Lithium batteries have received plenty of media attention lately, in great part because they are Elon Musk’s technology of choice for Tesla products. Lithium batteries offer a balance between service life and upfront investment: they last longer than conventional lead-acid batteries, while having a lower upfront cost than flow batteries.
Solar photovoltaic systems of all sizes can be enhanced with lithium batteries, ranging from utility-scale solar farms to rooftop installations in residential and commercial constructions. In all cases, the value proposition of batteries is adding a dispatchable power supply to an otherwise variable source.
Although lithium batteries are a much newer technology than lead-acid batteries, they offer a wide range of performance advantages. The attribute list of lithium batteries starts with a superior service life: many commercial batteries are rated for 10 years, which is equivalent to more than 3,000 cycles of use if charged and discharged on a daily basis. For comparison, lead-acid batteries only last for around 500 cycles in most applications.
Another advantage of lithium batteries is their compact nature. Assuming the same system capacity, a lithium battery array will only use 50% of the space required by a lead-acid system, while only having one-third of the weight.
Lithium batteries also have the design flexibility that characterises commercial solar power systems. Just like photovoltaic systems are divided into solar panels, lithium batteries can be ordered in discrete units like the Tesla Powerwall and Powerpack. As a result, battery systems can be configured for any project scale, ranging from a few kilowatt-hours of storage in a residential installation, to many megawatt-hours for a large commercial solar power system.
Another key performance feature of lithium batteries is their superior efficiency, which exceeds 95% in higher-end products. For comparison, lead-acid batteries only offer a round-trip efficiency of around 80%. In other words, if you store 100 kWh in a lithium battery array and 100 kWh in a lead-acid battery array, you can expect to get more than 95 kWh back in the first case but only around 80 kWh in the second case.
The upfront cost of lithium batteries is one of the main factors preventing them from reaching a wider market; in general, they have twice the cost of lead-acid batteries. However, keep in mind that lead-acid batteries are a mature technology, while lithium batteries are still evolving. The International Renewable Energy Agency (IRENA) predict that the price of lead-acid and lithium batteries will be similar by 2030.
When using lithium batteries, there is also a risk of thermal runaway, which is a chemical reaction where the battery burns out and suffers permanent damage. However, the risk is minimised if batteries are manufactured properly, and automatic controls can further reduce the chance of thermal runaway by preventing the conditions that cause it. In particular, lithium iron phosphate and lithium titanate batteries offer the best thermal stability and the lowest risk.
Lithium batteries come with a modular design that can complement commercial solar power systems of any scale, while offering a superior service life and efficiency than conventional lead-acid batteries. The best recommendation to avoid thermal runaway incidents is working with products from reliable manufacturers that are covered by a warranty.