Page - 185 - in Clean Water Using Solar and Wind - Outside the Power Grid

© 2019 The Author. This is an Open Access book chapter distributed under the terms of the Creative Commons Attribution Licence (CC BY-NC-ND 4.0), which permits copying and redistribution for non-commercial purposes with no derivatives, provided the original work is properly cited (https://creativecommons.org/licenses/by-nc-nd/4.0/). This does not affect the rights licensed or assigned from any third party in this book. The chapter is from the book Clean Water Using Solar and Wind: Outside the Power Grid, Gustaf Olsson (Author). doi: 10.2166/9781780409443_0185 A2.1 POWER AND ENERGY It is important to distinguish between power and energy. Power is energy per time unit, the rate of energy production or consumption. The SI (International System of Units) or metric unit of energy is joule (J) and 1 J is defined as 1 Ws (wattsecond). 1 J is the designated name for the work 1 newton ⋅ metre, in other words, the force 1 newton along the length 1 metre. The basic power unit watt (W) is defined as 1 J/s. 1 J = 1 Ws (wattsecond) 1 megajoule (MJ) = 106 J 1 gigajoule (GJ) = 109 J Kilowatt-hour (kWh) is a standard unit of electric energy. Since 1 kW (kilowatt) = 1,000 W and 1 hour = 3,600 seconds we get: 1 kWh = (103 W) ⋅ (3600 s) = 3.6 ⋅ 106 Ws = 3.6 ⋅ 106 J = 3.6 MJ (exact). 1 MW (megawatt) = 103 kW = 106 W (typically, a large industrial plant or wastewater treatment system has a power rating of the order MW). Appendix 2 Conversion of units Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user