Complete Off-Grid Solar + Battery Systems: Sizing, Installation, Performance

The Short Answer on Sizing

Most cabins and full-time off-grid setups land between 2,000W and 6,000W of panel capacity paired with 10–30 kWh of battery storage. Get those numbers wrong and you’re either burning money on excess capacity or running a generator every cloudy week.

I’ve been running a 4,800W system with 20 kWh of LiFePO4 storage at my off-grid property in the Ozarks for three years. I’ve also helped spec systems for a dozen readers and friends across Montana, Vermont, and the Texas Hill Country. The numbers below come from those builds — not from manufacturer datasheets.

Start With Your Load Calculation

Before you buy a single panel, you need a daily watt-hour number. Add up every device you’ll run, multiply by daily hours of use, and that’s your baseline. A typical off-grid cabin with LED lighting, a 12V refrigerator, laptop, phone charging, and a water pump runs 1,500–2,500 Wh/day. Add an electric water heater or induction cooktop and you’re looking at 4,000–6,000 Wh/day.

Don’t guess. Pull the nameplate wattage off every appliance or use a Kill A Watt EZ meter to measure actual draw. Nameplate ratings are worst-case; real consumption is usually 60–80% of that. The Kill A Watt EZ runs about $30 and will save you thousands in oversizing mistakes.

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Once you have your daily Wh number, add a 25% buffer for inefficiencies — inverter losses, wire resistance, battery charge/discharge losses. If your loads total 3,000 Wh/day, design for 3,750 Wh/day of usable production.

Panel Wattage: How Much Do You Actually Need?

Solar panels don’t produce their rated wattage all day. They hit peak output for roughly 4–6 hours depending on your latitude and season. That window is called peak sun hours (PSH), and it’s the multiplier that determines your array size.

The formula: Daily Wh needed ÷ PSH = array wattage required. If you need 3,750 Wh/day and you’re in central Texas with 5.5 PSH, you need a 682W array minimum. Round up to 800W to account for panel degradation (typically 0.5% per year) and real-world soiling losses. In Vermont in December, PSH drops to 2.8 — the same cabin needs a 1,340W array to break even. Seasonal adjustment matters more than most people admit, and it’s the number I see ignored most often in DIY builds.

For most off-grid builds, I use monocrystalline panels in the 400W–550W range. They’re the most efficient per square foot (20–23% vs. 15–17% for polycrystalline), and the price gap between mono and poly has essentially closed. The Renogy 400W Monocrystalline Panel is a workhorse — I’ve got six of them on my roof, and after three years they’re still testing within 2% of rated output. At roughly $0.55–0.70 per watt, Renogy hits the sweet spot of quality and cost for DIY builds.

If roof space is tight, look at the SunPower Maxeon 400W. At 22.8% efficiency — the highest available in residential-scale panels — and a 40-year performance warranty, you’ll pay a premium. But if you’re mounting on a small cabin roof or van, the extra watts per square foot justify it.

Battery Chemistry: LiFePO4 vs. AGM vs. Lead-Acid

This decision defines your system’s long-term economics. For a permanent off-grid system in 2024, use LiFePO4 (lithium iron phosphate). I’ve run both, and the math isn’t close.

A quality AGM battery like the Renogy Deep Cycle AGM costs roughly $200 per 100Ah at 12V (1.2 kWh). Safe discharge to 50% gives you 0.6 kWh usable, and it’ll handle 500–800 cycles at that depth. A 100Ah LiFePO4 battery costs $280–350 but discharges to 80–90% depth of discharge (DoD), giving you 0.96–1.08 kWh usable, and handles 3,000–5,000 cycles. Over a 10-year system life, LiFePO4 costs less per usable kWh by a factor of 3–4x.

The EG4 LifePower4 48V 100Ah LiFePO4 Battery is what I’d put in a new build today. It’s a 4.8 kWh module, rack-mountable, includes a built-in BMS, and communicates with compatible inverter-chargers via CAN bus. Stack four of them and you’ve got 19.2 kWh — enough to run a modest off-grid cabin for 3–4 days without sun.

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If budget is genuinely tight and you’re building a seasonal cabin system — not full-time — sealed AGM is still viable. The Renogy Deep Cycle AGM 200Ah 12V is reliable, requires zero maintenance, and handles cold better than lithium below -4°F without heating elements. For a summer-only hunting camp, AGM makes sense. For a full-time home, it doesn’t.

Flooded lead-acid (FLA) is the cheapest upfront option and still used in large off-grid homesteads where someone’s willing to check water levels monthly and manage equalization charges. The Trojan T-105 6V golf cart battery has been the industry standard for decades. But maintenance requirements and shorter cycle life make it a tough sell for anyone who isn’t already deep into battery management.

Inverter Sizing: Where Most DIYers Get It Wrong

Your inverter converts DC battery power to AC household current. Size it for your peak surge load, not your average load. That 1,500W well pump has a startup surge of 3,000–4,500W. A 10,000 BTU mini-split pulls 900W running but surges to 2,200W on startup. Add those together with your other running loads and you can easily hit 5,000–6,000W of simultaneous demand.

