I've been doing some research into renewable energy... You might be able to explain to me what a "deep cycle" battery is. A lot of the schematics I'm finding say that "deep cycle" batteries (commonly found on boats?) are the best for storing wind or solar energy. Do you know what those are and how they work? Why would they be an advantage?
Yes. A deep cycle battery is one that can be discharged most of the way and still be able to charge back up again.
For instance, your car battery is not deep cycle. If you discharge your car battery down to 10 percent or 20 percent regularly, it will stop taking a charge after a few discharges. In fact, if you find you have a dead battery in your car more than once, it might be damaged.
That wouldn't be good for renewable energy so deep cycle batteries are required. Still, avoiding deep discharges will allow them to last longer.
And yes, they are used in marine applications a lot because a marine application will frequently deep discharge the battery. But more popularly, deep cycle batteries are used in golf carts. At least the 6V version is.
They are Lead Acid batteries. And currently, that is the best option for renewable energy.
However, a better chemistry would be LiFePO4 not considering cost. This is a safe battery that can deep discharge more efficiently and deep discharge a great deal more times than Lead Acid.
The problem is cost. LiFePO4 can be had for as little as about $1 per Ah at a nominal 3.2V; Whereas Lead Acid is also about $1 per Ah (at about a 50% discharge level) but at nominal 6V
There are a few different kinds of comparisons that can be made, but this one shows that initially you get almost double the energy per dollar currently with Lead Acid.
There are other factors, however.
If the discharge is at a high Amp rate, then the efficiency of the LiFe PO4 batteries compare better. If the discharge is usually far below 50% then the cycle life of the LiFEPO4 batteries will compare better there as well. If maintenance is considered, the LiFePO4 batteries compare better on that count, too.
If all these things are considered together, there are a lot of renewable installations where LiFePO4 is a better fit.
Oh, just to note since some lithium chemistries have been in the news lately for bursting into flames, LiFePO4 is very safe.
Cold weather is a consideration when deciding what are the best batteries for a renewable energy installation
Lead Acid batteries don't work as well in cold or freezing temperatures, but they do work without damaging themselves much - one risk is having to deeply discharge them just to get the energy you need because they won't deliver as much in cold temps and then having them sit in the freezing cold waiting to be charged. If they are deeply discharged and it is very cold (zero degrees F or more) then the batteries could freeze and the cases might crack leaking acid or internal damage can occur. A charged Sealed Lead battery has no problems with the cold
LiFePO4 also won't give out it's rated energy in the cold, but it doesn't degrade as bad as Lead Acid. And there is no danger of damage if it is left in a very cold environment in a discharged state. The problem with LiFePO4 in the cold is that when the temps get below freezing it cannot charge without damage. The charger first has to warm the batteries to above freezing before it can start charging them or they will get permanent capacity loss. Obviously, this would require some smarts on the part of the charger.
As far as you application goes: how much energy do you need? Or, asked another way, what do you want to run when running off battery power only and for how long? Once we know the answer to this question we can size the battery and give prices for both options.
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