Off-grid & RV
Off-grid is not grid-tied with batteries added. It is a different design problem, because there is no backstop when the numbers are wrong.
The connection quote decides it
Utilities price a line extension per distance, and beyond a few hundred metres the figure gets large quickly. Where the extension costs more than a full off-grid system, off-grid stops being a preference and becomes the cheaper option.
Get that quote in writing before designing anything.
Where the money goes
| Component | Share |
|---|---|
| Battery bank | 30–45% |
| Panels | 15–25% |
| Inverter / charger | 10–15% |
| Charge controller | 5–8% |
| Racking | 5–10% |
| Wiring and protection | 5–10% |
| Labour and permitting | 10–20% |
Panels are the part everyone budgets carefully and they are a fifth of the job. The bank dominates, and it is the only component with a scheduled replacement.
Loads are cheaper to reduce than to supply
The largest lever in off-grid design, and the most underused. Moving water heating to propane, fitting an efficient fridge and killing phantom loads can halve daily consumption — and halving the load halves both the array and the bank, the two most expensive items.
A dollar spent on efficiency routinely displaces three to five dollars of generation and storage.
Winter sizes the system
December production across most of the US is 40 to 60% of the annual average. Size the array for the worst month and the bank for the longest cloudy run within it. An off-grid budget built from annual averages is short by roughly a third.
The generator is not a failure
Sizing a bank for the worst cloudy week of the year is enormously expensive. Two or three days of storage plus a generator for the rare shortfall costs far less in total. Budget for it, its fuel and an automatic start.
What gets forgotten
Low-voltage DC means high current, so cable is thick and expensive and must be sized for voltage drop rather than ampacity. Add overcurrent protection, a DC disconnect, grounding, and permits — a ground-mounted array is the tallest metal object in a field.
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Grid-Tied, Hybrid or Off-Grid: Three Systems, Three Different BudgetsThe most common surprise in residential solar is discovering that a grid-tied array does nothing during a blackout — and that it is designed that way on purpose.