For most off-grid homes, a 3,000W–6,000W pure sine wave inverter-charger is the right call. The “charger” part matters — it lets you run a generator input to charge batteries during extended cloudy periods without a separate charger unit. The Victron MultiPlus-II 48/3000/35-32 is the gold standard for systems up to 3,000W continuous. It’s 48V input (correct for any system over 1,500W), handles 6,000W surge, and integrates with Victron’s Color Control GX for full system monitoring. I’ve seen these units run flawlessly for 8+ years in harsh conditions.

For larger loads — full-size refrigerator, HVAC, power tools — step up to the Victron Quattro 48/8000 or the SMA Sunny Island 6.0H. Both handle 8,000W continuous and are built for whole-home off-grid use. The SMA handles generator integration exceptionally well if that’s a priority.

One spec that matters more than most people check: total harmonic distortion (THD). Pure sine wave inverters run under 3% THD. Modified sine wave units run 20–40% THD and will damage sensitive electronics, cause motors to run hot, and make audio equipment buzz. Don’t use modified sine wave in a permanent installation.

Charge Controllers: MPPT vs. PWM

The charge controller sits between your panels and your batteries, regulating voltage and current to charge safely. Two types: PWM (pulse width modulation) and MPPT (maximum power point tracking).

On any system over 400W, use MPPT. MPPT controllers run 93–97% efficient vs. 70–80% for PWM, and they allow higher-voltage panel strings into lower-voltage battery banks — less wire, less voltage drop, more flexibility in panel placement. On a 2,400W array, the efficiency difference between MPPT and PWM translates to 480–650 Wh/day of recovered production. That’s not theoretical — I measured it when I upgraded my own system.

The Victron SmartSolar MPPT 150/100 handles up to 5,800W of panel input at 48V battery voltage. It’s Bluetooth-enabled, integrates with the Victron ecosystem, and I’ve run one for three years without a single issue. For smaller systems under 1,200W, the Renogy Rover 40A MPPT is a solid budget option at around $120.

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Size your charge controller for 125% of your panel array’s short-circuit current (Isc). Running a controller at 100% of rated current continuously shortens its life. The spec sheet on every panel lists Isc — add them up for your string configuration and multiply by 1.25.

System Voltage: 12V vs. 24V vs. 48V

Small systems under 1,000W, RVs, boats: 12V is fine. Under 1,000W on a fixed installation: 24V works. Anything larger: 48V, no debate.

Higher voltage means lower current for the same power output. Lower current means smaller wire gauge, less resistive loss, and cheaper wiring runs. A 3,000W load at 12V draws 250A — that requires 4/0 AWG cable and generates significant heat. The same load at 48V draws 62.5A and runs fine on 6 AWG. On a whole-home system, the wire savings alone offset the cost difference between 48V and 12V batteries.

Pre-Configured Kits vs. Custom Builds

Pre-configured kits make sense if you’re building a system under 2,000W, you’re not comfortable with electrical work, or you need a fast deployment. Renogy, EcoFlow, and Bluetti package panels, charge controllers, batteries, and inverters in matched sets with documentation written for non-electricians.

The Renogy 2000W 12V Complete Solar Kit is a legitimate turnkey option for small cabins and van builds. It includes four 200W panels, a 40A MPPT controller, a 2,000W pure sine inverter, and wiring harnesses. You’re not getting the most efficient components, but you’re getting a system that works out of the box without a spreadsheet.

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For anything above 3,000W or any full-time residence, build custom. You’ll get better component quality, easier future expansion, and the ability to mix best-in-class equipment. A Victron inverter-charger, EG4 batteries, and Renogy or SunPower panels is a combination I’d put against any pre-packaged system at the same price point.

Real-World Performance Data: My Ozarks System

My 4,800W system runs twelve 400W Renogy mono panels, a Victron Quattro 48/5000 inverter-charger, 20 kWh of EG4 LiFePO4, and a Victron SmartSolar 150/100 MPPT. Here’s what it actually produces across seasons at 36° N latitude:

• June peak: 28–32 kWh/day production, 5.8–6.2 PSH, batteries at 95–100% SOC by noon
• September: 22–26 kWh/day, 4.8 PSH average, comfortable margin
• December worst case: 8–11 kWh/day on overcast days, 2.4 PSH, generator kicks in after 2 consecutive cloudy days
• Annual average: 19.4 kWh/day, which covers my 14–16 kWh/day consumption with a 20% buffer

My daily load includes an 18 cu ft chest freezer converted to refrigerator (200Wh/day), a 1.5-ton mini-split (4,200Wh/day in summer), LED lighting (150Wh/day), laptop and devices (300Wh/day), water pump (400Wh/day), and miscellaneous (600Wh/day). That’s roughly 5,850 Wh/day in summer, 3,200 Wh/day in winter when the mini-split runs less.

