Battery Backup for a Photovoltaic (PV) Solar System

The number of homes with solar power has increased rapidly over the last decade. However, the number of homes that also have battery backup is much smaller. Historically, this trend has largely been due to cost, with early adopters leading the charge to integrate battery backup systems. However, the cost of batteries has been coming down in recent years, largely attributed to the increased popularity of electric vehicles. R&D efforts in the electric car industry have driven battery prices down while at the same time increasing storage capacity and output. These efforts are indirectly benefiting homeowners interested in having backup capability.If you are a homeowner considering investing in battery backup, what should you know about these systems?

Backup Power in Emergencies

For homes that have solar power, but no battery backup, their system will unfortunately go offline if the power grid goes down. The reason for this is safety. The utility companies do not want solar powered homes back feeding power into the grid while their technicians are working to bring the grid back on line.

Solar systems with battery backup have special switching gear that isolates the home from the power grid. Thus, these homes can maintain essential functions like lighting and refrigeration during grid outages. This benefit is especially important in areas prone to extreme weather events, such as hurricanes or winter weather, which can disrupt power for extended periods.

The Metering Policies of Your Utility

Net metering policies play a significant role in determining the economic value of solar-plus-storage systems. Some utilities have true net metering, where the homeowners receive full retail rates for excess electricity they export back to the grid. In this situation, the economic argument for batteries is less compelling.

However, many utilities have started to scale back their net metering benefits. This can take many forms depending on the utility, but one example is when the utility buys back the excess electricity at the wholesale rate. In situations like this, battery storage becomes more appealing since it allows homeowners to retain the economic value of their solar energy without having to sell it back to the utility at a lower value.

Some utilities have what is called time-of-use (TOU) billing, where electricity rates vary depending on the time of day. Battery storage can offer significant savings in this situation, allowing users to avoid expensive peak rates by drawing from stored energy.

Initial Costs

Entry-level costs for a battery backup system typically range from $10-15K. A system in this range will have less backup capacity and be able to power fewer critical loads in the event of a prolonged power outage. Larger backup systems can cost tens of thousands of dollars more, but the backup capacity will be much greater. Fortunately, these systems are eligible for the 30% federal tax credit.

Maintenance and Replacement Costs

Modern lithium-ion batteries require relatively little maintenance and typically last 10 to 15 years.

In summary…

Battery systems offer financial and energy reliability benefits after the initial investment. As net metering policies continue to evolve, the attractiveness of battery storage will likely increase, making this a valuable investment for homeowners seeking greater control and flexibility over their energy use. As technology advances and battery costs decrease, PV solar systems with integrated storage will become a more feasible option and more broadly adopted.