Off-grid system planner

Why one plan instead of twenty calculators

Every off-grid system leans on the others. A heat pump adds to the solar load; a deep well pump decides the inverter and the generator, and hauled water decides how often you drive; the climate that sets your heating fuel, wood, pellets, propane, or a heat pump, also sets your winter sun, which sizes the array. Run them separately and the pieces quietly disagree. This planner takes one set of answers and works them through together, with the same assumptions the individual calculators use, so the numbers fit each other. Click "details" on any line to open that calculator and tune it.

How to use it well

Start with your ZIP so the sun, rain, and climate are real rather than guessed. Be honest about loads: the difference between a plan that works in January and one that does not is usually a freezer or a well pump someone forgot. Save the plan and come back to it as you build; each saved version gets its own link, so you can compare a lean first phase with the full build.

These are planning numbers with the same caveats as every tool here: conservative, rounded, and meant to get you to a real quote and a real design, not to replace them.

The inputs that move the answer most

Not all inputs matter equally. Four of them dominate almost every plan, and knowing which they are tells you where to spend your effort getting a real number rather than an estimate.

Location comes first, because it sets the worst-month sun that sizes the array and the heating degree days that size the fuel supply. A plan built on the annual average sun figure will be short in December by the gap between the two, which in northern latitudes is substantial. Entering a ZIP pulls 30-year normals rather than a guess.

Daily electrical use is the second, and it is the one people get wrong most often, usually downward. Every watt-hour on the list has to be generated, stored, and converted, and reducing a load is always cheaper than building the capacity to serve it. If you are still on grid, measure for a fortnight rather than estimating; the difference is frequently large.

Heat is the third, and it dwarfs everything electrical in a cold climate. The choice of fuel and the quality of the building envelope between them decide most of the annual operating cost, and a plan that heats with electricity from a battery bank in a northern winter is a plan for a system several times larger than the one you want.

Water is the fourth, because pumping is real work and because the choice between a well, catchment, and hauling changes both the electrical load and the shape of the week. A deep well pump run on demand is a different design from the same well pumping slowly into storage during daylight.

Reading the plan you get back

The plan is deliberately conservative and rounded, which means it will usually be a little larger than the minimum that would work. That is the right direction to err off grid, where being short happens in the worst week of the year and being slightly oversized costs money once.

Read it as a set of related decisions rather than a shopping list. If the array looks large, the fix is usually in the load list rather than in the panels. If the battery looks expensive, look at whether days of autonomy could be traded for a generator you were going to own anyway. If the heating fuel figure looks alarming, that is the envelope talking, and insulation is cheaper than fuel every year for the life of the building.

Then open the individual calculators from the detail links and tune the lines that matter to you. They use the same assumptions as the planner, so a change made in one place is consistent with the rest rather than quietly contradicting it.

From a plan to a build

A saved plan is a good document to take to the people who will actually sell you the equipment, because it states your loads, your location, and your assumptions in one place. Suppliers can then argue with the assumptions rather than guessing at them, which is a far more productive conversation than asking what you need.

From there the sequence is: confirm the local rules with the laws pages and a phone call, since what you may build is decided before what you should build; check the site itself with the site report and the parcel check; compare specific equipment in the spec tables; and price it against the price index so a quote can be judged rather than merely accepted.

If a quote is already in hand, the quote review will tell you what you are being sold, what is missing from it, and what to ask before signing. And for the reasoning behind any part of the plan, the free course walks the whole sequence in order, with the arithmetic shown.

Saving a plan, and comparing versions

Each saved plan gets its own address, so a lean first phase and a full build can sit side by side and be compared rather than argued about from memory. That is the most useful thing this tool does over a single calculator: it makes the trade-offs visible as a set rather than one number at a time.

A practical way to use it is to save three: what you would build if money were no object, what you would build on the budget you actually have, and what you would build if you had to close in before winter. The differences between those three are usually where the real decisions are, and they are much easier to discuss with a partner or a supplier as saved links than as a conversation.

Revisit them as the build progresses. Loads change, the building turns out warmer or colder than assumed, and a well comes in at a different depth than the district suggested. A plan updated with real numbers from your own site is worth considerably more than the one produced before anything was built.

What the planner does not do

It does not know your building. Heat loss depends on construction, air sealing, and glazing that no set of inputs this short can capture, so the heating figures are climate-driven brackets rather than a load calculation. It does not know your horizon, so the solar figures describe the resource arriving at your location rather than what your particular building site can see in December. It does not know your soil, your well yield, or your access road.

It also does not know what is legal where you are. Zoning, minimum dwelling sizes, septic approval, and rules about occupying a structure while building all decide what can be built regardless of what the arithmetic says, and they vary by county and sometimes by town.

Finally, it is not a design for construction. Conductor sizing, overcurrent protection, grounding, and bonding are safety decisions that need doing properly rather than approximately, and they are the subject of lesson six. Use the plan to decide what to build; use a competent design, and an electrician where appropriate, to build it.