On a grid-tied house the battery is a convenience and the grid is the backstop. Off-grid, the battery bank is the grid, and the generator is the backstop. Those two components carry the reliability of the whole property, and they are where most of the money and most of the regret sit.
The battery bank
The bank is sized from your winter loads and the days of autonomy you want — see sizing an off-grid system for a BC winter for how that number is arrived at. Two details decide whether the headline capacity means anything.
- Usable capacity, not nameplate. What matters is how much you can actually take out without shortening the bank’s life. Lithium iron phosphate chemistry allows a far deeper regular discharge than traditional lead-acid, so a smaller nameplate can deliver more usable energy.
- Cycle life at your depth of discharge. A bank cycled gently every day lasts far longer than the same bank cycled hard. This is why an undersized bank is expensive twice — once when the generator runs to cover it, and again when it wears out early.
Lead-acid still shows up in off-grid quotes because the up-front number looks attractive. It also needs a ventilated space, tolerates deep discharge poorly, and in a flooded configuration wants periodic maintenance that somebody has to actually do at a property they visit occasionally. For most coastal BC builds, lithium wins on total cost over the life of the system even when it loses on day one.
Budget for PST on the bank. As we set out in off-grid rebates and taxes in BC, the provincial exemption covers panels, wiring, controllers and inverters — batteries are explicitly excluded and are taxable.
Cold, and where you put it
Lithium batteries must not be charged below freezing without integrated heating or a conditioned space. On a coastal property this is a design decision, not a detail: an unheated shed on the Sunshine Coast will go below zero, and a bank that refuses to accept charge on the coldest mornings of the year is a bank that fails exactly when you need it.
Plan the battery location for temperature, ventilation, and the ability to get equipment in and out later. Anything you have to dismantle a wall to replace will not get replaced on schedule.
The generator
An off-grid generator is not the same purchase as a jobsite unit or an emergency standby set. Three things separate a good one in this role.
- Automatic start and stop. The inverter/charger should start the generator on low state of charge and shut it down when the bank is charged. Manual starting is fine for a week and a problem for a decade.
- Sized to the charger, not the house peak. The battery, not the load, is what the generator is really feeding. An oversized generator loafing at very light load runs inefficiently and, on diesel, wet-stacks. It should run near a useful load and stop.
- Fuel you can actually resupply. Propane stores well and suits remote sites; diesel and gasoline have their own handling and shelf-life realities. On an island, the honest question is how the fuel gets there in February.
Service intervals matter more than people expect, because the hours accumulate in the months when getting a technician out is hardest. Build the maintenance into the plan at design time.
The inverter/charger ties it together
In a modern off-grid system the hybrid inverter/charger is the controller: it converts DC to AC for the house, manages charging from the array, decides when the generator runs, and enforces the limits that protect the bank. Its continuous and surge ratings need to cover your real starting loads — well pumps and compressors are the usual culprits — not just your average draw.
Monitoring is not optional
If the property is empty for stretches, remote monitoring is what turns a developing problem into a scheduled fix rather than a wasted trip or a frozen house. You want to see state of charge, generator run hours and any faults from your phone, before you drive up.
What we specify, and why
We size the bank from your December loads, choose chemistry on total cost over the system’s life rather than the day-one price, place it somewhere that stays above freezing and can be serviced, and set the generator to cover the genuinely bad stretches instead of building a bank large enough to never need one. Then we make the whole thing visible remotely.
Sources
- Government of B.C., Bulletin PST 203 — Energy Conservation — batteries excluded from the solar PST exemption.
AC or DC coupling
There are two ways to get solar energy into an off-grid battery, and the choice shapes the equipment list.
- DC coupling runs the array through a charge controller directly into the battery. Fewer conversion steps, generally more efficient, and the traditional off-grid approach.
- AC coupling puts a normal grid-type inverter on the array and ties it to the AC side. More flexible for retrofits and for larger arrays, at the cost of an extra conversion.
Plenty of good systems use both — DC-coupled for the main array, AC-coupled for a later addition. What matters is that the components are specified to work together and that whoever commissions the system configures the charge profile for your actual battery, not a default.
Certification and who does the work
Off-grid does not mean unregulated. The electrical work is still permitted work, and equipment still needs to be approved for use in Canada. Ask directly whether the components carry recognised certification and who is pulling the permit — on a remote property it is tempting to let this slide, and it is precisely where insurance claims and resale problems originate.
It also matters for safety in a way that is easy to underestimate. A large battery bank stores a great deal of energy in a small space, and the protection, disconnects and wiring around it are not the place to economise.
Commissioning, and the first winter
An off-grid system is not finished when it is installed; it is finished when it has been through a winter and the settings have been adjusted to how the property is actually used.
- Verify the generator auto-start actually triggers at the state of charge you agreed, and that it stops when it should.
- Check the charge profile matches the battery manufacturer’s specification, including any temperature compensation.
- Confirm low-temperature charge protection behaves as expected before the first cold snap, not during it.
- Establish what normal looks like on the monitoring, so an abnormal reading is recognisable later.
Planning for replacement
Panels and inverters are long-lived; the battery bank is the component with a definite service life, and it is the one that will need replacing while you still own the property. Designing for that day is cheap at the outset and expensive to retrofit.
Leave physical access and clearance so a bank can be removed and replaced without dismantling the building around it. Choose a chemistry and format likely to still be obtainable in a decade. And keep the as-built documentation, because the person specifying the replacement — possibly not us, possibly not you — will need to know exactly what was there.
Maintenance that actually gets done
The realistic maintenance plan for a remote property is the one someone will actually perform. Generator servicing on hours rather than a calendar date, an annual look at terminals and connections, keeping the array clear of needles and moss, and a monitoring alert that reaches your phone. A plan more elaborate than that tends to be abandoned by the second year.
Frequently asked questions
How long will an off-grid battery bank last?
A well-specified lithium bank, cycled within its design limits and kept in a reasonable temperature range, should give many years of service — long enough that replacement is a planned event rather than a surprise. What shortens life is chronic deep discharge, charging outside the manufacturer’s temperature window, and a charge profile left on a generic default. All three are avoidable at design and commissioning.
How often will the generator actually run?
That is a design decision rather than a fixed property of the site. A larger array and bank mean fewer generator hours and a higher capital cost; a smaller system means more hours and more fuel. We set a target for a normal winter and size to it, then test the design against a bad winter. Anyone quoting a generator-hours figure without first knowing your loads is guessing.
Can I add more battery capacity later?
Sometimes, and it is easier if planned from the start. Mixing new and significantly older modules within one bank is generally poor practice, so the practical route is either designing headroom in at the outset or adding a separate, properly integrated bank later. Leaving physical space and electrical capacity for expansion costs very little during the initial build.
Do I need a generator at all?
Not strictly — you can size array and storage to cover even a poor coastal December without one. It is usually the more expensive path by a wide margin, because you are buying capacity to cover a handful of bad weeks that then sits idle for the rest of the year. Most well-designed coastal systems include a generator precisely so the rest of the system can be sized sensibly.
Designing an off-grid system for your property
This guide is one part of a bigger picture. Our off-grid and remote solar page sets out how we approach a whole system — array, storage, generator and monitoring — for cabins, islands and acreage across coastal BC, and the other guides in this series cover the grid-extension comparison, winter sizing, rebates and PST, and batteries and generators.