CHP feasibility study

Hey guys, was wondering if you could give me some advice on the following :
I want to install a chp machine to power a known intraday load profile. How do I pick which is the best sized generator to power my electric load since I will have the economic benefit of exporting to the grid. So how do I balance installed capacity with pricing ?
Apart from my electric : thermal ratio how do I bring the thermal bit into the equation?


Thanks