Three cloudy days
Can critical loads run without draining the battery below the operating reserve you planned?
Off-grid living
Off-grid works when the systems agree with each other.
Solar, batteries, water, wastewater and heating are not separate shopping lists. Every choice changes the load on another system.
Build the dependency map
Start with demand, then size supply.
A larger electric water heater changes the battery bank. A longer shower changes both fresh-water and wastewater capacity. A winter climate changes almost everything.
01Energy
Daily kWh, peak watts, heating/cooling and backup loads.
02Water
Source, treatment, tank size, freeze protection and daily gallons.
03Wastewater
Septic, approved onsite system, holding strategy or other locally permitted path.
04Resilience
What happens after several cloudy days, a frozen line or equipment failure?
Power
Your appliance list is an energy budget.
Write down daily electricity use before choosing panels or batteries. Heating, water heating, cooking and air conditioning can dominate a tiny-house load even when lights and electronics are trivial.
Open solar & battery planner →
NREL’s PVWatts can then estimate solar production using location and weather data instead of a generic national sun-hours assumption.
Fresh water
Tank size is only half the water plan.
Start with measured or realistic daily gallons, then decide how many days of autonomy you want. The source and treatment matter just as much as the tank. CDC notes that collected rainwater is not automatically safe for drinking, cooking or bathing and recommends appropriate testing and treatment for the intended use.
Wastewater
“Off-grid” does not mean “off-regulation.”
Wastewater is a public-health and land-use issue, and the acceptable system depends on the jurisdiction and site. EPA maintains technical and homeowner resources for onsite wastewater/septic systems; state and local rules determine what is actually permitted.
Failure-mode check
Ask what breaks first.
Freezing weather
What protects tanks, pumps, filters, drain lines and exterior plumbing when the temperature drops?
Full wastewater capacity
Can you stop water use safely, service the system, or move the house without creating a sanitation problem?
Primary heat fails
Is there a safe backup heat strategy that does not create an electrical or combustion hazard?
Water source is contaminated
Can you isolate the source, test/treat it, and maintain a separate safe drinking-water supply?
You leave for a week
What must remain powered, heated, drained or monitored so the house does not return to frozen pipes or moisture damage?
Primary references
Use location-specific data and local approvals.
NREL PVWatts — location/weather-based PV production estimatesNREL ↗Rainwater collection, testing and treatment guidanceCDC ↗Onsite wastewater / septic technical resourcesU.S. EPA ↗
This is systems-planning guidance, not an electrical, plumbing, wastewater or code design. Use qualified professionals and the applicable local authorities for final design and approval.