Can you make it so your house gets fed with your solar first.. then takes any additional drawn power from the mains as normal? Rather than just switching or using different sockets?
That is how it's fitted and works, no silly contracts.
Of course panels will improve and fall in price. Doesn't really matter though. You enter when you feel it's right for you. Most panels are guaranteed to be 80% efficient after 25-30years. So you lose less than 1% efficiency a year. They won't suddenly stop working in 25 years either.