45 terms
Home energy glossary
kW vs kWh, COP, SEER2, net billing, PPA — every term you'll meet in a solar, battery, heat pump or EV quote, in one sentence each.
- AFUE
- Annual Fuel Utilization Efficiency: the share of a furnace or boiler's fuel that becomes useful heat over a season. 95% AFUE means 5% is lost.
- Air sealing
- Closing gaps and cracks in a home's envelope to stop conditioned air leaking out. Often the cheapest energy upgrade.
- Balance of system
- Everything in a solar installation other than the panels: inverters, racking, wiring, disconnects and monitoring.
- Battery round-trip efficiency
- The share of energy put into a battery that comes back out, typically around 85–95% for home lithium batteries.
- Blower door test
- A diagnostic that depressurises a home with a fan to measure and locate air leaks.
- BTU
- British thermal unit: the heat needed to raise one pound of water by 1°F. 3,412 BTU equals 1 kWh.
- Coefficient of performance (COP)
- Heat delivered divided by electricity used. A COP of 3 means three units of heat per unit of electricity.
- Cold-climate heat pump
- A heat pump designed and tested to keep heating efficiently at very low outdoor temperatures.
- Community solar
- A shared solar farm that subscribers buy into or lease from, receiving bill credits without panels on their own roof.
- Degradation rate
- The yearly decline in a solar panel's output, commonly around 0.5% per year.
- Demand charge
- A fee based on your highest rate of power use (kW) in a billing period, common for businesses and some home tariffs.
- Depth of discharge (DoD)
- How much of a battery's capacity is actually used. Many home batteries allow close to 100%.
- Ductless mini-split
- A heat pump with indoor wall or ceiling units connected to an outdoor unit by refrigerant lines, with no ductwork.
- Energy audit
- An inspection of a home's energy use and losses, from a DIY walkthrough to a professional assessment with diagnostics.
- ENERGY STAR®
- A US government-backed label identifying products that meet energy-efficiency specifications.
- Export rate / feed-in tariff
- The price your utility or retailer pays for solar electricity you send to the grid.
- Ground-source heat pump
- A heat pump that exchanges heat with the ground through buried loops; also called geothermal.
- Heat pump water heater
- A water heater that moves heat from surrounding air into the tank, using far less electricity than a resistance tank.
- HSPF2
- Heating Seasonal Performance Factor (2023 test procedure): a US heating efficiency rating for heat pumps. Higher is better.
- Induction cooking
- Cooking with a magnetic field that heats the pan directly; fast, precise and efficient.
- Interconnection
- The utility approval process to connect a solar or battery system to the grid.
- Inverter
- Converts the direct current (DC) from panels or batteries to the alternating current (AC) your home uses.
- kW (kilowatt)
- A rate of power — how fast energy is used or produced at a moment.
- kWh (kilowatt-hour)
- A quantity of energy: 1 kW for 1 hour. The unit on most electricity bills.
- Level 1 / Level 2 charging
- EV charging from a standard outlet (Level 1) or a 240 V / 208 V dedicated circuit (Level 2), which is several times faster.
- Microinverter
- A small inverter mounted under each solar panel, letting each panel work independently.
- Nameplate capacity
- A system's rated maximum output under standard test conditions, e.g. an 8 kW solar array.
- Net billing
- A solar compensation scheme where exports are credited at a rate lower than the retail price.
- Net metering
- Exports offset imports one-for-one at the retail rate, usually reconciled monthly or annually.
- Off-peak
- Hours when electricity is cheaper on a time-of-use plan, often overnight.
- Payback period
- Years until cumulative savings equal the upfront cost of an upgrade.
- Peak sun hours
- Hours per day of sunlight equivalent to 1,000 W/m² — the key input for solar production estimates.
- Phantom load
- Electricity drawn by devices when switched off or idle; also called standby power.
- Power purchase agreement (PPA)
- A contract to buy electricity from solar panels a company owns on your roof, at a set price per kWh.
- R-value
- Resistance to heat flow for insulation. Higher R-values insulate better.
- SEER2
- Seasonal Energy Efficiency Ratio (2023 test procedure): a US cooling efficiency rating. Higher is better.
- Self-consumption
- The share of your solar output used in your home rather than exported.
- Smart panel
- An electrical panel that monitors and controls individual circuits, useful for battery backup and load management.
- Solar lease
- A contract where you pay a fixed monthly fee to use solar panels owned by a company.
- Solar loan
- Financing that lets you own a solar system with little or no upfront payment.
- Standby power
- See phantom load.
- Thermal envelope
- The boundary between conditioned indoor space and the outdoors: walls, roof, floor, windows and doors.
- Time-of-use (TOU) rate
- An electricity plan where prices vary by time of day, rewarding use in off-peak hours.
- Virtual power plant (VPP)
- A network of home batteries, EVs or smart devices coordinated to support the grid, often with payments to participants.
- Watt (W)
- The basic unit of power. 1,000 W = 1 kW.