by Dr. Jacob Klimstra
This editor’s letter is not about a famous 1980s song but about new opportunities for cogen/CHP and on-site power production. This June, Maria van der Hoeven, executive director of the International Energy Agency (IEA), cited its recent report by stating that in five years’ time, 25% of the world’s electricity supply will come from renewable sources. This will be predominantly the result of a steady growth in the installed capacity of wind turbines and photovoltaic panels. Generators based on biomass and biogas are also expected to contribute to the increase.
Reducing the use of fossil fuels and the associated emissions is the main reason that renewable energy is now globally promoted. Government-introduced incentive schemes compensate investors in renewable energy sources in case of negative financial yields. As a result, some countries have so many wind turbines and solar panels that the traditional electricity generators are at times almost completely excluded from the grid. Examples are found in Germany and Denmark.
Nevertheless, the intermittency of renewables ensure that fuel-based power plants still have to fill the gaps when the sun sets, the wind subsides or demand changes. Traditional power plants running on coal, for example, lack the necessary flexibility for this. Moreover, if only 1 GW of power from dispatchable power plants remains on line for a total demand of 10 GW, a substantial number of generating units should deliver this 1 GW. Having just two larger units of each 500 MW in parallel providing this 1 GW could result in insufficient reliability. Distributed generators, in contrast, have the right capacity and the right properties to provide fast ramping up and down of their output to enable the application of renewable electricity sources.
Policy makers often focus on making electricity production sustainable. Yet, there is a substantial demand for heat in the world, not only for space heating but also for sanitary water and for industries. Cogeneration systems have proven to provide electricity and heat at very high fuel efficiency, sometimes exceeding 90%.
If the demand patterns of power and heat do not fully coincide, heat storage offers a solution. Storing heat in water tanks is relatively cheap. The nice thing now is that in times of surplus electricity from renewables, and consequently low electricity prices, heating coils can easily be used to heat the water in such storage tanks. The extra investment costs are almost negligible. This can be seen as an integrated solution to make district heating systems and stand-alone cogeneration units even greener.
Distributed electricity generation can also help to stabilize voltage by injecting reactive power into the grid. Reactive power needs are best solved locally to avoid high transmission losses.
Ultimately, the prediction by the IEA about a gradual increase in the fraction of renewable electricity sources is a positive message for cogeneration and on-site power production. The utilisation factor of such generators might decrease somewhat compared with that in the past, but a reduction in global fuel consumption has always been the intention.
Nevertheless, distributed generation and cogeneration based on units of a moderate power capacity each will be an indispensable link in any future power supply systems.
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