Let’s do the math…with a little testing first. We bought a solar pack that advertized 100 Watts in bright sun. On a clear day around noon, we aimed it perfectly at the sun and measured. It only put out about 50 Watts. One of our engineers contacted their US engineering department and they admitted the design did not put out the 100 watts. “The new version coming out in early 2015 will provide 100W.”
Let’s say your device is Made in China, like ours, and is really only putting out 22 watts in bright sunlight . Can you use it to charge a car battery? Let’s do the math.
A typical car battery is rated at 42 amp hours at 12 volts That is about 500 Watt hours. That means you can fully charge the battery in 500 watt hrs/22 watt = ~ 24 hours of bright sunlight if aimed at the sun around noon. Figure it would take about a week to charge a car battery with no losses.
A laptop only draws 20–50 watts so it is possible to charge a battery that will run the lap top. You can also charge batteries that will run security lights and cameras.
Let’s figure out how much the electricity is worth. Where I live electricity at the plug costs 13 cents per kW-hr. If you use the device for 4 solid hours perfectly aimed at the sun you will generate 4×22 = 88 Watts hours. Call it 100 watt hrs for easy math. That means in 10 days you will generate 1 kWhr of electricity worth 13 cents. 1.3 cents per day. Use it every day for 2 years and you will have generated ~$8.00 of electricity.
Certainly there are some applications that can use it. I could use one to keep my tractor charged. It could run the bubbler pump in my pond. It could keep the battery for my deer camera charged.
Is it worth the trouble? I’ll leave it up to you to decide.