Insights · Negative prices · 06/11/2026 · Jan Gerstein
Negative electricity prices and Section 51 EEG: which rule applies to your solar plant
Negative electricity prices do not affect every solar plant in the same way. Whether your plant loses its market premium in those periods depends on its commissioning date, its capacity and your direct marketing contract. We sort the cases by the wording of the law, explain the extension under Section 51a and show when curtailing, self-consumption or a battery make economic sense.
What Section 51 EEG governs and what it does not
If you run a solar plant under subsidised direct marketing, you receive two payments: the market revenue through your direct marketer and the market premium through the grid operator. The market premium covers the gap between the reference value of your plant (anzulegender Wert) and the market value. This is where Section 51 of the Renewable Energy Sources Act (Erneuerbare-Energien-Gesetz, EEG) comes in. Since the Solar Peak Act (Solarspitzengesetz), subsection 1 reads: “For periods in which the spot market price is negative, the reference value is reduced to zero.”
If the reference value is zero, no market premium is paid for that period. It matters what the provision does not say: it does not oblige you to switch the plant off. It only governs the payment. Whether your plant keeps feeding in is decided by you and your direct marketer under your contract. The grid operator does not curtail your plant because of the price either; its interventions under the Energy Industry Act (Energiewirtschaftsgesetz) are grid-related.
What negative prices cost your plant in euros is what we assess in our negative price protection service. This article explains the legal position behind it: which version of the law applies to your plant, what the extension under Section 51a brings and which decisions you can take as an operator.
Which rule applies to your plant
Two facts decide: the commissioning date and the installed capacity. As a rule, each plant is governed by the version of the EEG in force when it was commissioned. The Solar Peak Act (Federal Law Gazette 2025 I No. 51) therefore introduced the current rule only for plants commissioned on or after 25 February 2025.
For plants commissioned from 1 January 2023 to 24 February 2025, Section 51 continues to apply in the version in force on 24 February 2025 (Section 100(46) EEG). Under that version duration matters: only once the price has been negative for a minimum number of consecutive hours does the reference value drop to zero, and then for the whole uninterrupted period. Shorter negative spells have no effect. Older plants are subject to longer minimum durations depending on their version, and some are not covered at all.
| Case | Commissioning | Capacity | Effect of negative prices |
|---|---|---|---|
| A | before 1 Jan 2023 | depends on version | rule of the version in force in the commissioning year: longer minimum duration (six or four consecutive hours, depending on version) and capacity thresholds; some plants are not covered |
| B | 1 Jan 2023 to 24 Feb 2025 | below 400 kW | no reduction of the reference value |
| C | 1 Jan 2023 to 24 Feb 2025 | 400 kW and above | reference value zero if the price is negative for at least two consecutive hours in 2026, from 2027 for one hour |
| D1 | from 25 Feb 2025 | below 100 kW, no intelligent metering system | no reduction yet, until the end of the year in which the intelligent metering system is installed |
| D2 | from 25 Feb 2025 | all others | reference value zero in every quarter-hour with a negative price |
Before we say anything about the effect, we confirm the commissioning date and installed capacity, for example from the Marktstammdatenregister (the federal register of energy installations). For plants commissioned before 2023 we look up the version of the commissioning year rather than assume a general rule.
Since the Solar Peak Act, every quarter-hour counts
For plants commissioned on or after 25 February 2025 there is no minimum duration any more. Since power for delivery from 1 October 2025 has been traded in quarter-hours on the day-ahead market, the spot market price is a quarter-hourly price (Section 3 no. 42a EEG). The reference value is therefore lost for every single quarter-hour with a negative price. A short negative spell at midday is enough.
Section 51(2) allows only two exceptions: plants below 100 kW until the end of the calendar year in which they receive an intelligent metering system, and plants below 2 kW until the end of the calendar year in which the Bundesnetzagentur (the Federal Network Agency) issues a determination under Section 85(2) no. 12 EEG, which is still outstanding. Whether the plant exports all of its output or is controllable plays no role for these exceptions. If you receive the fallback tariff in a month with negative prices, you must also report to the grid operator the volume fed in during those periods; otherwise the payment is reduced by 5% for each affected calendar day (Section 51(3)).
