Cogeneration
Cogeneration (Combined Heat and Power, or CHP) is a simultaneous generation of two useful energy forms (electrical and thermal) in a single process. Thermal energy, which remains unused in a conventional power plant (or is released into the environment affecting it adversely), is used in numerous industrial processes or, more often, for heating buildings or even entire blocks. Thermal energy can be used for steam production, water or air heating. One way to use cogeneration is also trigeneration where some energy is used for cooling. They can be fired by natural gas, biomass, lumber or hydrogen (for fuel cells). The choice of cogeneration technology depends on fuel availability and price.
Basic cogeneration advantage is increased fuel efficiency in comparison with conventional power plants which are used only for electricity production, as well as industrial systems which are used only in steam or hot water production for technical processes. Total cogeneration efficiency ranges from 70 to 85% (27-45% electricity and 40-50% thermal energy) while total efficiency in conventional power plants ranges from 30 to 51% (electricity).
Cogenerations have a significant role as a distributed energy source due to their positive effects: lower network losses, decrease of transmission congestion, improvement of voltage quality, increase of electricity supply reliability. Negative environmental effects are also diminished. Commercially available CHP technologies include steam and gas turbines, microturbines, reciprocating engines, Stirling engine and fuel cells with a wide capacity ranging from 1 kW for Stirling engine to 250 MW for gas turbines.
On 11 February 2004, an important European energy legislative document was adopted – Directive 2004/8/EC of the European Parliament and of the Council on the promotion of cogeneration based on a useful heat demand in the internal energy market.
The purpose of this Directive is the following:
- promoting high-efficiency cogeneration based on useful heat demand (savings of primary energy of at least 10% obtained by combined production instead of separate production of heat and electricity),
- decreasing network losses,
- decreasing greenhouse gases emissions.
In accordance with the above mentioned, the Ministry of Economy, Labour and Entrepreneurship, in the Regulation on a minimal share of incentivized electricity production from renewable energy sources and cogeneration, has decided to achieve a minimal share of 2% of electricity produced from cogeneration in total electricity consumption in the Republic of Croatia by the 31 December 2010.