Cogeneration
A CHP unit sized for the wrong
demand burns fuel to produce
an output the site can't fully use.
A CHP plant that’s wrong for the site is a costly mistake. The technology itself works; that’s rarely the problem. The problem is that a unit sized for the wrong demand burns fuel to produce an output the site can’t fully use, and the savings that justified the investment never arrive.
So the real question isn’t whether CHP works. It’s whether it works here, on this site, with this pattern of energy use. Answering that means starting from the building, not from the catalogue.
The most common way to get CHP wrong is to start with the machine. A supplier quotes a unit, the headline efficiency looks good, the payback on the spreadsheet looks good, and the site signs off. A year later the bills don’t match the promise.
The reason is almost always the same: nobody mapped the site’s energy demand before choosing the size. Total annual consumption, the one figure most businesses have to hand, isn’t enough for that. Two sites can burn the same amount of energy in a year and need completely different plants, or in one case no Combined Heat and Power at all, because what counts is when the energy is used, not just how much.
A feasibility assessment needs the shape of demand: how much electricity and how much heat the site uses through the day, through the week, and across the seasons. A hotel draws hot water every morning and night, all year round. A food factory might run three shifts in winter and one in summer. A site with a heated pool has a heat demand that hardly moves between July and January. The profile decides the outcome.
The most useful number to come out of a demand profile is the heat-to-power ratio: how much heat the site needs for every unit of electricity it uses. Every CHP unit has its own fixed ratio of heat to power output. The closer the unit’s ratio sits to the site’s, the more of the plant’s output gets used, and the better the economics.
Where people go wrong is by focusing on peaks. A site might need a great deal of heat on the coldest morning of the year, but a plant sized for that peak will sit half-idle the rest of the time. The number that counts is the baseload: the demand that’s there continuously, day and night, in summer as much as winter. CHP earns its return on the baseload. A conventional boiler can cover the occasional cold-morning spike, cheaply and only when needed, while the CHP unit is sized to run flat out against the demand that never goes away.
This is why some sites fit naturally and others don’t. A hospital, a large hotel, an industrial laundry: their heat demand runs around the clock. An office that empties at six and sits cold all weekend doesn’t, however large its annual bill.
The heat-to-power match tells you whether CHP makes technical sense. Whether it makes financial sense depends on a few more factors, and this is where a proper feasibility study earns its cost.
Running hours come first. A unit that runs 8,000 hours a year is a different investment from one that runs 3,000. The more hours the plant runs against genuine demand, the faster it pays back, which is one more reason baseload weighs heavier than peak.
Then there’s the gap between fuel and electricity prices. This is the quiet engine of CHP economics. The plant buys fuel and avoids buying power from the grid, so the wider the gap between the price of gas and the price of grid electricity, the more each operating hour is worth. That gap shifts with the energy market and varies from one country to another, so a serious study looks at local prices and where they’re heading.
Incentives deserve a clear word, because they’re often oversold. Many countries run support schemes for efficient cogeneration: tax relief, certificates, feed-in arrangements. These can improve a project’s return, but they are not the reason CHP works. CHP works because it wastes less fuel, and the incentive is recognition of that efficiency rather than the source of it. A project that only adds up because of a subsidy is fragile, since subsidies change. One built on the plant’s own efficiency, with any incentive as a bonus on top, is not.
Last comes integration. A CHP plant rarely arrives on an empty site. It has to work with the boilers, electrical connections and controls already in place, and the cost of fitting it into all that can decide the business case on its own. It’s also the part most often underestimated in a quick quote.
Theory is easier to trust with a case. Consider a logistics and cold-chain hub in central Italy: a large distribution site for temperature-sensitive goods, with a need for refrigeration that runs continuously and barely changes through the year.
On paper, a site like this looks like a poor CHP candidate, because its main energy need is cooling rather than heat. That is exactly what made it a good fit for trigeneration, which is CHP with an added stage that turns recovered heat into chilled water through an absorption chiller. Built around a roughly 1.2 MW engine, the plant produces electricity for the site while its waste heat drives the cooling the operation runs on. Because the demand for cooling is constant, the plant works steadily against a real, year-round load, and that match between machine and site is what makes the numbers work.
The lesson isn’t that every cold-storage site needs trigeneration, it’s that the answer came from studying how the site genuinely used energy, hour by hour, and then choosing the configuration that fit. The same study could just as easily have shown that CHP wasn’t worth it. That is the whole point of doing it.
If you’re weighing up CHP for your own site, the honest answer is that no one can tell you from a brochure. It depends on your demand profile, your operating hours and your local energy prices, which is what a feasibility assessment exists to measure. That assessment is the right first step, well before any choice of equipment. It’s the difference between a plant that delivers what it promised and one that turns into an expensive lesson.
How do I know if CHP is right for my business?
It comes down to your energy demand, not your energy bill. A site with a steady, year-round need for heat, or for cooling through trigeneration, is a candidate. A site that mostly needs electricity, with little continuous heat demand, usually isn’t. The only reliable way to know is a feasibility assessment that maps how your site uses energy across the day and the year.
What is a CHP feasibility study?
It’s an analysis of whether CHP makes technical and financial sense for a specific site. A good one looks at the hourly profile of electricity and heat demand, the expected running hours, the gap between local fuel and electricity prices, and how the plant would fit alongside existing equipment. It ends with a recommendation on size, configuration and expected return, or with the conclusion that CHP isn’t the right fit.
What’s the payback period for a CHP plant?
There’s no single figure, and any supplier who quotes one before studying your site is guessing. Payback depends mostly on how many hours the plant runs against real demand and on the gap between fuel and electricity prices where you are. A well-sized plant on a high-demand site pays back far faster than an oversized one on a site that doesn’t really need it.
Is CHP worth it without subsidies?
A properly sized plant should stand on its own efficiency, with any incentive as a bonus rather than the reason to invest. CHP saves money because it wastes less fuel than producing heat and electricity separately. Subsidies can shorten the payback, but a project that only works because of them is exposed when the rules change. The efficiency is the durable part.
Can CHP work on a site that needs cooling rather than heat?
Yes, through trigeneration. An absorption chiller turns the plant’s recovered heat into chilled water, so a site whose main demand is refrigeration or air conditioning can still use the full output. Cold-chain logistics, data centres and large hospitality sites often fit this model well, because their cooling demand is high and runs all year.
