Except that it is impossible to get electricity from your house into the grid. That's why there's been no hurry to meter it and that's why the payments are "deemed to be 50%" of your panel's output. Any electricity actually going beyond your meter is lost in heat at the first substation it meets. All helps global warming.......
Nick
I'm afraid you are misusing the term "grid". It's true that solar-generated power isn't transformed back up to the high voltages used on the Transmission network, but it's not accurate to say it's not available on the grid. All the homes downstream of the substation will be able to make use of any local generation, and it all acts to reduce load (and therefore generation requirements) on the grid as a whole.
Remember that although different parts of the National Grid operate at different voltages, it all operates at the same frequency. Extra load on the network causes the frequency to drop, excess generation causes it to rise. This effect will happen across the entire network simultaneously, regardless of the voltage or where the load or generation is occurring.
There are many mechanisms that the National Grid Company uses to balance generation and demand on the system, and various levels of response time involved. For example, some industries have special contracts which mean they have special kit installed in their supplies to drop power with sub-second response to help balance the grid.
All solar power generation is a useful resource, it reduces the need for fossil generation, and with the rapid growth of battery storage, it offers a real opportunity for small generators to participate in the market - which is potentially very lucrative. On September 14th last year at 12:00 (Noon), the spot price for electricity went from the base price of £100/MWh to over £1500/MWh. There's loads of companies putting together mechanisms to aggregate micro generators into tradeable blocks.
