Can you point me in the direction of some of these companies, please? Thanks.
Who is your current supplier, Bob? If they don't offer anything then I think Ovo are doing something for domestic customers. I work on the commercial side so all the current schemes I'm aware of (EDF, Ecotricity, LimeJump) are working with generators above the FiT limit, and if you get the FiT contribution currently you are much better sticking with that as the current price differential between the FiT Tariff and the wholesale price means you are already being paid far more than your electricity is worth on the market.
Domestic customers need to work in aggregation with loads of others to get their electricity output up to a tradeable amount, you can't buy and sell individual KWh on the market. Companies are starting to set these arrangements up but in these early days it's a great deal easier to do it with companies who can do things like covering their factory roofs with solar panels.