Everything you need to design an off-grid solar system: how it differs from grid-tied, the five core components, a worked sizing example from daily kWh to panel and battery capacity, realistic costs, and the mistakes that leave people sitting in the dark in December.
An off-grid solar system is a self-contained power plant. There is no utility behind it to cover a cloudy week, no meter to export surplus into, and no one to call when a design mistake shows up in February. Everything your household consumes has to be generated on site, stored on site, and managed on site.
That makes off-grid both more demanding and more satisfying than a standard rooftop install. This guide walks through how it differs from grid-tied solar, what each component actually does, how to size a system properly, what it realistically costs, and the design mistakes that cause the majority of off-grid disappointments.
Off-grid vs grid-tied vs hybrid
The honest advice first: if a grid connection is available and reasonably priced, grid-tied or hybrid will almost always deliver cheaper electricity than off-grid. Off-grid makes sense when there is no connection, when the utility's quote to run a line to your site is enormous, or when the supply is so unreliable that you'd be running a generator anyway. If you do have a connection and export is allowed, read our analysis on whether net metering is still profitable before ruling out a grid-tied design.
The five components of an off-grid system
1. Solar panels (the array)
Your generation source. For off-grid, prioritise low-light performance and temperature coefficient over headline efficiency — you care about output on a grey January morning, not peak output in June. Monocrystalline N-type modules are the current mainstream choice; our comparison of TOPCon vs HJT cells explains what the technology labels actually mean for real output. Browse specs across brands in the solar panel database.
2. Charge controller
Sits between panels and battery, converting array voltage to correct charging voltage and preventing overcharge. Two types:
PWM — cheap, simple, only suitable for very small systems where panel voltage closely matches battery voltage.
MPPT — actively tracks the array's maximum power point and typically recovers 15–30% more energy, more in cold and low-light conditions. For any serious off-grid system, MPPT is the only sensible choice.
3. Battery bank
This is the heart of an off-grid system and usually the largest single cost. It also determines whether your system feels effortless or constantly constrained.
LiFePO4 (lithium iron phosphate) — now the default. Usable depth of discharge around 80–90%, several thousand cycles, no maintenance, tolerant of partial charging. Higher upfront cost, lower cost per usable kWh over its life.
Lead-acid (AGM, gel, flooded) — cheaper upfront, but you can only safely use around 50% of nameplate capacity, cycle life is short, and flooded types need ventilation and regular topping up. Chronic partial charging kills them quickly, which is exactly what happens in a badly sized off-grid system.
Compare real products in our Tesla Powerwall vs BYD battery comparison and across the solar batteries knowledge section.
4. Inverter
Converts battery DC into the AC your appliances use. For off-grid you need an off-grid or hybrid inverter — a standard grid-tied string inverter will not work without a grid signal to synchronise to. Key specifications:
Continuous rating — must cover your realistic simultaneous load, not your theoretical total
Surge rating — motors in pumps, fridges, compressors and air conditioners draw several times their running current at startup. This is the spec most people under-size.
Pure sine wave output — modified sine wave damages motors and electronics. Don't compromise here.
Standby draw — an inverter idling 24/7 quietly eats a meaningful share of a small system's daily budget.
Compare models in the inverter database, and see Huawei vs Sungrow for how two major brands differ in practice.
5. Balance of system
Mounting, DC and AC cabling, breakers, fuses, isolators, surge protection and earthing. It's unglamorous and it's where corners get cut. Undersized DC cable is a fire risk and a permanent efficiency loss; missing surge protection ends systems in a single storm. Our grounding and surge protection guide covers this properly.
How to size an off-grid system: step by step
Off-grid sizing runs backwards from consumption. Every step depends on the one before it, so getting the first step wrong invalidates everything after it.
Step 1 — Build an honest load list
List every appliance, its wattage, and hours used per day. Multiply for watt-hours, then total for daily kWh.
Measure rather than guess where you can. A cheap plug-in energy meter on your fridge for a week will teach you more than any online wattage table. People consistently underestimate refrigeration and overestimate lighting.
Step 2 — Size the battery bank
You need enough storage for your days of autonomy — how long the system must run on stored energy alone during a stretch of bad weather.
