Cottage solar and off-grid power: sizing and gear

Off-grid solar is a different job from a grid-tied roof system. There is no utility to lend you power at night or in January, so every kilowatt-hour you use has to come from your panels, your batteries or a generator. The upside is independence and the freedom to put a cabin where a power line will never go. The cost is that design matters a great deal.

Start with the loads, not the panels

Write down everything you want to run and how long it runs each day. Convert to watt-hours: a 60 W device used for five hours is 300 Wh.

A sample seasonal cottage might look like this:

These are example figures. Your actual appliances may be higher or lower, so check nameplate ratings or a plug-in meter. Heating with electricity, running an electric kettle or using a washer and dryer quickly changes the picture. In off-grid work, the cheapest kilowatt-hour is the one you do not use. Propane, wood and efficient appliances often make more sense than electric resistance heating.

Panels: sized for the worst month

In summer, a few panels can be plenty. In December, you may get a small fraction of that. For a year-round home, size the array for the lowest-production month you must cover, or accept that a generator fills the gap. For a seasonal cottage used only from May to September, you can size to summer conditions and save money. Our guide to monthly solar output in Canada shows how steep the swing is.

A rough check: a kilowatt of panels in southern Canada may produce around 1,100 to 1,400 kWh a year, but much of it falls in summer. For a 1.9 kWh/day load, a modest array of one to two kilowatts may cover summer needs. A year-round version of the same loads would need more, and a tilt closer to your latitude helps winter output.

Batteries: where the money goes

Off-grid batteries must carry you through nights and cloudy stretches. A common design target is one to three days of autonomy, meaning storage for that many days of use without sun. With 1.9 kWh a day, two days of autonomy is about 4 kWh of usable capacity, and you should also allow for the depth of discharge your chemistry permits and for inverter losses.

Lithium iron phosphate is widely used in current systems, with lead-acid also still found. Each has trade-offs. Lithium usually costs more upfront and tolerates deep cycling, but it has cold-charging limits, so batteries should sit in a conditioned space, not in an unheated shed at minus 25 degrees. Our guide to sizing a home battery has a worked example, and home battery costs in Canada gives the typical range. Batteries commonly add several thousand dollars, and larger banks run well beyond that.

The generator question

A backup generator is the usual answer to a long run of grey, cold days. It tops up batteries and runs heavy loads. Designers often size the solar and battery for normal days and let the generator cover exceptions, instead of oversizing the system for a rare week. Noise, fuel storage and maintenance are the downsides. We compare the two in battery vs generator. Some people run hybrid systems that charge the battery from both sources.

Other parts of the system

• A charge controller to manage the panels’ output into the battery
• An inverter to supply standard household AC power
• Disconnects, breakers and fusing sized correctly for the battery
• Grounding and wiring suited to the load and weather
• Monitoring, so you can see battery state before it runs low

Off-grid does not mean unregulated. Local building and electrical rules may still require permits and inspection, and batteries and inverters should carry recognised certification marks, such as CSA or equivalent. Ask your provincial electrical safety authority what applies. Hire a qualified electrician for the wiring even if you assemble parts yourself, and read about what DIY involves in Canada before you commit.

When off-grid beats a grid connection

If a cottage is near an existing line, a utility connection plus a small grid-tied array may cost less and give you more reliability. If the nearest line is far, line extension quotes can be steep, and off-grid solar becomes competitive. Get both quotes, in writing, before you decide. For a grid-tied cottage that is empty much of the year, check whether your utility has seasonal rules and how credits behave when you are not home. Our net metering overview is the place to start.

Practical advice

Cut loads first. Pick efficient appliances and DC-friendly lighting. Put batteries in a sheltered, ventilated space. Keep a log of battery voltage in your first season. Allow for growth, since cottages tend to acquire a dishwasher or a hot tub sooner than planned. Most importantly, write the load table before you talk to a supplier, so that quotes are comparable.

Your own situation may involve a seasonal home, workshop or boat shed with different needs. The special cases hub collects related guides. Take your time with the design, since a well-sized off-grid system runs quietly for years and a badly sized one teaches expensive lessons in February.