How often this happens is shown by the data of the Bundesnetzagentur: in 2025 the day-ahead price was negative in 573 of 8,760 hours, in 2024 in 457 hours. For 2026 the SMARD data already show 462 hours up to 25 October 2026. On 1 May 2026 the price reached −499.99 €/MWh in individual quarter-hours, almost minus 50 cents per kilowatt hour. Negative prices often occur on sunny middays in spring and summer, more often at weekends and on public holidays than on working days, and therefore in hours when solar plants generate a lot. How many there will be in future cannot be predicted reliably.
- 573 h
- with a negative day-ahead price in 2025, according to the Bundesnetzagentur
- 457 h
- with a negative day-ahead price in 2024
- −499.99 €/MWh
- day-ahead price on 1 May 2026, according to SMARD
Section 51a: the zero periods are added at the end
The market premium from negative periods is not lost entirely. Section 51a(1) EEG extends the payment period by the number of quarter-hours in which the reference value fell to zero in the commissioning year and the 19 following calendar years, rounded up to full calendar days.
Solar plants have their own calculation (Section 51a(2)): the number of these quarter-hours is multiplied by a factor of 0.5 and added to the end of the support period as so-called full-load quarter-hours. Each month corresponds to a fixed allowance, for example 508 full-load quarter-hours in June and 73 in December. The support period is extended until the allowance is used up and ends with the month in which the last full-load quarter-hour falls.
This means three things for you. The extension comes after around 20 years, not today, and what it is worth then depends on the market in those years. What counts are the quarter-hours with a reference value of zero, not the volumes fed in; according to the wording, curtailing in those quarter-hours does not change the extension. And for plants in case C, Section 51a(1) applies in its old version; the conversion under subsection 2 does not apply to solar plants commissioned before 25 February 2025 (Section 100(46)).
By 31 January each year the transmission system operators publish in how many quarter-hours and hours of the previous year the reference value fell to zero under the individual versions (Section 51a(4)). These figures are the basis for tracking your own extension.
Controllability and the role of the direct marketer
Above 25 kW in direct marketing, you must equip your plant so that the direct marketer can retrieve the actual feed-in at any time and control the feed-in power remotely, and you must grant it that authority (Section 10b(1) EEG). The law requires that the direct marketer can curtail. Whether it does so at negative prices is not set out in the law but in your contract.
Section 9 EEG applies in addition: until an intelligent metering system is installed, the grid operator must be able to retrieve the actual feed-in and reduce the output remotely for plants of 100 kW and above, and reduce the output for plants from 25 kW. The cap at 60% of installed capacity concerns plants below 100 kW on the feed-in tariff or in tenant electricity schemes, not direct marketing. This equipment serves the grid, not the response to prices.
Who pays at negative prices is determined solely by the direct marketing contract. In practice, the models vary widely:
Spot price passed through
You receive the market price of your feed-in even when it is negative. If the plant keeps feeding in during negative quarter-hours, you pay the negative price.
Curtailment by the direct marketer
The direct marketer curtails at negative prices, in some contracts with compensation for lost revenue, in others without.
Price threshold per plant
Curtailment starts only below an agreed price, which should match the market premium of your plant.
Minimum revenue commitment
The direct marketer commits to a minimum revenue and bears the risk of negative quarter-hours in return. It will usually curtail itself.
Revenue sharing
The benefit from curtailment is shared between you and the direct marketer.
Check in your contract who curtails at negative prices, from which price, and who bears the cost if the plant keeps running. Under Section 21b(4) EEG you can change direct marketer at any time; in practice, terms and notice periods limit the change. You can change the form of sale only on the first day of a calendar month (Section 21b(1) EEG).
Curtail, keep feeding in, consume on site or store
The basic question is: what does a kilowatt hour earn you in this quarter-hour? If your contract passes the spot price through, it is the market price plus whatever market premium is still paid for that quarter-hour. If the sum is negative, every kilowatt hour fed in costs money.
