“Solar in Canada is a seasonal sport. Summer pays, but winter sets the rules. Margins are not waste. They are stability, silence, and fewer midnight alarms.” – MJ Martin
Sizing an Off grid System
Off grid power is not “solar panels plus batteries”, It is an energy budget, a power budget, and a winter reality check. In Canada, the limiting case is usually December and January, when days are short, sun angles are low, and snow can cover modules. A reliable design starts with two numbers: how many kilowatt hours you need each day, and how many watts you need at once. From there, you size the inverter for peak power, the batteries for autonomy, and the array for winter production, with margins that keep the system stable instead of fragile.
To keep the math concrete, this paper uses a reasonable off grid Canadian home profile: a well insulated house with efficient appliances, no electric space heat, and no electric water heating. Daily energy use is assumed at 10 kWh per day, which is typical for careful off grid living with a fridge, freezer, lighting, electronics, well pump, and occasional kitchen loads. We also assume you want two days of autonomy, meaning the home can run normally for two sunless days without needing emergency generator time. These assumptions are easy to scale up or down once you see the equations.
Any Home Can be Off Grid
The cover photo to this paper shows a friend’s rather large mansion outside of Toronto that I once helped to develop his desired off grid solution. It offered 5 wind turbines, its own telecommunications tower (not shown), 13 geothermal wells at the rear of the home, 2 fixed solar systems for heating water, and 4 sun tracking pedestal mounted solar arrays to harvest the sunshine (see below).
The solar panels had the arc of the sun for every day of the year programmed into the trackers for optimum alignment for 365 days and every second of sunshine. The trackers were accurate to within a 1/4 of a degree during all daylight hours for every day. A high speed snow dumping maneuver was programmed into the 2D trackers to shed accumulated snowfall too.
So, here are the steps required if you want to take your own home off grid:
Step 1: Build the Daily Energy Budget
Energy is measured in watt hours or kilowatt hours. Add up each load as watts times hours per day. A representative 10 kWh day might look like this in practice: refrigeration and freezer around 2 kWh, lighting 0.5 kWh with LEDs, electronics and networking 1 kWh, kitchen loads such as microwave, kettle, and dishwasher about 2 kWh combined if managed, laundry 1 kWh if not daily, well pump 0.5 kWh, and miscellaneous plug loads 3 kWh. The exact list varies, but the method does not. If your real number is 6 kWh per day or 20 kWh per day, the same steps apply. Once you have the daily total, add a design margin. A practical margin is 20 percent to cover seasonal behaviour changes, battery inefficiencies, and the days you entertain or run tools. So our design daily energy becomes 10 kWh × 1.2 = 12 kWh per day.
Step 2: Size the Inverter for Simultaneous Loads and Surges
Inverters are sized in watts or kilowatts for continuous output, and they also have a surge rating for short motor starts. The right way to size an inverter is to estimate the maximum simultaneous loads you will allow, then add headroom. In an off grid home, the peak often comes from kitchen appliances plus a pump or power tool. A realistic peak scenario might be: microwave 1.5 kW, kettle 1.5 kW, toaster 1.0 kW, fridge compressor 0.2 kW running, well pump 1.0 kW running, and miscellaneous loads 0.5 kW. That is 5.7 kW continuous if everything overlaps. You would not want to run at the edge of the inverter rating, because heat and voltage sag increase faults. Add 25 percent for stable operation, giving 5.7 kW × 1.25 = 7.1 kW.
Now check surge. Motors can draw several times their running power for a second or two. A common sizing approach is to ensure the inverter surge rating can cover motor starts with an additional margin. Motor starting kVA can be estimated from voltage and locked rotor amps when known, and many sizing guides recommend a 1.2 to 1.5 margin on calculated surge needs. In practice, for a home with a well pump and refrigeration, an 8 kW class inverter with a strong surge spec is a sensible target. Therefore, for this example, a 48 V, 8 kW inverter is a robust recommendation. If your home regularly runs two big kitchen appliances at once and a pump, consider 10 to 12 kW. If you are extremely disciplined with load scheduling, 6 kW can work.
Step 3: Size Battery Storage for Autonomy and Depth of Discharge
Battery sizing starts with energy, not power. Required usable battery energy equals daily energy times days of autonomy. We designed for 12 kWh per day and two days of autonomy, so usable storage needed is 12 × 2 = 24 kWh usable.
But batteries are not used to 100 percent. Lithium iron phosphate batteries are commonly designed around 80 to 90 percent usable depth of discharge for long life, while lead acid is often limited to about 50 percent. (MySolarSolutions) Off grid systems in Canada increasingly favour LiFePO4 for usable capacity, efficiency, and cold weather management, so assume 80 percent usable. Total nominal storage needed becomes 24 kWh ÷ 0.8 = 30 kWh.
Add another margin for winter capacity loss and aging. Batteries lose capacity in cold conditions and over years of cycling, and stable off grid design avoids planning on “brand new at room temperature.” A conservative additional 15 percent is reasonable for Canadian seasonal reality, so 30 kWh × 1.15 = 34.5 kWh. Round to 35 kWh nominal.