Battery capacity (kWh) = daily kWh × days of autonomy ÷ usable depth of discharge
For our 3.8 kWh household with 2 days of autonomy on LiFePO4 at 85% usable:
3.8 × 2 ÷ 0.85 = ≈ 9 kWh of battery
Choose autonomy by climate and consequence. One day is thin anywhere. Two days suits sunny regions with a backup generator. Three to four days is normal for cloudy northern climates or sites where running out simply isn't acceptable. Use the battery size calculator to test different autonomy assumptions quickly.
Step 3 — Size the solar array
Size against your worst month, not your annual average. This is the single biggest difference between off-grid and grid-tied design, because there's no grid to make up a December shortfall.
Array size (kW) = daily kWh ÷ (worst-month peak sun hours × system efficiency)
System efficiency of roughly 0.75 accounts for battery round-trip losses, inverter conversion, cable losses, soiling, temperature and charge controller overhead. If your worst month averages 2.5 peak sun hours:
3.8 ÷ (2.5 × 0.75) = ≈ 2.0 kW of panels
Note what happens in a cloudier location. At 1.8 peak sun hours in the worst month, the same household needs about 2.8 kW — a 40% larger array for identical consumption. Get your local figures and run them through the system size calculator, and check your country hub for regional conditions and pricing.
Step 4 — Size the charge controller
The controller's current rating must handle array short-circuit current with margin, and its maximum input voltage must exceed your string's open-circuit voltage at the coldest temperature your site sees. Panel voltage rises as temperature falls, and a cold winter morning is exactly when undersized controllers fail. Add roughly 25% headroom on both figures.
Step 5 — Size the inverter
Add up your realistic simultaneous load — not everything at once, but the plausible worst case — then confirm the surge rating covers your largest motor starting while other loads are running. A 3 kW continuous inverter with 6 kW surge suits most small off-grid homes; well pumps and air conditioning push you higher.
Step 6 — Decide on a generator
Most successful off-grid systems include a modest generator. It's not a failure of design; it's cheaper insurance. Sizing an array to cover the worst week of the worst month means massive over-generation for the other eleven months. A small generator covering perhaps 2% of annual energy is usually far cheaper than the extra panels and batteries it replaces.
What does an off-grid system cost?
Costs vary widely by country, import duties, brand tier and how much labour you do yourself, so treat these as proportions rather than prices. In a typical off-grid build:
Battery bank: 35–50% of total cost — the dominant line item, and the one where cheap choices hurt most
Panels: 15–25% — the cheapest part per unit of energy, which is why generous over-panelling is usually good economics
Inverter and charge controller: 15–20%
Mounting, cabling, protection: 10–15%
Labour and commissioning: 10–20% if not self-installed
For current per-kW pricing in your market, see Solar Panel Cost 2026. To compare the lifetime cost of an off-grid build against a grid connection or generator running costs, use the solar ROI calculator, and if you're financing, the solar loan calculator.
The panel-versus-battery rule. When your budget is tight, add panels before you add batteries. Extra panels fill the battery faster on marginal days and cost a fraction as much per kWh delivered. Over-panelling an off-grid array by 20–30% relative to the textbook calculation is standard practice, not overkill.
Seven mistakes that ruin off-grid systems
Sizing on annual average sun instead of worst-month sun. The system works beautifully all summer and fails in December. This is the classic off-grid failure.
Optimistic load lists. Every appliance you "forgot" is a permanent deficit. Build the list honestly, then add 20%.
Under-sizing the battery to save money. Chronic deep cycling destroys batteries early, so the saving evaporates within a few years.
Ignoring surge ratings. The inverter handles your running loads fine and then trips every time the pump starts.
Undersized DC cable. Low-voltage DC carries high current; voltage drop over a long run silently wastes energy and creates a fire risk.
No surge protection or proper earthing. Remote sites are exactly where lightning-induced surges are most likely and repair is hardest.
Not planning for growth. Households add loads over time. Choose an inverter and controller with headroom, and a battery architecture you can expand.
Should you go off-grid?
Go off-grid if there's no grid, if connection costs are prohibitive, or if supply is unreliable enough that you'd otherwise be running a generator. Choose hybrid instead if you have a workable connection and mainly want backup and savings — you get most of the resilience at a much lower cost per kWh.
And whichever way you lean, do the sizing arithmetic before you shop. An off-grid system is a set of interlocking constraints, and the cheapest possible version of the wrong design is far more expensive than a correctly specified one.
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