How to build a solar panel at home ??

A few days ago my uncle made a water heater with glasses for his pool because he spent a lot of money on gas, in the city where we live very cold and the water goes very cold there is still a bright sun.

So I asked my uncle and said that this was a solar panel but not to electrical power, this panel focused on the caliric energy.
When the glass heated up and the water in the pool went through a solar pump to the roof where the solar panels were, the water returned hot to the pool.
My uncle says he does not know how to make photovoltaic panels, but we are planning to start building variuos since the one I bought for the water pump came out very expensive, but it is still cheaper than paying the ditch for the electric light or the gas for the pool.
I listen to all your ideas.