A Guide To How Solar Batteries Work

Solar batteries play a large role in residential solar. Without some form of battery backup, solar homes would only provide solar-generated electricity during the day, making them reliant on the grid. However, with solar batteries, these homes can continue to function during power outages and without help from the grid at night. Adding a solar battery to your home can add comfort and resilience during an outage. If you can't find what you're looking for on this page, visit our "Battery Backup" blog posts. 

Solar Battery Types and Composition

While most solar homes use either lead-acid or lithium-ion batteries, four battery types dominate the solar battery storage space. These include lithium-ion, lead-acid, nickel-cadmium and flow batteries.

The basic concept of solar battery function doesn't change. You charge the battery, then it discharges electricity when you want it. The difference between these battery types comes in the specifics behind making this process happen.

Lithium-Ion Solar Batteries

Lithium-ion batteries use lithium ions to generate, store and disperse electricity. The anode, also known as the positive electrode, uses lithium cobalt oxide (LiCoO2). The negative electrode, also known as the cathode, uses carbon. These both get submerged in an electrolyte and a separator goes between them.

When the battery charges, the cathode attracts the lithium ions, and they cross the separator and connect to the carbon. When the battery discharges, the anode attracts the ions and they cross the barrier again to attach to the LiCoO2. The back and forth of this process allows the battery to charge and discharge multiple times before dying.

How Lead-Acid Batteries Work

Lead-acid batteries use water and sulfuric acid as the electrolyte and a chemical reaction, with an active material put on positive and negative plates, to generate a charge and discharge. When the battery discharges, the sulfate separates from the electrolyte and coats the plates. When the battery charges, it drives the sulfate back into the acid and water mixture.

Nickel-Cadmium

Nickel-cadmium batteries use nickel oxide for the cathode, a cadmium compound for the anode and a solution of potassium hydroxide for the electrolyte. This battery also uses the chemical reaction of these elements to charge and discharge the battery.

Flow Batteries

Flow batteries have the same general concept as a lithium-ion battery. The main difference between these battery types comes from how the electrolyte gets stored. In flow batteries, the electrolytes go into two separate chambers within the battery, separating the power and energy components from each other. 

Instead of separating a negative and positive electrode in an electrolyte, the electrodes dissolve into their respective tank of electrolyte. Then, the liquid gets pumped around the battery so the ions can flow back and forth and either charge the battery or generate a current. 

How Long Solar Batteries Last

Generally, solar battery life ranges between 5-15 years. However, depending on the battery type, this will vary widely. 

Some batteries require a little more TLC, while others can plug and go. These batteries may need priming before they can reach full capacity or require cleaning and electrolyte refilling.

The surrounding environment can also impact battery life. Overly hot or cold areas can decrease battery function.

Battery Charging and Discharging

Each time a battery gets charged and discharged, it goes through a cycle. Batteries typically get rated for the number of cycles they can handle instead of years. This difference comes because not everyone cycles batteries at the same rate. 

Lead-acid batteries can last 200-300 cycles. Typical lithium-ion home batteries used in solar homes can handle 10,000-15,000 cycles with warranties between 10 and 15 years. 

Before nickle-cadmium batteries can work at full capacity, they need priming. Priming can take anywhere from 5-100 cycles. These batteries reach their peak capacity between 100-300 cycles. After attaining their peak capacity, they slowly start to degrade. However, this battery may not need replacing for a while — batteryuniversity.com stated that testing showed that after 2,300 cycles, the battery still had a stable condition. 

Flow batteries have ratings of over 10,000 cycles and warranties for 20 years. However, it takes longer for a flow battery to start running and they need more space to reach the same amount of energy storage as other batteries, making them best suited for energy storage needs over 20 kWh. 

DC Versus AC Charging

Batteries use direct current (DC) — meaning they have a one-directional wave of electrical current that passes through them. However, because the power lines carry alternating current (AC), the current needs to switch from the DC generated by solar panels to the AC in our outlets. 

Most solar batteries take the AC from an inverter and convert it to DC for battery charging and then back to AC when powering the home. However, some solar batteries skip the initial inverting step and take the current straight from the solar panels and then invert it to AC when drawn. 

While AC charging provides a more direct route, not all solar homes come equipped for it. To ensure a positive experience, it's best to make sure that the solar installer can accommodate the battery option you want, whether you want it now or in the future.

Integrating Solar Batteries With the Power Grid

Because of the exorbitant cost of battery technology, many individuals who added residential solar even just a couple of years ago used their utility as a backup. However, with the cost of solar batteries falling, homeowners can now afford to store their excess solar power.

Current Power Grid

The power grid allows electricity generated by large power plants to power cities. The grid provides power through the generation of high-voltage AC, which goes through a series of transformers that lower the voltage so low voltage appliances can access it without issues.  

As more people see the benefits of residential solar, they have added solar to their homes, becoming their own electricity generator for all their daytime power. If they also have solar batteries, they no longer consume grid-generated electricity, which helps alleviate the stress on the grid during peak consumption times and decreases the need for scheduled power outages. 

Increasing Savings With TOU Metering

While time-of-use (TOU) metering can make adding solar a struggle for those who don't have battery backup, for those who do, it works in their favor. TOU metering means that at different times, electricity costs more or less for the consumer. 

Those who have solar batteries can choose when they want to use their excess solar power. This freedom allows them to avoid paying the highest utility rates, which typically occur in the evening.

Going Off-Grid With Solar Batteries

The dream for many who eye residential solar includes going off the grid. However, the actualization of this dream may not come to fruition with a typical residential solar installation. 

For off-grid living to become practical, homeowners have to meet a couple of requirements. They then have to determine the worth of going off-grid for their situation. 

Necessary Off-Grid Components

Off-grid homes need enough solar storage to meet their energy needs at all times. Typically, off-grid homes need enough solar storage to power the home between two and five days without a recharge. 

A backup battery won't do the trick and a typical solar array wouldn't gather enough energy during the winter. A grid-tied solar home typically needs at least two home batteries to meet all of its needs; an off-grid home would need even more.

Feasibility of Going Off-Grid

While adding solar, and even solar batteries, has become more economical, adding enough solar and batteries to go off-grid may not add up. Many homeowners with solar homes offset their utility bills with solar. Others use their home battery as if they are off-grid — and stay connected as an added backup. 

Typically an off-grid solar home makes the most financial sense for houses and cabins that never had a grid connection. Bringing the grid to these homes would cost the same as, or more than, making the home self-sustaining.

Deciding on a Solar Battery: Portable Versus Stationary

Determining which solar battery will best meet a homeowner's needs depends on their storage requirements. Some people need enough power to last several days. These individuals would do best with a stationary battery, such as the Tesla Powerwall

Others only need enough power for the essentials, or would rather have something they could move around the house or take with them on the road. These individuals can meet their needs with a portable solar battery, like the Goal Zero Yeti

No matter your personal solar storage needs, Go Solar Group has your back. We have three levels of battery backup to help customers with various needs continue to power their lifestyle.

10 Tips Guide

10 Free Tips from a Solar Customer

Custom Estimates