# Portable Solar water treatment

#### syed_husain

Joined Aug 24, 2009
61
Hello everyone,

i am doing a project to build a solar water treatment (to provide drinkable water) and also a rechargeable battery which will be automatically switched off when it is fully charged. this battery will heat water at night. we have to build a working prototype and were asked to boil at least 5 litre of water. Our solar water treatment is rectangular shape and it is made of polystyrene. is it okay or is there any other good alternative? look, we just started the project and got some serious problems.

1) how do we calculate how much power we need to boil 5 litre of water?
2) what type of solar panel we should use (we are first time using solar panel and choose 200 Watt solar panel)?
3) is it good to use copper coil or copper plate or other material as hot plate?
4) how we calculate the heat loss?
5) what type of battery should we use (Lithium-Ion battery)?
6) Most importantly are we ignoring any other obvious constraint?

N.B. the project's budget must not exceed $600. any advice will be much appreciated. #### Kermit2 Joined Feb 5, 2010 4,158 Finding a solar panel that outputs 200 watts for less than$600 ???

You may as well stop the project right there. Have you priced solar panels lately? It might be possible if you get individual 'cells' and do the building yourself, but it requires a very experienced technician for the soldering part alone. The bare cells are very hard to work with and are extremely fragile outside of any enclosure. Adding to the problem is the need for large batteries. They are not going to be cheap either.

At a minimum you would need three or four times the amount of money you suggest to successfully use the approach you have outlined.

Look into 'concentrated' solar techniques, and use the suns power for adding heat to the water. The infrared output of our nearest star is FREE. You just have to capture it.

#### syed_husain

Joined Aug 24, 2009
61
Finding a solar panel that outputs 200 watts for less than $600 ??? You may as well stop the project right there. Have you priced solar panels lately? that is exactly my thought. the lowest price i got was AUD$568. 200 Watt is not compulsory but i am not sure how much power i need to boil water or how to calculate it. if i get an idea to calculate the required power after compensating heat loss then we can decide what rated power solar panel we need.

here i have attached a simple calculation without considering any heat loss. it is for 2 litres of water. we found that we need to keep the water at boiling temperature at least for 2 minutes. but i need a precise power to boil 5 litres of water after considering heat loss.

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#### Kermit2

Joined Feb 5, 2010
4,158
If you only have to kill micro-organisms then 160 deg F. is all you require(google pasturization). Boiling the water into steam is required if you must 'distill' the water to remove non-organic compounds like lead or toxic metals. Some pesticides and similar compounds can pass over with steam distilling and therefore special water filters are required with them.

If you do some reading on water purification these problems are all covered. Are you dead set on an electrical powered solution? Will the suns own heat be ignored in favor of generating heat by other methods?

#### syed_husain

Joined Aug 24, 2009
61
Some pesticides and similar compounds can pass over with steam distilling and therefore special water filters are required with them.
thanks for that. did not think of that.
Are you dead set on an electrical powered solution?
yes, it was the easiest we found. no microcontroller
Will the suns own heat be ignored in favor of generating heat by other methods?
no, actually we are harvesting sun's energy in more efficient way.

could you give any suggestion on the battery?

#### marshallf3

Joined Jul 26, 2010
2,358
I requires 8.34 BTU to raise the temperature of a gallon of water one degree F

Find a physics book with all the equations in it. You'll need to know the starting temperature, the mass of 5 liters of water and a way to convert BTUs to Watts

Plenty of conversion websites that have stuff like this: http://www.borino.com/GYC/wattsbtu_calculator.htm

Actually there's a very comprehensive website called http://www.onlineconversion.com/

A propane camping stove is a far more logical method.

#### wayneh

Joined Sep 9, 2010
16,102
1) how do we calculate how much power we need to boil 5 litre of water?
Look for a steam table that includes lower (hot water) temperatures. It'll give the heat content of water at any temperature, as well as the heat of vaporization. That phase change should be avoided - it takes a LOT of energy to vaporize water.
2) what type of solar panel we should use (we are first time using solar panel and choose 200 Watt solar panel)?
You shouldn't, for the heating. Solar cells are maybe 11% efficient at best. You'll be MUCH better off using the solar heat directly. For your electrical needs, you need to determine the electrical load and design around that. Solar electricity isn't cheap, so optimize.
3) is it good to use copper coil or copper plate or other material as hot plate?
It's a good conductor, but the rest of the design dictates what materials you should use.
4) how we calculate the heat loss?
A chemical engineering text on thermodynamics will have information on heat loss from various geometries. But there's a lot involved; conduction, radiation, convection. Ideally you minimize all of these as much as possible.
5) what type of battery should we use (Lithium-Ion battery)?
Depends how much power you need. I think lead-acid is probably the most economical, especially if you can get a used car battery or such.
6) Most importantly are we ignoring any other obvious constraint?
Well, you didn't mention whether you have a size or weight limit for you solar collector. I don't think a 10ft diameter parabolic reflector would have any trouble bringing a 5L insulated pot to boiling. The amount of solar energy available is of course proportional to area.