CHP power sizing: how to select the right unit for your site
The output of a cogeneration unit determines the economics of the project for its entire service life — 20–25 years. Oversizing raises CAPEX and leaves the unit underloaded; undersizing fails to cover the base load and does not deliver the calculated savings. Below is the sizing sequence: what data is required, how to separate base and peak load, and how to match the result against the model range.
1. Base load, not peak load CHP power sizing
CHP output is selected against the base load — the consumption level the plant never drops below during working hours. Peak loads are covered from the grid: the simultaneous start-up of production lines, compressors and refrigeration equipment creates short spikes that there is no point in sizing installed capacity for.
A unit sized for peak load runs underloaded most of the time. This lowers the fuel utilisation factor, raises specific consumption and extends the payback period. A unit running at rated output in base-load mode delivers the maximum economic effect per operating hour. CHP power sizing
The capacity utilisation factor applied in the feasibility study of 01.07.2026 is 0.9. For the DvGA-500 this equals 450 kW of calculated electrical output and 3,600,000 kWh of annual generation over 8,000 operating hours.
2. What data the calculation requires
■ Electrical load profile — hourly, daily or monthly for the past 12 months. Hourly data gives the most accurate result.
■ Electricity bills for the same period — to verify volumes and the tariff in force.
■ Plant operating regime — hours per day, days per week, working days per year, scheduled shutdowns.
■ Thermal load profile — heating, hot water, steam, process heat, broken down by season.
■ Connection specifications — gas pipeline capacity, gas pressure, capacity of the grid connection point.
Hourly consumption data is supplied by the electricity provider or read from the plant's own meter with a data interface. Where some of this data is unavailable, Dieselmash engineers calculate indicative values based on the type of production.
3. The calculation sequence
The calculation is carried out in four steps.
■ Step 1. From the annual profile, identify the consumption level sustained during working hours throughout the year. That is the base load. One-off spikes are excluded.
■ Step 2. Assess the summer and winter profiles separately. At an industrial plant they can differ by a factor of three to four, so an annual average is not suitable for sizing — the reference point is the minimum sustained level.
■ Step 3. Determine the planned annual running hours. Payback depends directly on them: from 4,000 h/year upwards on natural gas, payback is 2.0–3.0 years; at 12–16 hours a day with seasonal heat demand it is typically 3–4 years.
■ Step 4. Match the base load against the model range, then verify that a heat consumer of the corresponding volume exists.
4. Matching against the model range
■ base load 400–500 kW — DvGA-500 (about 720 kW of thermal output);
■ 550–620 kW — DvGA-630 (about 900 kW of thermal output);
■ above 620 kW — DvGA-750 or a cascade of two units;
■ small production sites, biogas farms, greenhouses up to 1 ha — DvGA-315 (about 450 kW of thermal output).
A cascade of two DvGA-500 units delivers 1 MW and allows output to be regulated: one unit runs at base load, the second comes online as demand rises. It also means generation does not have to stop entirely while one of the units is under scheduled maintenance.
Space required: a containerised DvGA-500 module needs about 25–30 m², the DvGA-630 about 30–35 m². For a cascade, the area is calculated per unit, allowing for maintenance access.
5. Allowing for the plant's growth
Expansion plans are taken into account but are not built into the output of the first unit. Equipment due to be commissioned in two or three years creates no load today, while an oversized unit runs underloaded throughout that period and does not pay back at the calculated rate.
Where load growth is confirmed by an equipment commissioning schedule, a cascade is the more rational approach: the first unit covers the current base load, the second is added as growth materialises. The site, the gas inlet and the electrical section are designed for both units from the outset — cheaper than rebuilding the infrastructure later.
6. Thermal load as the second criterion
Electrical output sets the basic size of the unit; thermal output sets the size of the second half of the economic effect. The CHP unit recovers heat from the exhaust gases (550–600 °C) and the engine coolant (up to 90 °C).
The scale of the saving on heat depends on how evenly heat is consumed through the year: the closer the heat demand profile is to the unit's operating regime, the greater the effect. In the feasibility study of 01.07.2026 the displaced heat amounts to 2,228 Gcal per year at UAH 2,000/Gcal — about UAH 4.5 million of annual saving; this volume is calculated for the heating season.
Where there is no heat consumer, the unit operates with excess heat rejected, and payback is calculated on the electrical side alone and increases. This does not rule the project out, but it changes its economics, so the heat balance is assessed at the calculation stage rather than after installation.
7. Common sizing mistakes
■ Sizing for peak load. Leads to excessive output and underloading. Peaks are covered from the grid.
■ Sizing for installed equipment capacity. The combined rating of electrical loads is always higher than actual consumption: equipment does not run simultaneously or at full load.
■ Using an annual average. Averaging hides the seasonal difference and produces an output that matches neither the summer nor the winter regime.
■ Calculating without the thermal side. Half the economic effect comes from displaced heat. A project costed on electricity alone looks worse than it is — or better, if no heat consumer actually exists.
■ Ignoring the operating regime. The same unit at a site running 8,000 h/year and at one running 2,000 h/year gives fundamentally different payback.
Technical specifications of the models are given in the article “DvGA-500 and DvGA-630: technical specifications”. The questions to settle before signing are covered in “Five questions before buying a CHP unit”.
Reference figures from the feasibility study
Feasibility study of 01.07.2026 for the DvGA-500: 8,000 h/year, gas UAH 30/Nm³, electricity UAH 12/kWh. Annual electricity generation — 3,600,000 kWh, displaced heat — 2,228 Gcal. Turnkey project cost — UAH 20 million, annual economic effect — UAH 11.7 million, payback period — 1.7 years.
This is a baseline calculation. An individual feasibility study reflecting the plant's tariffs, operating regime and fuel type is prepared within 3–5 working days free of charge.
Send us your consumption profile for the past 12 months and the plant's operating regime. Our engineers will select the model and prepare a feasibility study with a payback calculation.
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