Off-grid tools & calculators

Which tool answers which question

The tools here divide roughly into four jobs, and knowing which job you are doing saves opening six of them.

Deciding whether a place will work is where most people start. The site report takes any address and returns its real sun, climate, elevation, and distance figures alongside the county off-grid verdict. The parcel check goes deeper on a specific parcel, pulling flood, wetland, slope, and access data with its sources shown. The laws pages cover what is actually permitted, state by state and county by county.

Sizing the systems is the arithmetic stage. The solar calculator and battery calculator handle power, the wire gauge calculator the conductors between them, the heat-loss calculator and firewood calculator the heating, water usage and rainwater and well pump the water, and the septic calculator the part that decides whether you may legally occupy the building at all.

Costing it comes next. The cost estimator turns a design into an annual figure, the generator calculator and the propane calculator cover the fuel that a solar system alone will not, and the price index gives this month's market ranges so a quote can be judged rather than merely accepted.

Living there is the fourth. The garden calculator and food storage calculator work from your frost dates, the coop calculator and fencing calculator from your livestock, and the driveway calculator from the road that everything else arrives on. Maintenance reminders put the seasonal jobs on a schedule rather than in your memory.

They are meant to be used together

Off-grid systems constrain each other, so a number produced in isolation is usually the wrong number. The load list sizes the array; the array sizes the controller; the battery decides what the inverter can deliver; the climate at your site decides all of it; and the local rules decide whether any of it may be built. Run separate calculators without a common set of assumptions and the pieces quietly disagree.

That is what the system planner is for. It takes one set of answers and works them through together using the same assumptions the individual tools use, then lets you open any line in its own calculator to tune it. For most people it is the right place to start and the right place to return to as the design changes.

The arithmetic is shown on purpose

Every calculator here publishes its method: the formula, the constants, where those constants came from, and what version of the formula produced your answer. Several carry worked validation cases so you can check the tool against a known result rather than trusting it.

That is not decoration. A result you cannot check is a result you should not act on, particularly when it is deciding how much money to spend or whether a system will carry you through a winter. If you find an error in any of it, the corrections page is how to report it, and corrections are logged publicly with the date rather than quietly edited away.

Why the arithmetic is simple on purpose

None of the calculators here use a model more complicated than the problem requires. That is deliberate. An off-grid design is dominated by a handful of inputs that swing the answer enormously, and a tool that produces a precise-looking figure from an estimated load list is offering false confidence rather than accuracy.

So the formulas stay simple enough to check by hand on paper, the constants are published with their sources, and the assumptions are stated on the page rather than buried. Where a result depends heavily on one input, that is worth knowing, because it tells you which number deserves a measurement rather than a guess.

The practical consequence is that these tools are best used to bracket a problem and to test how sensitive it is, rather than to specify equipment to the last watt. Run each one twice, once with optimistic inputs and once with pessimistic ones, and design for somewhere near the pessimistic end. Off grid, being slightly oversized costs money once, and being short happens in the worst week of the year.

Where to start

If you have no land yet, start with the laws pages for the regions you are considering and the cost estimator for a sense of scale. If you have a parcel in mind, run the site report and the parcel check on it before anything else. If you have land and are designing, start with the load list and then open the planner.

What none of them will do

No calculator here will tell you whether to do this. They size systems and estimate costs; they cannot weigh a February morning against a mortgage, or tell you whether the person you are doing this with wants the same life you do. Those questions decide more outcomes than any arithmetic on this site, and the first lesson of the course is about them rather than about equipment.

They also will not replace the professionals whose judgment carries liability: a licensed electrician for the parts of a system where a mistake starts a fire, a soil evaluator for whether a septic system can be permitted, a driller for what a well will actually cost and yield, and a structural engineer where a design needs one. These tools are for arriving at those conversations with real numbers and specific questions, which is what makes them short and productive.

And they cannot see your parcel. Terrain, horizon, soil, and the road in all move the answers, sometimes substantially, and none of them is visible in a set of form fields. Use the site report and the parcel check for what public data can say about a specific place, then walk it with the printed checklist for everything data cannot.

And if you would rather have the reasoning than the arithmetic, the free course covers the same ground in the order the decisions actually arrive, with each lesson pointing at the tools that belong to it.