A lead acid battery is a sort of rechargeable battery that shops electrical vitality through the use of chemical reactions between lead, water, and sulfuric acid. The expertise behind these batteries is over 160 years previous, however the cause they’re nonetheless so standard is as a result of they’re sturdy, dependable, and low cost to make and use.
In case you’re trying to retailer vitality produced by a photo voltaic array, lead acid batteries generally is a sensible choice, however newer applied sciences could show extra handy and compact.
The article under is all about lead acid batteries for photo voltaic storage, however we even have a extra common article about dwelling photo voltaic batteries.
How a lead acid battery works
Whereas the chemistry of lead acid batteries is kind of easy, writing out all of the chemical equations could make it appear very sophisticated, so we’ll attempt to clarify it with out all of that.
The only model of a lead acid battery consists of three issues:
- A steel plate manufactured from lead and antimony with a adverse cost
- A positively-charged steel plate manufactured from lead dioxide
- A mix of sulfuric acid and water
The adverse plate is named an anode, the constructive plate is named a cathode, and the water/acid combination is named an electrolyte.
A easy lead acid battery. Picture supply: LibreTexts.org
When the plates are suspended within the electrolyte combination and related to wires, the battery is able to present electrical energy!
As electrons stream out of the battery, the acid within the electrolyte begins to stay to the lead on the electrodes, changing their outer surfaces to steer sulfate and leaving further hydrogen ions floating within the water.
As electrons are despatched alongside the wires, lead sulfate varieties on the plates whereas the battery discharges. Supply: Dynamic Science
Charging the battery provides electrons again in and breaks the electrochemical bonds between the lead and sulfate. The sulfate recombines with the free hydrogen ions within the electrolyte to make sulfuric acid once more.
There’s a downside to the lead acid design. If the battery is discharged an excessive amount of, among the lead sulfate can’t be damaged down and recombined with the free hydrogen, which ends up in a everlasting coating on the lead plates known as sulfation. Sulfation enormously reduces the lifespan of the battery.
To ensure that lead acid batteries to work for lengthy durations of time, they should be discharged not more than half of their whole battery capability regularly.
Automotive batteries vs deep cycle batteries
Automotive batteries should not well-suited for storing vitality for dwelling use as a result of they’re designed to present brief bursts of electrical energy which might be used to begin a automobile. In reality, these kinds of batteries are known as beginning, lighting, and ignition (SLI) batteries.
SLI batteries are made with skinny, porous lead plates which might be designed to attract as a lot electrical energy as doable from the electrolyte at one time. That surge of vitality is named present, and it’s measured in amps.
Automotive batteries are made utilizing 6 cells wired in sequence. When the battery is totally charged, every cell produces round 2 volts, resulting in a complete voltage of 12 volts. Volts occasions amps equals wattage, or whole energy accessible at one time.
Be taught extra: Amps, volts, and watts
Deep cycle batteries for solar energy storage don’t have to produce a bunch of instantaneous power to start anything, so they have thicker lead plates that will last a long time and draw power from the electrolyte more slowly and evenly.
Deep cycle battery banks for solar storage
Deep cycle batteries tend to be large rectangular boxes made of a plastic composite material, which makes them easy to stack next to one another. Because they don’t have to start a car, they can produce less wattage individually, and can be wired together to make battery banks.
Many deep cycle batteries for energy storage have only one large cell and produce 2 volts. And, the larger the cell – the more energy it can store. Other 2, 3, and 6-cell designs are found in batteries of 4, 6, and 12 watts, respectively. Battery banks made for storing solar energy are wired together to produce 12, 24, or 48 volts.
For example, six 2-volt batteries can be wired in series (negative to positive all down the line) to make a 12-volt battery bank, or four 12-volt batteries can be wired in series to make a 48-volt battery bank.
If you think of electricity like water, the battery voltage corresponds to the pressure in a hose. Higher pressure means a greater rate of flow. Current, measured in amperage, defines how wide the opening of the hose is. The two together determine wattage, or the rate of flow.
Energy storage capability is measured in amp-hours per 20 hours, which means it’s measured by the amount of energy it would take to deplete the battery in 20 hours. Imagine a hose attached to a barrel. A bigger battery is like a bigger barrel, because it holds more energy (water).
You might see a 2-volt battery that is rated to store 1100 amp-hours. That means the battery can put out 55 amps for 20 hours. At 2 volts, that means the battery would be making 110 watts at any given time (2 volts x 55 amps = 110 watts).
But 2 volts is not very high pressure. It would be like holding the hose level with the barrel. There’s a lot of water behind it, but it just trickles out. The idea is to create more pressure so the energy can flow at a higher rate.
