- Off-grid solar sizing starts with your daily load in Wh - multiply by 1.25 for losses, then size panels and batteries
- In most of the continental US, 1 watt of solar panel produces 4-5Wh per day on average annually
- Battery storage should cover 2-3 days of your daily load to handle cloudy weather and seasonal variation
- LiFePO4 battery chemistry is the only practical choice for permanent off-grid installations - 10+ year lifespan
- A proper off-grid system requires a charge controller, inverter, and battery bank - not just panels and a power station
Size your off-grid solar system by calculating daily load in watt-hours, multiplying by 1.25 for losses, then sizing panels to produce 1.5x that amount daily. Battery storage should cover 2-3 days of load without sun. LiFePO4 is the only practical battery chemistry for permanent off-grid installations.
Off-Grid Solar vs. Portable Power Stations
Before getting into system design, it's worth being clear about what we mean by "off-grid solar." A portable power station with solar panels is a portable off-grid power source. A dedicated off-grid solar system is a permanent installation designed to be a property's primary power source.
The difference matters because they serve different purposes, have different components, and require different levels of installation expertise. This guide covers both, but is primarily focused on the more substantial setup: dedicated solar systems for cabins, homesteads, and properties without utility power.
If you're looking for a portable solution to keep essentials running during outages at a grid-connected home, our home backup guide is more appropriate. This guide is for people building a primary power system for a property without grid access, or planning for true energy independence.
The Four Components of Every Off-Grid Solar System
Regardless of scale, every off-grid solar system has the same four elements. Understanding each one is essential before looking at any product or kit.
1. Solar Panels
Panels capture sunlight and convert it to DC electricity. The key specifications are wattage (how much power they generate in full sun), efficiency (how much of available sunlight they convert), and temperature coefficient (how much performance drops in heat). For most residential off-grid applications, monocrystalline panels are the correct choice — higher efficiency in the same footprint, better low-light performance, and 25-year warranties from reputable manufacturers.
Panel sizing is based on your daily energy consumption divided by your location's peak sun hours. A property in Arizona gets 5.5–6.5 peak sun hours per day. A property in the Pacific Northwest might get 3.5–4.5 in summer and 1.5–2.5 in winter. These numbers dramatically affect how many panels you need.
2. Charge Controller
The charge controller sits between the panels and the battery bank, regulating the flow of energy to prevent overcharging. There are two types: PWM (pulse width modulation) and MPPT (maximum power point tracking). MPPT controllers are significantly more efficient — typically 20–30% better energy harvest — and are the right choice for any system over 200W. PWM is only appropriate for very small, budget-constrained systems.
Renogy is the dominant mid-market provider for MPPT charge controllers with a strong reputation for reliability at accessible price points.
3. Battery Bank
The battery bank stores energy generated during daylight for use at night or during cloudy periods. Battery selection is the most consequential decision in an off-grid system and the one where the most money is wasted on the wrong choice.
Two chemistries dominate the current market: lead-acid and lithium (LiFePO4). Lead-acid batteries are cheaper upfront but deliver only 50% of their rated capacity safely (deeper discharge damages them permanently), last 3–5 years, and require maintenance. LiFePO4 batteries cost 3–4 times as much initially but deliver 80–90% of rated capacity, last 10–15 years, and require no maintenance. Over a 10-year period, LiFePO4 is typically cheaper. We recommend LiFePO4 for all new installations.
4. Inverter
The inverter converts DC battery power to AC for standard household appliances. Key specifications are continuous output wattage, surge wattage (for motor startup), and inverter type (pure sine wave vs. modified sine wave). Pure sine wave is non-negotiable for any system that will power motors, electronics, or sensitive equipment.
For larger systems, a hybrid inverter that handles both solar charging and battery management is the most efficient architecture. These eliminate the need for a separate charge controller.
How to Size Your System
Proper system sizing follows a three-step process:
Step 1: Calculate daily energy consumption (Wh/day)
List every appliance, its wattage, and how many hours per day you use it. Multiply wattage by hours to get Wh, then sum all appliances. Add 25% for system inefficiencies. This is your daily energy target.
