What is a solar battery?

A solar battery is a battery that stores energy from a solar PV system for later use. It allows you to keep appliances running when the sun is down or during a power outage. If your rooftop solar system and battery are large enough, you can run your home mostly on solar power. Besides, using electricity from your battery can be cheaper per kilowatt-hour than using electricity from the utility grid, depending on the time of day and electricity tariffs in your area. Batteries also eliminate the risk of electricity prices going up and feed-in-tariffs going down.

Solar battery types

  • Lead-acid-This is the cheapest battery type at present. However, its lifespan is shorter and depth-of-discharge is lower compared to other storage options. It is recommended not to run lead-acid batteries to a depth of discharge any higher than 50%. Discharging the battery beyond that can negatively affect its lifespan.
  • Li-ion-This storage solutions are priced higher than other battery options. However, they are more lightweight and smaller in comparison with lead-acid batteries. Unlike lead-acid batteries, lithium-ion batteries are able to easily handle deep discharges of 80% or more, which means that they have a higher usable capacity.
  • Saltwater– While a traditional lithium-ion battery uses the element lithium as its primary ingredient for conducting electricity, a saltwater battery’s main ingredient is sodium. It is the same element found in table salt. This makes saltwater batteries easier to recycle. The main flaw of this type of storage solution is that it has lower energy density and costs much.
solar battery
electric meter

Things to look into when choosing a solar battery

Battery size/kWh

Battery sizes are expressed in kilowatt-hours (kWh). The kWh in a battery bank is used at night or in lowlight conditions when the solar production is not enough to power your appliances. There are differences in size. E.g. smaller batteries can be 2kWh sizing up to 20kWh or even more. To compare, if you are consuming around 0,75-1 kW energy an hour, 10kWh battery would last around 10-12 hours and the 13 kWh battery will last 13-16 hours.

Energy capacity/kW

The energy capacity of a battery is measured in kilowatt-hours. Do not be confused by the difference between kilowatts, a measurement of power, and kilowatt-hours, a measurement of energy. A battery’s power rating tells you both how many appliances your battery can power at once and which appliances those are. Most of the batteries available on the market today have a continuous power output of around 5 kW.

Roundtrip efficiency

Round-trip efficiency is the percentage of electricity put into storage that is used later. To put it simply, you’ll lose some kWh of electricity when you invert it from direct current (DC) electricity to alternating current (AC) electricity, or when you put electricity into a battery and take it out again. The higher the roundtrip efficiency, the less energy is lost in the storage process. Typically it is about 80%.

Battery lifetime

Battery lifetime is measured with three different metrics: expected years of operation, expected throughput, and expected cycles. Battery life is defined in years while a battery’s expected throughput and cycles are like a car’s mileage warranty. Solar batteries have a super high cycle life. This means that they don’t require frequent maintenance or replacement. After charging and discharging solar batteries thousands of times, they still remain highly functional.


Solar batteries are considered very safe, which means the risk of putting a solar battery on the side of your house is similar to having mobile phones or laptops at home. However, all solar batteries have to meet certain safety requirements in order to be certified for installation in homes and businesses. For this reason, make sure the solar battery you are planning to buy meets all these requirements.

Electric car charging from a solar battery
an Electric car charging from a solar battery

How to choose a solar battery

Choosing the right solar battery is essential to meet your performance expectations. What needs to be considered is your budget, where you live, and what type of solar panels you have. The other most important questions you’ll need to answer are how much electricity your solar system produces and how much power you consume. These you can see in your monthly electricity bill and the solar system monitoring app.

As an example, according to HTW Berlin solar battery study, if your solar system has an output of 10 kW and 4000 kWh/a is consumed in a house, the usable storage capacity of the battery should not exceed 6 kWh. If the power consumption is twice as high, the battery capacity can also be larger – up to 12 kWh. The choice of a larger battery would mean that the degree of self-sufficiency would only increase slightly because the benefit of every additional kWh of storage capacity is increasingly stagnating.

Recommended optimal size of a solar battery

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Roofit.solar offers full packages of solar systems, including solar batteries, inverters, and other necessary devices. Contact us below and get a fully customized premium solar roof that will protect your home for the decades to come.