Generation · Solar
Enough sun to carry the whole place.
A panel on a balcony charges a phone. An array sized for a property runs a well pump in February, on the shortest day of the year, after four days without sun. Those are different problems, and they are solved with different arithmetic.
By Dan Whelan, founder of New World Survival
Researched from government agencies, university extension services, and other published sources. See our sources
FROM THE FIELD
Equipment bought before the previous step's number is known turns out to be the wrong equipment. That lesson appears in account after account: panels bought before the load was measured, batteries bought before the array was sized, wire run before the route was final. The seven guides below are in a specific order because each one produces a number the next one needs. Skipping ahead costs more than patience does.
The boundary
Three pages already cover household solar.
Portable panels, a first rooftop system, running a few circuits through an outage. Those pages answer the questions a household asks, and most readers never need anything past them.
This section answers a different question. Not how to add solar to a house, but how to size an array that carries a property through its worst month, stores what it makes, and keeps running when the weather does not cooperate.
The difference is scale and permanence, not skill. A renter with a folding panel and a homesteader with a ground-mounted array are doing the same physics at different sizes.
What changes
The arithmetic runs off the worst month.
A household system that falls short in December is an inconvenience. A property system that falls short in December is a well that does not pump. Four things change when the array has to carry everything.
Sizing moves to December
An annual average hides the month that actually breaks the system. Sizing is done against the lowest sun month for the site, which is why two properties at the same latitude can need very different arrays.
Storage is measured in days
Household backup thinks in hours. Property scale thinks in days without sun, which sets the size of the battery bank and, with it, most of the budget.
Idle draw stops being trivial
Inverters, controllers and monitoring draw power continuously whether anything is switched on or not. Over a full day that standing load is large enough to change the panel count.
You own the maintenance
No utility crew arrives. Panel cleaning, connection checks, battery monitoring and winter snow clearing become household work, and a system nobody can service is a system that fails quietly.
From the field · This is the line accounts draw between the systems that last and the ones that don't. Not the panel count, not the battery chemistry, but whether someone in the household actually checks the connections, clears the snow, and reads the monitor.
What this hub covers
Seven guides, in the order they build on each other.
Each one assumes the numbers from the one before it. The same property runs through all seven, so the figures introduced on the first page are the figures still being spent on the last.
Sizing an array for a property
Daily load, standing draw, and the worst-month arithmetic that decides how many panels the property actually needs.
2Battery banks: chemistry, sizing, lifespan
What days of autonomy cost in capacity, and why chemistry decides how much of a bank you can actually use.
3Charge controllers and inverters
Where an array's output becomes usable power, and the surge rating that decides whether a well pump starts.
4Ground mount, roof mount and tracking
Orientation, tilt, airflow and snow, and why adding panels usually beats adding moving parts.
5Wiring, disconnects and code
What the system demands electrically, why DC faults behave differently, the permit path, and where a licensed electrician stops being optional.
6Solar through winter
Short days, low sun angles, snow cover, and the temperature limits on charging a battery bank.
7When household solar stops being enough
The point where roof space, shade or winter load pushes a household into property-scale planning.
Start upstream
If you have not sized a household system yet.
Property scale is a step past these three, not a replacement for them. Read whichever matches where you are now.
Solar Basics
Using portable solar during an outage, and what a small panel realistically does.
Read the guide200W Solar
A first portable setup, sized and wired, with honest limits on what it carries.
Read the guideRooftop Solar Primer
What a homeowner should understand before signing anything, including interconnection.
Read the guideEvery page in this hub starts from one number: what the property actually uses in a day. If you have not measured that yet, the household power use guide shows how, and the power needs calculator works it out from a device list.
Sources
Where these numbers come from.
- National Renewable Energy Laboratory, National Solar Radiation Database. Site-specific solar resource data, including the monthly variation that worst-month sizing depends on.
- NREL PVWatts Calculator. Modelled system output by location, tilt and orientation.
- U.S. Department of Energy, Solar Energy Technologies Office. Photovoltaic system fundamentals and performance guidance.
- U.S. Energy Information Administration. Residential electricity consumption data used for load comparison.
- National Fire Protection Association, NFPA 70 (National Electrical Code). Photovoltaic system requirements, referenced throughout the wiring and disconnects guide.