Maximize heat from a 12 V, 100 W solar panel and 26 AWG nichrome wire

Question

I am heating a nonconducting material. The power source is connected directly to 12 guage copper wire. One 30 inch strand of 26 AWG nichrome 80 wire runs between the copper wire posts.

Since sunlight exposure is variable, current and voltage is variable. Would running four 8 inch strands between the two copper poles increase the temperature achieved? How do I increase the 200 degrees temperature achieved?

I am trying to maximize the energy going into the non-conductive material (dry sand) to store energy. I have an 8.5 A solar charge controller with a 13 V cut in and a 14.2 V cut out.

My knowledge base is extremely limited. I thought by regulating the connection I would be limiting the energy being stored as heat in the sand.

The current prototype is about the size of a 5 lb can of coffee surround by 3.5 inch of fiberglass insulation. It has 2 poles approximately 3 inches apart of 12 g wire covered with 5 inch PEX with 30 inches of 26g nichrome 80 wire wrapped between the poles with each end connected to a pole.

Hope this information helps, any assistance provided in simple terms would be appreciated.

Answer 1

Your problem is how to keep the solar panel at its optimum voltage/current point, which is unsurprisingly called the maximum power point. A solar panel produces no power when the voltage is zero but current is high, and no power when the current is zero but voltage is high. Somewhere in between is the maximum power point which is the optimal voltage and current where the most power is produced.

A solar panel produces current and voltage along one of these curves on this chart from Wikipedia. Notice this is a very small cell; yours makes much higher voltage and current but the shape is about the same. Each coloured line shows a possible output range - a different line depending on the amount of sunlight. The blue line shows (roughly) where the MPP is.

To match the MPP you have a few options:

• Figure it out once and don't adjust it. Design the heating element so it has the resistance (you get to choose) which is good for about the MPP of the highest curve (or perhaps a little bit lower). Call it good enough - accept that some power is wasted when less power is available - you don't care so much because there wasn't as much power to begin with.

  This might also be good for an experiment when the amount of sunlight isn't changing throughout the experiment.

• Use an off-the-shelf MPP-tracking (MPPT) converter or charge controller, which automatically adjusts its input current and voltage to keep it on the MPP. Many MPPT charge controllers have a "dump load" terminal - unused excess power will be "dumped" into whatever load you connect there, which would be your heating element.

• In your application, you could make your own crude MPP tracker pretty easily. Just have several heating elements in parallel, and a controller that's able to monitor the solar panel voltage and switch each one on and off, and program it to turn on maybe one element every 30 seconds, but turn off one element if the voltage is below a certain point. You can see from the chart the MPPT is roughly a constant voltage, so make the controller try to keep that voltage. It's not perfect, but good enough and better than the first option.

The resistance of a nichrome heating element depends on the length of wire, and the number of parallel strands. You can use that to design elements with any resistance you want.

Answer 2

You are trying to heat the sand by electric power from solar panel. Have u thought of using Fresnel lens or mirrors placed in a concave manner to heat an object at focal point?