First off. Richer people tend to have larger houses, so use more energy. In the UK the grants are such that for me in a smaller house. A heat pump is the same price as a replacement boiler. You could up the grant amount but unless you're going to have a regressive policy of giving more to the rich you aren't going to give the rich all the heat pump and solar they need/can install.

Personally rather than giving someone benefits to pay for electricity I'd rather install solar on their roof.

So for a government, this needs not cost more than what they are doing now.