just under 40 panels. At 2.5ft by 5ft, that's about 500 square feet of panelling.

If we use the net-zero figures, we need 30 kWh per day at an insolation rate of 5.25 kWh per square meter per day, which is 5.71 kWh output. With the same 200W panels that's just under 30 panels and 375 square feet.

Step 5 – Conclusions

We can draw several conclusions from these calculations.

1. It's cheaper and easier to build a net-zero setup than a completely off-grid renewable electricity solution.
2. A system that provides enough electricity to cover a normal home's peak use is absolutely enormous and, therefore, very expensive.
3. New homes built with renewable energy in mind will do a lot better than retro-fitted homes.
4. Homes with relatively small amounts of roof (or other) space for PV panels compared to their floor space are unlikely to hit net-zero.
5. As always, reducing wasted energy, insulating, sealing off air currents and all the other energy-saving measures are vitally important to minimise the burden on your PV panels.
6. Most residential installations will generate renewable electricity that reduces the overall on-grid bill throughout the year, but which rarely provides 100% of the home's requirement.