Solar Power Batteries - Some Basics...
When the sun shines or the wind blows, the electricity generated by your home-based solar or wind power system will go in one of three directions: 1) to power appliances, 2) back into the grid, if not needed by your home or business, via
net metering; or 3) into a battery storage system for later use. If option #2, you may not need batteries at all. Familiarize yourself with the concept of
net metering (or, essentially allowing the grid to counter the ebb and flow of power availability from your solar panels or wind turbines).
If you think that batteries
will be part of your system, then you'll want
deep cycle, lead-acid batteries. You do not want car batteries. You'll also want to learn a few big words to throw around at cocktail parties to show the world how much you know about the batteries among us. Enjoy - and share this knowledge with your friends and family at your next cookout!
- Deep Cycle - Deep cycle batteries differ from the much more common car batteries. Deep cycle batteries are designed to withstand constant discharging (drawing of power from them) and recharging (collecting generated power that is not immediately needed). They act as storage receptacles to be called upon to parcel out power more evenly than a starting battery would, as for use in appliances. Car batteries, on the other hand, are designed primarily to offer up a surge of power - all at once - for vehicle ignition. Deep cycle batteries have internal construction featuring thick, solid lead plates as opposed to the more numerous and much thinner, sponge-like lead composite plates found in car batteries. Be aware that any battery that has a cranking amp rating (which would only apply to things that have a motor) is not a deep cycle battery. You're looking for a battery that has an amp-hour rating.
- Lead-Acid Batteries - The dominant type of battery recommended for use with home-brewed energy generation. Low cost, long lasting, and easy to find. Yes, there are nickel-iron (NiFe) and nickel-cadmium (NiCad) batteries out there, but they don't seem to compare favorably with lead-acid batteries when factoring in cost, durability, efficiency, useful life, etc. Lead-acid batteries further break down as follows:
- Wet-Cell or "Flooded" Batteries - The most common lead-acid battery. These batteries have the plastic caps on top, similar to older car batteries, where one can top off individual battery cells with distilled water. They require regular maintenance (topping off of individual cells with water when needed), are problematic to ship (they are considered to be hazardous materials), and must be stored in properly ventilated locations (they give off hydrogen and oxygen gases). However, they are available everywhere and are the least expensive of the lead-acid types.
- Gel-Cell Batteries - Gel-cell batteries (and AGM batteries, see below) are sometimes referred to as "maintenance-free" batteries. They feature a sealed construction so you cannot access the individual cells. The cells contain a gel substance where the electrolytes live as opposed to the water cells found in wet-cell batteries. Gel-cell batteries are immune to tip overs which can spill caustic battery acid everywhere, they last longer in temperature extremes, don't lose their charge very quickly, do not give off hydrogen emissions, and are easier to move around due to the gel construction. However, you must be very careful not to overcharge them, they tend to be expensive compared to AGM and wet-cell batteries, and they don't have the lengthy useful life that you would expect for the price.
- AGM (Absorbed Glass Mat) Batteries - AGM batteries feature a sealed construction similar to gel-cell batteries, which means they are also maintenance-free batteries. The electrolytes in the cells of AGM batteries are suspended in an absorbed glass mat, so even if they break, there is no issue with spillage as there might be with wet-cell batteries. AGMs are made to take abuse, can be shipped without concern for hazardous materials classifications, work well in extreme temperatures, are very shock or impact resistant, lose charge at a very low rate, and will not vent hydrogen gas. However, they are more expensive and not quite as long-lasting as wet-cell batteries. If ventilation issues and occasional maintenance isn't a concern, than wet-cells make a better economic choice.
- Storage Capacity - The amount of juice, or charge, that your batteries can hold.
- Charging / Discharging Rate - The speed at which a battery can be "charged up" vs. the speed at which a fully-charged battery loses charge. The lower the discharge rate, the better; i.e. a battery with a 2% discharge rate beats one with a 15% discharge rate.
- Amps (short for amperes) - At this point, the use of drinking analogies can help with our friends the amperes. Amps are the measurement of current through a circuit, sort of like the flow of beer into your pint glass. The faster your buddy pours beer into his glass (isn't that always the case?), the higher your "amperage rating". The slow, civilized way (yeah, right) that you pour beer into your glass means that you'll have a lower "amperage rating". And, you'll drink less beer or use less power, which means you'll be less fun to be around. So drink up.
- Amp-Hours - This is the main form of measurement of a deep cycle battery's storage capacity. When a deep cycle battery is fully charged, it is at full storage capacity. As power is drained from the battery by various appliances, the battery is being discharged. When a battery has been completely discharged it has reached 100% "depth of discharge" (DOD). (You should take all measures to make sure this never happens - most batteries should not be reduced to less than 20-50% of full charge.) The battery's amperage rating is multiplied by the time it takes to "empty it out", which gives you the amp-hours (Ah) rating. Most deep cycle batteries are measured for amp-hours on a twenty hour period.
- Efficiency & Internal Resistance - It might take 110 watts to charge a 100 watt battery, because batteries are not 100% efficient. The higher you go on the amp-hour scale, the higher a battery's "internal resistance".
I realize that this article is far from a comprehensive resource on batteries, especially as they relate to alternative power installations. I expect to make numerous edits over the life of this article. If you have a comment or something to add, please send an e-mail to
matt.henterly@ecoswap.net.