Wiring batteries in series to increase the voltage is like adding pressure to the water. Take the battery bank from earlier: wiring the six 2-volt batteries in series doesn’t increase the energy stored, it just increases how fast it flows by the pressure in the “hose”.
In this case, the series of batteries can still produce 55 amps for 20 hours, but this time they produce it at 12 volts, for a total of 660 watts of power (55 amps times 12 volts).
Conversely, wiring two batteries in parallel increases the amperage, but not the voltage. Parallel wiring connects the negative terminals of both batteries and the positive terminals of both batteries. Parallel wiring is acceptable if you’re connecting batteries of 12 volts together, but most people will need a battery bank that can produce 24 or 48 volts; in this case, they will need to wire in series-parallel.
Series-parallel wiring connects two or more strings of batteries wired in series. This increases both the total energy stored as well as the voltage, as seen in the image below.
Designing a battery bank
Designing a battery bank for solar storage is a balancing act of finding the right voltage, the right current, and the right amount of stored energy.
Most homes need a total of around 900 kilowatt hours (kWh) of electricity per month, or 30 kWh per day. To serve those needs, you’d need a battery bank capable of storing 625 amp-hours at 48 volts.
An important rule of designing a battery bank is to not allow a current of more than 100 amps. The main idea here is to build a battery bank with a high enough voltage so that the current will not exceed 100 amps.
Battery voltage drops as the battery is reduced from a full charge, so it’s important to take that into consideration when planning your battery bank. If you plan to run a lot of appliances on battery power alone, it’s a good idea to choose a 48-volt battery bank so you can draw as much as 4,800 watts at a time.
When you are using home appliances, each one requires a certain amount of power, and most have an operating wattage and a higher startup wattage. Ideally, a battery bank will be able to meet all of your needs at a time when multiple appliances are running.
Different types of deep cycle lead acid batteries for solar
Here’s where the rubber meets the road. There are three main types of deep cycle lead acid batteries, and each has its own benefits and drawbacks. They include:
- Flooded lead acid batteries
- Absorbent Glass Mat (AGM) batteries
- Gel batteries
The first kind is inexpensive and long-lasting, but requires regular maintenance to keep the electrolyte in balance with the water inside the battery case.
The other two fall under the broader category of “sealed lead acid batteries”. While they are designed to be maintenance-free by sealing the electrolyte inside the case, they’re also more expensive and may not last as long.
Flooded lead acid batteries
The least complicated and least expensive kinds of deep-cycle batteries are flooded lead acid (FLA) batteries. These batteries are the most similar to the image of the simple lead acid battery shown below, with cylindrical lead plates submerged in an electrolyte bath of water and acid.
Eight 6-volt flooded lead acid batteries make up a 48V bank. Image source: Otherpower.com
FLA batteries could also be cheap, however they’re additionally sophisticated to take care of, as a result of the electrolyte contained in the battery case evaporates over time, requiring you so as to add distilled water at common intervals. In case you don’t add the water usually sufficient, the battery’s lifespan might be enormously decreased.
As a result of they’re constructed to be opened, FLA batteries should be saved upright and given sufficient air flow to forestall a buildup of the hydrogen gasoline that’s launched when the battery discharges. This implies maintaining a financial institution of deep cycle FLA batteries appropriate for dwelling vitality storage can take up a whole lot of house, as proven within the picture above.
If correctly cared for and discharged to not more than half of their capability regularly, FLA batteries can final from 5 to eight years in a house vitality storage setup.
Sealed lead acid batteries
Because the title suggests, sealed lead acid (SLA) batteries can’t be opened and don’t require water refills.
A financial institution of sealed lead acid batteries for RV use. Picture supply: AM Photo voltaic
As an alternative, they use one in every of two strategies to maintain almost all of the water current within the electrolyte contained in the battery physique—both by including absorbent fiberglass separators between the constructive and adverse plates or by turning the electrolyte right into a gel. These designs imply SLA batteries may be positioned on their sides and stacked for simple storage.
Regardless of these enhancements, SLA batteries nonetheless should be vented to forestall hydrogen gasoline buildup. This vent is managed by a valve, which is why SLA batteries are generally additionally known as “valve-regulated lead acid”, or VRLA batteries.
As referenced above, there are two foremost sorts of SLA batteries: Absorbent Glass Mat (AGM) and gel batteries.
AGM batteries (Absorbent Glass Mat)
AGM batteries had been developed when battery producers had been searching for one of the simplest ways to maintain the electrolyte near the plates to be used in high-vibration functions like golf carts.
