Every winter, the same posts show up on off-grid solar forums. “System was fine in August. Now the batteries hit 20% by 4 PM.” The cause is almost always the same: the array was sized for summer production, not December. An off-grid system has no utility safety net. When the math is wrong, the lights go out.
We’ve designed and reviewed hundreds of stand-alone systems over the last decade. After a while, you see the same failure modes repeat. Most trace back to four numbers: daily load, winter peak sun hours, battery bank capacity, and inverter surge rating. Get those right and the system works year-round. Get one wrong and you will be running a generator by February.
This guide walks through the calculator logic we use in the field. Exact formulas, three worked examples from cabin to family home, and the code compliance checklist we run on every project. We also cover how to move from spreadsheet sizing to solar design software that turns a load audit into a permit-ready proposal.
TL;DR — Off-Grid Solar System Sizing Calculator (2026)
A typical off-grid home needs 8–15 kWh/day and a 4–8 kW array. BloombergNEF puts 2025 average LFP battery packs at $81/kWh. We break down exact sizing formulas, three worked examples, and the software workflow we use on every residential and C&I project.
In this guide:
- Calculate daily loads with a step-by-step AC/DC worksheet
- Size arrays for winter production, not summer averages
- Pick battery chemistry using 2026 cost data and TCO math
- Size inverters for surge loads like well pumps and fridges
- Move from spreadsheet sizing to professional design software
- Avoid the 6 mistakes that kill off-grid systems in winter
- Confirm code compliance with NEC 690, NEC 706, and IEC 62124
The 4 Core Formulas Every Installer Needs
Off-grid sizing comes down to four equations. Write them on the whiteboard in your office. Every system we spec starts here.
Daily Load: Wh/day = Σ (appliance watts × hours of daily use)
Add every device the client plans to run. Multiply wattage by daily runtime. Sum the results. That is your baseline.
Array Size: W = Daily load (Wh) ÷ Winter PSH ÷ 0.75
Winter peak sun hours (PSH) are what separate systems that work in January from systems that don’t. The 0.75 factor accounts for real-world losses: wiring voltage drop, charge controller inefficiency, battery round-trip losses, inverter conversion, and temperature derating.
Battery Bank: kWh = Daily load (kWh) × Days of autonomy ÷ DoD
Days of autonomy is how many sunless days the bank must carry the load. Depth of discharge (DoD) is the usable percentage of the battery. For lithium iron phosphate (LiFePO4), plan on 80% DoD. For flooded lead-acid, stop at 50%.
Inverter: W = Peak simultaneous load × 1.25
Peak load is not the sum of every device in the house. It is the highest combination that could run at once. Add a 25% margin for motor surge and future expansion.
Pro Tip
We always add a 1.2× safety margin to the daily load before we size anything else. Clients forget devices. Guests bring extras. That 20% buffer has saved more systems than any other single decision we make.
Step 1 — Daily Load Worksheet
The most common error in off-grid sizing is underestimating consumption. Clients remember the fridge and the lights. They forget the well pump, the modem, and the phantom loads from standby electronics.
We split every load into AC and DC. AC loads run through the inverter and incur conversion losses. DC loads bypass the inverter and run straight from the battery bank. In a 48V system, DC LED lighting and 12V refrigeration can cut daily consumption by 15–20%.
| Appliance | Quantity | Watts (each) | Hours/day | Wh/day |
|---|---|---|---|---|
| LED lighting | 10 | 8 | 5 | 400 |
| Refrigerator (efficient) | 1 | 120 | 8 | 960 |
| Well pump (1 HP) | 1 | 2,000 | 0.5 | 1,000 |
| Microwave | 1 | 1,200 | 0.25 | 300 |
| Laptop | 2 | 60 | 4 | 480 |
| Wi-Fi router | 1 | 15 | 24 | 360 |
| Phone chargers | 4 | 10 | 2 | 80 |
| Subtotal | 4,580 | |||
| With 1.2× safety margin | 5,496 |
For existing homes, we verify with a Kill-A-Watt meter. Nameplate ratings lie. A fridge rated at 600 W might average 120 W because the compressor only cycles 20% of the time. A well pump rated at 2,000 W might draw 6,000 W for 2 seconds on startup. The running average matters for daily load. The surge matters for inverter sizing.
Pro Tip
Never use nameplate wattage for cycling loads. A Kill-A-Watt left on a fridge for 48 hours gives you the true daily average. For new builds without appliances, use the adjusted averages in the table above.
