500 kW CHP unit vs 500 kW diesel generator: which to choose for your facility

500 kW CHP unit vs 500 kW diesel generator: which to choose for your facility

500 kW CHP unit vs 500 kW diesel generator: which to choose for your facility

One of the most common questions in consultations: we have a 500 kW load — which do we take, a gas cogeneration unit or a diesel generator? We compare them across seven parameters and give a ready-made decision matrix.

These are two different tools, not two competing products

Before comparing specifications, understand this: a gas CHP unit and a diesel generator of the same electrical output solve different tasks. They're often placed side by side in showrooms, but economically they operate in different scenarios.

A diesel generator is usually a backup or seasonal source of energy. It switches on when the grid goes down, runs for a few hours or days, then switches off until the next event. Key expectations — fast cold start, reliability after long standby, simple maintenance. The economics of such a generator are defined primarily by the cost of the machine itself and its fuel reserve.

A cogeneration unit is the primary energy source for a facility operating around the clock. It starts up once, runs for thousands of hours in a row, and alongside electricity produces thermal energy. Key expectations — a stable fuel utilization factor, high lifespan, low cost per kilowatt-hour. CHP economics are defined primarily by the difference between the cost of energy produced and the cost of energy bought from external sources.

That said, businesses often need to choose one tool for a specific site. In that case comparison makes sense — but only in the context of your specific load profile

How much does the purchase cost (CAPEX): 500 kW CHP unit vs 500 kW diesel generator

A 500 kW diesel generator is the most affordable solution in terms of equipment cost. The full sum of purchase, installation, connection and commissioning usually amounts to 40–55% of the equivalent budget for a cogeneration unit of the same output.

Approximate turnkey cost of a 500 kW CHP unit on natural gas is around UAH 20 million with VAT. The difference is easy to explain: besides the engine and generator, a CHP unit contains heat recovery equipment — exhaust gas and cooling system heat exchangers, circulation pumps, thermal loop control automation. Plus a gas pipeline from the connection point is needed — often a separate construction project with design work, approvals and permits. A diesel generator doesn't require any of that: fuel is delivered by tank trucks and stored in tanks.

But CAPEX is only the "ticket to the theatre". The real cost shows up in OPEX, which is paid year after year.

How much does operation cost (OPEX): 500 kW CHP unit vs 500 kW diesel generator

The key parameter here is the price per unit of useful energy. Let's take a baseline assumption: the facility runs 8,000 hours per year, needing 500 kW of electrical power. Annual output — 3.6 million kWh (allowing for a 0.9 power utilization factor).

For a diesel generator of this class, realistic fuel consumption is around 115–125 liters of diesel per hour. At a diesel price of UAH 55 per liter, this results in annual fuel costs of about UAH 50–55 million.

For a gas CHP unit of the same output, natural gas consumption is around 1.08 million Nm³ per year. At an industrial gas price of UAH 30 per Nm³, that's UAH 32.4 million — substantially cheaper. Plus the CHP unit also produces thermal energy in parallel, which either replaces purchased heat (another source of savings) or is sold.

It's exactly this difference that keeps diesel generators from being the primary energy source for continuous production. Their economics work for irregular operation: grid backup, peak loads, sites without gas. Once a facility switches to 24/7 mode, diesel consumption quickly turns all the CAPEX savings into a loss.

Comparison by lifespan and maintenance

Dieselmash engines of the 6GChN25/34 and 8GChN25/34 series, used in both diesel generators and gas CHP units, are designed for a resource of no less than 80,000 operating hours before major overhaul. Overall unit lifespan — 20–25 years.

All engines are medium-speed: 500–750 rpm (600 for the 500 and 630 kW models), which is what determines their high lifespan and low noise level compared with higher-speed analogues. This is a significant advantage for both gas and diesel versions.

Maintenance, however, has different frequency. A diesel engine requires more frequent changes of oil, injectors, nozzles, fuel pumps, plunger elements, and fuel filters. A gas engine is cleaner, but has its own specific consumables: spark plugs, high-voltage wires, ignition coils, and ignition system sensors. In terms of total annual service cost the two are comparable, but the CHP has a more predictable cost structure.

Environment and legislation

Gas CHP units on average produce 30–40% less CO₂ per unit of energy generated than diesel generators of the same output. For NOx and particulate matter the difference is even more significant.

Ukrainian legislation does not yet impose direct restrictions on the use of diesel generators, but emissions from stationary sources are regulated by environmental standards. When an installation runs continuously at an industrial site, permits from environmental authorities are needed — and these are always easier to obtain for gas.

Plus there's a more subtle but increasingly important factor — reputation. Large customers from the EU increasingly require Ukrainian suppliers to declare their production's carbon footprint. Gas CHP performs noticeably better here.

When diesel is the right choice

Despite unfavourable economics for continuous operation, a diesel generator remains the optimal solution in several scenarios.

■  The site is not connected to the gas network and connection is economically impractical (remoteness, weak pipeline pressure, refusal by the local gas utility).

■  A backup source is required in case of grid outages — running a few hours a day at most, annual operating hours not exceeding 500–1,000.

■  Marine and river vessels, where a compact autonomous source is needed and gas equipment is impractical for safety reasons.

■  Mobile and temporary sites: construction sites, field camps, drilling rigs.

■  Sites with highly irregular load, where average consumption is much lower than peak and a CHP unit would run under-loaded.

When a gas CHP unit is the right choice

■  The facility runs continuously or in 2–3 shifts with year-round load (food processing, district heating, greenhouses, large farms, greenhouse complexes).

■  There's a constant need for thermal energy or steam — then the economics are tripled: electrical, thermal, and process steam.

■  There's a connection to the gas network with sufficient pressure, or the ability to obtain biogas from own feedstock.

■  A long operating horizon of 8–10 years or more is planned — CHP delivers maximum effect over this period.

■  The priority is low cost per unit of energy produced and full energy independence, not a low upfront budget.

Decision matrix: if you have X, take Y

Below is a simple table for quick navigation. It doesn't replace an individual feasibility study, but it helps you understand the direction.

There's no universal answer. The right decision is always individual — it depends on your load profile, gas availability, regional tariffs, and your facility's development plans 5–10 years ahead.

Dieselmash manufactures both cogeneration units and diesel generators. We're not interested in "selling you a CHP unit at any cost" — we're interested in you getting the equipment that will actually solve your task and pay back.

Describe your situation in the form, and our engineers will prepare a calculation for both options with a fair comparison within 3 business days. This lets you make the decision based on numbers, not on general impressions.