Page - 119 - in Clean Water Using Solar and Wind - Outside the Power Grid

Handling variable production 119 all times. The net capacity factor of a power plant is defined as the ratio of its actual output over a period of time to its potential output if it were possible for it to operate at maximum power output continuously. Wind capacity factors range from 20% to around 50% so the power density will be reduced accordingly. For solar PV the capacity factor depends on the latitude and weather pattern. Some typical values are 9% (UK); 13–15% (Massachusetts, US); 18% (Portugal); 19% (Arizona, US). It ought to be mentioned that the capacity factor is also below 100% for conventional power systems. For hydroelectricity, the global average is 44% (Kumar et  al., 2011, p. 446) and the range is 10–99% depending on design and local conditions. The averages of the continents vary from 32% (Australia, Oceania) to 54% (Latin America). In the US the downtime for coal-powered thermal plants is around 12% and for nuclear plants 10%. Of the three approaches for reconciling electricity supply and demand, energy storage gets most of the attention and most of that interest is focused on batteries. The electric vehicle market has led to sharp gains in cost-performance of battery systems – a trend expected to continue. The use of hydrogen for energy storage is getting increasing attention, which should be of major benefit for RE systems. Batteries for energy storage are considered in 10.3–10.4 and hydrogen storage in 10.5. There’s a lot of confusion about how much storage capacity is actually needed, and what cost targets the storage must meet. Energy storage depends on the load profiles for each individual application and on consumer requirements. 10.1.2 Load profile The most efficient way to use renewable energy, from solar or from wind, is to feed the power directly to the load. Due to the intermittent nature of the production, it does not always fit the load profile. Lighting is the best example of the mismatch between generation and load – the load is turned on when solar PV generation is not available. On the contrary, cooling is an apparent example of a load that follows the availability of the solar resource: the more sun, the hotter the weather and the higher the demand for cooling. Commercial and domestic loads usually follow quite strict timings, for example work hours and times of meal preparation. Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user