Step 2 — Winter Peak Sun Hours
Peak sun hours measure the equivalent number of hours per day at 1,000 W/m². It is not daylight hours. A December day in Seattle might have 8 hours of daylight but only 1.5 peak sun hours.
Design for the worst month. In the northern hemisphere, that is December or January. Sizing on annual averages guarantees a shortfall every winter.
| Location | Winter PSH (Dec/Jan) | Annual Avg PSH |
|---|---|---|
| London, UK | 1.5–2.0 | 3.2 |
| Berlin, Germany | 1.5–2.0 | 3.5 |
| Seattle, WA | 1.5–2.0 | 3.8 |
| New York, NY | 2.5–3.0 | 4.5 |
| Denver, CO | 3.5–4.5 | 5.5 |
| Los Angeles, CA | 4.5–5.5 | 5.8 |
| Phoenix, AZ | 5.0–6.0 | 6.5 |
| Sydney, Australia | 5.0–6.0 (summer) | 5.5 |
| Madrid, Spain | 3.0–3.5 | 5.0 |
| Rome, Italy | 2.5–3.0 | 4.5 |
| Paris, France | 1.5–2.0 | 3.4 |
| Amsterdam, Netherlands | 1.5–2.0 | 3.3 |
| Vancouver, Canada | 1.0–1.5 | 3.5 |
| Albuquerque, NM | 4.5–5.0 | 6.0 |
| Minneapolis, MN | 2.5–3.0 | 4.6 |
For precise figures, we use NREL PVWatts v8. Enter the project address, set the array tilt to latitude, and read the December production column. PVWatts is accurate to within ±10% annually (NREL PVWatts Version 5 Manual, 2014). Monthly variance can be ±30%, which is why we always size for the worst month plus a buffer.
Pro Tip
If the roof faces east-west instead of south, apply a 15–20% production penalty in winter. The sun is lower, so azimuth matters more in December than in June. Compensate with a larger array or steeper tilt.
Step 3 — Solar Array Sizing
With daily load and winter PSH in hand, array sizing is straightforward.
Array watts = Daily load (Wh) ÷ Winter PSH ÷ 0.75
The 0.75 factor is conservative. It includes:
- Wiring losses: 2–3%
- Charge controller inefficiency: 2–5% (MPPT)
- Battery round-trip efficiency: 5–10% (LiFePO4)
- Inverter conversion: 2–5%
- Temperature derating: 5–15% in hot climates
- Soiling and snow: 2–10% seasonally
For winter-dominated climates, we add a 1.3× oversizing buffer. An oversized array charges the bank faster on marginal days and reduces generator runtime. In sunny climates like Arizona, 1.1× is enough.
Temperature derating matters in both directions. On a cold December morning at -10°C, a 425 W panel might output 460 W because silicon is more efficient at low temperatures. But the voltage also rises. You must verify that the open-circuit voltage at the lowest expected temperature does not exceed the charge controller’s maximum input.
Array tilt should equal latitude for year-round production. For winter-optimized systems, add 15°. A 40° latitude site should tilt to 55° for December peak production. Steeper angles also shed snow faster.
| Month | PSH | Snow Loss | Soiling | Net PSH |
|---|---|---|---|---|
| October | 4.0 | 0% | 3% | 3.9 |
| November | 2.8 | 5% | 4% | 2.6 |
| December | 2.5 | 15% | 5% | 2.0 |
| January | 2.7 | 12% | 4% | 2.3 |
| February | 3.5 | 8% | 3% | 3.1 |
Step 4 — Battery Bank Sizing
Battery sizing is where most off-grid systems fail. A bank that looks adequate on paper often crumbles after three cloudy days.
Battery kWh = Daily load (kWh) × Days of autonomy ÷ DoD
Days of autonomy depend on climate and client tolerance for generator use.
| Climate / Generator | Days of Autonomy |
|---|---|
| Sunny, no generator | 3 days |
| Sunny, auto-start generator | 2 days |
| Mixed / marine, no generator | 4–5 days |
| Mixed / marine, auto-start generator | 3 days |
| Overcast / northern, no generator | 5–7 days |
| Overcast / northern, auto-start generator | 3–4 days |
DoD by chemistry:
- Flooded lead-acid: 50% DoD
- AGM lead-acid: 50% DoD
- LiFePO4 (LFP): 80–90% DoD
In 2026, LiFePO4 is the clear choice. BloombergNEF reports average LFP pack prices at $81/kWh (BloombergNEF Battery Price Survey, 2025). Stationary storage packs have dropped to $70/kWh, a 45% decline from 2024 (BloombergNEF Battery Price Survey, 2025). Residential installed cost ranges from $750–$1,250 per usable kWh fully installed (EnergySage / VIP Energy Service, 2026).
