Air Temperature Need For Effective Solar Heat

[StoshJ]

As was stated, there are many factors, but I can give me recent experience. I have 6 4x20 panels (It think 6).. Anyway, the temp out here in So Cal has been 78-81 the last week. Cloudy till noon. My pool is sitting at 88. Neighbors pool at 74 (no solar). So it's very possible to get the water temp above the ambient outside temp.

[Xndman]

In regard to the speed through the panels, I would have thought that the water flowing through the panels more quickly would have less time to "heat-up" from the panels. Also, I do have my panels on the ground. I assume they'll work better if I get them off the ground.

Thanks!!

[Xndman]

One last question. Does anyone have any thoughts regarding good materials to use to build a rack for 3 2x20 panels? I could always use plywood, but that would require an extremely large piece. Are there any other materials people have used? I'd like something I could angle up the side of the pool (like is often seen in pictures of above ground solar heaters).

Thanks!!

[mas985]

In regard to the speed through the panels, I would have thought that the water flowing through the panels more quickly would have less time to "heat-up" from the panels. Also, I do have my panels on the ground. I assume they'll work better if I get them off the ground.

Thanks!!

Maximizing heat transfer is key for a solar panel. According to thermodynamics, heat transfer is proportional to the temperature differential between surfaces or materials. Therefore, the higher the temperature difference between the water and the panel, the higher the rate of transfer (BTUs/hr) will be.

Another way to think of it is that if the water is moving too slowly in the panel, it will heat up to the panel temperature before leaving the panel. At this point it is not transfering any more heat to the water. Ideally, you want the water to leave the panel only slightly warmer than entering so that heat is continually transfered to the water at the highest rate. This why when the panel is 10 degrees warmer than the pool water, raising the pool temperature the first 5 degreees is much quicker than the last 5 degrees.

Having said all that, higher flow is only better for heat transfer. To lower your electric bill, you may still want to run at low speed. Even though the heat transfer is less, it may still be more than enough.

Also, too much flow can be damage a panel as well but that is usually at pressures exceeding 25 psi.