Lithium-ion solar home batteries

How to choose and properly size a solar home battery system

Lithium-ion solar home battery
Lithium-ion solar home battery © SimpliPhi

About the author: Greg Dorsey is a Maine certified solar installer with Goggin Energy of Portland, Maine, read his bio here. 

Home battery systems have recently improved in two substantial ways. The first improvement is in the batteries themselves. When lead/acid batteries were state-of-the-art, your battery bank could not be discharged beyond 50% capacity without damaging the batteries. Lead/acid batteries also needed special maintenance and even then they had a relatively short lifespan if used continuously.

The latest lithium-ion batteries require little maintenance, offer a longer lifespan and often, the ability to fully discharge the battery without detrimental effect. No longer being limited to using only half of the stored power in a battery effectively doubles their capacity.

The second big improvement is the advent of ‘smart’ battery controls. Battery systems would previously be charged and discharged without much control; the latest batteries on the market use sophisticated micro-processors to decide when the battery system should store energy, they can send energy where you need it, when you need it.

These new systems can even ‘learn’ from your personal consumption and generation patterns to store power more appropriately. This is very important, because solar arrays that are not connected to the grid need power to make power.

If you have a solar tracker mounting system that stops facing west and the battery system is then completely depleted, it will not be able to start the inverter, nor will it have the power needed to turn the tracker back towards the sun. Battery controls can now be programmed to disable high consumption mechanical equipment like dryers and air conditioners when capacity is low, to ensure there is always enough power to start up the system again. 

Smart battery systems are able to recognize if you do laundry, shower, or cook with electric stoves in something of a regular pattern. This helps them determine whether they are better to top up their own capacity, or instead feed power into the grid when rates are high, without compromising their ability to keep you sufficiently powered up. 

Even with all these advances, you will still want to start with updated, efficient, appliances that don’t overload the storage system’s capacity. Old freezers, refrigerators or well pumps may take more amperage than newer more efficient models do to get started, and even though it’s only for a split second, if that demand is too great, the battery system’s inverter might not be able to deliver sufficient power to operate some older appliances. Rather than installing an oversized battery system, you are far better off to upgrade to newer and more efficient appliances.

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