Case D2: curtail from the first negative cent
The market premium is zero in every negative quarter-hour. If your contract passes the price through, every kilowatt hour fed in costs the negative price. Curtailing avoids that cost; the market premium would be lost anyway.
Cases B and C: running on can pay
As long as the market premium is paid, curtailing only pays once the negative price exceeds the premium in absolute terms. In case C it depends on duration: if the day-ahead result from the previous day shows that the minimum duration will be reached, the premium is lost for the whole period.
Consume on site
Electricity you use in your own business is not affected by Section 51, as it earns no market premium. Moving cooling, charging points or compressed air into negative quarter-hours reduces feed-in and grid purchases at the same time. Take care with rooftop plants receiving the full-export bonus: even small self-consumption costs the bonus for the whole calendar year, and after a full-export notification a payment of 2 € per kW for all twelve months is added (Section 48(2a) and Section 52 EEG). Plants with a tender award follow their own rules on self-consumption, which we check for each plant beforehand. More on self-consumption for businesses under commercial solar.
Store
On a plant that exports all of its output, a battery rarely pays for itself through negative prices alone. For stored electricity, the payment follows the entitlement that would have existed without intermediate storage (Section 19(3), second sentence, EEG). Since 21 October 2026 mixed operation with grid power has been possible under the demarcation option, but until 30 September 2027 only with the consent of the grid operator and the metering point operator, only in direct marketing, with a separate balancing group and a suitable metering concept. Where self-consumption is added, it is usually the real gain; see solar with battery storage.
Worked example with assumed figures
A simplified example with assumed figures, not a statement about a real plant. It shows the calculation for a 750 kWp rooftop plant, in operation since June 2025 (case D2), in direct marketing with the spot price passed through.
| Item | Value | Assumption |
|---|---|---|
| Annual generation | 712,500 kWh | 950 kWh per kWp |
| of which in negative quarter-hours | 64,125 kWh | 9% of generation |
| Market premium that would have been paid without Section 51 | 2.0 ct/kWh | assumed average |
| Average spot price in these quarter-hours | −1.5 ct/kWh | equals −15 €/MWh |
| Lost market premium | €1,282.50 | 64,125 kWh × 2.0 ct |
| Cost of feeding in at a negative price | €961.88 | 64,125 kWh × 1.5 ct |
| Shortfall when feeding in | €2,244.38 | per year, sum of both items |
| Shortfall when curtailing in these quarter-hours | €1,282.50 | lost market premium only |
The figures are assumed. The result depends on how much of your generation falls into negative quarter-hours, how high your market premium is and what your contract provides. For the zero periods the support period is extended under Section 51a, for solar with a factor of 0.5; what that will be worth in 20 years cannot be quantified today.
Wind and biogas: what is different
For wind turbines, Section 51 applies as it does for solar plants, with the same dependence on commissioning date or bid date (Section 100(46) names both). The difference lies in Section 51a: for wind, the extension under subsection 1 is counted in quarter-hours and rounded up to full calendar days, without the 0.5 factor and without full-load quarter-hours. Wind also generates at night and in winter, so negative quarter-hours affect wind farms differently from solar plants.
For biogas plants that do not use biomethane and whose reference value was set in a tender, Section 51b EEG applies: the reference value already drops to zero when the spot market price is 2 cents per kilowatt hour or less. Sections 51 and 51a do not apply to these plants. This only covers awards from bid dates on or after 24 February 2025; Section 51b does not apply to earlier awards (Section 100(37) EEG). Because biogas plants can shift their generation in time, the schedule matters more here than switching off. What else we plan at wind and biogas sites is described under wind and biogas operators.
What you should check now
Five facts are enough to assess the effect of negative prices on your plant:
01
Commissioning and capacity
Date and installed capacity from the Marktstammdatenregister or your grid operator’s documents. They determine case A to D.