The 20 kWh battery bank gives me 3.4 days of autonomy at summer loads and 6.25 days in winter. Between March and October I almost never touch the generator. December through February, I’ll run a 3,500W propane generator for 2–3 hours every 4–5 days during cloudy stretches — roughly 8–10 gallons of propane per month in the worst winter months.

Seasonal Adjustments That Actually Matter

Tilt angle is the most underrated seasonal variable. Fixed-mount panels at your latitude angle optimize for the equinoxes. Adjusting tilt seasonally — steeper in winter (latitude + 15°), shallower in summer (latitude – 15°) — increases winter production by 10–15%. On a 4,800W array in December, that’s an extra 1–1.5 kWh/day. Worth the twice-yearly adjustment if your mount allows it.

Snow is a real concern above 35° N. Panels at a 30° tilt or steeper shed snow naturally in most cases. Panels mounted flat — common on van roofs — lose production for days after a storm. In heavy snow country, mount at minimum 30° and use tempered glass panels; they shed snow faster than plastic-framed units.

LiFePO4 batteries lose roughly 20% capacity at 32°F and won’t charge below 32°F without a battery heater. Most quality 48V LiFePO4 batteries from EG4, Epoch, and SOK include internal heating elements that activate automatically. If yours don’t, insulate the battery enclosure and add a thermostatically controlled heat tape. AGM handles cold better for charging but loses capacity fast in sustained cold — a 100Ah AGM at 20°F effectively delivers about 60Ah.

Wiring, Fusing, and Safety Basics

Every circuit needs overcurrent protection within 18 inches of the positive battery terminal. The main battery-to-inverter cable needs a Class T fuse or ANL fuse rated for 125% of the inverter’s maximum input current. On a 48V 5,000W inverter, that’s 104A max draw — use a 125A ANL fuse.

Wire sizing is non-negotiable. Undersized wire creates resistance, heat, and voltage drop. Use the NEC ampacity tables and size for no more than 3% voltage drop on any run. For a 48V system, 3% drop is 1.44V — manageable. On a 12V system, 3% is 0.36V, which is why 12V systems need much heavier wire for the same power.

Ground everything. Panel frames, charge controller chassis, inverter chassis, and battery negative all go to a single grounding electrode. A floating ground in a solar system is a shock hazard and produces ground fault issues that are miserable to diagnose. I’ve spent two days chasing a fault that turned out to be a single ungrounded panel frame.

If you’re not comfortable with DC electrical work, hire a licensed electrician for the battery-to-inverter connections and main panel integration. The panel-to-charge-controller wiring is lower stakes, but anything touching the battery bank carries enough current to start fires or cause serious injury.

Monitoring: Know What Your System Is Doing

A system without monitoring is a system you can’t optimize. At minimum, you need a battery state of charge (SOC) display and a production meter. The Victron Color Control GX gives you real-time SOC, production, consumption, and historical data on a touchscreen display — it’s what I use and it’s worth every dollar of the $250 price tag.

For budget builds, the Renogy One Core monitoring hub integrates with Renogy components and gives you remote monitoring via smartphone app for around $100. Not as capable as Victron’s ecosystem, but it covers the basics.

Track your daily production and consumption for the first full year. You’ll find inefficiencies you didn’t know existed. My monitoring data showed my chest freezer-turned-fridge drawing 40% less than I’d estimated — which meant I had more headroom for power tools than I’d planned for. That kind of data changes how you manage the system.

What a Complete System Costs in 2024

Realistic budget breakdown for a 4,800W system with 20 kWh LiFePO4 — the size I’d recommend for a full-time off-grid cabin with modest loads:

• Panels (12x 400W Renogy mono): $2,400–$3,000
• Batteries (4x EG4 48V 100Ah LiFePO4): $5,600–$6,400
• Inverter-charger (Victron Quattro 48/5000): $1,800–$2,200
• Charge controller (Victron SmartSolar 150/100): $400–$500
• Mounting hardware, racking: $600–$900
• Wire, fuses, disconnects, breakers: $400–$600
• Monitoring (Victron Color Control GX): $250
• Miscellaneous (conduit, connectors, grounding): $200–$300
• Total DIY installed: $11,650–$14,150

Add $2,000–$4,000 for professional installation if you’re not doing it yourself. That’s a $13,000–$18,000 all-in system that will run for 15–20 years with minimal maintenance. Contractor-installed systems of similar capacity run $25,000–$40,000. The DIY math is compelling if you’re willing to put in the work.

The Bottom Line

Get your load calculation right. Size your array for your worst-case seasonal PSH. Use 48V LiFePO4 batteries for any permanent installation. Run MPPT charge control. Those four decisions account for 90% of whether a system works long-term.

Starting from scratch and want something vetted out of the box: the Renogy 2000W kit gets you running fast. Building a full-time system: spec it custom around Victron inverter-charger hardware and EG4 batteries. That combination has the best track record I’ve seen across the dozen systems I’ve helped build.

My generator ran 11 times last winter. Sized right, that’s what off-grid looks like.

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