Sorry about that-I couldn’t resist! (In case you forgot, sodium is represented chemically as ‘NA’.)

In arranging for out of the water winter storage this year, I found my facility now bans the storage of Lithium batteries while the boats are away for the winter. I also discovereed that more and more insurance companies are no longer offering insurance to boats with Lithium batteries. It seems there is a revolt in the works over Lithium batteries.

Part of the problem is that all lithium batteries are being treated (out of ignorance) as the same. They are not. As the energy density increases, so too does the risk of a thermal runaway condition, where the battery goes on fire. Lithium Iron Phosphate is among the few chemistries that have an almost no risk of thermal runaway. They are not quite as energy dense, but in return rival non-lithium batteries in safety. There have been demonstrations where they have tried to get a LiFePO4 battery to start a thermal runaway, event to the point of shorting cells with nails through them and while the cell gets very hot, it does not have any effect on adjacent cells. All it takes is a few fires attributed to lithium batterys to ignite opposition.

Sodium is the sixth most abundant element in the earth’s crust by volume and it turns out, you can make a sodium based battery. Sodium batteries are considered to be even safer than Lithium. While they are slightly less energy dense, they can be fully discharged without affecting battery live. Thie makes the usable capacity similar for the same volume. Further, they can be charged when the temperature is below freezing, unlike lithium, so the solar panels can be left connected to trickle charge them all winter long.

All of this has encouraged me to build a Sodium battery to replace the lithium ones on Risa. Like lithium based batteries, they also require a battery management system (BMS) to maintain optimum health of the battery. The BMS maintains cell balance, prevents charging and discharging at high or low cell temperatures, and maintains current limits on both charging and discharging.