Question 9.2: Calculate the total energy produced per year by one hundred ......
Calculate the total energy produced per year by one hundred 3-MW wind turbines of the type in the previous exercise assuming that the wind is available at the nominal velocity during 15% of the time (as is often the case in Germany); during 25% of the time. Assuming that there is a gas-fired plant backup in the case where there is no wind, estimate the amount of gas needed and the \ C O_{2} emission assuming 50% efficiency.
There are 8760 h in a year. The produced energy is 3.9 GWh (15%) or 6.6 GWh (25%). For 100 wind turbines this means 390 and 660 GWh, respectively. In order to get electricity all of the time (2.63 TWh), 2.23 TWh is missing in the first case and 1.97 TWh in the second one. With 50% gas – fired plant efficiency we need 5.3 and 3.9 TWh, respectively. The gross heat from combustion of natural gas is on the order of 10.8 kWh/Nm³ . We would need respectively 2.63\times10^{9}{\mathrm{~and~}}1.97\times10^{9}{\mathrm{m}}^{3} of gas under standard conditions. The \ C O_{2} emissions are (calculated with 0.5 kg/kWh) 1.3\times10^{9}{\mathrm{~and~}}1\times10^{9}{\mathrm{m}}^{3} , respectively.