Off-Grid Solar Sizing Guide for Cabins, Cottages, RVs & Winter Use

To size an off-grid solar system properly, you need to know your daily energy use, local peak sun hours, battery backup needs, inverter load, and cold-weather conditions. This is especially important in Canada, where winter sunlight, snow, temperature, and seasonal cottage use can change system performance dramatically.

An off-grid solar system is only reliable when all the major parts are matched correctly. The solar panels need to produce enough energy. The battery bank needs to store enough power for nighttime and cloudy days. The inverter needs to handle your appliances. The wiring and protection need to be safe for the current flowing through the system.

Whether you are powering a cottage, remote cabin, RV, boat, shed, hunting camp, farm outbuilding, or backup solar system, the sizing process starts with the same basic steps. Calculate your loads, estimate solar production, size your batteries, select your inverter, and build in a margin for Canadian weather.

Step 1: Work Out Your Daily Energy Use

The first step is to list every electrical device you plan to run. Include the obvious loads, such as a fridge or water pump, but also include smaller items such as LED lights, phone chargers, routers, fans, security cameras, and control boards.

For each device, find the wattage and estimate how many hours per day it will run. Multiply watts by hours to get watt-hours.

Formula:

Daily energy use (Wh) = Watts × Hours used per day

This example adds up to 1,710Wh per day, or about 1.7kWh.

In Canada, it is smart to add at least 25% extra capacity for real-world losses and seasonal variation. Wiring losses, inverter losses, battery charging losses, cold temperatures, snow cover, and cloudy weather can all reduce available power. In this example, a safer daily sizing target would be around 2.1kWh to 2.3kWh.

Step 2: Estimate Your Solar Panel Wattage

Solar panel output depends heavily on your location and season. A cottage in southern Ontario will not produce the same winter solar power as a system in Alberta on a clear summer day. Northern locations, shaded lots, low winter sun, and snow-covered panels all reduce production.

Start with average peak sun hours for your location. Peak sun hours are not total daylight hours. They represent the amount of strong sunlight your panels can use to produce meaningful energy.

Basic formula:

Solar array size (W) = Daily energy target (Wh) ÷ Peak sun hours

Then adjust for losses by dividing by 0.75 to 0.80.

Example:

• Daily energy target: 2,200Wh
• Average peak sun hours: 4 hours
• Panel wattage before losses: 2,200Wh ÷ 4 = 550W
• Adjusted for real-world losses: 550W ÷ 0.8 = about 690W

In this case, you may want around 700W of solar panels. That could mean two 350W panels, three 250W panels, or another combination that fits your roof, rack, trailer, or ground mount.

If the system must work in winter, size it using winter production numbers, not summer numbers. For seasonal cottages used mainly from spring to fall, you may not need to size as aggressively for December and January.

Step 3: Calculate Battery Storage

Your battery bank keeps the system running overnight and during cloudy weather. For Canadian off-grid systems, battery sizing is often more important than panel sizing because weather can change quickly and winter solar production can be limited.

Decide how many days of autonomy you want. For a weekend cottage or RV, 1 to 2 days may be enough. For a remote cabin, communication system, or full-time off-grid home, 2 to 3 days is often a better starting point.

Formula:

Battery storage needed (Wh) = Daily energy use × Days of autonomy

Example:

• Daily energy target: 2,200Wh
• Days of autonomy: 2
• Usable battery storage needed: 2,200Wh × 2 = 4,400Wh

Now adjust for the battery type. Lead-acid batteries should generally not be deeply discharged if long life is the goal. LiFePO4 batteries usually allow deeper usable capacity and are a strong choice for off-grid solar, RVs, and cottages.

If you need 4,400Wh of usable storage and use LiFePO4 batteries with about 90% usable capacity, you need roughly 4,900Wh of rated battery capacity. With lead-acid batteries at about 50% usable capacity, you may need roughly 8,800Wh of rated capacity.

