FAQs About Solar Batteries

Q: What is the best battery for solar power?
A: A deep cycle battery is best for your off-grid solar power system. The four common kinds of deep cycle battery for power systems are lead-acid, AGM, gel, and lithium-ion batteries. Lithium-ion batteries are the best but also the most expensive. You must weigh the costs against the benefits when deciding what kind of battery to purchase for your system.

Q: What is the lifespan of a solar battery?
A: Between 5 and 15 years depending upon the type, the manufacturer, and the solar battery’s design. The lifespan can be increased by following the manufacturer’s guidelines regarding installation, useable temperature range, maintenance, and good charging and discharging discipline.

Q: How many batteries do I need for a 5000 watt inverter?
A: The quantity of batteries is not entirely dependent on the inverter size. It also relates to the input voltage of the inverter, the system’s energy requirement, and the size and capacity of the batteries.

The short answer is that if you are running your system on 48V and require 40,000 Watt Hours of energy, you will require 8 x 130Ah 12V solar batteries connected in two parallel rows with 4 batteries in series in each row. If in any doubt, consult with a solar power system installation expert.

Q: How many batteries can a 100 Watt solar panel charge?
A: Again, this question is not so straightforward as it seems because there are many other factors you need to take into account. These include the capacity of the batteries, the voltage of your system, your location and its average hours of sunlight, the temperature of the location where your batteries are, and the efficiency of your solar power system.

In theory, a 100W panel produces 100 Watt Hours of energy for each hour of sunshine. If your panel is tilted at the most efficient angle during 6 hours of bright sunshine, you’ll get (100×6=) 600 Watt Hours of energy. In reality, there are inefficiencies in any system.

There will be a drop in voltage across the electric cables, losses due to resistance in the charge controller, and dust on the solar panel can reduce the electricity generated.

As a rule of thumb, assume you’ll only get two-thirds of the energy you might expect. That means (600×2/3=) 400 Watt Hours of energy. If you are running your system on 12V, that means (400/12=) 33.3Ah of energy needs storing. However, you won’t want to deplete your battery when you’re drawing power because that shortens its lifespan.

That means you’ll need to keep your battery half full at all times, and you can only store half of its capacity every day. As a rule of thumb, you require a battery with twice the storage capacity as you require, so (33.3×2=) a battery with a capacity of 66.6Ah.

When a battery is stored below its optimum temperature range, this reduces the amount of energy it can store, so you’ll require more batteries. However, with this simple example, a single 100Ah 12V battery will be sufficient to store the electricity generated by a single 100W solar panel.

Q: How many solar batteries are needed to power a house?
A: The average American home uses approximately 30,060 Watt Hours per day according to the US Energy Information Administration. If you require 30,060Wh per day and your system runs on 48V, you will require a battery bank that provides at least (30,060/48=) 626.25Ah of storage.

The easiest way to do this would be to purchase 8 x 100Ah 12V solar batteries. You would need to connect 4 solar batteries in series to be compatible with the 48V power system, and you would need to connect 2 of these 4-battery groupings in parallel rows to provide you with a total 800Ah capacity.

This is more than the 626.25Ah requirement, but this excess capacity would enable you to store more on exceptionally sunny days and provide more energy when your demand is higher than usual.

If in any doubt about how many batteries you require, it is always best to consult an expert solar power system installer.