Whether your whole house is off-grid or you have a portable emergency power system, the solar batteries are a critical part of your system. The electrical energy from your solar power system must be used immediately or else it must be stored as another form of energy.
Bank of solar gel-cell batteries
Furthermore, the sun doesn’t always shine and if you’re off the grid you’ll need to rely on stored energy to meet your electrical needs. For portable emergency energy systems you’ll often need to generate energy in one place and use it another.
Batteries are like storage jars for electrical energy. When you charge batteries with solar energy, the electrical power is used to perform a chemical reaction. When you use the battery, the reaction is reversed and the chemical potential energy is converted back into electricity.
With each charge-discharge cycle the battery will loose a small fraction of its capacity permanently. However, when treated with care, the batteries in your system can perform well for many years.
Solar Battery Types
Small consumer devices like digital cameras, radios, and gps receivers take standard battery sizes, like AA, C and D. A pack of rechargeable can provide many uses without having to buy new batteries. These batteries are most often Nickel-MetalHydride (NiMH) chemistry. You may see older Nickel-Cadmium (NiCd) cells but these are less common and have some issues with memory effect and can be very finicky about how they are charged.
Your iPad and hybrid gas electric car need batteries that are flat, whether they are large or small. This is accomplished with Lithium-Ion (LiIon) packs.
For your solar power system, the most common battery chemistry is lead-acid. Truth be told, this technology is over a hundred years old. Although, there have been improvements made as the technology matured.
The most common lead-acid battery formats are:
- Flooded batteries
- Gelled Electrolyte a.k.a. “Gel-Cell”
- Absorbed Glass Mat (AGM)
Large home scale power systems typically use the flooded lead-acid batteries You can get a hundreds of Amp-Hour’s of capacity out of this format. You’ll need to take care to keep the cells well ventilated because they give off hydrogen gas when charged.
One hassle with flooded batteries is their need to be “watered.” That means water must be added to maintain the electrolyte level. Automatic watering systems are available to help you keep your batteries topped off and avoid damage to your cells. Since the electrolyte is liquid, flooded batteries must be operated in an upright position.
Large capacity battery banks usually employ low voltage cells connected in series to provide the desired DC voltage. The 2V cells must be connected with high quality, low resistance connector cables to minimize losses.
Sealed Batteries
Both the Gel-Cell and AGM batteries are sealed and the electrolyte is immobilized. They can be operated in any orientation, which makes them ideal for usage on boats and vehicles. They have vents that will let gas escape if overcharged, however doing this results in damage to the battery and reduction or total loss of capacity.
Gel-cells employ a gelled electrolyte that fills the spaces between the lead plates. AGM cells alternate between lead plates and layers or fiberglass that’s soaked in electrolyte solution.
Sealed batteries find application in small to medium sized solar power systems with cells coming in 6V, 12V, or 24V formats. They are also especially suited to portable power systems.
Battery Safety
A word or two about safety is in order when talking about solar storage batteries. The battery bank for even a small solar installation must be treated with care. Batteries:
- Source a lot of current
- Are very heavy
- Contain corrosive acid
There is a saying that goes “It’s the volts that jolts, but the mils that kills” – this means that while you can get a seriously unpleasant shock from high voltage, it’s the current that can kill you. When you shuffle your feet across the carpet and get zapped when you touch the light switch you’re feeling the effects of high voltage. The typical carpet shuffle shock is delivered with over 13000 volts, but the reason you don’t drop dead at the light switch is that the amount of current is tiny.
On the other hand, the 24 or 48 volts from a solar battery can kill because of the high amperage delivered. Here are some safety guidelines when working around your solar battery bank:
- Know what you are doing – tinkering is fine, but around high capacity batteries is not the place to do it.
- Never work on or around batteries when you’re tired or sleepy – it’s just too easy to make a mistake that could injure you and your equipment. A screwdriver or wrench dropped across charged battery terminals can vaporize in a flash sending white hot debris shooting off in any direction.
- Don’t move heavy batteries alone – a solar battery can easily weigh more than 100 pounds (45kg), get help if you have to move one of these into position. You can easily blow out your back wrestling these things around.
- Wear eye protection – especially around flooded batteries. These contain corrosive acid that can be exposed.
We hope these safety tips cause you to think and act with more awareness and caution around solar battery systems.
Buying Solar Battery Systems
Of course you want a good price on batteries. And, many other parts of a solar power system can reliably bought used. However, for batteries we recommend that you always buy new. It’s just too hard to assess the condition of solar batteries.
A key consideration when buying batteries is shipping. As mentioned, these things weigh a lot! Flooded lead acid batteries will be shipped dry, you will have re-constitute the electrolyte yourself. You will usually only have to the choice of ground shipping by truck. For this reason it’s important to try to shop as locally as possible.
If you live in ”solar country” you will likely have a nearby source of batteries. But no matter where you are, always buy batteries from a distributor on your continent, international shipping of batteries is just too expensive.
Click over to our Stores page for dealers near you.