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Blog | Solar Power Primer

In my Survival Guide I touched on alternative energy as a possible source of electricity in the future (and now for some). I mentioned that alternative energy can generate electricity from wind power, water (hydro) power, solar power and other natural sources of power. Since the book was released, I have been reading almost everything I can about alternative energy sources, especially solar generated power using photovoltaic (PV) panels.

The following is a primer to help introduce you to PV (solar panels) operation.

Photovoltaic (PV) panels generate electricity by having the sun (or other light source) shine on the panel. The light source's photons strike the panel displacing electrons in the semiconductors that make up the solar panel, thus causing a voltage to be generated and current to flow if a circuit is connected to the panel's connections. The voltage output of a PV panel is direct current (denoted as VDC, meaning Volts Direct Current), like the voltage available from a battery.

Solar PV panels range in size and power capability from a very small panel, rated less than a watt output, capable of charging a couple of AA size nicad batteries or powering a small radio to the larger panels used in PV installations, typically rated around 48 watts. Most systems use a multitude of these panels (2 to 48 panels).

In a few cases the panel can be hooked directly to the device that needs power. This is called "direct" use of the panel. An example is using a PV panel to operate a water pump that fills a storage tank. The pump operates when the sun shines on the panel (during the day), but not at night.

However, in the majority of cases the solar panels are used to charge a battery, or bank of batteries, that are the main source of power. Thus the batteries are charged during the day when the sun is shining. But the power can be used even when the sun is not shining, such as at night when lighting is needed. These batteries are typically "deep cycle" batteries that can stand going from a full charge to empty many times over. A standard automobile battery is not designed for this type of use, but marine or golf cart batteries are usually deep cycle batteries. If you decide to install a PV system, there are batteries that are recommended for this type of application.

One of the main problems in designing a "solar powered system" is "sizing the system." The challenge is to make sure that you have a large enough battery bank to be able to supply your electrical needs during periods when the sun doesn't shine, like winter months or during the stormy season, and to have enough solar panels to be able to charge the system fully while the sun is shining. The sizing process is very dependent on how many devices (appliances, etc.) the system must supply power for and how many hours the devices are operated daily.

Along with the problem of making sure the batteries receive an adequate charge is the problem of over-charging the batteries, a condition that can destroy the batteries or greatly reduce their life. A device called a "charge controller" is connected between the solar panels and the battery bank and shuts off the charging when the batteries are fully charged.

Most PV systems for homes are 12 volt (DC) operation, even though other voltage systems do exist (such as 24 VDC, 48 VDC, etc). Twelve volts seems to be the most common because there are devices that will work directly off 12 volts, like those used in our automobiles. But most of our common household devices use 110 VAC (Volts Alternating Current). To allow us to use devices that are 110 VAC from a 12 VDC system, we need a device to convert the 12 VDC electricity to 110 VAC electricity. Such a device is called an "inverter" and is commonplace in the recreational vehicle market. An inverter is rated in size in watts for the maximum amount of power it can handle. As an example, a 100-watt inverter would only light one 100-watt light bulb. Practical inverter sizes range from as small as 100 watts to over 2000 watts (or 2-KW, meaning 2 thousand watts).

Most PV systems have a backup source of electricity or multiple forms of electricity generation. Typically a PV system will have a backup generator to provide power while the PV system is being worked on, when the power demands exceed the output capability of the PV system, or to charge the batteries when the sun has not provided enough light to allow the panels to charge the batteries.

In an elaborate system other forms of alternate energy sources may be combined with the PV system, such as a wind generator or a hydro-electric generator working off the flow of water. This is mentioned for reference. To design or install such a system as this requires professionals experienced in this area.

This is just a quick primer on PV solar panels and systems. For more information you might want to get Home Power magazine, available on most newsstands, or by contacting them at 916-475-0830. If you are serious about a PV system, the Solar Electric Independent Home book (B&A #2802, Click here to purchase) is a great place to start understanding what is needed. Another recommended book is, The Independent Home: Living Well with Power from the Sun, Wind, and Water (B&A #2805, Click here to purchase) by Michael Potts.

I hope this helps those that are not already familiar with these products and systems.