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What do negative prices cost your plant?

Enter your plant’s capacity, your minimum price and your fees. We run the numbers on actual IBEX day-ahead prices for the last 12 months and a typical Bulgarian solar yield profile.

How we calculate

Actual IBEX prices · 1 September 2025 – 31 August 2026

Your plant

DC peak capacity of the modules. 1 MWp = 1,000 kWp.

Below this IBEX price the plant is curtailed. At 0 it only stops when prices turn negative.

Fees per MWh produced

You pay them even when the price is negative.

€2.72/MWh excl. VAT from 1 July 2026 – EWRC (КЕВР) Decision Ц-13.

per contract

As agreed with your balancing group coordinator. Leave at 0 if you are not sure.

per contract

Your trader’s fee under your contract. Leave at 0 if you are not sure.

Total fees €2.72/MWh

Result

Estimate

IBEX · Day-ahead · 1 September 2025 – 31 August 2026

Loss avoided over 12 months

€1,019

What you would have paid had the plant kept running in curtailed hours where the price does not cover your fees.

Curtailed hours
169 h
price below your minimum while the plant produces
Energy in those hours
85.0 MWh
6.2% of expected output
Expected output
1,362 MWh
over 12 months, PVGIS profile

In this model the net effect peaks when your minimum price equals your fees (€2.72/MWh): €1,328.

By month

  1. Sep 2025 curtailed hours: 22 h loss avoided: €153
  2. Oct 2025 curtailed hours: 0 h loss avoided: €0
  3. Nov 2025 curtailed hours: 0 h loss avoided: €0
  4. Dec 2025 curtailed hours: 0 h loss avoided: €0
  5. Jan 2026 curtailed hours: 0 h loss avoided: €0
  6. Feb 2026 curtailed hours: 1 h loss avoided: €1
  7. Mar 2026 curtailed hours: 15 h loss avoided: €31
  8. Apr 2026 curtailed hours: 65 h loss avoided: €656
  9. May 2026 curtailed hours: 24 h loss avoided: €61
  10. Jun 2026 curtailed hours: 30 h loss avoided: €98
  11. Jul 2026 curtailed hours: 12 h loss avoided: €19
  12. Aug 2026 curtailed hours: 0 h loss avoided: €0

Total curtailed hours: 169 h loss avoided: €1,019

TokPirate curtails and restarts your plant automatically on 15-minute IBEX prices.

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Methodology

How we calculate

All inputs are public and there is a single formula, so you can check it yourself.

  1. Prices

    We take the IBEX day-ahead price for every hour in the period 1 September 2025 – 31 August 2026.

  2. Output

    For every hour we estimate your plant’s output: your capacity (kWp) × the typical yield of 1 kWp for that month and hour, from PVGIS.

  3. Curtailment

    Any hour priced below your minimum price counts as curtailed – the plant produces nothing.

  4. Loss

    For every curtailed hour: energy × (fees − price) whenever the price does not cover your fees. Summed by month and for the whole period.

The formula

loss avoided
= Σ E × max(0, fees − price), over hours with price < minimum price
E
= capacity (kWp) × yield of 1 kWp for that month and hour ÷ 1,000, in MWh
fees
= grid access + balancing + trader admin fee, in €/MWh

If your minimum price is above your fees, the calculator also shows the revenue forgone in curtailed hours where the price would have covered your fees.

Data

Sources and limitations

Sources

Prices
IBEX (Independent Bulgarian Energy Exchange) day-ahead market, Bulgarian bidding zone – 8,758 hourly prices for the period 1 September 2025 – 31 August 2026. Data from the ENTSO-E Transparency Platform, as compiled by Ember – European Wholesale Electricity Price Data (licensed CC BY 4.0).
In this period
169 hours with a negative price. The lowest price was −€79.49/MWh (26 April 2026, 14:00–15:00 Sofia time).
Solar output
PVGIS 5.3 by the European Commission’s Joint Research Centre, PVGIS-SARAH3 database, averaged over 2005–2023. A 1 kWp system, fixed mounting at the optimal 36° tilt, 14% system losses, 42.2° N, 24.7° E (Plovdiv area) – about 1,363 kWh per kWp a year.
Grid access fee
€2.72/MWh excl. VAT from 1 July 2026 – EWRC (КЕВР) Decision Ц-13.
Last updated
Data downloaded on 25 September 2026.
Guide: negative electricity prices in Bulgaria

What we leave out

  • 15-minute prices. Since 1 October 2025 IBEX has cleared in 15-minute intervals; here we use the average price of each hour. Short negative intervals inside an otherwise positive hour are averaged away, so the real effect of curtailing every 15 minutes can be larger.

  • Actual weather. Output is the typical yield for the month and hour, not the actual yield on a given day. On a cloudy negative-price day the loss is smaller, on a clear one it is larger.

  • Your contracts. We assume you receive the IBEX price minus your fees for every MWh. Premiums from the Electricity System Security Fund (ФСЕС), fixed-price contracts, imbalance costs and schedule deviations are not included.

  • Your plant. Location, tilt, orientation, shading and losses of your plant all change its output.

  • Curtailment. We assume the plant stops completely for the whole hour and restarts right after it.

An estimate. The result is an estimate based on historical prices and a typical yield profile – not a forecast, an offer or a guarantee of savings. Future prices and your contracts may produce a different result.

Stop losing money on the next negative price.

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