The TCO math is simple. A 20 kWh LFP bank at $900/kWh installed costs $18,000 and delivers 6,000+ cycles. An equivalent lead-acid bank costs $8,000 but delivers only 500–1,000 cycles at 50% DoD. By year 4 or 5, the LFP investment pays for itself through avoided replacement costs.
Round-trip efficiency also favors lithium. LFP systems achieve 94–98% round-trip efficiency (Journal of Energy Storage Research, 2024). Flooded lead-acid is closer to 75–80%. That difference means 15–20% less array is required to charge the same daily load with LFP.
Cold weather derates battery capacity. At 0°C, LFP usable capacity drops 10–15%. At -10°C, it can drop 25%. If the battery will operate below freezing, size for the derated capacity or install a battery heating system.
Pro Tip
Size the battery bank for the client’s worst-case scenario, not their average day. A system that works 350 days per year but fails on the 5 darkest days of winter is a failed system. We always ask: “How many consecutive cloudy days can you tolerate before starting the generator?” The answer drives autonomy days.
Step 5 — Inverter Sizing
Inverter sizing is not about average load. It is about peak simultaneous load plus motor surge.
Inverter watts = Peak simultaneous load × 1.25
Peak simultaneous load is the highest combination of devices that could run at the same time. For a typical off-grid home, that might be: well pump (2,000 W) + fridge (700 W) + microwave (1,200 W) + lights (200 W) = 4,100 W.
Motor surge is the killer. A 1 HP well pump draws 2,000 W running but 6,000 W for 1–2 seconds on startup. A fridge compressor draws 700 W running but 2,100 W on startup. If the inverter cannot supply that surge, the motor stalls and the inverter trips.
| Load | Running Watts | Surge Watts | Duration |
|---|---|---|---|
| Well pump (1 HP) | 2,000 | 6,000 | 1–2 sec |
| Fridge compressor | 700 | 2,100 | 0.5–1 sec |
| Chest freezer | 500 | 1,500 | 0.5–1 sec |
| Microwave | 1,200 | 1,200 | None |
| Circular saw | 1,500 | 2,250 | 1–2 sec |
We always specify pure sine wave inverters. Modified sine wave units cost less but damage compressor motors, transformers, and variable-speed electronics. You will spend the savings on a new fridge in year two.
System voltage matters for inverter selection. A 48V system uses smaller cables, experiences lower voltage drop, and accepts higher-wattage inverters than 12V or 24V systems. For any off-grid home over 2 kW, we recommend 48V.
Generator integration requires an inverter-charger with auto-start support. We size the generator to 1.2× the peak load. A home with 8 kW peak load gets a 10 kW generator. The inverter-charger must also handle the generator’s charging current without overheating.
Step 6 — Charge Controller Sizing
The charge controller sits between the array and the battery. It regulates voltage and current to prevent overcharging. For any system over 200 W, we specify MPPT. PWM controllers are cheaper but waste 20–30% of panel output in winter compared with MPPT (Renewables Now Field Testing, 2026). The money you save on the controller, you spend on generator fuel.
Controller amps = Array watts ÷ Battery voltage × 1.25
The 1.25 factor is the NEC safety margin. A 6,000 W array on a 48V battery needs: 6,000 ÷ 48 × 1.25 = 156A. That requires dual 80A MPPT controllers or a single 150A unit.
| Brand | Model | Max Voltage | Max Current | Price Tier |
|---|---|---|---|---|
| Victron | SmartSolar MPPT 150/85 | 150V | 85A | Premium |
| Victron | SmartSolar MPPT 250/100 | 250V | 100A | Premium |
| Epever | Tracer 8420AN | 200V | 80A | Mid |
| Outback | FlexMax 80 | 150V | 80A | Premium |
| Morningstar | TriStar MPPT 60 | 150V | 60A | Mid |
Low-voltage disconnect (LVD) protects the battery from deep discharge. We set LVD at 20% state of charge for LFP and 50% for lead-acid. Temperature compensation adjusts charge voltage based on battery temperature. Cold batteries need higher voltage. Hot batteries need lower voltage. A remote temperature sensor is essential for every bank.
