Basically, break it up into different arguments, because you are assessing
For this case, its probably wise to split it up into positive effects for society/env and negative effects
So you could first argue that there have been many environmental problems caused by the use of AC generators, for example the dramatic impact on atomospheric pressure from the burning of fossil fuels due to the increased demand for electricity --> then you could talk about the heat pollution, and how rivers/creeks/dams etc have been subject to various levels of pollution, and thus have had adverse effects on people's leisure activities such as fishing
Then you could argue the benefits, such as the creation of hydroelectric schemes with AC generators (Niagra falls was the first i think?) has provided jobs and security for thousands, and thus there has been less pressure on govt's to provide welfare support. Additionally, this has produced a cleaner source of electricity --> less burning of fossil fuels --> good for env
Basically, its bullshit, but as long as you are putting forward a balanced assessment you will do well