Home Energy system Solar batteries: how renewable backup batteries work

Solar batteries: how renewable backup batteries work


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Not all solar energy systems are equipped with a solar battery. In fact, only around 4% of residential solar installations had battery backup in 2020, although the numbers are growing rapidly. Instead, many solar power systems send electricity into a home without any on-site solar energy storage. At this point, through a connection to the conventional power grid, the solar power system “sells” the additional energy back to the utility company. At night, these grid-connected systems only consume conventional electricity and buy it from the power company.

Adding a battery system offers two main advantages. First, it gives homeowners the option of tapping into the battery during the hours when the utility is selling electricity at a higher rate, called peak hours, if they are using “Time of Use” pricing ( PDF).

Rush hours are often the weekdays when most people are at home and using electricity, often around 8-10 a.m. and 6-8 p.m. on weekdays. Second, a back-up battery helps prevent power cuts if the power grid is cut or at night.

While battery systems add to the cost of a solar power installation, these benefits can also cover costs. To know if solar batteries are right for you, it helps to understand how they work.

How solar batteries work

When your home does not need all the energy produced by your solar panels, the excess energy is stored in the battery. When solar panels do not generate enough energy to meet the building’s energy needs, the battery drains the reserve power to make up the difference.

Solar batteries typically contain two materials, which 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:

  • Connect your solar panels only to a solar battery system, filling and discharging it frequently in response to sunless times when you still need electricity. This is useful when you are in an “off-grid” area away from electric utilities.
  • Connect Your Solar Panels to a Solar Battery System and Grid (PDF). You can choose to top up your battery and keep it just as a backup, rarely discharging it, and mostly selling and buying excess electricity from the utility company.
  • If you live in an area where electricity rates vary depending on the time of day, you can configure your system to use battery backup at the most expensive times and to purchase electricity from the grid at the time. of the cheapest periods.

Eventually, batteries lose their ability to respond effectively and store energy for future use. Solar battery manufacturers often offer warranties or guarantees to boost your confidence in how long these products will last, but their lifespan can vary widely depending on different factors.

A bit about inverters

Inverters play an important role in how the battery stores and converts solar energy. While solar panels produce electricity in direct current, or DC, the power grid and homes generally use alternating current, or AC. An inverter can convert alternating current to direct current or vice versa, and most solar batteries include an inverter to store energy as direct current, as well as an inverter to convert it back to alternating current for use in the grid. or in the house.

Because current reversing is not perfectly efficient, battery manufacturers are still experimenting with how to reverse current less often and increase battery efficiency. Therefore, some batteries will not have inverters for input and output 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 need.

Final thoughts

Solar energy is only available for part of the day. Adding a solar energy storage battery system ensures that you always have power when the sun is not around. Solar batteries are designed to work for many years, but eventually they lose efficiency and stop working, usually before the life of a solar panel, which often lasts 25 to 40 years.

A professional solar power system installer can help you select a battery that works well for your goals, whether you want to be completely off the grid, have an emergency store for outages, or keep your costs down with the company. electricity during peak hours.