- Rapid shutdown
- A required feature that cuts voltage inside and near the array to a safe level shortly after it is triggered, so firefighters on a roof are not exposed to full string voltage. Matching labels tell responders how the system works.
- Open-circuit voltage
- The voltage a module or string shows with nothing connected to it. It climbs in cold weather, and designers use the corrected figure to make sure a string never exceeds what the inverter and conductors can tolerate.
- Temperature coefficient
- A percentage that says how much a module's voltage or power changes for each degree of temperature shift. Hotter cells make less voltage and power, which is why hot roofs and cold mornings are both design checks.
- Maximum power point tracking
- Electronics in an inverter or charge controller that keep adjusting the load on the array so it operates where voltage times current is highest. It recovers output as sun, shade and temperature change through the day.
- Microinverter
- A small inverter bolted behind a single module that converts its DC to AC right at the roof. Shade on one panel affects only that unit, and with no high-voltage DC string, rapid shutdown is simpler.
- Power optimizer
- A DC-to-DC converter attached to each module that adjusts its output before it reaches a central string inverter. It reduces shading losses and can supply the module-level shutdown the code calls for.
- Combiner box
- An enclosure where several string circuits are joined onto one output, usually with fuses or breakers for each string. It reduces the number of long home-run conductors and gives one place to isolate and test strings.
- Fire access pathway
- A clear, unobstructed strip on a roof running from eave to ridge so firefighters can walk up and ventilate. The array layout must leave these corridors, and conduit and equipment cannot sit across them.
- Ridge setback
- The strip of roof near the peak left free of modules to give firefighters ventilation room. Its depth depends on how much of the roof the array covers, so the coverage percentage is calculated before the layout is drawn.
- BESS-ready panel
- Service equipment in a new home arranged to accept a battery later, with reserved space, a suitable busbar and designated backup circuits. The point is to avoid tearing up finished work when a battery is added.
- Solar access roof area
- The portion of a building's roof that gets enough unshaded sun to be useful for panels. The Energy Code uses it to cap how large a required system can be and to decide when exceptions apply.
- Net energy metering
- A billing arrangement in which a customer's generation offsets or earns credit against power drawn from the grid. California rules for how exported energy is valued have changed over time, so the concept matters more than any one rate.
- Peak sun hours
- A way to express daily sunshine as the number of hours at a standard reference intensity. Multiplying system size by this figure and by losses gives expected daily energy, the starting point of most output estimates.
- Azimuth and tilt
- Azimuth is the compass direction a module faces and tilt is its angle from horizontal. In California, south-facing arrays at moderate tilt usually yield the most, and deviations are weighed against roof shape and shade.
- Roof standoff and flashing
- A post fastened into the rafter that lifts the rail above the roofing, sealed by a flashing that sheds water over the hole. It is the common weak point for leaks, so sealing order and fastener location matter.
- Drainback system
- A solar water heater in which the heat-transfer fluid empties into a reservoir whenever the pump stops. Because the collectors are dry on cold nights, freezing risk is reduced, and the piping must slope so it drains fully.
- Unglazed pool collector
- A simple black panel, often polymer, with no glass cover that heats pool water directly as it passes through. It works well at low temperature rises, so it suits swimming pools but not domestic hot water.
- Differential controller
- A thermal system control that compares collector temperature with tank temperature and starts the pump only when the collector is sufficiently warmer. It also shuts down the pump when gain stops, protecting efficiency.