02
Metering system
Below 100 kW: is an intelligent metering system installed, and in which year? The exception under Section 51(2) depends on it.
03
Direct marketing contract
Who curtails at negative prices, from which price, and who bears the negative price if the plant keeps running?
04
Your own loads
Which consumers can you move into the midday hours without putting a full-export bonus at risk?
05
Voluntary switch
Plants whose reference value has so far not been reduced at negative prices can switch to the new rule by declaration in text form and then receive 0.6 cents per kilowatt hour more (Section 100(47) EEG). The declaration takes effect at the earliest at the end of the year in which the intelligent metering system is installed. The rule is subject to EU state aid approval (Section 101(1) EEG); check whether that approval has been granted before you make a declaration.
The Bundestag is debating a draft EEG 2027 (Bundestag document 21/7867). Planned according to the government draft are, among other things, two-sided contracts for difference from 100 kW and the end of the fixed feed-in tariff for new plants. What this changes for existing plants we will assess once the act has been passed.
Sources
- Section 51 EEG, reduction of the payment entitlement at negative prices
- Section 51a EEG, extension of the payment period at negative prices
- Section 51b EEG, biogas plants in tenders
- Section 100 EEG, transitional provisions (subsections 37, 46 and 47)
- Section 9 EEG, technical requirements
- Section 10b EEG, requirements for direct marketing
- Section 19 EEG, payment entitlement and intermediate storage
- Section 21b EEG, change of form of sale and of direct marketer
- Section 48 EEG, solar plants (full export)
- Section 52 EEG, payments for breaches of obligations
- Section 3 EEG, definitions (no. 42a spot market price)
- Solar Peak Act (Solarspitzengesetz), Federal Law Gazette 2025 I No. 51
- Bundesnetzagentur: electricity market data 2025 (5 January 2026, German)
- SMARD, electricity market data of the Bundesnetzagentur
About the author
Jan Gerstein, Managing Director of StromWert GmbH
Managing Director and responsible qualified electrician. Trained electrician, then more than 20 years in wind energy, above all in commissioning and quality assurance onshore and offshore.
Frequently asked questions on negative electricity prices and Section 51 EEG
Do I have to switch off my solar plant when electricity prices are negative?
No. Section 51 EEG only provides that the reference value, and with it the market premium, is lost in negative periods. The EEG contains no obligation to switch off. Whether curtailing makes economic sense depends on the commissioning date and capacity of your plant and on your direct marketing contract.
Does the Solar Peak Act also apply to my existing plant?
For plants commissioned before 25 February 2025, the negative price rule of the version in force at commissioning continues to apply; for commissioning from 2023, Section 100(46) EEG says so expressly. Plants without a negative price rule can switch voluntarily under Section 100(47); this rule is subject to EU state aid approval.
How long does the electricity price have to be negative for the market premium to be lost?
For plants commissioned on or after 25 February 2025, one quarter-hour is enough. For plants of 400 kW and above commissioned from 2023 to 24 February 2025, it takes at least two consecutive hours in 2026 and one hour from 2027. Older plants have longer minimum durations depending on their version.
What applies to solar plants below 100 kW at negative prices?
Plants below 100 kW commissioned on or after 25 February 2025 are exempt from Section 51 until the end of the calendar year in which they receive an intelligent metering system. After that, they too lose the payment in negative quarter-hours. For plants commissioned from 2023 to 24 February 2025, Section 51 applies only from 400 kW.
Do I get the lost market premium back?
Not as a payment. Section 51a EEG extends the support period by the zero periods, for solar plants with a factor of 0.5 and converted into full-load quarter-hours. The extension is added to the end of the roughly 20 years.
Does my direct marketer curtail at negative prices?
That depends on the contract. Above 25 kW, the direct marketer must be able to control your plant remotely (Section 10b EEG), but this does not create an obligation to curtail at negative prices. Some contracts provide for curtailment, others pass the negative price on to you.
As of 6 November 2026. This article does not replace legal advice. The version of the EEG that applies to your plant is decisive. For the EEG 2027, the status of the government draft applies.