Solar glossary

The words on quotes and bills, in plain language.

Azimuth: The compass direction a roof or panel faces. In Canada, south-facing (about 180 degrees) usually produces the most energy over a year.
Battery backup: Using a home battery to power some or all circuits during a grid outage. It needs equipment that safely disconnects the home from the grid.
Curtailment: When a solar system produces less than it could because output is deliberately limited, for example by an inverter export limit or a utility requirement.
DC vs AC rating: The DC rating (kWp) is the combined capacity of the panels. The AC rating is the inverter's output limit. The two can differ, and both may appear on a quote.
Degradation: The gradual loss of panel output over time. Quality modern panels typically lose around 0.4 to 0.5% per year after the first year.
Delivery charges: The part of your electricity bill that pays for moving power through transmission and distribution lines. Some of these charges are fixed and remain after going solar.
Depth of discharge: How much of a battery's total capacity can be used before recharging. A battery with a higher usable depth of discharge gives you more usable kWh.
ESA: The Electrical Safety Authority, which oversees electrical permits and inspections in Ontario, including for rooftop solar systems.
Export: Solar electricity your home doesn't use at the moment it is produced, which flows out to the grid through your meter.
Interconnection: The process and agreement for connecting a solar system to the utility grid, including applications, approvals and any meter changes.
Inverter: The device that converts the DC electricity from solar panels into AC electricity your home and the grid can use.
IRR: Internal rate of return. A way to express a solar investment's return as an annual percentage, so it can be compared with other uses of your money.
Irradiance: The strength of sunlight reaching a surface, measured in watts per square metre. Higher irradiance means more power from your panels.
kW: Kilowatt, a measure of power, or the rate at which electricity is produced or used. Solar system sizes are described in kW.
kWh: Kilowatt-hour, a measure of energy. Using 1 kW for one hour equals 1 kWh. Your electricity bill charges you per kWh.
kWp: Kilowatt peak, the rated DC capacity of a set of solar panels under standard test conditions. A 7 kWp system has 7 kW of panels.
Load displacement: A solar setup designed to supply power used on site rather than to export it. Ontario systems taking the HRSP solar rebate must be load displacement and can't use net metering.
Microinverter: A small inverter mounted under each panel, so each panel works independently. It reduces the effect of shade and allows panel-level monitoring.
Net billing: An arrangement where exported power is credited at a set value, often lower than the price you pay to buy power, rather than one-for-one.
Net metering: An arrangement where exported solar power is credited against your bill. In Ontario, unused credits roll over for up to 12 months.
NPV: Net present value. The total value of future savings minus costs, adjusted for the fact that money today is worth more than money later.
Ontario Electricity Rebate: A provincial rebate applied to eligible Ontario electricity bills. It is 15.7% for prices effective November 1, 2026.
Payback period: The number of years it takes for a system's savings to equal what you paid for it, after any rebates.
Peak sun hours: The number of hours per day that sunlight averages a standard full intensity. It is a shorthand for how much solar energy a location receives.
Performance warranty: A manufacturer's guarantee that panels will still produce a minimum share of their original output after a set period, often 25 to 30 years.
Pitch: The slope or angle of a roof. Most common residential pitches work well for solar, and tilted panels shed snow more easily.
Power optimizer: A device under each panel that conditions its DC output before sending it to a central inverter, reducing losses from shade or mismatch.
Round-trip efficiency: The share of energy you get back from a battery compared with what you put in. Modern lithium batteries are typically around 90%.
Self-consumption: The share of your solar production that your home uses directly instead of exporting. Higher self-consumption matters most when exports earn little.
Setback: Required clear space on a roof, usually along ridges and edges, for fire access and safety. Setbacks reduce the area available for panels.
Shading loss: The reduction in output caused by shade from trees, chimneys or buildings. It can be significant, especially on string inverter systems.
String: A group of panels wired together in series and connected to one inverter input. Shade on one panel can reduce output across the whole string.
Tiered: An Ontario price plan with a flat price at any time of day, and a higher price once monthly use passes a set threshold.
TOU: Time-of-Use, Ontario's default price plan, with off-peak, mid-peak and on-peak prices depending on the time and day.
ULO: Ultra-Low Overnight, an Ontario price plan with very cheap power from 11 pm to 7 am and very expensive power from 4 to 9 pm on weekdays.