Step 2: Size your battery bank
Your battery bank should store enough energy for your daily consumption multiplied by the number of cloudy days you want to plan for (typically 2–3 days). Divide by 0.8 (for 80% depth of discharge on LiFePO4) to get the required rated capacity.
Step 3: Size your solar array
Divide your daily energy consumption by your location's peak sun hours. Add 25% for panel efficiency losses. This gives you the minimum panel wattage needed to fully recharge your battery bank on an average day.
Size your system for winter sun hours, not annual average. A system sized for summer will leave you chronically undercharged from November through February. This is the single most common sizing mistake in DIY off-grid installations.
Complete System Packages by Scale
Lights, phone charging, small TV, and a 12V compressor refrigerator. Suitable for weekend use and short stays. Not designed for continuous habitation or high-draw appliances.
Full-size refrigerator, well pump (1/3 HP), lights, devices, TV, router, and occasional power tools. Designed for year-round habitation with conservative usage habits.
Whole-home coverage including well pump, refrigerator, freezer, washer/dryer, HVAC, and workshop loads. Requires professional electrical design and installation. Typically includes backup generator integration for extended cloudy periods.
All-in-One Solar Generator Kits vs. Component Systems
For small and medium systems, all-in-one solar generator kits — like EcoFlow's Delta Pro with solar panels, or Renogy's complete kit packages — offer a compelling alternative to building from individual components.
| Factor | All-in-One Kit | Component System |
|---|---|---|
| Installation complexity | Low — plug and play | High — requires wiring knowledge |
| Expandability | Limited to manufacturer's system | Fully customizable |
| Cost at small scale | Often better value under 5 kWh | Usually more expensive under 5 kWh |
| Cost at large scale | More expensive over 10 kWh | Better value over 10 kWh |
| Portability | Some models portable | Typically fixed installation |
| Support | Single manufacturer support | Multiple vendor relationships |
For most cabin and small off-grid applications, a quality all-in-one system from EcoFlow, Bluetti, or a Renogy complete kit is the right starting point. The engineering has been done for you, the components are matched, and support is simpler. Component systems make sense when your needs exceed what packaged kits can accommodate, or when you need specific customization for an unusual installation.
Where DIY Ends and Professional Work Begins
This is something most solar content sites gloss over, and it matters both practically and legally.
DIY is appropriate for: setting up a portable power station with panels, wiring DC components (panels, charge controller, battery bank) in a standalone system, and installing pre-engineered kit systems that don't connect to your home's electrical panel.
Professional work is required for: any system that connects to your home's AC electrical system, any system over 50V DC (which is most systems over a few panels), permits required in most jurisdictions for permanent installations, utility grid interconnection of any kind, and anything that touches your main electrical panel.
The permit and inspection requirement isn't something to work around. Off-grid solar installations that lack permits can create insurance issues and complications when you sell the property. A licensed electrician familiar with solar installations is the right resource for permanent systems.
Gas Backup for Off-Grid Systems
Quick Answer
Most serious off-grid installations include a gas generator as backup to the solar array. The Generac Guardian 14kW (Model 7223) is right-sized for a typical off-grid cabin or small homestead and runs on propane - practical for off-grid fueling. For a full homestead with well pumps and workshop loads, step up to the 24kW Guardian (Model 7210) which includes a 200-amp transfer switch. Both work cleanly with Schneider or Outback inverter-chargers' auto-start signal, enabling hands-off operation during solar shortfalls.
Most serious off-grid installations include a gas generator as a backup to the solar array. Not because solar fails - but because weather does. Three straight days of heavy cloud cover in January, a snow-covered panel array, or an unexpected battery bank maintenance day can all leave you without power at exactly the wrong moment. A standby generator that kicks in automatically via transfer switch eliminates the "watching the battery monitor drop" experience that off-grid veterans all recognize.
