The only way self-generation would work would be if efficiency of solar panels at least doubles. It's on the cards, but not while the Government is encouraging bulk uptake of the low-efficiency panels by subsidising them.
The cost of the solar cells far exceeds the price of the electricity they generate even over 25 years.
The only reason that people are rushing to install at present is because of the crazy feed in tariff established by the government. This means you get paid about 45p/unit of electricity generated by solar power. Currently you can buy this same unit of electricity for about 11p/unit.
This means that it almost pays you to rig up a huge bank of lights running from the mains to illuminate your solar cells at night to continue getting the subsidy.
Of course, who pays for this....you guessed it the electricity consumer. Every one of us pays about £18 on our electricity bill to electricity companies. They then have to earmark this "tax" and spend it by subsidising daft things like solar cells.
If only they would spend the money getting insulation standards up to Nordic levels and getting heatpumps installed there would be real saving.
So, running your aircraft from electricity generated by solar cells is a non starter. The cost of the cells and the batteries would far exceed any savings on Avgas.