A reference guide
Off-Grid Handbook: Power and Water for Cabins and Homesteads
Off-grid solar means generating and storing all of your own electricity, with no connection to the utility grid. No monthly bill and no power company. Also no safety net when something has been sized wrong.
What an off-grid system actually is
Every off-grid system, from a shed light to a full homestead, is the same four parts doing the same four jobs.
Solar panels generate direct current whenever light hits them. They are the cheapest part and last for decades.
A charge controller sits between the panels and the batteries, converting whatever the panels are producing into the correct charging voltage. Without one, panels destroy batteries.
Batteries store the energy so you have power at night and through bad weather. This is the most expensive part, the shortest-lived, and the least forgiving of design mistakes.
An inverter converts stored direct current into the alternating current that household appliances expect.
Everything else is wiring, protection, and mounting. The engineering is not mysterious. What makes off-grid difficult is that all four parts have to be sized against each other and against how you actually live.
Sections
Solar power
Panels, charge controllers, batteries, inverters, and the wiring and safety that tie them together.
Water
Solar well pumps and hand pumps, sized on the depth to water and the width of the casing.
Backup power
The three ways to keep a grid-connected house running during an outage.
Worked projects
Sheds, tiny houses, cabins and full-time homesteads, with every figure computed rather than estimated.
Why this is not the solar you see on suburban roofs
Grid-tied solar treats the utility as an infinite battery. It sends surplus out during the day and pulls power back at night, so a system that falls short simply buys the difference. Nobody notices.
Off-grid has no such fallback. If your array and battery bank cannot carry you through a cold, overcast week in December, the lights go out. That single difference drives everything: it is why off-grid systems are sized against the worst month rather than the annual average, why battery choice matters so much, and why the honest cost is higher than the panel price suggests.
It also means the expensive mistakes happen at the design stage, long before anything is bolted to a roof.
What this site is
A reference guide. The aim is to explain how the parts work, what the numbers on a specification sheet actually mean, and where money gets wasted, so you can specify a system yourself or ask an installer better questions.
You will find three kinds of thing here:
- Reference articles explaining each component, the trade-offs between them, and the safety practice that goes with them.
- Calculators for the arithmetic that decides a system: wire sizing, battery runtime, daily power budget, and array sizing.
- Buying guidance comparing the equipment that is actually worth considering, and explaining why.
Wiring guidance here follows the NEC (NFPA 70), the electrical code used in United States buildings. An RV or a van conversion is under ANSI/RVIA LV instead, and a boat is under ABYC, which this site does not cover.
Who it is for
Mostly people building small to mid-sized systems for cabins, homesteads, and tiny houses, where there is no utility service and the system has to stand on its own.
It also covers backup power for homes that do have grid service, for riding out outages. That is a genuinely different problem with different equipment and different rules, so it is kept separate rather than blended in. Connecting a battery system to house wiring that can reach the utility is the one area where a mistake can injure someone outside your home.
Start here
If you are new to this, read them in this order.
How an off-grid solar system works end to end, the vocabulary you need to read the rest of the guide, and the order in which the decisions have to be made.
Solar Generator vs DIY Solar: What the Box Trades Away
A solar generator puts the battery, inverter and charge controller in one case. What that buys you, what it costs you in solar input, expansion and voltage, and which loads each shape of system suits.
How to read a solar panel datasheet, what monocrystalline and polycrystalline actually change, why panels never make their rated power, and how wiring them in series or parallel affects the rest of the system.
Working safely with solar panels: why an array is live whenever there is light, DC arc hazards, roof and ground-mount risks, and safe wiring practice.
Types of Solar Charge Controllers: PWM, MPPT and Sizing
What a charge controller does, how MPPT and PWM differ, how to size one correctly, and why panel voltage decides which type is worth buying.
How off-grid batteries actually work: chemistry differences, usable versus rated capacity, cycle life, and how to compare real cost per kilowatt-hour.
How to Size an Off-Grid Battery Bank
A step-by-step method for sizing an off-grid battery bank, including days of autonomy, depth of discharge, inverter losses, and the cold-weather derate people forget.
Lithium vs AGM: Where Each One Still Wins
A direct comparison of lithium, AGM and flooded lead-acid for off-grid use, on usable capacity, cycle life, real cost per kilowatt-hour and cold weather behavior, including the two cases where lead-acid is still the right answer.
The real hazards of an off-grid battery bank: short-circuit energy, hydrogen venting, thermal runaway, and the overcurrent protection that prevents all three.
What an off-grid inverter does, why pure sine wave matters, how to size continuous and surge capacity, and how off-grid, hybrid, and grid-tie inverters differ.
Conductor sizing, voltage drop, overcurrent protection, grounding, and disconnects for off-grid DC systems, following the NEC.
DC Voltage Ratings: Why a 48V Switch Is Not for a 48V Bank
A 48 volt battery bank is never at 48 volts. Published maximum voltage ratings for common battery switches and fuses, why a part labeled 48V is the wrong part, and how to check a rating against the number that matters.
Fuse Interrupt Rating: 12V Is Not 48V
Interrupt capacity is the fuse specification most off-grid builds get wrong. Published AIC figures for Class T, ANL, AMG and MRBF terminal fuses, and why one of them changes verdict entirely between 12 and 48 volts.
Generators for Off-Grid Systems
Choosing and sizing a generator for an off-grid system: why it charges the bank rather than running the house, why an inverter/charger can refuse dirty power, and why propane usually beats gasoline off-grid.
Solar Well Pumps: How They Work and How to Size One
How a solar well pump system works, the three things to find out before you buy, and how to size the pump and its solar array.
What Size Generator for a Well Pump: The Start Decides It
How big a generator a well pump needs: why the start sets the size, Franklin Electric's minimum generator for each submersible motor, and how to read a jet pump's code letter.
Off-Grid Solar in Cold and Difficult Climates
How cold, snow, short winter days, and extreme heat affect an off-grid system, and how to size and site one so it works in the month that matters.
Who is writing this
Matt Harrington. About