comparing photovoltaic cells and solar pipes

[euan]

Hi. In an experiment where I compare the efficiency of photovoltaic cells and heating water with solar energy, how much water should I compare to how many cells? For example, for 100g of water, what would be the equivalent surface area of cells I should use? Does that make sense? Any help appreciated.

[jake-the-peg]

Think you might be barking up the wrong tree here.

you're comparing the efficiency of the two so want to keep everything constant apart from one thing.

Maybe you take 2 panels of the same size and expose them for the same time and compare the rise in temperature of the water with the energy generated by the photovoltaic cells

Remember Q (energy)=mc T (where m is the mass of water, c the specific heat capacity and T the tenperature difference) So you can convert the electrical energy to a temperature rise.

Or maybe you see how long it takes each cell to raise the temperature by the same amount (or generate an equivilent amount of energy.

Does that help any?

[euan]

Thanks for your help, I think I have some idea of what I do