Generac is the default recommendation in the off-grid community for a practical reason: their dealer network and parts availability is the widest in North America. When you're rural enough to be off-grid, getting a replacement part shipped within a week matters more than the last 5% of efficiency. Two picks from Northern Tool + Equipment:
Right-sized for a typical off-grid cabin or small homestead where the solar array covers day-to-day needs and the generator handles winter shortfalls and heavy loads. Runs on propane, which is practical for off-grid sites - a 500-gallon LP tank gives realistic multi-week runtime. Starts automatically via transfer switch when battery voltage drops below a set threshold, or can be set for manual start. Professional installation required, total installed cost $8,000-$12,000 plus gas line work. Works cleanly with a Schneider or Outback inverter-charger's generator start signal for true hands-off operation.
The largest air-cooled Guardian, for homesteads running well pumps, workshop tools, livestock waterers, and full residential loads simultaneously. 24kW on LP is enough to run a whole house plus heavy-duty equipment during a sustained solar shortfall. 200-amp automatic transfer switch is included - a meaningful cost saving over the smaller units where the ATS is sold separately. Aluminum enclosure handles coastal, humid, or corrosive environments. Total installed cost typically $10,000-$15,000 with gas plumbing and electrical work.
For a true off-grid site where running gas lines isn't practical, a portable inverter generator with a manual transfer interlock is a valid alternative - lower cost, more flexibility, but requires you to walk out and start it. See the generator comparison page for portable options.
Whole-Home Battery Storage and Solar Integration
For homeowners moving beyond portable power stations into permanent home energy storage, Greenworks makes two products worth considering as part of a full solar installation.
10kWh LiFePO4 battery storage, stackable to 80kWh. Works with new or existing solar. Includes SmartSwitch for grid-independent backup operation. Qualifies for the 30% federal residential clean energy tax credit under Section 25D - verify eligibility with your tax professional. Requires professional installation.
7,600W output, accepts both AC and DC solar input, compatible with new and existing PV systems. Pairs with the PowerHub battery. Microgrid-capable for grid-independent operation. 12-year warranty. Requires a licensed solar installer.
Frequently Asked Questions
How do I size an off-grid solar system?
Calculate your daily load in watt-hours (Wh). Size your battery bank to cover 2-3 days of that load. Size your solar array to produce 1.5-2x your daily load in peak sun hours. Add a charge controller sized for your panel array and an inverter sized for your maximum simultaneous load.
How many solar panels do I need to go off-grid?
It depends on your daily consumption. For a modest off-grid cabin using 3,000Wh per day, you need roughly 1,000-1,500W of solar panels to generate adequate power through seasonal variation. In cloudy climates or for winter use, size up by 50-100%.
What batteries are best for off-grid solar?
LiFePO4 (lithium iron phosphate) is the best choice for permanent off-grid installations. 3,000-6,000 cycle lifespan, safe chemistry, good temperature tolerance, and high depth of discharge. Lead-acid batteries are cheaper upfront but have shorter lifespans and lower usable capacity.
Can a portable power station work as an off-grid solar system?
For modest loads - lighting, phone charging, small appliances - yes. For full residential loads including heating, cooling, and cooking, no. Portable power stations top out at 2,000-4,000Wh; a full residential off-grid system requires 10,000-40,000Wh of battery storage.
Do I need a gas generator for an off-grid solar system?
For serious off-grid installations, yes — a gas generator is the standard backup to the solar array. Not because solar fails, but because weather does. Three straight days of heavy cloud cover, a snow-covered panel array, or unexpected battery maintenance can leave you without power. A Generac standby generator that kicks in automatically via transfer switch, triggered by low battery voltage, eliminates the anxiety of watching battery levels drop. Generac is the default recommendation for off-grid because their dealer network and parts availability is the widest in North America — when you're rural enough to be off-grid, parts availability matters more than last 5% efficiency.
What size Generac generator do I need for off-grid backup?
For a typical off-grid cabin or small homestead, the Generac Guardian 14kW (Model 7223) is right-sized — runs on propane for practical off-grid fueling, and works cleanly with Schneider or Outback inverter-chargers' auto-start signal. For a homestead running well pumps, workshop tools, and full residential loads simultaneously, step up to the 24kW Guardian (Model 7210) which includes a 200-amp transfer switch. Both require professional installation, total installed cost $8,000–$15,000 with gas plumbing and electrical work.