The mat on this case is manufactured from a positive fiberglass mesh that sort of appears like a gauze pad, and is positioned between the adverse and constructive plates in every of the cells of the battery.
An instance exhibiting the inside elements of a typical AGM battery. Picture supply: Bosch
As a result of an AGM battery traps almost all the electrolyte contained in the battery, it may be discharged to a larger depth whereas permitting the sulfate to recombine with the free hydrogen.
Excessive-quality AGM batteries may be discharged to 80% of their capability over tons of of cycles, and usually final 4 to six years in a house vitality storage setup. Discharging to not more than 50% remains to be beneficial for max battery life.
These benefits come at a value, although, and AGM batteries usually price 1.5 to 2 occasions as a lot per kilowatt-hour (kWh) of vitality storage. AGM batteries additionally take up barely extra space per kWh, however once more, they are often stacked on their facet as a way to save house in a house storage setup.
Select AGM batteries for photo voltaic vitality storage should you choose to not keep a strict schedule of testing and watering FLA batteries, you need versatile mounting choices and lengthy life, and also you’re prepared to pay for it.
Gel batteries
Like AGM batteries, gel batteries are designed to maintain the electrolyte contained in the battery and stop it from evaporating or spilling.
On this design, the sulfuric acid is suspended in a silica gel, which makes the battery very secure and has a low self-discharge price over lengthy durations of time.
An instance of a deep cycle gel battery. Picture supply: Taico
Gel batteries are the most secure lead acid batteries as a result of they launch little or no hydrogen gasoline from their vent valves. They carry out nicely in locations the place excessive temperatures are a priority, and may be discharged under 50% and retain their lifespan.
The drawbacks of gel batteries are that they retailer much less vitality in the identical house as different lead acid battery sorts, and the gel doesn’t carry out nicely in low temperatures.
Additionally, gel batteries require cautious charging with particular good chargers which might be designed to restrict the voltage used to cost the batteries and stop overcharging. Failing to make use of these chargers can lead to a battery that dies years earlier than its time.
Select gel batteries for photo voltaic vitality storage should you dwell in a scorching local weather and might’t retailer your batteries someplace cool or well-ventilated, and likewise should you can completely 100% make certain they’re by no means charged at voltages outdoors their particular vary.
Are lead acid batteries higher than lithium ion batteries?
The brief reply to this query isn’t any, lead acid batteries should not higher than lithium ion batteries.
It’s value noting, nonetheless, that lithium ion is a more recent battery expertise that has particular benefits over lead acid, together with:
- Larger vitality density (extra vitality in a smaller house)
- Greater tolerance for temperature modifications
- The flexibility to be frequently discharged to 80% and nonetheless final 10 years
For instance, a lithium ion battery just like the Tesla Powerwall takes up just about 4.5 cubic feet, hangs on a wall, stores 13.5 kWh of usable energy, and has a warranty that says it will last for at least 10 years while still being able to store 70% of its initial capacity. With daily discharge of up to 80%, that’s something like 33,000 kWh served.
Whereas a deep cycle battery bank made up of flooded lead acid batteries that could discharge up to 10.4 kWh per day would take up 8.2 cubic feet on the floor, require regular maintenance, and last for about 7 years total, serving about 28,000 kWh.
Are lead acid batteries cheaper than lithium ion batteries?
There is no such thing as a low-cost battery, but there is a difference in price between these two kinds of batteries, of course.
Buying the lead acid batteries we described above along with all the testing and watering equipment would cost around $7,500 including installation costs. Buying the Powerwall at current prices (early 2022), would cost $12,000 with installation costs.
Energy storage costs can qualify for the federal solar tax credit as long as the batteries are set up to charge only from solar panels. That means you can save 26% of that cost for a total of $4,440 for the lead acid batteries or $8,800 for the Powerwall.
Dividing the cost by the expected lifetimes, the lead acid costs $634 per year of service, and the Powerwall would cost $880 per year, or 39% more.
Reviews of lead acid batteries
For more information, check our pages on the best solar batteries and Trojan lead acid batteries.
Key takeaways
- Lead acid batteries for solar energy storage are called “deep cycle batteries”.
- Different types of lead acid batteries include flooded lead acid, which require regular maintenance, and sealed lead acid, which don’t require maintenance but cost more.
- Lead acid batteries are proven energy storage technology, but they’re relatively big and heavy for how much energy they can store.
- Deep cycle lithium ion batteries are more expensive than nearly all lead acid batteries, but are much more compact and maintenance-free.
