Teardrop Trail: June 4, 2017

In the last few months, I’ve been working on a larger solar system to pump water at the ranch. We live out in the Texas Hill Country and occasionally experience power interruptions, and I wanted to use solar power to improve our emergency preparedness. The experience of designing and building that system led me to rethinking the teardrop solar system.

A New Battery

Two 100-watt solar panels provide enough power to meet our modest camping needs, but I felt the battery could be improved. We were using a marine battery, but it was a compromise between high starter current (which we would never use)  and deep-cycle power for camping use. An Absorbed Glass Mat (AGM) deep-cycle seemed a better match. I ordered an Optima D34M Blue Top that could supply up to 55 Amp/hours of power and fit into the modest available space.

And a way to measure it

Of course, fully discharging any lead-acid battery will shorten its life and normally one leaves at least a 50% charge. How do you know when you’ve reached 50% remaining power? You can estimate from the battery voltage, but measuring power directly would be best. That led to the second upgrade; a digital energy meter. It shows voltage, current and power, as well as the total power in watt/hours consumed since the last reset. Using the Optima battery as an example, I could use up to 330 watt/hours of power ((55 amp/hours / 2) * 12 volts = 330 watt hours) before it was wise to recharge.

Electric Kettles for Camping?

Finally, we enjoy electric kettles for heating water, and they’re perfect for camping. In many campgrounds, shore power is available and we can heat water for tea, coffee and washing up with ease. Would it be possible to use an electric kettle on solar power?

Researching electric kettles and hot pots I found one model that only used about 1000 watts. A lot of power, but within reach of a not-too-expensive 12-volt to 120-volt inverter. It looked like fun to see if I could make it work, and I ordered an inverter and the necessary wiring to hook it up. Besides; the same inverter could be used to power a Crockpot or Slow-cooker — something we’ve already shown is practical.

The picture tells the story. The new battery, inverter and hot pot were connected and did indeed heat 12 ounces of water to boiling. It used 164 watt/hours of energy as measured by the new digital meter — about half of the available battery storage. Not too practical, but a fun experiment!