How Batteries Are Rated
This is the measure of how much energy a battery can store. The amp hour capacity is often listed as a C20 rate, which means this is the total energy capacity of the battery when charged or discharged steadily for 20 hours. (The C rating of a battery computes the total amount of current – amps – that can be delivered over a length of time.) Some batteries are listed at C100 (100 hours) or C6 (6 hours); when comparing batteries, be sure to match the C ratings.
When comparing batteries, the next important factor is seeing how many times you can cycle a battery to what depth. In all flooded lead-acid batteries, the more deeply you discharge them, the fewer cycles they will have. Many lead-acid batteries will have the most extended life if only cycled down to 70% state of charge (SOC). This means that out of a 100 Amp Hour battery, you only have 30 Amp “usable Amp Hours” to achieve a long life from that battery. Many larger industrial batteries are designed to be cycled much more deeply – some as deep as 20% SOC. Using the same theoretical 100 Amp Hour battery, this means that you have 80 usable Amp Hours.
Flooded cells have about 2 VDC output potential; this difference is how they are connected to achieve the desired voltage. Standard automotive batteries have six cells to provide a 12 VDC power supply. Battery models such as the L-16 or “golf cart” batteries are prevalent in renewable energy. These are batteries with three cells that provide a steady 6 VDC power supply that can be connected to provide 12, 24, or 48 VDC power for home or business stand-alone (off-grid) or battery backup inverters.
Larger industrial-sized batteries often comprise large individual 2 VDC cells either on their own or built into cases. These batteries are designed for larger off-grid systems such as microgrids or systems that require large amounts of stored energy.
The Different Types of Batteries
The industry standard for renewable energy systems, flooded lead-acid batteries (sometimes called “flooded”) are the most affordable and reliable energy storage source. These fully recyclable batteries come in various shapes and sizes, using sulfuric acid and lead plates while encased in plastic. A typical flooded battery comprises cells, each with an electrical potential of about 2 VDC. Flooded batteries range from 6-celled 12 VDC automotive types to massive industrial 2 VDC batteries.
Pros: Cost-effective, reliable storage, long reliable service life (when well maintained), fully recyclable
Cons: Low energy density (heavy, not a great choice for mobile applications), potential exposure to hazardous materials (lead, sulfuric acid), decreased storage capacity when drained too deeply or left to sit with a low state of charge, regular maintenance required (adding distilled water, cleaning and tightening terminals)
Similar to the flooded lead-acid battery in size and chemistry, these batteries differ in that the electrolyte (in this case, acid) is either in gel form or absorbed in a fiberglass matting. Doing this removes the need for regularly adding distilled water, so they are often called maintenance-free lead-acid batteries.
Pros: Little to no maintenance (excellent for hard to service applications), easy to transport and ship (without exposure to acid spills), long reliable service life
Cons: Lower Amp Hour capacity per battery with a higher cost per Amp Hour storage than standard flooded batteries
The cutting edge of battery technology and most common battery for use in mobile applications (electric vehicles, laptops, phones, power tools, etc.), lithium-ion batteries are finding their way into a home’s or business’s renewable energy operations. They have a tremendous life expectancy and no memory from over-discharging or incomplete charging. With several new manufacturers hitting the market, we hope to see these batteries soon take over for the lead-acid series. At present, the cost is often a bit too high for the storage capacity needed for many renewable energy systems.
Pros: Superb life expectancy regardless of the depth of discharge, high energy density (light for their capacity), no maintenance or upkeep.
Cons: Very particular charging parameters, cost per amp-hour storage