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  • Sarah Lozanova

Adding Batteries To An Existing Solar System



An estimated 6% of the residential solar systems installed in 2020 have battery storage, but this number varies widely by location. In Hawaii, where there is a lack of net metering laws, approximately 80% of home solar power systems have energy storage. Solar batteries are also more prevalent in California than in other states because of the Self-Generation Incentive Program and public safety power shutoffs designed to prevent wildfires.


The prices of advanced lithium-ion solar storage batteries have fallen in recent years, making them more affordable to homeowners. In addition, some states or utilities offer battery rebates or tax incentives, including California, Hawaii, Illinois, Maryland, Massachusetts, and Oregon. But some may require the homeowner to install the solar system and batteries simultaneously.


As storage systems increase in popularity, many homeowners want to add batteries to their existing solar panel systems. Solar batteries are especially appealing in areas with an unstable electric grid, such as areas regularly impacted by severe weather. Also, some homeowners can reduce their electric bills more with a battery due to the utility rate structure in some areas. Let’s explore this topic so you can better serve your existing customers.


Is It Possible To Add Solar Batteries To An Existing Solar Array?


Yes, it is possible to retrofit an existing solar system with a battery bank. This is an excellent way to reduce the impact of blackouts by making solar electricity available 24/7.


Solar panels are almost always compatible with energy storage systems. However, if the solar system wasn’t originally designed to have battery backup, you will need to either replace the existing solar inverter or install an AC-coupled battery.


What To Consider Before Adding Batteries


Before you plan your approach for a battery retrofit project, it’s essential to consider several factors.


What Type Of Inverter Does The Array Currently Use?


Unless the solar system was designed to have battery storage, you would either need to replace the inverter or install an AC-coupled solar battery, such as the Tesla Powerwall or the Panasonic Evervolt AC-coupled battery. These types of batteries have a storage inverter built into the battery, so they can work with both microinverters or a standard string inverter.


However, some homeowners knew they would want to add a battery in the future and installed a storage-ready solar system with a hybrid inverter, such as the Solaredge Storedge. In these cases, they can pair a DC-coupled battery with their system, but this situation is rare.


It’s also worth considering the expected remaining lifespan of the existing inverter. For example, many string inverters have a lifespan of 10 to 15 years. So, if the equipment is already 10 years old, it might be better to replace the inverter with a hybrid inverter and go with a DC-coupled solution.


Is The System AC- Or DC-Coupled?


An AC-coupled system with batteries has two separate inverters. One inverter converts the direct current (DC) power from the solar panels to alternating current (AC) power. This energy can power the house, and the excess can go to the electric grid. The other inverter works with the battery, which stores DC power.


By contrast, a DC-coupled system has a hybrid inverter that can invert current from both the solar panels and the battery. This option allows the DC current from the solar panels to directly charge the batteries. When feeding energy from the battery to the home or the power grid, it can also convert DC power to AC.


If you install an AC-coupled battery and keep the existing inverter, the upfront cost would likely be lower, but the system could be a bit less efficient. In the long run, this could add up. If your customer wants to keep their costs down, it is probably the better option because they won’t have the added expense of replacing the inverter.


However, a DC-coupled system is a good choice if they are more concerned about system efficiency. With a DC-coupled system, the solar panels can charge the batteries directly without converting the power, reducing inefficiencies.


Are There Any Permit Or Legal Requirements To Adding Storage In Their AHJ?


The local authority having jurisdiction (AHJ) will likely have permitting requirements for installing a battery energy storage system. In addition, it might be necessary to update the interconnection agreement with the local utility company. Therefore, check with your AHJ before starting the project to learn about their requirements and specifications.


Battery Capacity Needs


Properly sizing the battery storage capacity is essential, so start by considering how your customer wants to use the stored energy. For example, some homeowners just want emergency power during outages, while others want whole-house backup power.


Unfortunately, whole house backup can be costly, especially if they have big loads, such as air conditioners, electric heating, or a hot tub. For this reason, most off-grid systems don’t usually have many big loads, or the homeowners use them very sparingly.


To size the battery storage system, determine their household loads and how frequently they need to run them. Most smaller battery systems can handle relatively light loads, such as a refrigerator, the electrical components on a furnace, some lights, a Wi-Fi router, and a few electronics, but will get depleted quickly by power-hungry devices.


Customer Expectations


It is critical to gauge your customers’ expectations on how much electricity the batteries can supply during an outage. It might not be possible to run electric water heaters, electric clothes dryers, heat pumps, air conditioners, power tools, or electric ranges without multiple batteries. Solar installers usually add a critical load panel to prioritize the most important loads.


Financial Savings From the Battery


If your customer lives in an area with time-of-use (TOU) rates and net metering, they can save even more by installing a battery and drawing from it when rates are highest. In areas with TOU rates, the cost of power is usually higher in the late afternoon and early evening and lowest in the middle of the night. Likewise, electricity might cost more per kWh in the summer than in the winter.


In addition to time-of-use rates, some residential customers might also receive demand charges. With both demand chargers and time-of-use rates, having solar batteries will help your customers lower their electricity bill by using stored power when electricity is the most expensive.


Federal Tax Credit for Energy Storage


The Inflation Reduction Act has expanded when homeowners are eligible for a tax credit for installing a residential battery storage system with a capacity of 3 kWh or more. Now, the batteries don’t need to be installed with a solar energy system to qualify for the 30% tax credit. And systems installed between 2022 and 2032 are eligible. Your clients should discuss their eligibility for the tax credit with a tax professional.


How Much Does It Cost To Install Solar Battery Storage On An Existing Array?


Adding a battery storage system can easily cost $10,000 to $20,000. It can be more expensive if the customer needs more than one battery and replaces their existing inverter. Usually, the cost of one installed battery with a ten or 13-kWh capacity starts at around $13,000.


Adding Solar Battery Storage Could Be Right For Your Clients


Severe weather is becoming more common, causing blackouts to be more common. Due to falling battery prices and more incentives, many homeowners with solar systems want to add backup energy storage. Although this is certainly possible, proper planning and knowledge are critical. GreenLancer can help installers plan energy storage retrofits. Contact us today to get started.