Battery Energy Storage Systems (commonly known as BESS) are an increasingly important component of solar energy projects, improving the reliability, flexibility, and overall grid performance of solar energy. This is because BESS help solve a core challenge of solar energy: solar panels generate electricity when sunlight is available, not necessarily when electricity demand is highest.
A Battery Energy Storage System (BESS) is a system that stores excess electricity from solar panels and discharges electricity later to provide energy when it is needed. BESS are a complete, engineered solution that typically includes: batteries that store the excess energy, a power conversion system of inverters/converters that move electricity between the battery and the building or grid, a battery management system which provides monitoring and protection to keep the battery operating safely, and energy management controls which has software that decides when to charge and discharge energy as well as how to respond to operating conditions.
How Solar + Battery Systems Work Together
When the sun is shining, solar panels generate electricity that is first used to power their building or site. If the panels make more power than is needed at that moment, the extra electricity can charge the batteries in the BESS. When the sun stops shining, the battery can then use the excess electricity it has stored and supply it to the site. In some cases, BESS can also send excess electricity to the grid. BESS systems include controller systems that decide when to store energy versus when to use it based on solar production, electricity demands, and local utility rules.
In addition to storing energy for use during the evening hours, BESS systems can also:
- Smooth out short drops in solar output and help keep power steady when disruptions to sunlight happen during the day (such as clouds passing overhead).
- Reduce wasted solar energy by storing extra solar when there is too much power at once.
- Provide backup power to keep selected lights, equipment, or critical loads running during an outage.
How BESS Helps the Electric Grid
The electric grid must keep energy supply and demand balanced all the time. Batteries can charge and discharge energy rapidly which helps the grid in several ways:
- Energy shifting (load shifting): charging when electricity is plentiful and discharging when demand is higher.
- Peak support (capacity support): helping meet peak demand and reducing stress on the grid during the highest-use hours.
- Operating reserves and fast-response services: supporting grid stability by quickly adjusting power output when needed.
- Transmission and distribution support: reducing peak loading on equipment and potentially delaying the need for some infrastructure upgrades in specific locations.
Battery Energy Storage Systems play a critical role in making solar energy more reliable and effective by aligning energy availability with demand. In addition to improving on-site energy management, BESS provide important grid-support services that enhance overall system resilience. When properly designed and integrated, solar-plus-storage solutions increase renewable energy utilization, mitigate peak demand impacts, and contribute to a more flexible, reliable, and resilient electric grid.
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