Off-grid budgets go wrong in a predictable way: panels are priced carefully and everything else is estimated. Panels are typically 15 to 25% of the total.
Where the money goes
| Component | Share of a typical build |
|---|---|
| Battery bank | 30–45% |
| Panels | 15–25% |
| Inverter / charger | 10–15% |
| Charge controller | 5–8% |
| Mounting and racking | 5–10% |
| Wiring, breakers, fuses, combiner | 5–10% |
| Labor and permitting | 10–20% |
The battery bank dominates, and it is the only component with a scheduled replacement.
The replacement cost nobody amortises
Panels last 25 to 30 years with a slow output decline. Inverters last 10 to 15. Batteries last 5 to 15 depending on chemistry and how they are treated.
A lead-acid bank replaced twice over the life of the panels can cost more in total than the entire rest of the system. Lithium's higher purchase price often works out cheaper per delivered kWh over the same period, and that is the comparison that matters — not the price on the day.
Divide bank cost by (usable kWh × rated cycles) to get cost per kWh delivered. It is the only number that compares chemistries honestly.
The generator is not optional, and it saves money
Sizing a battery bank for the worst cloudy week of the year is enormously expensive. Sizing for two days and running a generator on the rare occasions it is needed costs far less in total.
Budget for the generator, its fuel storage and an automatic start if the system supports it. Then size the bank to a realistic two or three days.
Loads are cheaper to reduce than to supply
This is the largest lever in off-grid design and it is almost always underused.
Replacing an electric water heater with propane or a heat pump, switching to a DC or high-efficiency fridge, and dealing with phantom loads can halve a daily consumption figure. Halving the load halves 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. Do that arithmetic before ordering anything.
What gets forgotten
- Wire. Off-grid systems run at low DC voltage where current is high, so cable is thick and expensive. Long runs need sizing for voltage drop, not just for ampacity.
- Overcurrent protection. Fuses, breakers, a combiner box, a DC disconnect. Required, and not trivial in cost.
- Grounding and lightning. A ground-mounted array is the tallest metal object in a field.
- Permits and inspection. Varies enormously by jurisdiction; some require an engineer's stamp.
Work the array from real winter figures on the system sizing calculator, then the bank on battery sizing — an off-grid budget built from summer averages is short by roughly a third.