The Fundamental Difference
A grid-tied system uses the utility grid as its energy buffer. Surplus solar production flows out through a bi-directional meter, earning a credit; when the panels are not producing enough, the home draws from the grid. No batteries are required, though they can be added.
An off-grid system has no utility connection. All energy consumed must either come from the solar array at the moment of production or be drawn from a battery bank charged by previous production. The design must account for the longest realistic period of low solar generation — typically several overcast days in succession — without running out of stored energy.
Grid-Tied Systems
How They Work
The core components of a grid-tied system are the solar array, a grid-tie inverter, a production meter (or a combined bi-directional meter), and the connection to the utility distribution panel. The inverter converts the DC output of the panels to AC power matched precisely to the grid's frequency and voltage. Critically, grid-tie inverters are required by safety regulations to shut down during a utility outage — a feature called anti-islanding — to prevent energised wires from endangering utility workers.
Because of the anti-islanding requirement, a standard grid-tied system without batteries provides no power during a grid outage. The panels may be producing at full capacity while the sun shines, but the inverter will not operate. This is one of the primary reasons homeowners in Canada choose to add battery storage to grid-tied systems.
Net Metering in Canadian Provinces
Net metering programs allow grid-tied system owners to receive credits for surplus energy exported to the grid. The terms differ substantially by province:
- Ontario: The Independent Electricity System Operator (IESO) Net Metering regulation allows residential systems up to 10 kW (or up to 500 kW for larger properties) to net meter. Credits offset future consumption at the retail electricity rate. Unused monthly credits roll forward; any annual surplus is forfeited rather than paid out in cash. IESO net metering details.
- British Columbia: BC Hydro operates a net metering program for systems up to 100 kW. Annual surplus credits are paid at a wholesale generation rate — significantly below the retail rate used for offsetting consumption.
- Alberta: Alberta's micro-generation regulation allows systems up to 5 MW. Surplus credits are calculated at the hourly pool price, which fluctuates. This creates variability in the financial return on exported energy.
- Quebec: Hydro-Québec offers a net metering option for residential systems up to 50 kW, with annual surplus credited at a set generation rate.
Grid-Tied with Battery Backup
Adding a battery bank to a grid-tied system requires a hybrid inverter (also called a storage-ready or AC-coupled inverter) capable of managing three energy flows: solar generation, grid import/export, and battery charge/discharge. Systems such as the Tesla Powerwall, Enphase IQ Battery, and SolarEdge Energy Bank are designed specifically for this topology and include integrated software for managing those flows.
With a properly designed hybrid system, the home can continue operating during a grid outage using solar generation and battery storage. The size of the battery determines how long the home can sustain critical loads without grid power.
Off-Grid Systems
Design Constraints
Off-grid design is driven by two worst-case scenarios: the home's daily energy consumption and the lowest number of consecutive days of useful solar production the battery bank must bridge. In most of Canada, designers target a 3–5 day autonomy period for sizing the battery bank, though northern or high-latitude installations may extend this.
The solar array must be sized to fully recharge the batteries within a reasonable period after the autonomy buffer is consumed. This typically means an off-grid array is 20–40% larger than a grid-tied array serving the same home, purely because there is no grid to compensate for shortfalls.
Battery Technologies
Two technologies dominate residential off-grid battery banks in Canada:
- Flooded lead-acid (FLA): The lowest upfront cost per kilowatt-hour of storage. FLA batteries require regular maintenance — periodic equalisation charges, electrolyte top-up with distilled water, and good ventilation because they off-gas hydrogen during charging. Usable capacity is typically limited to 50% of rated capacity to maintain cycle life. At 50% depth of discharge, well-maintained FLA batteries deliver 500–800 cycles.
- Lithium iron phosphate (LFP): Higher upfront cost but 80–90% usable depth of discharge, 3,000–6,000 cycles at full depth, and no maintenance beyond monitoring. LFP chemistry is significantly safer than other lithium variants (cobalt-based) because it does not undergo thermal runaway under most fault conditions. Most manufacturers now include battery management systems (BMS) that handle cell balancing and charge control. NRCan energy storage information.
For new off-grid installations in Canada, LFP has become the default choice despite higher initial cost. The longer cycle life means the cost per kWh delivered over the system's life is often lower than FLA when a full lifecycle analysis is applied.
Off-Grid Inverters and Charge Controllers
Off-grid inverters are bidirectional: they invert DC battery power to AC for home loads and also rectify AC generator power to charge the battery bank when available. Leading units from Schneider Electric, Outback Power, and Victron Energy combine inverter, charger, and system monitoring functions. Most support generator auto-start, allowing a backup propane or diesel generator to run automatically when battery state of charge drops below a set threshold.
Solar charge controllers regulate the flow of current from the array into the battery bank. MPPT (Maximum Power Point Tracking) controllers are standard in all competently designed systems because they extract 10–30% more energy from the array than older PWM (Pulse Width Modulation) controllers, particularly in cold temperatures where panel voltage rises.
Backup Generation
All viable Canadian off-grid residential systems include a backup generator. Extended cloudy periods occur in every province; a generator ensures the home does not run out of power. Typical off-grid homes consume generator fuel for 200–500 hours per year, depending on location and battery bank size. Propane generators are common because propane is widely available and stores indefinitely — unlike diesel, which degrades in cold storage.
Cost Comparison Overview
| Parameter | Grid-Tied (No Battery) | Grid-Tied + Battery | Off-Grid |
|---|---|---|---|
| Typical system cost (5 kW) | $12,000–$18,000 | $20,000–$32,000 | $30,000–$55,000+ |
| Grid access required | Yes | Yes | No |
| Power during outage | No | Yes (limited) | Yes |
| Utility bill impact | High reduction | High reduction + backup | No utility bill |
| Maintenance complexity | Low | Moderate | High |
Which Configuration Applies Where
Grid-tied systems — with or without batteries — are appropriate for any home within the utility service territory that wants to reduce electricity costs and potentially earn net metering credits. They are also the right choice for homeowners who prioritise lower upfront cost and minimal ongoing maintenance.
Off-grid systems are appropriate for properties beyond the utility service boundary, typically rural or remote properties where the cost of a utility line extension would be prohibitive. In British Columbia, for instance, BC Hydro has published service extension cost estimates in the range of $25,000–$100,000+ per kilometre; for properties several kilometres from the nearest distribution line, off-grid solar is often less expensive than a grid connection even before accounting for ongoing energy savings.
Off-grid systems also suit homeowners who have a strong preference for energy independence, provided they understand and accept the ongoing responsibilities of system management, battery maintenance, and generator operation.