Passive solar design reduces or eliminates the need for mechanical heating and cooling. But even the most optimally designed passive building still needs electricity: for lighting after dark, for appliances, for water pumping, for communications, and for the small motors that run the liquid waste treatment system. An off-grid energy system produces all of this electricity on-site from renewable sources, with no connection to a utility grid and no ongoing fuel costs.

The most mature and cost-effective off-grid energy technology for most locations is solar photovoltaic (PV) combined with battery storage. Solar PV converts sunlight directly into electricity; batteries store that electricity for use when the sun is not shining. Together, they form a complete, self-contained power system that can be scaled from a single cabin to a full community microgrid.

Off-grid energy design requires a careful, quantitative approach. The size of the solar array, the capacity of the battery bank, and the design of the distribution system must all be matched to the actual energy needs of the building. Undersizing leads to power shortages; oversizing wastes money on equipment that will never be used. The starting point is always a thorough load analysis: understanding exactly how much energy the building needs, when it needs it, and which loads are most critical.