoids the energy tax on that energy. In Romania, renewable self-consumption may be exempt from excise on notification. Check the site's own scheme with its adviser.

Solar plus battery: self-consumption, export limits and curtailment

Where solar and storage stand

SolarPower Europe puts the ratio of C&I solar to C&I storage in Europe at 30:1 at the end of 2025, and the share of C&I solar installed with a battery at about 20% for commercial and 10% for industrial sites in 2026 (SolarPower Europe 2026). Most business solar has no battery, so retrofits are a large part of the market.
In the Netherlands, 8,558 requests for more feed-in capacity (5,693 MW) were on the regional grid operators' waiting lists at the end of June 2026 (Solar Magazine, 6 Oct 2026).

What a stored kWh of solar is worth

Value per kWh of surplus = round-trip efficiency × the import price it replaces − the export price it gives up.

Illustrative, Netherlands, medium voltage: the import price a self-used kWh replaces is the transport kWh charge €0.0226 (Liander 2026) + energy tax €0.03735 in the 50,001 kWh to 10 million bracket (Belastingdienst) + a supplier price of €0.10 (assumption) = €0.15995. Export earns €0.05 (assumption); feed-in pays no transport charge on Liander's tariff. At 90% round trip (assumption): 0.9 × 0.15995 − 0.05 ≈ €0.094 per kWh of surplus. Shifting 40,000 kWh of surplus a year (assumption) would be worth about 40,000 × 0.094 ≈ €3,760.

Energy charged from the site's own solar avoids the energy tax on it; energy charged from the grid pays it, losses included. Whether exported kWh carry any tax for a C&I connection depends on its netting rules, which Zorowatt's research did not verify.
In Romania a self-consumed MWh avoids the per-MWh network charges and levies (Romanian business tariffs 2026: no kW charge), and renewable self-consumption may be exempt from excise on notification (fiscalitatea.ro).

How much surplus a battery can actually shift

At most one battery-full per cycle. Illustrative: on a sunny day the site exports 300 kWh. A battery with 200 kWh usable at 95% charge efficiency (assumption) takes in about 200 ÷ 0.95 ≈ 211 kWh of that surplus; the other ≈ 89 kWh are still exported.
Only on days with surplus. Winter days may have none, so the battery's solar value is seasonal; the rest of the year it can shave peaks or trade.
Only if the site has load to use it later. Energy stored at noon and exported in the evening earns only the evening export price after losses — little or nothing more than exporting it at noon.
Illustrative, from Zorowatt's scenario notes: a Romanian farm needs to shift 15% of 195 MWh of solar, about 29 MWh a year, roughly 120 kWh a day over about 250 sunny days (assumptions), to reach a grant's 70% self-consumption rule.

Export caps and curtailment

Where export is capped — by the grid operator, the contract or a congested feeder, possibly at zero — surplus above the cap is curtailed. A battery that stores it saves energy that would otherwise be lost, so the export price given up is zero: at 90% round trip and the €0.15995 import price above, 0.9 × 0.15995 ≈ €0.144 per kWh.
A study needs the cap in kW and the times it applies, and it should simulate curtailment explicitly rather than assume every surplus kWh can be exported.

Negative prices

In 2025 the day-ahead market had 584 negative-price hours in the Netherlands, 576 in Germany and 187 in Romania (Electricity Maps: NL, DE, RO). On a dynamic contract, exporting at a negative price costs money; storing the surplus — or curtailing it — avoids that. A simulation that allows negative prices must also stop the battery from charging and discharging at once just to burn energy through its losses.

Size for the client's demand, not for the export

A UK installer writing in POWER Magazine argues that storage gets cut at capital approval when it is sized to absorb solar export; his advice is to size it against the site's half-hourly demand and quote it as a separate line with its own case (POWER, 23 Sep 2026). In practice: start from the 15-minute load and the solar profile together, and let the battery's jobs — peak, solar, trading — compete for the same kWh in the simulation.

Sites that did it

Belt Tomaten, a greenhouse in IJsselmuiden: 2,088 kWh in two containers with 837.2 kWp of solar, to store daytime surplus for the night and reach about half of its electricity from solar (Solar Magazine, 24 Jun 2026).
ALDI Nord's model store in Gütersloh: up to 58 kWh / 50 kW of second-life cells, raising autarky to 45% (vendor: Voltfang).
Kampert dairy farm near Dortmund: 38.4 kWh with 41 kWp of solar, shifting solar to the milking (vendor: Tesvolt).

Getting the solar data

Best: the grid meter's export channel and the inverter's production data for the same year.
For planned solar, a modelled year from PVGIS, the EU Joint Research Centre's free solar tool, which asks only to be acknowledged (PVGIS usage conditions). The Workspace can add a PVGIS solar year to a site's meter data before sizing, without changing the data itself.

Frequently asked questions

Does storing solar pay on its own?: It depends on the gap between the import and export price. In Zorowatt's illustrative Romanian farm, a battery storing surplus at a gap of €0.12 per kWh pays back in about 32 years on its own; with a peak to shave, a connection limit or a grant, the case changes.
Is a bigger battery always better for solar?: No. Above the typical daily surplus, extra kWh fill only on the sunniest days. The year's simulation shows where the next kWh stops paying.
What if my export is capped?: Then surplus above the cap is lost unless it is used or stored, and the battery's value per stored kWh rises to the full import price after losses. The study needs the cap and when it applies.
Does stored solar avoid taxes?: In the Netherlands, energy charged from the site's own solar avoids the energy tax on that energy. In Romania, renewable self-consumption may be exempt from excise on notification. Check the site's own scheme with its adviser.

Related guides

Sources

Last checked: 2026-10-30. Every figure in this guide comes from the source linked next to it, with the retrieval date Zorowatt's research recorded (28–30 October 2026), or from arithmetic shown step by step. The prices, efficiencies and volumes in the examples are illustrative assumptions.

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