if we want to deliver a thousand terawatt hours a year using these systems you could use 142 00:29:07 coal-fired power stations or 30 000 solar pv arrays or 12 309 wind turbine arrays of average size 00:29:18 where each array is like 10 win windows this is this is where we're getting the extra numbers from so each of these sites will have to be built and constructed and maintained and then when they wear out they need to 00:29:30 be decommissioned so renewables have a much lower energy return on energy invested ratio than fossil fuels and they and the the truth is they may not be strong enough to power the next industrial era 00:29:45 so gas and hydro power generation has to balance with demand supply and demand has to balance otherwise the grid will age