Lead-acid batteries have been in the market longer than other types of commercial batteries. They have been widely used to complement solar photovoltaic systems in remote locations not covered by power networks. This is also the type of battery used to start a regular gas car engine, not to be confused with the lithium-ion batteries that power electric vehicles.
The use of lead-acid batteries to complement commercial solar arrays is viable, but it is very important to understand what they can and what they can’t do. This article will provide an overview of the strong and weak points of lead-acid batteries.
Lead-acid batteries offer a lower upfront cost than other rechargeable commercial batteries. You can expect to pay around AU$250 per kWh of storage capacity, assuming you select a high-end product. Lower-tier batteries can be purchased for even less.
Lead-acid batteries are also a mature technology that has existed for decades, and their supply chain is well established throughout the world. For this reason, lead-acid battery suppliers and technical assistance are easy to find. Recycling programs are found almost everywhere, which diminishes the environmental impact of these batteries.
The main limitation of lead-acid batteries is their short service life, which ranges from 500 to 1000 cycles in most applications. Assuming the batteries are charged and discharged daily, this results in less than three years of use. Considering that commercial solar arrays last for more than 20 years, you can expect to replace the batteries many times during the rated service life of solar panels.
Lead-acid batteries offer a round-trip efficiency of around 80%, which means you only get back around 4 kWh for every 5 kWh stored. For comparison, the best lithium-ion batteries in the market offer an efficiency above 95%. When faced with high electricity tariffs like those of Australia, losses increase the operating cost significantly.
Another limitation of lead-acid batteries is that their service life is reduced dramatically if they are not fully charged between discharging periods. This induces a chemical reaction called sulfation, which drastically reduces the battery’s capacity to hold charge. Lead-acid batteries also suffer a service life reduction from being discharged too deep frequently. Most manufacturers recommend a 50% depth of discharge, which means you can only use half of the installed capacity if you want to make these batteries last.
A final limitation of lead-acid batteries has to do with their weight and volume. If you compare a lead-acid battery array and a lithium-ion battery array of the same capacity, you will find that the lead-acid system is two times larger and three times heavier.
Lead-acid batteries can be used to complement commercial solar power if you are looking for a low-cost energy storage solution, but being aware of their limitations is very important. To maximise their service life, make sure lead-acid batteries are fully charged between cycles and pay attention to the depth of discharge specified by the manufacturer.