Lead, Lithium, and Saltwater - Finding Ways To Store The Power Of The Sun

Residential solar panel systems generally include two basic components - solar panels and an inverter (or micro-inverters). These connect to the home's electrical panel and a utility meter.

The panels capture energy from the sun and convert it to electricity that is then sent to the inverter. The inverter transitions that electricity to alternating current, which homes use. Power not needed at the home in the moment gets sent to other consumers connected on the grid.

Homeowners receive credit on their utility bills for the power they contribute to the grid, while maintaining the ability to draw on the grid when needed.

Solar with Storage Versus Without

Links to an electric grid benefit households with solar though financial and practical gains in the form of credits on utility bills and access to power when the sun isn't shining. But when the grid is down, the solar panels cannot produce.

There's another option that allows homeowners to have energy at the ready even during a mishap with the grid: an energy storage system or battery.

The inclusion of a battery in household solar systems can allow for complete autonomy from the larger energy grid. Households with storage systems draw on stored solar energy much as they would from the grid, but now from extra energy kept in solar batteries. So if the grid goes down, they still have access to power.

Larger Use Of Solar Storage

Households aren't the only ones who can benefit from solar storage. Solar-plus-storage systems, as they're known, can alleviate strains on standard energy infrastructure and lower energy costs.

Solar farms, for example, use batteries to store energy that supplements and energy generated from fossil-fuels. Storing the energy while the sun is shining and then releasing it at peak hours when solar cannot produce enough or any power at all drives down kWh per hour pricing and avoids reliance on fossil fuels and firing up highly polluting peaker plants.

Solar Storage Batteries – The Options

Choosing the right battery for your solar system requires consideration of the materials it contains, capacity, efficiency, and cost. There are three main contenders for solar storage batteries.

Lithium Batteries

Today, Lithium-ion (Li-ion) batteries, essentially larger versions of the batteries used to power cell phones and computers, have proven to be the most efficient adoption for solar storage. Like most batteries, Li-ion batteries need to hold some charge at all times, termed the depth of discharge (DoD). For Li-ion batteries, the DoD is 90%, meaning they can last longer and drop down to 10% capacity without issue.

The lifespan of a Li-ion battery is relatively long and their compact nature accompanies an overall lower cost than comparable storage options. They are not the most affordable, however, and issues around recycling continue to factor into the choice of a solar battery.

Even though lithium batteries can be recycled, less than 5% of Li-ion battles actually get recycled. The expense of recycling outweighs the results, and retrieving the cobalt and nickel they contain is increasingly of concern. When Li-ion batteries end up in landfills, these chemicals – as well as manganese and lithium itself – can seep into the ground. This contaminates soil and groundwater alike.

This makes lithium iron phosphate (LFP) batteries, an alternative chemistry, an appealing option. Because LFP batteries do not contain cobalt, there's less concern about hazardous materials escaping after their lifecycle runs out and the fire hazard is eliminated.

As a newer iteration of lithium batteries, LFP batteries are not as compact as Li-ion batteries, but have a longer lifespan. LFP batteries withstand higher temperatures than Li-ion batteries, but generally offer less power at a given moment than their Li-ion counterparts.

Lead Batteries

Lead-acid batteries were the first rechargeable batteries to enter the market and continue to be used in automotive and industrial contexts. Trusted and inexpensive, lead-acid batteries tend to weigh more than their lithium-ion counterparts.

While the lead they contain is highly toxic, it is also easily recycled. With careful handling, the impact of lead acid batteries on the environment can be lessened.

Lead-acid batteries have an ideal DoD of about 30 to 40%. In a pinch, this can be pushed further. The drawback, however, is that each time a lead-acid battery experiences a deeper DoD, it shortens its lifespan. At optimal DoD, lead-acid batteries last about 15 years.

Saltwater Batteries

Recently, saltwater batteries have entered the solar storage arena. Instead of using heavy metals to store energy, saltwater batteries use a concentrated saline solution as electrolytes.

With no potentially harmful components, saltwater batteries have a long lifespan, are rechargeable, and boast a 100% DoD. They also tolerate a broad range of temperatures.

The science of saltwater batteries continues to expand, but their usage remains rare in household solar storage. Even when they're incorporated into residential storage systems, their power output at a given moment is somewhat limited and they occupy considerable space. They are unquestionably the safest and most environmentally friendly solar storage system, however.