What is hydro pumping and what are its benefits
By João A. Peças Lopes*
Hydro pumping has been used for decades to support electric system management. When there is an extra capacity to produce electricity in periods where consumption is low, this solution is used to transfer electricity between periods. This is done by pumping water from a lower to a higher altitude reservoir.
Hydro pumping is used particularly in situations where the technical restrictions resulting from exploring thermal power plants make it impossible to adapt the actual production to the variations in consumption. This situation occurs, for instance, in systems that produce large amounts of electricity from nuclear power as these units are not flexible enough to adapt to the lower voltage levels which occur in off-peak hours. This led Spain to invest largely in Hydro Pumped Storage Power Plants in the 1970s and 1980s in order to facilitate nuclear power generation. In some systems, with the increase in wind power generation, another situation started occurring in which wind resources were higher than consumption levels. Even though in this case it is possible to shut down or reduce wind power generation, something which is not possible in the case of nuclear power plants, we would be wasting a renewable energy. Therefore, a more interesting solution is to store this energy instead.
Furthermore, pumping systems today are a lot more flexible and can react quickly to different levels of consumption and generation, particularly in systems where these levels vary frequently, as is the case of wind power. Therefore, pumping systems provide an additional service which consists of having the capacity to compensate for deviations in forecasts. This is an asset particularly for systems where the wind power component is significant, as is the Portuguese case.
Hydro Pumped Storage Power Plants operate on the market and acquire electricity during off-peak periods, at low prices, which will make the pump engines work. Then, the electricity is provided to the system during the high consumption periods in which the price of electricity is higher. It is easy to demonstrate that this exploration cycle is economically interesting as long as the electricity price during peak hours is higher than the ratio between the price during off-peak hours and the income value of the power plant’s operating cycle. Typically, the income in these facilities varies between 70% and 80%, which, considering the market price fluctuation during off-peak hours, allows the pumping power plant to provide electricity to the grid at prices ranging between 25 and 45 €/MWh. It is important to highlight that the market price for the corresponding peak hours is typically much higher. This means that by providing this hydro production solution to the market during peak hours, it is possible to avoid using the thermal power plants, which are more expensive and produce more emissions. This will lead to lower market prices, which in turn will benefit the consumers who will be paying lower prices for electricity during these periods.
Given the features of the current power system in Portugal, only with investments in higher pumping storage capacity is it possible to fully benefit from the clean and sustainable energy we obtain from wind power generators. In fact, this will make it possible to minimise possible wastes in the generation of electricity from renewable sources, reduce CO2 emissions, guarantee operational safety, and reduce the country’s energy dependence, as well as the price of electricity during peak hours.
*Full Professor at FEUP and Researcher at INESC TEC
Jornal i, 21 August 2012
