Solar PV system design

Solar PV design works out how much of a roof or site can carry panels, how much energy they are likely to produce and how to connect them safely to the building and the utility. We design grid-connected systems for commercial, institutional, agricultural and multi-unit residential buildings, including systems with battery storage, and coordinate the structural, fire and utility pieces that decide whether a project goes ahead.

Solar is a mature technology, and the panels themselves are rarely the hard part. The work that decides whether a project performs is everything around them: whether the roof can carry the weight and will outlast the array, how snow and shading affect output across a Canadian year, where the inverters and disconnects go, and how the system connects to an electrical service that may already be close to capacity. Each province and utility also has its own rules for connecting generation and crediting exported energy.

What we design and build

• Feasibility reviews: usable roof or ground area, shading, orientation and a production estimate.
• Array layout, including setbacks and access paths for firefighters and maintenance.
• String and inverter design, DC and AC wiring, disconnects and rapid shutdown where required.
• The point of interconnection with the building's electrical service, and any upgrades it needs.
• Utility interconnection applications and the drawings they require.
• Battery storage integration for backup or demand reduction.
• Monitoring so you can see production and catch faults.

How a grid-connected system fits into the building

Panels produce direct current. An inverter converts it to alternating current that matches the building's supply, and the output connects to the building's distribution through a disconnect and a breaker or tap. The building uses the solar power first. When production is more than the building needs, the surplus flows out through the meter to the grid; at night or on dull days, the building imports from the grid as usual.

Because the system can send power back into wiring that people may be working on, the design includes clearly labelled disconnects, anti-islanding protection in the inverter so it stops when the grid is down, and rapid shutdown of rooftop conductors where the code requires it. The Canadian Electrical Code has specific requirements for renewable energy systems; check the current edition and your province's amendments.

How it works

1. Brief. We start by asking why: lower energy bills, an emissions target, a green building rating, resilience, or a requirement from a tenant or funder. The reason shapes the system size and whether storage makes sense.
2. Feasibility. We review roof area, orientation, shading, the age and condition of the roof, the electrical service and the utility's rules. A roof near the end of its life is usually replaced before the array goes on. A structural engineer confirms the roof can carry the array and the extra snow drifting it may cause.
3. Concept and estimate. We lay out the array, select equipment and model expected annual production. This gives you the numbers you need for a financial decision.
4. Design and interconnection. We prepare the electrical drawings, specifications and the utility's interconnection application. Drawings for permit are sealed by a licensed professional engineer where required.
5. Construction and commissioning. Installation is done by licensed electrical contractors under permit. We review submittals, visit site, and attend commissioning, including checks of the disconnects, rapid shutdown and monitoring.

What to have ready

• Roof drawings, the roof's age and any recent roof inspection report.
• Twelve months of utility bills, ideally with interval data.
• Existing single-line diagram and main switchboard details.
• Your goals for the system: energy offset, budget, storage, rating programs.

What you get

A feasibility summary with the usable area, a recommended system size and an estimated annual production. A design package with array layouts, the single-line diagram, wiring and equipment specifications, labelling and the interconnection documents the utility asks for. A commissioning checklist so you know the system was started up and tested properly, and record drawings that show what was built.

A typical case

A school board wants a rooftop array on a single-storey school with a large flat roof. The feasibility review finds that one wing has a roof replaced recently and the other is due for replacement within a few years, so the array is placed on the newer wing only, with space left for a second phase after the reroof. Rooftop mechanical units and their service paths take part of the area, and setbacks for fire access take more. The usable area, not the budget, ends up setting the system size.

The electrical review shows the main switchboard has no spare breaker space large enough for the inverter output, so the design uses a connection on the supply side of the main disconnect, which is permitted under specific conditions and needs utility agreement. The interconnection application goes in early, because utility review can take longer than the design. The school receives a production estimate by month, so staff can compare it with the monitoring data once the system is running.

Who it's for

• Owners of commercial, institutional and industrial buildings with large flat roofs.
• Condominium and rental building owners looking to lower common-area energy costs.
• Farms and rural sites with space for ground-mount arrays.
• Organizations with emissions or green building targets.

For background, read how a building solar PV system works, net metering and microgeneration in Canada, battery energy storage for buildings and snow loads on roofs.

Common questions