Many homeowners choose to pair a photovoltaic solar panel and a deep cycle battery as their initial introduction to the technology. Smaller systems with this configuration are excellent sources of remote or limited application alternative energy. The concept easily scales upward to larger solar battery systems in homes that operate off grid (completely disconnected from the local power utility.)

The two primary equipment decisions are the size of the solar panel or panels to be used and the capacity of the battery or battery bank.

Let’s consider an “off the shelf” commercial package as an example of energy potential and uses.

Xantrex markets a portable power pack, the XPower 1500 for $400 – $450. It’s essentially a 12v battery paired to an inverter with two standard AC outlets and one 12v DC socket. (Solar panels produce DC power, which must be converted to AC for use by appliances and devices.)

The battery can store 60 amp hours. Match this power pack with a typical 40-watt solar panel and the total system cost will be about $800. Given the battery’s capacity, the user would gain enough energy to run the following devices:

- 150-watt, 18-cubic foot refrigerator for four hours
- compact fluorescent light bulb (8 watts) for 75 hours
- 30-watt portable cooler for 14 hours
- 200-watt computer for 2 hours

Both solar panels and batteries are wired in series to increase the total voltage and amp hour capacity of the system.

The size of any battery bank is determined by:

- The storage capacity required according to intended use.
- The maximum discharge rate of the batteries.
- The maximum charge rate.
- The minimum temperature at which the batteries will be used.

The most common batteries matched with photovoltaic panels are lead acid units with the “deep cycle” designation. This means they can be drained down to 20% of their full charge over and over again.

Any battery or battery bank paired with a solar system should have a sufficient number of amp hours to provide power during the longest period in which the location will have no sun or when cloudy conditions will prevail.

Generally high energy applications are completed during periods of peak sun or with the use of a back-up generator while battery banks are used for minimal draw tasks at night.

This is why it’s important to know exactly what you hope to accomplish with your solar panels and deep cycle batteries so your system can be sized appropriately.

The configuration of the system is simple:

1) Photovoltaic solar panel connected to a charge controller – The charge controller is designed to keep the batteries charged at full capacity without over-charging and will contain a blocking diode to prevent a reverse current from draining the batteries at night.

The charge controller may also include a meter to help track the degree of power being generated.

2) Charge controller connected to deep cycle battery or batteries

3) Batteries connected to an inverter where DC power is converted to AC

Beginners should be aware that there’s never any perfect math in these configurations. Output ratings for panels and batteries rarely equate to actual power generated.

The combination and “tweaks” are endless. This is why starting with a simple solar panel paired to a deep cycle battery with limited intended applications is an excellent introduction to the basics of residential solar energy. You will gain both a functioning alternative energy system and a foundation to attempt more complicated and powerful installations in the future.

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