Seite - 186 - in Clean Water Using Solar and Wind - Outside the Power Grid

186 Clean Water Using Solar and Wind: Outside the Power Grid In a thermal power plant, we must distinguish between the electric power (MWe) and the thermal power (MWth). 1 GW (gigawatt) = 103 MW (a typical power capacity of a large nuclear power plant). 1 TWh = 1,000 GWh = 106 MWh = 109 kWh = 1012 Wh The annual electric energy use for a nation is typically expressed in TWh. For example, all used water treatment in Sweden requires annually about 0.6 TWh = 600 GWh. Consequently, there is an average power level of 600/8,760 = 0,068 GW = 68 MW every hour of the day and night. With nine million inhabitants, every citizen uses on average 7.5 W for used water treatment. About the same power and energy is used for supplying drinking water. We still see the old unit horsepower in American publications: 1 horsepower = 1 hp = 746 W A2.2 PRESSURE The metric unit for pressure is pascal (Pa), where 1 Pa = 1 Newton/m2, which is a very low pressure. 1 bar = 105 Pa = 0.1 MPa; 1 MPa = 10 bar Old units are: 1 psi (pound/inch2) = 6,895 Pa; 1 bar = 14.5 psi A2.3 HEAT CONTENT Before it was realised that heat was a form of energy, it was measured in terms of its ability to raise the temperature of water. The calorie and the British thermal units were defined in this way. Calorie (cal): In a traditional definition one calorie is the amount of heat required to raise the temperature of 1 gram of water by 1°C, from 14.5°C to 15.5°C. British thermal unit (Btu) is the English system analogue of the calorie. 1 Btu is the amount of heat required to increase the temperature of one pound of water (which weighs exactly 16 ounces) by 1°F. 1 Btu = 251.9958 cal. Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user