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Battery Basics
Posted by Mark Bentley on Jun 10, 2015
Batteries are in the news, thanks to Tesla and their PowerWall. It’s a very important product, but it should be noted that solar-powered battery backup is nothing new. Thousands of Americans have gone completely off-the-grid using a combination of renewable energy and battery backup. For that matter, people in areas prone to blackouts have been using battery backups for decades. If this is something you’re interested in, read one. We’re here to help… as always.
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Let’s take a look at the most popular battery technologies in these systems, AGM and Li-Ion.


Absorbed Glass Mat (AGM) is a type of lead-acid battery, specifically, a “valve-regulated lead-acid” battery, or VRLA. Yes, that’s a mouthful. The biggest difference between AGM batteries and their traditional lead-acid brethren is that they use a fiberglass mat to separate the plates. This means they do not need to be topped off, they don’t vent, and they can be placed in any position. You might think “Hey, that’s how my car battery works,” and you’d be correct, they are very similar.

Where these units differ is in the way they are charged and discharged. Think about your car battery for a second: You ask it to generate a lot of amperage for a short period of time. It has to come up with enough power to turn over a mechanical engine, but only for a few seconds. After that, its life is pretty easy. In fact, car batteries are not good at deep discharging, where power is doled out over a long period of time.

A home battery has a very different role. It is asked to put out a steady stream of electrons for an unknown amount of time, until it is so exhausted it can no longer generate the minimum voltage. Golf carts, electric vehicles, and the UPS on your home computer are all deep cycle batteries. Since AGM batteries do not vent gas, they are can be used indoors.

That slow discharge has a direct relationship to its ability to charge, as well. That’s why golf courses plug in those carts every night, and leave them charging all night.

For home use, the major advantage of AGM batteries is cost. They are significantly less expensive than Lithium batteries.

Many homeowners are concerned about toxicity of lead batteries. Lead is very bad for the environment and for living things, especially humans. Even small amounts of exposure can have serious side effects. Some of us are old enough to remember when lead was in paint, toys, and even added to our gasoline!

The good news is that lead is easily recycled, and lead-acid battery recycling exceeds 99% in the United States. Unlike some material, lead, like steel, can be reused pretty much indefinitely — there is virtually no difference between freshly mined lead and recycled lead.

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Lithium-ion batteries (sometimes called Li-ion or just LIB) date back to the 1970s, but didn’t really appear on the general market until the 21st century. This technology received some negative press when some of them were overcharged, causing nasty fires in laptops and other consumer electronics. Since then, the formulation has been changed to a mix of Lithium, Iron and Phosphate, making combustion pretty much impossible. You almost certainly carry a LIB around with you every day in your smartphone.

Like AGM batteries, LIBs can handle deep cycles, but they are far more robust. You can routinely discharge an LIB to 15% of its rated capacity without fear of damage, and their maximum number of charging cycles is from 2,000 to 5,000. Compare this to the 500 to 1,000 cycles for most lead-acid batteries, and you can start to see why they cost so much more.

Unlike lead acid batteries, LIBs can be “fast charged” right up to 100% of capacity. Lead battery charging has a tapering effect, where getting the last 20% of capacity requires a slow charge. This flexibility is making LIBs popular for solar installations, where the predicability and consistency of charging is unknown due to weather variations.

LIBs have a much higher energy density than lead, which is why Tesla was using them in their cars before they started selling wall-mounted batteries. While weight is not a huge issue for a home installation, size can be. AGM batteries do not work well in hot weather, and are significantly hamstrung above 92F. LIBs, in comparison, can provide usable output up to 120F.

From an environmental impact, don’t be fooled by their names: while lead is in fact the largest component of a lead-acid battery, the actual amount of lithium in an LIB is quite small. Most of the mass is aluminum and copper. LIB recycling is still not a mature industry, but improvements are being made every year.

Comparing these two solutions is complex, and will vary depending on the customers requirements. Factors that have to be included go far beyond the basics covered above, and must consider:

• Initial cost
• Replacement cost
• Installation cost
• Maintenance cost
• Disposal cost
• Environmental impact
• Reliability
• Safety
• Life cycles
• Heat/Cold exposure

OK, nobody wants to come up with a model that factors in all of that. Except us, of course — Geostellar has done all the homework already! Let us help you figure out the best solution for your needs, at the best price, and with our industry-leading guarantee.

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