Overbuilding renewables may have unintended consequences, making power grids more expensive and less reliable. Hence more businesses may choose to generate their own power behind the meter, installing combined heat and power systems fuelled by natural gas. Modelled IRRs already reach 20-30%. Capturing waste heat also boosts efficiency to 70-80%, which can be 2x higher than grid power, lowering total CO2 by 6-30%. This 17-page note outlines the opportunity and who might benefit.