Falling costs mean new windfarms are now £20 cheaper per megawatt hour than coal or gas-fired plants, according to new analysis New onshore windfarms are now the cheapest way for a power company to produce electricity in Britain, according to Bloomberg New Energy Finance (BNEF). Costs have dropped to $85 (£55) per megawatt hour (MWh) compared with the current costs of about $115 for constructing coal or gas-fired plants, its analysis found.