According to reports, in the past, the majority of residential solar energy users deploying battery storage systems used lead-acid batteries, especially for off-grid batteries. However, this situation has been changing in recent years. With the continuous development of residential energy storage systems, lithium iron phosphate batteries are increasingly being used. So, which one is more suitable for energy storage systems, lithium iron phosphate batteries or lead-acid batteries?
Lead-acid batteries have traditionally been used as backup power sources for residential solar energy facilities. Historically, lead-acid batteries have been cheaper than lithium iron phosphate batteries, making them more attractive to residential users. However, due to the short cycle life, low energy density, narrow operating temperature range, slow charging speed, and significant environmental impact of lead, the future application of lead-acid batteries will be greatly limited.
The working life of lead-acid batteries is shorter than that of lithium-ion batteries. Although some lead-acid batteries can be charged and discharged up to 1000 times, the charge-discharge cycles of lithium-ion batteries range from 1000 to 4000 times. The lifespan of most lead-acid batteries is about 5 years, with corresponding warranty periods. Therefore, residential users will have to replace lead-acid batteries multiple times over the overall lifespan of solar energy facilities. The energy storage efficiency of lead-acid batteries is lower than that of other energy storage technologies such as lithium-ion batteries. Due to their low efficiency, they cannot charge or discharge as quickly as lithium battery energy storage systems.
The discharge capacity of lead-acid batteries is lower, which means that consuming too much energy will quickly degrade their energy storage capacity. Research by the National Renewable Energy Laboratory (NREL) found that releasing 50% of the energy in lead-acid batteries can complete 1800 charge-discharge cycles before the energy storage capacity drops significantly. If discharged to 80% capacity, it can only withstand 600 charge-discharge cycles, after which its capacity will decrease significantly.
Due to the relatively low energy storage efficiency of lead-acid batteries and their inability to fully discharge, lead-acid batteries require more energy storage capacity and space than lithium-ion batteries. Lead-acid batteries are also much heavier than lithium-ion batteries, requiring more robust supports for placement and more space than lithium-ion battery packs. Lead is a toxic heavy metal, and although it is recyclable, improper handling can still cause pollution.
Lithium iron phosphate batteries are rapidly becoming the preferred battery for many power applications, with more and more residential solar energy facilities adopting lithium-ion battery energy storage systems. Although the upfront cost of lithium iron phosphate batteries is higher than that of lead-acid batteries, the cost of lithium-ion batteries is rapidly decreasing.
In recent years, the average cost analysis report of energy storage has evaluated the costs of various battery energy storage technologies. In the latest survey report in November 2017, it was found that the installation cost of lead-acid battery energy storage systems paired with residential solar energy ranged from $598 to $635 per kilowatt-hour. The installation cost of lithium-ion batteries ranged from $831 to $1,089 per kilowatt-hour. Based on these data, the cost of a 14kWh lead-acid battery can be as low as $8,372, while the cost of an equivalent capacity lithium-ion battery can be as low as $11,634. However, the low cost of lead-acid batteries hides many other costs, such as shorter working life and higher operating costs.
Over time, the costs of various battery systems will vary greatly. Surveys show that energy storage systems using lithium-ion batteries have lower costs per megawatt-hour than lead-acid batteries. The cost of lead-acid battery systems per megawatt-hour ranges from $1,160 to $1,239, while the cost of lithium-ion battery systems per megawatt-hour ranges from $1,024 to $1,274.
For these reasons, it is crucial to understand the current costs of lithium-ion batteries and lead-acid batteries used in residential energy storage systems. They can be used as independent energy storage systems or paired with residential solar energy facilities to meet some or all of the energy needs of residential users or businesses. In terms of working life, it is expected that lithium-ion batteries will operate for about 10 years and will be able to charge and discharge to higher levels without significantly reducing capacity.
Lithium-ion batteries can also charge more quickly at higher voltages. Although lead-acid batteries can take up to 16 hours to fully charge, even the slowest-charging lithium-ion batteries can be fully charged in about four hours. In terms of weight, lithium-ion batteries for residential energy storage systems are much lighter than lead-acid batteries. In addition, the normal operating temperature range of lithium iron phosphate batteries is wide, from -20 to 75°C; there is no memory effect, and they can operate with the battery remaining full without losing capacity rapidly to below the rated capacity value, regardless of the amount of energy.
In summary, lithium-ion batteries are more advantageous than lead-acid batteries in energy storage applications, and as costs decrease, they will be used more widely in energy storage systems.
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