On the other hand, decentralized sources also have their drawbacks. These drawbacks result primarily from their instability in terms of energy production. In most cases, solar or wind power plant is used as an energy source. In essence, these renewable energy sources are volatile, which entails increased demands on the transmission system and its regulation. Cogeneration is an exception in this respect and therefore it stands somewhere “in the middle” between conventional energy and renewable resources.
Combined heat and power generation, or cogeneration, is still mostly based on burning fossil fuels, but it is a very efficient way of producing energy. The overall efficiency of cogeneration ranges somewhere between 70 – 90 % and the savings of primary energy sources amount to approximately 40 – 50 % as compared to separate production. In other words, we need up to 50% less fuel to produce the same amount of energy.
The CHP unit produces the electric power and it continues to use the residual or waste heat from the production of power – the production is therefore simultaneous and highly optimized. The CHP unit is also very flexible, as it can be turned on and off relatively easily and does not depend on the weather. This flexibility is also due to the fact that the heat can easily be turned into cold by connecting an absorption unit. Another option is, for example, the production of process steam.
All of this serves the combination of flexibility, stability and reliability. In many cases, the CHP unit also serves as a backup source of energy; it can also operate in the so-called island mode. Thanks to the SCR (selective catalytic reduction) technology, it is possible to discuss the levels of NOx released into the air which, in the case of cogeneration, is closer to the renewable sources. Although these are “emission-free”, it is necessary to take into account a the annual utilization rate which is much lower in the renewable resources (25% for the solar power plants, 35% for the wind power plants) than in the cogeneration which, as a matter of fact, is capable of running continuously with the exception of the necessary service breaks (up to 95%). In the case of biogas, we get into the situation where the energies are produced as if from nothing, or more precisely, from waste. In this case, it is a renewable energy source.
In Europe, the cogeneration accounts for about 11% of the power production and about 15% of the generation of heat. As its primary source, the cogeneration employs 42 % of natural gas, 28 % of biogas and the rest consists of either the solid fuels or heat oil. The total installed electrical capacity is higher than 130 GWel and the heat capacity is higher than 280 GWt. It is obvious therefrom that there is still a lot of room for expansion of this technology.
Then, is cogeneration that key of switching to the prospective completely carbon-free power engineering from renewable energy? At TEDOM, we talk about cogeneration as an imaginary bridge between the “old” and “new” power engineering. Unfortunately, it is not possible to switch to the emission-free power engineering in a snap of fingers – it must be done with prudence, step by step and, most importantly, effectively. In our opinion, cogeneration, side-by-side with renewable sources, will certainly have a very important role in this transition and, from the point of view of the entire power engineering sector, will enable their greater flexibility, safety and stability.