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Solar Battery Bank Sizing Calculator

Free Canadian solar battery bank sizing calculator. Size your battery in Ah and kWh for off-grid cottages, cabins, or grid-tied backup based on daily load and autonomy.

Solar Battery Bank Sizing Calculator

Usable energy needed
15,000 Wh
Gross capacity needed
19,069 Wh
Bank capacity (Ah)
397 Ah
Bank capacity (kWh)
19.1 kWh

How to use this calculator

Enter your average daily load in watt-hours (Wh), choose your system DC voltage (12V, 24V, or 48V), set days of autonomy, then pick battery chemistry. The tool returns capacity in both Ah and kWh.

If you don’t know your load, take a monthly utility bill (kWh) × 1000 / 30. NRCan’s residential average is ~30 kWh/day in cold provinces with electric heating, but for backup-only or off-grid sizing, exclude heating loads (which usually run on propane or wood) — typical cottage loads run 3–8 kWh/day.

The formula

Usable energy needed (Wh) = Daily load × Days of autonomy
Gross capacity (Wh)       = Usable / (DoD × Inverter eff × Battery eff)
Bank capacity (Ah)        = Gross capacity / System voltage

DoD is depth of discharge (90% LiFePO4, 50% AGM/Gel). Inverter efficiency is typically 92% for a quality pure-sine inverter. Battery round-trip efficiency is 95% LiFePO4 and 80–85% lead-acid.

Worked example — 5 kWh/day cottage in Ontario

Off-grid cottage at 45° N latitude with 5,000 Wh daily load, 3 days of autonomy on a 48V LiFePO4 system:

  • Usable energy: 5,000 × 3 = 15,000 Wh
  • Gross capacity: 15,000 / (0.90 × 0.92 × 0.95) = 19,065 Wh
  • Bank size: 19,065 / 48 = 397 Ah at 48V (or 19 kWh)

That maps to four EG4 LL-S 48V 100 Ah modules, two Pylontech Force-H2 stacks, or one Tesla Powerwall 3 plus expansion. With AGM lead-acid the same load needs about 800 Ah at 48V — double the cells, triple the cabinet space, and replacement every 5–7 years vs 12–15 for LiFePO4.

Battery chemistry — the dominant cost driver

Per Solar Industry Magazine Canada and HomeStars 2025 pricing data, typical 2026 installed costs in Canada:

  • LiFePO4 lithium: CAD$1,000–1,400 per kWh installed (EG4, Pylontech, BYD, Tesla Powerwall, Discover AES)
  • AGM lead-acid: CAD$500–700 per kWh nameplate, but you need 1.8–2× kWh to match usable energy — net cost similar or higher
  • Flooded lead-acid (Rolls Surrette, Trojan): CAD$350–500 per kWh nameplate, still common on remote cottages because Rolls cells handle cold better than mass-market lithium and are road-truck serviceable

Most Canadian off-grid installers in 2025–2026 quote LiFePO4 by default for new builds. Rolls Surrette flooded cells remain a niche choice for hard-access northern Ontario, Quebec North Shore, and remote BC sites where battery replacement logistics dominate the decision.

CSA C22.1 and CEC compliance

The calculator handles the energy maths. CSA C22.1 (Canadian Electrical Code) Section 64 covers renewable energy systems and Section 26 covers battery installations:

  • Battery enclosure ventilation per CEC Section 26-500 (lead-acid) and CSA C22.2 No. 340 (lithium ESS)
  • DC disconnect and overcurrent protection per CEC Section 64-066
  • Cable sizing per CEC Table 2 — see the Solar Panel Wire Size Calculator for sizing using AWG (Canadian convention is AWG for wire, m² for area)
  • ESA / ECRA inspection in Ontario; equivalent provincial AHJ elsewhere
  • CSA-certified equipment required (most US-listed gear is dual UL/CSA)

For grid-tied storage, your installer must work with the LDC (Local Distribution Company — Toronto Hydro, BC Hydro, Hydro-Québec, etc.) for interconnection approval per the CSA C22.3 No. 9 standard.

How to estimate daily load

A typical Canadian load table for cottage or backup sizing:

  • Fridge (Energy Star 18 cu ft): 1.2 kWh/day
  • Well pump (1/2 HP, 1 hour): 0.5 kWh/day
  • LED lighting (8 fixtures × 5 hours × 10W): 0.4 kWh/day
  • Internet (Starlink/Xplore + router): 1.0 kWh/day for Starlink, 0.4 kWh/day for cellular
  • Laptop + phone charging: 0.3 kWh/day
  • Mini-split heat pump (2.5 kW × 6 hours): 5–8 kWh/day in shoulder season
  • Microwave/induction/coffee: 0.5–1.0 kWh/day

Add 15% for inverter standby, BMS draw, and Starlink dish heater (which can pull 50–100W continuously in winter). Real-world cottage baselines run 3–8 kWh/day in shoulder season; winter occupation with electric heat assist can reach 15–20 kWh/day.

Sources cited

  • CSA C22.1 (Canadian Electrical Code, 2024 cycle adopted by most provinces)
  • CSA C22.2 No. 340 Battery Energy Storage Systems
  • NRCan PV Watts and CanmetENERGY off-grid sizing guides
  • Solar Industry Magazine Canada 2025 cost survey
  • HomeStars 2025 Canadian residential solar & storage pricing report
  • Canada Greener Homes Loan program guidelines

Cross-check your design with a Master Electrician or NABCEP/CETC-certified solar professional licensed in your province before purchasing. The Canada Greener Homes Loan and most provincial rebates require certified installer sign-off; DIY installs forfeit eligibility.

Frequently asked questions

What battery size do I need for an off-grid Canadian cottage?
For a typical lake cottage running 4–6 kWh/day with three days of autonomy (Canadian winters demand more reserve), you need around 350–500 Ah at 48V of usable LiFePO4 capacity, or roughly 17–24 kWh of nameplate. Lead-acid would need nearly double that.
Why three days of autonomy in Canada when most US guides say two?
Canadian winters at 50°+ latitude can deliver only 1–2 hours of usable solar on overcast December days. December insolation in Toronto averages 1.6 kWh/m²/day vs 5.5 in summer — a 3× swing. Three to five days of autonomy keeps the cottage running through prairie blizzards or lake-effect snow events without firing the genset.
Should I pick 24V or 48V?
24V suits trailers, RVs, and small cabins below 5 kWh/day. 48V is the standard for hybrid inverters from Schneider Electric, Outback, Victron, EG4, and Sol-Ark, and required for stack-style residential batteries (Tesla Powerwall, Pylontech, BYD). 48V cuts cable current by 4× compared to 12V, which matters for CSA C22.1 compliance and reduces copper cost on a remote site.
Do batteries handle extreme cold?
Most LiFePO4 cells block charging below 0°C to prevent lithium plating, and capacity drops 10–15% at -10°C even with discharge allowed. For unheated cottages, oversize the bank by 20–30% and either specify self-heated batteries (EG4, Battle Born heated, Discover AES) or insulate and heat the battery enclosure. Lead-acid tolerates cold better but loses capacity at ~1% per °C below 25°C.
Are there Canadian rebates for batteries?
The Canada Greener Homes Loan (interest-free up to CAD$40,000) covers PV plus battery for primary residences. Some provinces add their own — BC's CleanBC Better Homes program, Ontario's Save on Energy battery program, and Quebec's Hilo program. Cottages and second homes generally don't qualify for the Greener Homes Loan; check each provincial program separately.

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