Naked Science Forum

Non Life Sciences => Technology => Topic started by: thedoc on 08/08/2015 12:50:01

Title: Can a solar panel heat water to more than 55 celsius?
Post by: thedoc on 08/08/2015 12:50:01
Alan Torley asked the Naked Scientists:
   
I would like to prove that a 1m square solar panel can produce 70L of water raising it from 10C to 55C?

The manufacturer of solar panels say the solar panel has a useful energy rating of 4.19kWh/m2.

I would like to see the calculation as the Change in the incoming water and winter sunshine differ.

I hope you get the idea. cause I too am confused.
In SA how much can 1m2 of solar panel heat water to?

What do you think?
Title: Re: Can a solar panel heat water to more than 55 celsius?
Post by: evan_au on 09/08/2015 05:33:51
If you are interested in using solar power to heat water, it's much more effective to use a solar water heater than to use photovoltaic cells, which then heat the water with electricity.

This is because residential photovoltaic cells have a fairly low efficiency (currently around 10%); most of the energy is wasted as heat. But heat is exactly what you want, for hot water.

At ground level, the amount of energy in sunlight is about 700W/m2, when the collector is perpendicular to the incoming sunlight. This usually means mounting the collector at an angle determined by your latitude, so that the sunlight strikes it face-on, at some time of the day, on some days of the year.

At other times of the day, and other days of the year, sunlight will strike the collector at an angle, so that you collect less power - and also lose more by reflection.

Quote from: Alan
70L of water raising it from 10C to 55C
An increase of 45C for 1cm3 of water requires about 45 Calories, or 188 Joules.

For 70l of water, this is 13MJ, or 4 kWh. I assume that this is per-day?

Quote
useful energy rating of 4.19kWh/m2
This seems far too high for 1 day of output from a 1m2 photovoltaic cell- could this be a figure per month?
Title: Re: Can a solar panel heat water to more than 55 celsius?
Post by: Bored chemist on 09/08/2015 10:21:33
Quote from: evan_au on 09/08/2015 05:33:51
If you are interested in using solar power to heat water, it's much more effective to use a solar water heater than to use photovoltaic cells,


The OP didn't mention PV
The figure cited
4.19kWh/m2.
(presumably, per day) isn't a million miles of 800W/m2 for a 12 hr day.

There's no theoretical reason why you couldn't boil water with solar power.
How hot do you want it?