I set up seed starting shelves in a shed away from the house and initially listed only the lights and heat mats when I worked out the power. One cold morning I went out to water the trays and checked the shed thermometer. The pots had bottom heat, but the thermometer showed that the air was colder than I wanted for the tender seedlings, so I carried them back inside.

The shed had a solar system with a Vatrer 48V 100Ah self-heating battery. The system had already supplied the shed before I set up the seedlings.I checked the temperature limits for the electrical components, and that got me thinking about how much more draw the heat mats and lights would add on top of what the shed was already using. The heat mats did their job on the tray bottoms, but the shed air was still cold enough that I was not comfortable leaving the seedlings out there.

The seedlings spent the next few days on a table indoors while I reconsidered which trays could stay in the shed.…