The average output from wind farms for the whole of the UK last year was 24% of it’s theoretical maximum output, although the figures do vary from wind fam to wind farm.
The problem with wind farms contributing electricity production to the grid is that they need back up from conventional power stations all the time. So no matter how many wind turbines are erected, not a single conventional power station will be shut down.
Regrettably, the large scale wind turbines will do nothing to alleviate global warming, despite all the “information” published by the BWEA (British wind Energy Association) and wind farm developers.
Revenue produced by wind farms comes primarily from 2 sources: electricity produced and Renewable Obligation Certificates (ROCs). A ROC is a piece of paper given by OFGEM to the wind farm operators for each megawatt hour (MWh) of electricity produced. These are then sold on the open market to companies which produce too much pollution – ie. coal fired power stations. At the moment, approximately one half of a wind farms revenue comes from selling ROCS. Several years ago up to 2/3rds of their revenue came from ROCS.
The electricity distributors are required by law to obtain at least 4% of their energy from renewable sources. Therefore they have to buy electricity from companies producing electricity from renewable energy sources. Coal fired power stations (in particular) have to buy ROCs to offset their emissions. These are tagged on to consumers’ electricity bills.
Whether it is good for investment, I would not like to say. Personally, for many reasons, I would not invest in wind farms for environmental and ethical reasons. If all the conventional and nuclear power stations were turned off, wind farms would be unworkable.
Wind turbines on a small local scale are a very different case. I have no problem with these. I even use one myself when it’s not broken.