How many batteries is that? It depends on the module size you choose. If you use common 48 V, 100 Ah LiFePO4 modules, each is about 4.8 kWh nominal. 35 kWh ÷ 4.8 = 7.3 modules, so you would install 8 modules. If you use 5 kWh wall batteries, you would need 7 units. If you use 14 kWh class batteries, you would use 3 units for 42 kWh and enjoy extra buffer. The key takeaway is that a stable Canadian off grid home at this load level typically lands in the 30 to 45 kWh battery range.
Step 4: Size the Solar Array for Canadian Winter Production
Solar array sizing is where many systems fail, because designers size to annual averages instead of the worst month. Canada’s solar resource varies widely by location and season, and Natural Resources Canada provides mapping for photovoltaic potential and insolation across the country. (Natural Resources Canada) For off grid design, you generally size to the winter month you must survive, then accept that summer will overproduce.
A practical winter design assumption for much of southern Canada is about 2 peak sun hours per day in the darkest period, after you account for low sun angle and weather. Some published Canadian insolation [is the measure of solar energy – sunlight] references show low winter averages around this level for major cities. (N.A.P.S. Solar Store) Now add system losses. Between inverter losses, wiring, charge controllers, temperature effects, and imperfect orientation, a net system efficiency of 75 to 80 percent is a reasonable planning value for off grid.
Array power required equals daily energy ÷ (sun hours × efficiency). Using 12 kWh per day, 2.0 sun hours, and 0.75 efficiency gives: 12 ÷ (2.0 × 0.75) = 8.0 kW of PV. That is the array needed to meet the daily load in winter on an average winter day, not counting snow cover. Because snow and multi day storms are real, you add margin and you pair the system with a generator for resilience. If we add a further 25 percent PV margin, the design array becomes 8.0 × 1.25 = 10 kW.
How many panels is 10 kW? With modern 400 W panels, that is 10,000 W ÷ 400 W = 25 panels. With 450 W panels, it is about 23 panels. Roof area and racking matter, but this result surprises many people in a good way: a truly comfortable off grid Canadian home often needs on the order of two dozen full size panels, plus enough battery to carry nights and storms.
Putting the Example System Together
For a Canadian off grid home using 10 kWh per day, designed with 20 percent energy margin and two days of autonomy, a stable design would use an 8 kW 48 V inverter with strong surge capability, about 35 to 40 kWh of LiFePO4 battery storage, and about 10 kW of solar PV, which is roughly 25 panels at 400 W each. If your daily energy is higher, scale batteries and PV linearly. If your peak simultaneous loads are higher, increase inverter size. The single most important upgrade for reliability is to reduce electric heating loads and shift high draw activities to sunny hours. Finally, because Canada can deliver week long low sun events, most serious off grid homes still keep a generator as a backstop, not as a failure of solar, but as a form of practical engineering resilience.
About the Author:
Michael Martin is the Vice President of Technology with Metercor Inc., a Smart Meter, IoT, and Smart City systems integrator based in Canada. He has more than 40 years of experience in systems design for applications that use broadband networks, optical fibre, wireless, and digital communications technologies. He is a business and technology consultant. He was a senior executive consultant for 15 years with IBM, where he worked in the GBS Global Center of Competency for Energy and Utilities and the GTS Global Center of Excellence for Energy and Utilities. He is a founding partner and President of MICAN Communications and before that was President of Comlink Systems Limited and Ensat Broadcast Services, Inc., both divisions of Cygnal Technologies Corporation (CYN: TSX).
Martin served on the Board of Directors for TeraGo Inc (TGO: TSX) and on the Board of Directors for Avante Logixx Inc. (XX: TSX.V). He has served as a Member, SCC ISO-IEC JTC 1/SC-41 – Internet of Things and related technologies, ISO – International Organization for Standardization, and as a member of the NIST SP 500-325 Fog Computing Conceptual Model, National Institute of Standards and Technology. He served on the Board of Governors of the University of Ontario Institute of Technology (UOIT) [now Ontario Tech University] and on the Board of Advisers of five different Colleges in Ontario – Centennial College, Humber College, George Brown College, Durham College, Ryerson Polytechnic University [now Toronto Metropolitan University]. For 16 years he served on the Board of the Society of Motion Picture and Television Engineers (SMPTE), Toronto Section.
He holds three master’s degrees, in business (MBA), communication (MA), and education (MEd). As well, he has three undergraduate diplomas and seven certifications in business, computer programming, internetworking, project management, media, photography, and communication technology. He has completed over 60 next generation MOOC (Massive Open Online Courses) continuous education in a wide variety of topics, including: Economics, Python Programming, Internet of Things, Cloud, Artificial Intelligence and Cognitive systems, Blockchain, Agile, Big Data, Design Thinking, Security, Indigenous Canada awareness, and more.