Solar Panels in Basic Terms

Oct 29, 2012 by

Here is a brief conversation I witnessed between two friends.  The first friend is asking the second for some basic information on solar panels, and I thought the reply was a really straight-up, straight-forward and easy to understand discussion of how they work.

First Friend
I’m trying to find a formula to determine how to design a solar panel system. I wanted a grid down solar system with a battery backup and about a 3500 watt inverter. I am thinking I want to power my fridge, fans and lights. Can I use deep cycle marine batteries? How do they rate panels?  Does 45 watts mean 45 watts per hour? Could I link 10 of them together?

Solar Panels on a Rustic Rural BuildingSecond Friend
The basic method of determining how much power you will need from a solar panel system is figuring out the wattage needed by those things you wish to power. If you are interested in using an inverter to power 120 volt lights, appliances, etc…. then you should find the rated amps (amperage) for the device (usually on a tag or plate attached on the back or bottom) and multiply it times the voltage ( 120 in this case) to give you the wattage. In the case of lights and small tabletop appliances, you will not have to worry about much “reserve” but larger motor driven units, such as a refrigerator or A/C must have enough capacity to supply “start up” amps. Use the basic wattage numbers to figure the minimum size inverter and you will have an idea about what you have to have size-wise for the inverter.

Supply to the inverter is also determined by the amount of power being used by the inverter. Deep cycle marine batteries are a good choice, though there are “wet glass mat” type batteries made for this type of application. Remember that if you use normal car starting-type batteries, once they are drawn down to below 10 volts, the ability to hold a charge is lowered, and that will eventually cause the demise of the battery.

Also inverters are not 100% efficient…they use a portion of your input power to operate, so look for the highest efficiency (which is sometimes rated as a percentage) and a “sine wave” output is best, especially if you are going to be powering sensitive electronics.

Yes, you can link 10 batteries together in parallel to give yourself a large ampacity at 12 volts DC to supply the inverter. There are also 24 volt DC panels, and you would have to use either 24 volt batteries, or use a series/parallel interconnection between the batteries to give a large capacity… this means that you also have to use an inverter rated at 24 volt input.

Panels are rated in watts, indicating the voltage output at an amperage the panel is capable of delivering, at “full light” conditions…. I guess you could call it a watt/ hour rating…but it depends on light conditions.

This is just the “Basics”… the Solar Energy industry is constantly changing, and the installation of a system is becoming less expensive…just Google the terms associated with solar power and you’ll find a ton of info.

Sounds so straightforward, doesn’t it?

~ Sandy Taylor

1 Comment

  1. Beth

    something that you all might find useful Solar Panels on a smaller scale
    http://www.videojug.com/film/how-to-make-a-solar-powered-usb-charger

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