Battery Enclosures

Install your batteries in a warm, dry location. 55-80 degrees F. is the optimum temperature range; lower or higher than this and performance diminishes significantly. Because batteries produce a potentially explosive mixture of hydro­gen and oxygen, venting is needed to prevent a buildup. Since hydrogen is lighter than air it has a tendency to rise. If venting is placed at the top of the battery enclosure and air is brought in from the bottom, this gas will move up and out of the battery area. When possible, power venting of the battery enclosure to the outside is a wise move. Also remember that most basements will draw air, not expel air, if not power vented.

Pre-built battery enclosures are used in remote lighting systems or anywhere a battery bank is installed where protection from tampering and weather is required. Large home battery bank enclosures are typically custom built. Banks of one to four batteries for water pumps, automatic lighting, telemetry or radio equipment are often installed in one of our off-the-shelf enclosures. These enclosures can be mounted on the ground or up on a pole behind the array to provide a higher degree of protection from vandals.

Another option here is to place the batteries out-of-doors in a heated outbuilding. You can also place the batteries on the outside of an exterior wall with the control and power conditioning directly through the wall indoors. Keeping the batteries simultaneously warm and adequately vented can be challenging, yet with proper planning is not that difficult.

Overcurrent Protection

Batteries have the potential to discharge incredible amounts of power over a very short period of time, melting conductors and possibly starting a fire. This is why we spend so much time and energy on overcurrent protection. It is not so much the PV module that we need to protect against, but the batteries. PV modules are current limited which reduces the danger, yet modules and their conductors also require protection. The idea of a fuse or breaker is to include a "weak link" in each circuit which will open if the current exceeds that which the conductor can safely handle.

In a typical PV system, we deal with both AC and DC power. Standard components purchased at building supply stores are typically rated for AC use. These are fine for inverter output circuit protection. DC overcurrent devices required between the battery, inverter, controller and modules are much more specialized. They are generally heavier duty and more costly.

Of primary importance is to place a current limiting fuse and disconnect on the main battery conductor and assure that all components on the DC side are rated for DC use.

If you are installing your own system, please obtain a copy of the National Electric Code, work with your inspector and be safe.

Used Batteries

Used lead acid batteries, especially large two volt telephone type cells can sometimes be found for sale. While used solar modules and inverters are usually an acceptable risk, used batteries are a high risk proposition. Should you consider them? In our experience, it is difficult to know just how an older battery has been used. Has the previous user taken good care of the cells or have they been neglected? Have they actually been load tested or just cleaned up and recharged? Our recommendation is to get as much information as you can on the cells, and load test them, or ask the seller for a load test. Without this test your are really guessing as to the remaining life.

If you are considering telephone cells, realize that they are normally shallow cycle lead calcium grid construction, and should not be used in a system designed for deep cycle use.

Click on image to pop it up in a full sized windowBattery Installation and Wiring

Batteries may be wired in either series or parallel configuration. When a battery is wired in series the positive terminal is wired to the next battery's negative terminal. This increases the voltage while maintaining amperage of the two batteries. With parallel wiring the positive terminal is wired to the next battery's positive terminal. and the negative to the next negative. This arrangement increases amperage while maintaining voltage. One common mistake is to believe that both amperage and voltage will increase when wiring batteries together. It will not; only one value will increase with respect to the arrangement. A battery bank may combine both series and parallel wiring configurations. Series strings of batteries are used to achieve the correct voltage, then a number of these series strings are attached in parallel to increase the amp hours of the total battery bank.

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