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Not every solar power system has a connected solar battery. In fact, only about 4% of residential solar systems had battery backup in 2020, although the numbers are growing rapidly. Instead, many solar power systems send electricity to a house without solar energy storage on site. At this point in time, the solar system “sells” additional energy back to the energy supplier through a connection to the conventional power grid. At night, these grid-connected systems only draw conventional electricity and obtain it from the energy supplier.
Adding a battery system offers two main advantages. Firstly, it gives homeowners the option of using battery power during the hours when the electricity supplier sells electricity at a higher price, called the peak periods, by using the “Time of Use” pricing (PDF).
Peak times are often the days of the week when most people are at home and consuming electricity, often 8-10 a.m. and 6-8 p.m. on weekdays. Second, with a battery backup, you can avoid power interruptions when the power grid fails or at night.
While battery systems add to the cost of a solar power system, these benefits can also cover the costs. To learn more about whether solar batteries are right for you, understanding how they work will help.
This is how solar batteries work
When your home doesn't need all of the energy generated by your solar panels, the excess energy is stored in the battery. When the solar panels do not generate enough energy to meet the building's energy needs, the battery discharges reserve energy 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, the most popular type of solar battery today.
The way you configure your solar battery system affects how it works. You have three main options:
- Just connect your solar panels to a solar battery system and often fill and discharge it in response to the times when there is no sun when you still want electricity. This is useful when you are in an off-grid area that is away from electricity suppliers.
- Connect your solar modules to a solar battery system and to the power grid (PDF). You can choose to fill your battery and keep it just as a backup, rarely discharge it, and mainly sell and buy excess power from the electricity company.
- If you live in an area where electricity prices vary depending on the time of day, you can configure your system to use battery backup at the most expensive times and to get power from the grid at the most expensive times best times.
Eventually, batteries lose their ability to respond efficiently and store energy for future use. Solar battery manufacturers often offer warranties or guarantees to increase your confidence in the lifespan of these products, but their lifespan can vary widely based on several factors.
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A little bit about inverters
Inverters play an important role in storing and converting solar energy in the battery. While solar panels produce electricity in direct current or direct current, the electrical grid and homes generally use alternating current or alternating current. 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 that can be used on the grid or in the home.
Because current reversal is not perfectly efficient, battery manufacturers are constantly experimenting 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 to make sure you have all of the external inverters you will need.
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Final thoughts
Solar power is only available for part of the day. Adding a solar power storage system ensures you always have electricity when the sun isn't shining. Solar batteries are designed to last for many years, but at some point they lose efficiency and stop working, usually before a solar panel's lifespan, which is often 25-40 years.
A professional solar power installer can help you choose a battery that fits your goals well, whether you want to be completely off-grid, have backup storage for outages, or want to minimize your costs to the power company during peak hours.