The Basics of a Solar Battery

A solar battery provides backup power for your home solar system, allowing you to use energy even after the sun goes down. Unlike backup generators, solar batteries are safe and maintenance-free.

The best way to choose a solar storage battery is based on its power ratings, storage capacity and roundtrip efficiency. Also consider your energy usage and the federal tax credits for solar with storage.

Solar Cells

The solar battery’s most important component is the PV (photovoltaic) cell. A solar cell is a flat sheet of silicon that generates electricity when exposed to sunlight. Solar cells can be made from crystalline or amorphous silicon. Some have a thin antireflection layer that helps improve their efficiency by reducing light reflectance.

When light shines on a solar cell, its photons begin “knocking loose” electrons in both the top and bottom silicon layers. These electrons dart around the layers but can’t generate electricity unless they reach the semiconductor junction. To make this happen, manufacturers beef up — or dope — the two silicon layers with trace amounts of additives. The n-type layer gets doped with phosphorus, while the p-type layer is doped with boron.

The resulting electrons and holes seek to restore their equilibrium by diffusing back across the junction against the electric field. However, some of the electrons are slung by the electric field toward the metal conductor strips on the surface of the solar cell. This slingshotting of electrons gives the solar cell its electricity-generating power.

Most PV systems require a charge controller to manage the flow of current between the PV module and the batteries. This ensures that the batteries are not overcharged or drained too deeply. Many lead-acid, lithium ion and nickel cadmium batteries have warranties that cover up to 10,000 cycles.

Battery Chemistries

In a battery, positively charged ions flow through a solution of electrolytes. They move solar battery from the negative electrode (anode) to the positive electrode (cathode). This movement generates a flow of electrons that can power your lights and appliances.

These ions must be prevented from coating the electrodes as they move, because this would stop the flow of electricity and create a short circuit. The cells are generally built with one or more barriers between the different half-cells, allowing the ions to pass but preventing them from mixing.

Scientists and manufacturers are constantly working on new battery chemistries that offer higher energy density, better load capabilities or longer life spans. Alkaline and nickel-metal-hydride batteries have been the go-tos since Georges Volta’s pile of carbon-zinc, and are slowly making way for lithium-ion batteries.

Some types of batteries are also designed to require less maintenance. Lithium iron phosphate batteries, for example, are ideal for remote solar-powered environmental monitoring systems or other off-grid applications that aren’t regularly staffed with battery maintenance personnel.

Battery chemistries are usually named for their active materials or chemical symbols, and commonly shortened to letters. For example, Lithium cobalt oxide is often referred to as Li-cobalt, and other battery chemistries are given similar abbreviations. This helps to avoid confusion between different battery types. A key aspect of a battery is its temperature range: it should supply power within the discharge, storage and charge temperature ranges and degrade or retain capacity at lower temperatures.

Storage Capacity

Typically, solar batteries are sized in kilowatt-hours, or kWh. A battery’s kWh is its power capacity; how long it can run a load before draining or being fully charged.

The most important factors that influence the sizing of your solar home battery are what electricity loads you want to run, and when. You may want to use your solar battery to run appliances and systems during peak pricing hours or for self-sufficiency, or you may simply need a backup in the event of a power outage.

All batteries have an optimal level of energy they can be used before negatively impacting performance and lifespan, known as the depth of discharge or DoD. For example, lithium-ion batteries are designed to have a DoD of about 80%.

For homeowners on a flat rate structure, a solar battery can help to offset utility rates during peak pricing hours by allowing you to pull from your solar storage instead of the grid during those times. This is also known as “arbitrage.” However, you must make sure your system is properly sized in order to take advantage of this opportunity. For this reason, Franklin Home Power recommends pairing your solar panel array with a battery that has at least the capacity to cover your electricity usage during peak hours. You can find this out by using our simple solar and battery sizing calculator.


Solar batteries store solar energy and convert it to electricity as needed. They can help you save on your electricity bills and reduce dependence on the power grid. But like any other battery, solar batteries require maintenance.

One of the most important things to look for when choosing a solar battery is its projected lifespan. You can get a good idea of this by looking at its spec sheet, or consulting with its manufacturer.

The lifespan of solar batteries can also be impacted by how often it’s used. To prevent degradation, use a solar battery only as directed, and solar cell manufacturer don’t cycle it more frequently than recommended.

Another important consideration is to make sure your solar batteries are stored in a cool, dry place. If they’re exposed to extreme heat or cold, it can significantly shorten their lifespan and prevent them from achieving their full number of charging cycles.

It’s also a good idea to clean the terminals of your solar batteries on a regular basis — ideally at least once every three weeks. This can help reduce corrosion, which is a common cause of reduced charging capacity and shorter lifespan. If you have flooded lead-acid batteries, it’s also a good idea to apply a non-hardening sealant to the terminals and cables. This can further prevent corrosion and prolong the life of your solar batteries.