The energy system of a regenerative building has two tiers: passive first, then active. No amount of solar panels compensates for a poorly designed building envelope; passive performance is always the priority. Passive solar design — the use of building orientation, glazing placement, thermal mass, insulation, and shading to manage heating and cooling without mechanical energy input, is covered comprehensively in Book 4 of this series, Heating and Cooling Buildings. In a well-designed passive solar building in a temperate or arid climate, passive strategies can meet 60 to 90 percent of space heating needs and most of the cooling load through natural ventilation. Active off-grid energy systems, solar photovoltaic arrays, battery banks, charge controllers, and inverters, supply the electrical loads that passive design cannot eliminate: lighting, appliances, water pumping, and communication. A properly sized off-grid system can supply all of a household’s electrical needs indefinitely from sunlight alone. Book 7…