To convert Wh to Ah:

Battery capacity (Ah) = Battery capacity (Wh) ÷ Battery voltage

For example, 4,900Wh on a 24V system equals about 204Ah. On a 48V system, it equals about 102Ah.

Batteries should be selected based on your system voltage, usable capacity, discharge rate, and temperature requirements.

Step 4: Think About Cold Weather Before Choosing Batteries

Cold weather is a major sizing factor in Canada. Batteries do not all behave the same in low temperatures. Lead-acid batteries lose usable capacity in the cold. LiFePO4 batteries are efficient and long-lasting, but many should not be charged below 0°C unless they have low-temperature charging protection or built-in heating.

If your battery will be installed in an unheated cottage, garage, shed, boat compartment, RV storage bay, or off-grid enclosure, check the temperature rating carefully.

• For winter charging: choose LiFePO4 batteries with low-temperature cutoff or self-heating features.
• For seasonal use: disconnect loads and store batteries at the manufacturer’s recommended charge level.
• For full-time off-grid use: consider an insulated battery box or heated battery space.

Step 5: Choose the Right System Voltage

Most off-grid solar systems use 12V, 24V, or 48V battery banks. The right choice depends on power level, wire distance, inverter size, and future expansion plans.

A 12V system is fine for basic lighting and small DC loads. For larger inverters, fridges, pumps, tools, and longer cable runs, 24V or 48V usually makes more sense.

Step 6: Size the Inverter

The inverter converts battery power into AC power for regular appliances. In Canada, most household outlets use 120V AC, while some larger appliances may require 240V AC.

To size the inverter, add up the loads that may run at the same time. Then check surge power. Fridges, freezers, pumps, tools, microwaves, and air conditioners may need much more power for a few seconds when they start.

Example:

• Fridge: 150W running with startup surge
• Lights: 50W
• Laptop: 60W
• Water pump: 500W running with startup surge
• Microwave: 1,000W

A 2,000W inverter may handle a small system, but a 3,000W inverter may be more practical if you run a pump, microwave, or power tools. For a larger cottage or full-time cabin, you may need a bigger inverter or a split-phase system designed by a professional.

Step 7: Size the Charge Controller

The charge controller manages solar charging and protects your batteries. MPPT charge controllers are usually the best choice for off-grid systems because they handle changing sunlight better and harvest more usable energy from the panels.

Basic current estimate:

Charge controller amps = Solar array watts ÷ Battery voltage

For example, a 700W solar array on a 24V battery bank may produce around 29A before design margins. A 40A MPPT charge controller may be a better fit than a 30A controller, depending on voltage limits and system layout.

Make sure the controller supports your battery type. If you use LiFePO4, choose a controller with lithium settings or custom voltage programming.

Step 8: Wiring, Breakers, and Safety

Off-grid systems can carry serious current. Safe wiring is essential, especially in remote areas where help may not be close by.

• Use proper wire size: Wire gauge must match current, distance, and acceptable voltage drop.
• Install fuses and breakers: Protect batteries, solar panels, charge controllers, inverters, and branch circuits.
• Add disconnects: Solar, battery, and inverter disconnects make maintenance safer.
• Protect from moisture: Use suitable enclosures for cabins, boats, RVs, and outdoor installs.
• Use professional help when needed: For permanent buildings or high-power AC systems, use a qualified electrician familiar with local electrical rules.

Quick Canadian Off-Grid Sizing Example

Final Thoughts

Sizing an off-grid solar system in Canada requires more than a basic panel calculation. You need to account for daily loads, local sunlight, winter conditions, battery temperature limits, cloudy days, inverter surge, and safe wiring.

For a small seasonal cottage or RV, the system may be fairly simple. For a year-round cabin, remote property, or full-time off-grid home, it is worth planning carefully and building in extra capacity for winter and bad weather.

A well-sized system will recharge properly, protect the batteries, support your appliances, and give you reliable power when the grid is not available.