Fixed price or day-ahead market? A biogas plant in the second half of 2025

Almost a tie: not on RDN alone, but FIP with flexibility came close to the fixed price almost entirely. In the second half of 2025 the average RDN price was PLN 456.3/MWh (55% of the FIT of PLN 828.4/MWh), 2× operation gives PLN 564.1/MWh (68% of FIT), and 3× operation PLN 614.7/MWh (74% of FIT). FIP with 2× operation reaches PLN 821.4/MWh, that is 99% of FIT, and with 3× operation PLN 872.1/MWh (105% of FIT). The half-year shows seasonality: compared with the analysis for H1 2025 there were 60 hours with a negative price instead of 251.

A reminder of the mechanism

The support rules (Articles 70a–70f of the Act on Renewable Energy Sources (ustawa o OZE)), the scenarios and the model assumptions are described in the first analysis in the series. You will find the results for the previous half-year in the previous analysis in the series (H1 2025).

Seasonality and quarterly quotations

Negative prices occur mainly in spring and summer, when sunny middays coincide with low demand. In the autumn–winter half-year they are rarer, but the market then has higher average prices (PLN 525.9/MWh in November, PLN 492.4/MWh in December). A practical remark follows: a half-yearly calculation is not enough to assess an installation, because flexibility earns differently in spring and in winter. From October 2025 the source data from energy-charts.info have a 15-minute step; in the model they were averaged to hours, and for FIP settlement the Act refers to hourly volume-weighted average day-ahead prices. The reference prices remain those from the regulation of 8 November 2023: FIT PLN 828.4/MWh and FIP PLN 713.7/MWh; an installation from 2019 has a FIT of PLN 906.4/MWh after indexation. You will find a broader comparison of support systems in the analysis support systems for biogas plants in Poland.

Figures for the half-year

The price of an "installation from 2019" is 95% of the 2019 reference price (PLN 617.5/MWh) after cumulative indexation by the annual average CPI for 2019–2024 (Article 70e(3); GUS: 102.3; 103.4; 105.1; 114.4; 111.4; 103.6).

The FIT in the table is 95% of the reference price for the "up to 500 kW" class. From 28/12/2024 FIT is available to installations smaller than 200 kW, so for a 0.5 MW installation it is a reference point, and the support actually available remains FIP (the 200 kW – 1 MW class).

Monthly averages range between PLN 382.0/MWh in August and PLN 525.9/MWh in November. Even the most expensive month is 63% of the FIT price. Hours with a negative price (60) are excluded from settlement; the gain from this is PLN 6.7/MWh.

Daily profile: 12:00 is PLN 317.2/MWh, 19:00 is PLN 724.2/MWh. The spread of PLN 407.0/MWh gives a flexibility premium of PLN 107.8/MWh (2×) and PLN 158.4/MWh (3×).

What "99% of FIT" means

FIP with flexibility (PLN 821.4/MWh) equals the FIT of PLN 828.4/MWh to within a few zlotys, but it is made up of different elements. FIT is a fixed amount, with no market risk and no expansion expenditure. FIP + 2× is a lower fixed price (90% of the reference price for the 500 kW–1 MW band) plus the market plus a premium from the profile, requiring an additional genset and gas storage. There is also risk on the balance side: a positive balance from months with high prices reduces premiums in the following ones (Article 93(11) of the Act on Renewable Energy Sources), and a balance that is not offset at the end of the period is returned to the settlement operator (paragraph 12). In the model the balance is calculated monthly and is not carried forward, so the result is an upper estimate.

Is a double-membrane roof enough

In the model, "2×" operation means that a genset with its capacity increased to about 1.0 MW runs only in the 12 most expensive hours of the day, and "3×" that a genset of about 1.5 MW runs in the 8 most expensive hours; the same daily energy (about 10.96 MWh) is therefore produced in a shorter time, at higher power. Biogas from fermentation flows around the clock (in the model about 216 Nm³/h, resulting from the 0.5 MWel capacity, 40% electrical efficiency and 53% methane content), so the rest of the day is storage in the double-membrane roof. The gas balance for this half-year gives an average of 2,698 m³ of capacity for 2× (95th percentile: 3,629 m³) and 3,710 m³ for 3× (4,839 m³). A single double-membrane roof with a diameter of 26 m has, according to DLG, a gas capacity of about 2500 m³ (we adopt this as an assumption for Polish installations too): in this half-year it accommodates the 2× demand on 42% of days, and the 3× demand on 3% of days. Two roofs, that is 5000 m³, cover all days of the half-year in the model in both variants (the maximum demand did not exceed 5000 m³).

How much can be spent on flexibility

The premium for operating in expensive hours is, in this half-year, PLN 107.8/MWh for 2× and PLN 158.4/MWh for 3× relative to continuous operation. After annualisation (×2, an assumption) this gives an annual surplus of PLN 434 thousand for 2× and PLN 639 thousand for 3×; divided by the instalment factor (12-year depreciation, cost of capital of 10% or 6%), this gives a budget for an additional genset and gas storage of PLN 2,960–3,642 thousand for 2× and PLN 4,352–5,355 thousand for 3× (the lower value at a 10% cost of capital, the higher at 6%). The cost ranges are assumptions, not quotations: €500–800/kW of additional capacity plus €20–70/m³ of missing storage, at an exchange rate of PLN 4.3/€, which gives PLN 1,092–1,780 thousand for 2× and PLN 2,254–3,804 thousand for 3×. Conclusion from the calculation: both variants (2× and 3×) pay back across the whole assumed cost range. The same benefit from the price profile occurs under FIP and in pure RDN (under FIP it is sometimes slightly larger, because flexible operation avoids hours excluded from settlement), because it comes from the market and not from support; FIT does not provide it, because it pays the same for every hour.

A third option: an energy store

A 0.5 MW / 1 MWh store, one cycle per day, 85% efficiency, adds PLN 37.2/MWh to continuous operation (revenue of PLN 493.5/MWh). The average of the daily differences between the average price of the two most expensive and the two cheapest hours of the day is PLN 524.2/MWh. The annual surplus is PLN 150 thousand; with 15-year depreciation, servicing at 2.5% of capital expenditure per year and average capacity degradation of 2% per year (assumptions), this allows spending PLN 823–1,006 thousand on the store, that is PLN 823–1,006 per kWh of capacity. The assumed system cost range is PLN 600–1,200/kWh, and an additional grid connection PLN 50–400 thousand; these are assumptions, because there are no firm Polish prices for a project of this scale. After deducting the connection (PLN 50–400 thousand) from the budget at a 6% cost of capital, the permissible system cost is PLN 606 to 956/kWh; the store would pay back only in part of the range (low connection cost, low cost of capital, a cheaper offer). The model ignores distribution charges for off-take, the capacity charge and the balancing market, so the result is rather optimistic.

Conclusions for this half-year

• RDN with flexibility (PLN 564.1–614.7/MWh) is 68%–74% of FIT; FIP + 2× (PLN 821.4/MWh) is PLN 7.0/MWh lower than FIT.
• Fewer hours with a negative price (60) than in spring means that the benefit of switching off falls to PLN 6.7/MWh.
• An additional genset and gas storage: the 2× variant pays back across the whole assumed cost range; the 3× variant pays back across the whole assumed cost range.
• The energy store adds PLN 37.2/MWh and would pay back only in part of the range (low connection cost, low cost of capital, a cheaper offer).