Worked Example — Small Cabin / RV (3–5 kWh/day)
Location: Colorado, 3.5 winter PSH
Daily load: 3.5 kWh
Peak load: 2.5 kW
Surge load: 5.5 kW
Array sizing: 3,500 Wh ÷ 3.5 PSH ÷ 0.75 = 1,333 W. With 1.2× buffer = 1,600 W. We specify 4× 425 W modules = 1,700 W.
Battery sizing: 3.5 kWh × 2 days autonomy ÷ 0.80 DoD = 8.75 kWh. With cold-climate 15% derating = 10.1 kWh. We specify one 48V 200Ah LFP battery = 9.6 kWh nominal, 7.7 kWh usable. For headroom, we upgrade to 48V 280Ah = 13.4 kWh nominal.
Inverter: 2.5 kW peak × 1.25 = 3.1 kW. With 5.5 kW surge requirement, we specify a 3 kW pure sine wave inverter with 6 kW surge capacity.
Charge controller: 1,700 W ÷ 48V × 1.25 = 44A. We specify a 60A MPPT for headroom and expandability.
Installed cost (2026): $8,000–$18,000 including panels, battery, inverter, charge controller, BOS, labor, and permits.
Worked Example — Mid-Size Off-Grid Home (8–15 kWh/day)
Location: Oregon, 2.5 winter PSH
Daily load: 12 kWh
Peak load: 5 kW
Surge load: 8 kW
Array sizing: 12,000 Wh ÷ 2.5 PSH ÷ 0.75 = 6,400 W. With 1.3× winter buffer = 8,320 W. We specify 20× 415 W modules = 8,300 W.
Battery sizing: 12 kWh × 3 days autonomy ÷ 0.80 DoD = 45 kWh. With 10% cold derating = 49.5 kWh. We specify three 48V 350Ah LFP batteries = 50.4 kWh nominal, 40.3 kWh usable.
Inverter: 5 kW peak × 1.25 = 6.25 kW. With 8 kW surge, we specify a 6 kW split-phase inverter with 12 kW surge.
Charge controller: 8,300 W ÷ 48V × 1.25 = 216A. We specify dual 100A MPPT controllers.
BOS breakdown: Wiring and conduit ($2,500), disconnects and breakers ($800), ground-mount racking ($3,200), labor ($4,500), permits ($1,000). BOS typically runs 20–30% of total project cost.
Installed cost (2026): $25,000–$50,000.
Worked Example — Full Off-Grid Family Home (20–30 kWh/day)
Location: Minnesota, 2.5 winter PSH
Daily load: 25 kWh
Peak load: 8 kW
Surge load: 12 kW
Array sizing: 25,000 Wh ÷ 2.5 PSH ÷ 0.75 = 13,333 W. With 1.3× buffer = 17,333 W. We specify 42× 415 W modules = 17,430 W. Due to roof space constraints, this often becomes a ground-mount array.
Battery sizing: 25 kWh × 3 days autonomy ÷ 0.80 DoD = 93.75 kWh. With 15% cold derating = 107.8 kWh. We specify six 48V 350Ah LFP batteries = 100.8 kWh nominal, 80.6 kWh usable. For critical loads, we add a seventh battery.
Inverter: 8 kW peak × 1.25 = 10 kW. With 12 kW surge, we specify a 10 kW split-phase inverter with 20 kW surge capacity.
Charge controller: 17,430 W ÷ 48V × 1.25 = 454A. We specify five 100A MPPT controllers in parallel, each handling 3,480 W.
Generator: 12 kW auto-start propane generator. Propane stores indefinitely, unlike gasoline. The auto-start controller triggers when battery state of charge drops to 20%.
Installed cost (2026): $50,000–$90,000+.
Code Compliance — NEC 690 / 706 & IEC 62124
Off-grid systems are not exempt from code. In 2026, NEC Article 706 adds battery management system (BMS) documentation requirements and short-circuit current rating (SCCR) labeling. Section 710.15 is new for combined PV, storage, and EV charging systems.
Our compliance checklist for every off-grid install:
| Requirement | NEC Reference | Action |
|---|---|---|
| DC disconnect within 10 ft of array | 690.13 | Install lockable disconnect |
| Battery disconnect | 706.15 | Separate disconnect for each battery string |
| Inverter bypass | Article 690 | Manual bypass for maintenance |
| Rapid shutdown | 690.12 | Array-level shutdown for fire safety |
| BMS documentation | Article 706 | Data sheet and commissioning report on site |
| SCCR labeling | Article 706 | Label all components with fault current rating |
| Grounding electrode | 690.47 | Dedicated ground rod for stand-alone systems |
| Arc-fault protection | 690.11 | DC arc-fault detector on array circuits |
IEC 62124 is the international standard for off-grid PV system design verification. It defines performance testing for stand-alone systems, including energy autonomy and battery state-of-charge protocols. For export projects or international certifications, we reference IEC 62124 in our documentation package.
