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Solar power systems use two types of batteries, lithium ion and lead acid, for storage. With it you can run just about any appliance or device, but what about a car? After all, deep cycle and car batteries are both batteries right? However, using solar batteries on cars is not as straightforward as it may seem, or even advisable.
A solar battery cannot start a car because it will not be able supply the cold crank amps needed by the engine. If the battery is powerful enough, it might produce 50% of the CCA needed by the car, but that could damage the engine.
Differences between Solar Batteries and Car Batteries
Car batteries are lead acid, and so are the batteries used in solar power systems. AGM, gel, lithium are all deep cycle batteries and regularly used in solar arrays, so why not cars? The problems lies in the way these batteries are constructed.
The biggest difference between solar and car batteries is the way they supply current. Solar batteries generate low to medium current over an extended time. Car batteries produce a powerful current over a short time frame to start the engine.
Deep cycle batteries are also meant to be discharged repeatedly, though the rate depends on the battery type. Solar lead acid batteries like the Renogy 100ah AGM, can be discharged 50% then recharged and discharged at 50% again.
You can do this several times without causing damage or overcharging. Lithium batteries have even higher discharge levels than AGM and other lead acid batteries.
Car batteries are different. After the initial current is supplied to the engine, the battery lets the alternator provide most of the power the car requires. Usually no more than 20% of the battery capacity will be used up. This alone shows why solar batteries are not for starting any car.
Contrast this with solar batteries where 50% or in the case of lithium, 70%-90% is used up regularly. heavy solar power users recharge these daily, and that is fine because that is what these batteries are for.
If you force a solar battery to discharge high current, its internal circuits may not be able to handle it. The components are built for long term, low to medium current usage and the abrupt change could stress the system components.
The same goes for a car battery. If you run it like a solar battery, its energy supply will get used up quickly. You cannot charge it like a deep cycle battery so it won’t last as long, making it useless for solar power applications.
Cold Cranking Amps
Cold cranking amps or CCA is the system used for measuring the amps generated by a battery at 0 F / -18 C for 30 seconds. The higher the CCA rating the greater the amp burst.
Most car batteries have a CCA rating of 300 to 600A, while solar batteries are only half that. The higher CCA enables car batteries to supply engines the needed power to start up.
On the other hand, lead acid batteries can handle deeper and longer charges. That is why they are ideal for solar panels, which needs storage for the energy being produced.
Are there solar batteries with high CCA ratings? Yes there are, and in theory is compatible with cars. But as we will show in the next section, there re other design differences between solar and car batteries that you should be aware of. The following info will make clear why deep cycle batteries are not suitable for car use.
Design Comparison: Solar vs. Car Batteries
Car and solar batteries have some similarities design wise, but there are several important differences too. It is these disparities that make it difficult to use solar batteries to run a car.
Car battery plates are thinner compared to those used for solar. This is why they cannot withstand repeated charging and discharging. Solar AGM batteries for example, have thick lead plates that can withstand multiple charges. Heavier batteries mean thicker plates and longer life cycles.
Just like using solar panels to charge electric cars , it is possible to power cars with a solar battery. But there are many reasons why it is not a good idea to do it as shown here.
In terms of capacity there is no real issue. Most car batteries are at 70 amps or so, and there are solar batteries larger than that. However, the unique properties of each means you should not substitute one for the other.
Can a Car Battery be Used with Solar Panels?
If you cannot use solar batteries to start a car engine, can you use a car battery for solar energy storage? A solar battery is used to store solar energy generated by solar panels. Since these panels cannot run at night, any extra current produced goes to waste. With a battery you can store these for use anytime.
Car batteries cannot be used to store solar energy however. Car battery capacity is around 30 to 80 hours at most, whereas solar batteries are in the hundreds or thousands of hours. Even if your solar panel recognizes a car battery, it is too small to be practical.
So why is the capacity limited? Because car batteries are not meant for deep cycling. They produce a lot of current at startup but that is it. When the engine starts the alternator is in control and the battery takes a backseat.
A solar battery is different. When you connect it to a solar panel, the battery accepts power continuously from the panels until it is full. You can run DC powered devices directly from the battery or use an inverter for AC powered electronics.
As a solar battery runs the energy gets drained and will require recharging. For FLA it is at the halfway mark, for lithium it is 70% to 90%. You can do these hundreds or thousands of times because that is what the battery is for. You cannot do that with a car battery.
Can You Use a Car Battery as a Home Battery?
If you have a car battery, can you use it to power a home? Suppose you have an off grid cabin and want to use a car battery to run appliances, is it possible? Well the answer is not a simple yes or no.
A car battery can run a few small light bulbs easily, but electric pumps, ovens or AC units are out of the question. An inverter is also required to run any appliance that uses AC power.
Another potential problem is wiring the inverter to the car battery. Some inverters are particular about the kind of batteries they work with. Inverters use battery power when it runs, and if you have large appliances on solar, that battery power will get drained fast.
Why Car Batteries are Not Practical For Solar Power Use
A good sized 12V car battery gives you 80ah, which is about 960 watts. That is almost 1 kilowatt and sounds like a lot. For a car it is, but for solar power that isn’t. Here is a few examples.
A typical 22 cu ft refrigerator uses 300 to 600 running watts, but its surge watt requirement is 1200 to 1500 watts. So your car battery will not able to run it. Other appliances like a microwave, heater, well pump or washing machine are excluded too.
If you run a few 5W light bulbs, a 60W TV and a 55W ceiling fan, the battery will last a few hours. But if you add a blender or coffee maker the power drains rapidly. So the bottom line is for simple appliances, a car battery will do in a pinch.
But the problem again, as mentioned earlier, is the inability of car batteries to be recharged repeatedly. Using them like a solar battery will cause permanent damage to the battery and possibly appliances.
Solar batteries have improved in terms of capacity, longevity and affordability. But when it comes to running a car, it is not quite there yet. Theoretically it is possible, but you are putting the battery and your vehicle at risk by doing so. Best leave solar batteries to run solar power and car batteries for your ride.