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Not every solar power system has a connected solar battery. In fact, as of 2020, only about 4% of residential solar installations had a backup battery, although the numbers are rising fast. Many solar power systems instead send electricity to a home without an on-site solar energy storage system. At this point, the solar power system “sells” additional energy back to the utility via a connection to the conventional power grid. At night, these grid-connected systems only draw conventional electricity and buy it from the utility.
Adding a battery system allows for two main benefits. First, it gives homeowners the ability to use battery power during hours when the utility company is selling electricity at a higher price, known as peak hours, by using Time of Use pricing (PDF).
Peak times are often the days of the week when most people are home and using electricity, often between 8am and 10am and 6pm and 8pm on weekdays. Second, with a battery backup, you can avoid power interruptions when the grid goes out or at night.
While battery systems add to the cost of a solar power system, these benefits can also offset the cost. To learn more about whether solar batteries are right for you, it helps to understand how they work.
This is how solar batteries work
When your home does not require all of the energy generated by your solar panels, the excess energy is stored in the battery. When the solar panels are not producing enough energy to meet the building’s electricity needs, the battery discharges the reserve power to make up the difference.
Solar batteries typically contain two materials that react inside the battery to both store and discharge electricity – lead-acid, an older and cheaper type, and lithium-ion, currently the most popular type of solar battery.
How you configure your solar battery system affects how it works. You have three main options:
- Only connect your solar panels to a solar battery system, and charge and discharge it frequently in response to the no-sun periods when you still need power. This is useful when you are in an area that is “off the grid” and away from utility companies.
- Connect your solar panels to a solar battery system and to the grid (PDF). You can choose to fill up your battery and only keep it as a backup, rarely discharge it and mostly sell and buy excess power from the electric company.
- If you live in an area where electricity prices depend on the time of day, you can configure your system to use a backup power supply and draw power from the grid at the most expensive times most favorable times.
Eventually, batteries lose their ability to respond efficiently and store energy for future use. Solar battery manufacturers often offer warranties or guarantees to build your confidence in the lifespan of these products, but their lifespan can vary widely based on various factors.
A little bit about inverters
Inverters play an important role in how the battery stores and converts solar energy. While solar panels generate electricity in direct current or DC, the power grid and homes generally use alternating current or AC. An inverter can convert AC to DC or vice versa, and most solar batteries contain an inverter to store the energy in DC form and an inverter to convert it back to AC for grid or home use.
Since reversing current is not perfectly efficient, battery manufacturers are always experimenting with how to reverse less often and increase battery efficiency. As a result, some batteries do not have input and output inverters included in the system. Talk to your solar installer about the battery system you are considering so you can make sure you have all the external inverters you need.
Final Thoughts
Solar power is only available part of the day. Adding a solar power storage battery system ensures you always have power when the sun isn’t shining. Solar batteries are designed to last for many years, but eventually they lose efficiency and stop working, usually before the lifespan of a solar panel, which is often 25 to 40 years.
A professional solar power system installer can help you choose a battery that fits well with your goals, whether you want to be completely off-grid, have backup storage for outages, or want to minimize your utility bills during peak periods.
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