Stand-alone attestation documentation should include: load calculation summary, array and battery sizing sheets, single-line diagram, equipment datasheets, commissioning test results, and maintenance schedule. We generate these in solar proposal software and deliver them as a branded PDF.
From Sizing to Permit-Ready Design
You have got the numbers. Now turn them into a permit-ready design. Our solar design software handles 3D layout, string sizing, and BOM generation in one workspace.
Book a DemoNo commitment required · 20 minutes · Live project walkthrough
From Spreadsheet to Software — The Installer Workflow
Manual sizing is where design starts. It is not where design ends. Once the load worksheet, array target, and battery bank are defined, the next step is professional modeling.
Our workflow on every off-grid project:
- Client intake — Load audit, site photos, roof or ground-mount preferences
- Spreadsheet sizing — The four core formulas from this guide
- PVWatts verification — NREL production check for the worst month
- Array layout — Module placement, string configuration, and roof or ground-mount design in solar design software
- Shade analysis — Confirm winter irradiance assumptions with solar shadow analysis software
- Financial modeling — 25-year production, LCOE, payback, IRR, and NPV in our generation and financial tool
- Proposal generation — Branded PDF with equipment specs, production guarantees, and financing options in solar proposal software
Moving from spreadsheet to software cuts design time from hours to minutes. Clara AI assists with proposal copy and design suggestions. The cloud platform means no desktop install, no per-project credits, and no version conflicts between team members.
A sized system is only valuable when it is presented to the client. Our proposals include the load worksheet, component list, production model, and code compliance checklist. Clients notice the detail. Detail builds trust.
2026 Cost Ranges & LFP Economics
| Archetype | Daily Load | Array | Battery | Inverter | Est. Cost (2026) |
|---|---|---|---|---|---|
| Small cabin / RV | 3–5 kWh | 1.5–3 kW | 10–20 kWh | 2–3 kW | $8,000–$18,000 |
| Mid-size off-grid home | 8–15 kWh | 4–8 kW | 20–40 kWh | 4–6 kW | $25,000–$50,000 |
| Full off-grid family home | 20–30 kWh | 8–15 kW | 40–60+ kWh | 6–10 kW | $50,000–$90,000+ |
BloombergNEF data shows average LFP pack prices at $81/kWh in 2025 (BloombergNEF Battery Price Survey, 2025). Stationary storage packs have fallen to $70/kWh, down 45% from 2024 (BloombergNEF Battery Price Survey, 2025). Residential installed cost ranges from $750–$1,250 per usable kWh (EnergySage / VIP Energy Service, 2026). A 10 kWh home battery now runs $8,000–$11,000 before incentives (EnergySage / VIP Energy Service, 2026).
Over 10 years, the TCO comparison looks like this:
| Chemistry | Initial Cost | Replacement Cost (yr 5–7) | 10-Year Total |
|---|---|---|---|
| Flooded lead-acid (20 kWh) | $8,000 | $8,000 | $16,000 |
| LiFePO4 (20 kWh usable) | $18,000 | $0 | $18,000 |
By year 4 or 5, LFP breaks even. By year 10, it is cheaper and has delivered 6,000+ cycles versus 1,000–1,500 for lead-acid.
Policy note: The US federal residential investment tax credit (§25D) expired on December 31, 2025. There is no residential solar tax credit in 2026. Commercial and third-party owned residential projects may still claim §48E through December 31, 2027 (IRS, 2026) (Solar.com, 2026).
European residential CAPEX in 2025–2026:
| Country | Residential (€/kWp) |
|---|---|
| Germany | 1,200–1,800 |
| France | 1,500–2,200 |
| Spain | 1,100–1,600 |
| Italy | 1,300–1,800 |
| Netherlands | 1,100–1,500 |
(Solar Data Atlas, 2025)
6 Sizing Mistakes That Kill Off-Grid Systems
We see these errors on every forum and in too many designs that cross our desk.
1. Designing for annual average PSH instead of winter worst-month. A system sized on 5.5 annual average PSH in Denver will fail in December when PSH drops to 3.5. Always design for the darkest month.
