Solar panels can save you thousands of dollars in electric bills over their lifespan, but they only generate power during daylight hours. Solar batteries eliminate this limitation by providing an energy storage system that ensures you have power during cloudy days and nighttime. Solar batteries are generally worth it for homeowners living in areas with higher electricity costs, no net metering programs, frequent electricity outages, or limited hours of sunlight.
Stand-alone solar panels are an excellent investment, but a battery bank improves their functionality.
Installing a solar battery is generally worth it when the savings exceed the cost of ownership. Several scenarios highlight the benefits of energy storage:
- Avoiding the highest kWh prices on a time-of-use tariff, where electricity prices vary depending on the time of day.
- Reducing energy demand charges if they are part of your electricity costs.
Using solar panels alone cannot provide backup power during blackouts or suboptimal conditions due to their variable output. However, a charged battery can keep your appliances running during these times. Additionally, if your local electric company charges higher rates during certain hours, you can avoid these costs by switching to a solar battery.
A solar battery is also useful if your local power company does not offer net metering. Without net metering, you won't receive credit for sending excess solar power to the grid. However, a battery allows you to store and use that extra energy. This option is financially sensible only if the cost of battery ownership is less than what you would pay for grid electricity at night.
A solar battery is a device that stores electrical charge in chemical form, allowing you to use that energy at any time, even when your solar panels battery storage are not generating power. Although often called solar batteries, these battery backup systems can store charge from any electricity source. This means you can recharge a battery with grid power when solar panels have low productivity or use other renewable sources such as wind turbines.
There are different types of battery chemistries, each with its own advantages and limitations. Some batteries are suitable for applications requiring a large amount of energy in a short time, while others work best for providing a steady output over a longer period. Common chemistries used in solar batteries include lead-acid, lithium-ion, nickel-cadmium, and redox flow.
When comparing solar batteries, consider both the rated power output (kilowatts or kW) and energy storage capacity (kilowatt-hours or kWh). The rated power indicates the total electrical load a battery can support, while the storage capacity shows how much electricity the battery can hold. For example, if a solar battery has a rated power of 5 kW and a storage capacity of 10 kWh:
- The battery can power up to 5,000 watts (5 kW) of electrical load simultaneously.
- With a storage capacity of 10 kWh, it can sustain a maximum load of 5 kW for two hours before depleting its charge (5 kW x 2 hours = 10 kWh).
- If the battery powers a smaller load of only 1,250 watts (1.25 kW), it can last for eight hours on a full charge (1.25 kW x 8 hours = 10 kWh).
It’s important to note that the rated power of solar panels and battery storage systems are not necessarily the same. For instance, you could have a 10 kW home solar system paired with a battery that has a rated power of 5 kW and a 12 kWh storage capacity.
All solar batteries have the same basic function, but each type is suited for different applications. Your solar battery will offer higher reliability and a better return on investment when its chemistry matches the specific needs of your application.
For instance, some electricity consumers face higher kWh prices at certain times of the day or additional charges for sudden peaks in consumption. In such cases, you need a battery capable of delivering large amounts of electricity in a short time. Lithium-ion batteries are well-suited for this task, unlike redox flow batteries.
Regardless of the battery type, consider the depth of discharge (DoD), which indicates a battery’s usable capacity. Exceeding the DoD can drastically shorten a battery’s service life or cause permanent damage. For example, using 70% of the stored energy is acceptable with a battery rated for 80% DoD, but not with one rated for 50% DoD.
Knowing your average energy consumption can help you determine important factors like your ideal battery capacity, or how much energy a battery can store.
- Lithium-ion batteries are recommended for home solar systems due to their long service life, which is suitable for daily charge cycles.
- Lead-acid batteries are viable for backup power systems used occasionally or as part of an off-grid system.
Home batteries can be classified based on how they interact with solar panels:
- Direct current (DC)-coupled batteries use the same inverter as your solar panels, connecting to the DC side.
- Alternating current (AC)-coupled batteries have a separate inverter that connects directly to your home’s AC wiring.
You can only use DC-coupled batteries if you have a hybrid inverter designed to manage both solar panels and energy storage simultaneously. If your solar panels have a traditional inverter that cannot handle energy storage, you need an AC-coupled battery with a dedicated inverter.
If you intend to use your battery as a backup power source, check its specifications to ensure it can operate off-grid. Not all solar batteries are designed to function during power outages, and many models require synchronization with the grid.
