Storing solar energy

he popularity of solar power has been on the rise in recent years. With the cost of solar panels being cheaper than ever, it is now easier for homeowners to go green and save money. However, solar energy does have its limitations - energy supply stops during nighttime and becomes scarce on cloudy days. Your home solar PV system may also be affected by outages and disruptions in a local grid, leaving your house without electricity for hours.

It thus became necessary to find ways to store energy generated by solar energy systems. Several methods developed over time, such as pumped hydro, thermal, and mechanical energy storage. However, these units require a lot of space and are difficult to install, which is why they're not typically suitable for home use.

Most people opt for solar battery storage, as it is a reliable and the most affordable source of backup power for homes which helps to increase energy independence and save money on energy bills.

Battery types for storing solar energy

As the system detects spare solar energy being generated, it diverts it to charge the batteries. When you start consuming more energy than your solar system generates, the battery helps out by providing stored power before you draw it from the grid.

There are several types of solar batteries on the market. Let’s take a closer look at the benefits each type can provide.

Lead-acid vs. lithium-ion batteries to store solar energy

Lithium-ion and lead-acid are two of the most common types of battery chemistry for solar energy storage.

Lead-acid batteries have been around for a long time and are regarded as the first type of rechargeable battery ever made. They are a less expensive solution for solar energy storage than lithium-ion batteries but have lower energy density and shorter discharges. In addition, energy losses from lead-acid batteries reach 15-20%. And yet, lead-acid batteries can be an efficient and cost-effective choice for off-grid solar systems that don't get used frequently.

Lithium-ion batteries are a more advanced option for solar energy storage. Their chemistry resembles the one found in smartphones and laptops but is optimized for handling larger systems such as a solar array. With energy losses of only about 2-8%, they are generally the best choice for solar battery storage.

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The downside of lithium-ion batteries is that they are not the most affordable storage option. You should also take all the necessary safety precautions - lithium-ion batteries can explode when overcharged, overheated, or shorted.

AC-coupled vs. DC-coupled solar energy storage

Solar panels generate direct current (DC) which must be transformed into alternating current (AC) to be used by most home appliances. In DC electrons only flow in one direction, while in AC they keep switching directions, constantly moving forward and backward.

There are two types of solar batteries in terms of how they are linked to a solar panel: DC-coupled and AC-coupled.

DC-coupled battery storage charges directly from a solar panel using a solar charge controller. It comes with a battery inverter to supply AC electricity to home appliances. These battery storage systems are considered more efficient due to less energy loss as AC is converted to DC only once. Besides, DC-coupled batteries can be easily charged from solar panels even when the grid goes down.

Nevertheless, DC-coupling storage has its drawbacks. For instance, it doesn’t work for PV systems that use microinverters. Another disadvantage is that DC-coupled batteries are more difficult to incorporate into an already existing solar installation.

AC-coupled storage is equipped with its own built-in inverter. This allows it to directly convert stored DC energy into AC energy to electrify your home appliances. Adding an AC storage doesn't require much time and effort since it comes with all the necessary hardware and can easily fit into an existing solar power system. Another advantage is that AC batteries can keep working even if your solar panels or inverter fail.

However, AC-coupled battery storage is less efficient because the energy needs to be converted twice: from AC to DC for charging and back to AC for powering a home.

Solar panels work by converting sunlight into electricity through the photovoltaic effect. When sunlight hits the panels, electrons are released, generating an electric current.

Things to keep in mind when choosing a solar battery storage

As you can see, there are so many different types of batteries out there, but how can you store solar energy with maximum benefit? Let’s go through some of the things that you should consider before choosing storage of solar energy for your home.

Solar battery capacity

The number of kilowatt-hours your batteries store is determined by their capacity. Most solar batteries are labeled with two capacity ratings, with "total" meaning how much a battery stores and "usable" showing what percentage of energy is actually sent to power your home. So, a 10-kWh total capacity battery with a 90% usable capacity can provide you with only 9 kWh of the energy it stores.

Power rating

A battery's power rating tells you much energy it can provide simultaneously. This indicator will help you understand the number of home appliances your battery storage will be able to power.

Lifetime

The lifespan of your solar battery comprises three indicators: expected throughput, estimated cycles, and years of operation. Throughput shows how much electricity is going through it over its full lifetime, and the battery cycle shows how many times you can charge and discharge it.

Safety

Even though all solar battery storage options have to meet strict requirements in order to get certification for home installation, there are slight differences between batteries in terms of safety. For instance, a lithium iron phosphate (LFP) battery is safer than a nickel manganese cobalt (NMC) battery, as the latter has a slight chance of overheating and catching on fire.