2. Undersized inverter ignoring motor surge. A 3 kW inverter handles the running load fine. It trips when the well pump draws 6,000 W on startup. Size for surge, not average.
3. Cheap PWM controller wasting 20–30% of winter production. PWM controllers cost $50. MPPT controllers cost $300. The MPPT pays for itself in the first winter through avoided generator runtime.
4. Battery bank with under 2 days autonomy in cloudy climates. Two cloudy days should not trigger a generator. Three to five days of autonomy is the minimum for year-round off-grid living.
5. No expansion headroom in inverter and charge controller specs. Clients add loads. Size the inverter and charge controller 25% above today’s peak. Future-proofing is cheaper than replacement.
6. Skipping shade analysis. A tree that casts no shadow in June can block 40% of the array in December when the sun is 23° lower. Confirm with solar shadow analysis software before finalizing the design.
Frequently Asked Questions
How do I calculate what size solar system I need?
Add up every appliance’s wattage multiplied by daily run hours to get Wh/day. Multiply by 1.2 for safety margin. Divide by winter peak sun hours and 0.75 system efficiency to get array watts. For battery bank, multiply daily load in kWh by autonomy days and divide by DoD.
How many solar panels do I need for off-grid?
Divide your daily load in Wh by winter peak sun hours and 0.75 efficiency. Then divide that array wattage by your chosen panel wattage. For a 5 kW array using 425 W panels, you need 12 panels. Always round up and add 20–30% for winter buffer.
How big a battery bank do I need for 3 days of autonomy?
Multiply daily load in kWh by 3 days, then divide by usable depth of discharge. For LiFePO4 at 80% DoD: 10 kWh × 3 ÷ 0.8 = 37.5 kWh of battery capacity. In cold climates, add 15% for temperature derating.
Do I need a backup generator for off-grid solar?
For year-round homes in low-insolation climates, yes. Size the generator to 1.2× your peak load and ensure your inverter-charger supports auto-start. In sunny regions with oversized arrays, a generator may only run 5–10 days per year. Seasonal cabins can skip the generator if they accept limited winter use.
Is LiFePO4 worth the higher cost than lead-acid?
Yes. At 2025 BloombergNEF prices of $81/kWh for average LFP packs, the total cost of ownership breaks even with lead-acid by year 4–5 and delivers 6,000+ cycles versus 500–1,000 for flooded lead-acid. The higher round-trip efficiency also means a smaller array.
How much does an off-grid solar system cost in 2026?
A small cabin system runs $8,000–$18,000. A mid-size off-grid home costs $25,000–$50,000. A full family home with generator backup ranges from $50,000–$90,000+. Stationary LFP battery pack prices have dropped 45% since 2024, making lithium the default choice for new builds.
Can an off-grid solar system power a whole home?
Yes, if sized correctly. A typical family home uses 20–30 kWh/day. That requires an 8–15 kW array, 40–60+ kWh of LFP storage, and a 6–10 kW inverter. The key is eliminating resistive heating loads (electric water heaters, space heaters) and using propane or wood for thermal needs.
Can I expand my off-grid solar system later?
Only if you plan for it. Size the charge controller, inverter, and battery rack 25% above initial load. Choose a battery with parallel expansion capability. And document the spare capacity in your original design so the next installer knows what room is available.
What maintenance does an off-grid system need?
Monthly: check battery state of charge, clean array soiling, inspect cable connections. Quarterly: test generator auto-start, verify inverter fault logs, tighten battery terminal torque. Annually: professional inspection of ground connections, array mounting, and BMS calibration.
Final Checklist + Next Steps
Before you sign off on any off-grid design, run this checklist.
| Check | Status |
|---|---|
| Load audit completed with 1.2× safety margin | ☐ |
| Winter PSH confirmed via PVWatts or local data | ☐ |
| Array sized for worst month + oversizing buffer | ☐ |
| Battery bank sized for 3+ days autonomy at winter temperature | ☐ |
| Inverter surge capacity verified against all motor loads | ☐ |
| Charge controller amperage includes 1.25× NEC margin | ☐ |
| Code compliance: NEC 690, 706, and local AHJ requirements | ☐ |
| Shade analysis confirms winter irradiance assumptions | ☐ |
| Proposal ready with equipment specs and financial model | ☐ |
Start your off-grid design in SurgePV. Import your load worksheet, confirm shade with solar shadow analysis software, model 25-year production in our generation and financial tool, and send a branded proposal with solar proposal software. The calculator gets you the numbers. The software gets you the contract.
