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Air-Source Heat Pumps
Air-to-water heat pumps
A type of air-source heat pump that uses water, instead of air, in the distribution system and provides heat through a radiator or baseboard. View Image
Ducted
A heat pump that uses ductwork (connected to an indoor air-handling unit) as the indoor distribution. View Image
Ductless
Heat pumps that use refrigerant pipes as the indoor distribution. Small copper refrigerant pipes are connected to indoor units that each have their own heat exchanger and fan for circulating conditioned air. View Image
Indoor Unit
The part of an air-source heat pump that release hot air in the winter and cold air in the summer into a home. Indoor units can be ducted or ductless. Ductless options include wall, ceiling, or floor mounted units. View Image
Integrated Controls
The use of one system to control two separate heating systems. Integrated controls can be a single thermostat or multiple connected thermostats. Integrated controls are sometimes used when air-source heat pumps are used in conjunction with a backup heating system such as an oil or propane boiler.
Mini-splits
A common term used to describe a ductless air-source heat pump.
Multi-Zone
A heat pump where one outdoor unit connects to more than one indoor units. Multi-zone indoor units can include a mix of ducted and ductless units.
Outdoor Unit
The part of an air-source heat pump that is outside where the refrigerant absorbs heat in the winter and rejects heat in the summer to transfer heat between the indoors and the outdoors and condition the home.
Single-Zone
A heat pump where one outdoor unit connects to one indoor unit, which could be either a ducted air-handling unit or a ductless indoor unit. A home can have multiple single-zone systems.
Automated Wood Heat
Boiler
A fuel-burning apparatus or container for heating water. In an automated wood heating system, the boiler burns wood pellets.
Bulk Pellet Storage
A large container, usually a large canvas bag, that stores wood pellets before they are burned to generate heat. A residential bulk pellet storage container typically holds between three and five tons of pellets.
Thermal Storage
A system which stores thermal energy for use in supplementing or offsetting heating system output. A hot water tank is used for thermal storage in an automated wood heating system.
Wood pellets
Small pieces of dried and compressed wood. Wood pellets are burned instead of fossil fuels in an automated wood heating system.
Wood pellet boiler
A common term used to refer to automated wood heating systems. A wood pellet boiler is a boiler that burns wood pellets as the fuel.
Clean Energy Home Solutions
Air-Source Heat Pump
A heating and cooling system that transfers heat between the indoor and outdoor air to heat your home in the winter and cool your home in the summer.
Air-source heat pumps run on electricity instead of burning fossil fuels. Colloquially they are also referred to as “mini-split” or “ductless,” although these terms refer to a specific kind of air-source heat pump. View Image
Battery Storage
A device that stores energy in the form of chemical energy for use at a later time as electrical energy.
Electric Vehicle (EV)
A vehicle that uses electricity to charge a battery, which then discharges its energy to propel the vehicle. View Image
Ground-Source Heat Pump
A heating and cooling system that transfers heat between the earth and the indoors to heat your home in the winter and cool your home in the summer.
Ground-source heat pumps run on electricity instead of burning fossil fuels. Also called “Geothermal.” View Image
Heat Pump Clothes Dryer
A clothes dryer that reuses the heat used to dry clothing instead of venting it to the outdoors. All heat pump components are located inside the dryer and no connection to the outdoors, not even a vent, is needed. Heat pump clothes dryers run on electricity instead of burning fossil fuels.
Heat Pump Water Heater
A hot water heating system that transfers heat from the air (often in a basement or mechanical room) to a hot water tank to heat hot water. Heat pump water heaters run on electricity instead of burning fossil fuels. View Image
Induction Stove
An electric stovetop that uses magnetic fields to generate heat in cookware instead of generating heat from an electric resistance coil. Induction stoves are more efficient and offer more temperature control precision than traditional stoves. View Image
Solar Hot Water
A hot water system that uses heat from the sun to heat a fluid in solar collectors that is then circulated to a hot water tank where the fluid transfers heat for domestic hot water use (e.g., showers, washing dishes). Also called “Solar Thermal.” View Image
Solar Photovoltaics (PV)
Solar panels that use the sun’s radiation to generate electricity. View Image
Energy Efficiency
Air Sealing
The process of ensuring that there are as few gaps in a building’s envelope as possible for conditioned indoor air to escape and unconditioned outdoor air to get in. Air leakage in buildings can represent 5%-40% of space conditioning costs. Air sealing often involves sealing gaps in attics, crawl-spaces, and floor joists; re-sealing windows; replacing broken or jammed vents; and replacing the rubber seals around door frames.
Ductwork Upgrades
Air sealing and insulating ductwork to improve the efficiency of a heating and cooling system by ensuring that more of the heated or cooled air gets delivered to where it is needed.
Energy Efficiency
The concept of using less energy to perform the same work. Weatherization is an important type of residential energy efficiency. Other examples include using more efficient lighting and appliances.
Insulation
The material used to slow heat transfer through the building envelope (walls, roof, floors, etc.). Common types of insulation include fiberglass, cellulose, and foam board.
Programmable Thermostat
A thermostat that can be set to adjust the temperature of a home based on the time of day and week, in order to use less energy when it is not needed.
Weatherization
The process of making a home better protected from extreme weather, which often involves sealing up air leaks and adding insulation in your home.
General
Boiler
A fuel-burning apparatus or container for heating water, typically used for home heating and/or hot water.
Carbon Footprint
The total greenhouse gas (GHG) emissions caused by an individual, event, organization, service, or product.
Clean Energy
Technologies that significantly reduce or eliminate the use of energy from non-renewable sources through efficiency or conservation or by producing energy from the sun, wind, water, biomass, or any renewable, non-depletable or recyclable fuel.
Electric Resistance Heating
Heating systems which produce thermal energy by passing an electric current through a high resistance material, converting electrical energy into heat. Electric resistance heating is not as efficient as heat pumps, another heating solution that runs on electricity.
Electrical Service
The amount of amperage that your electrical panel can handle, or the amount of electricity your electric panel is able to distribute. A fully electrified home typically needs 200-amp electrical service.
Fossil Fuels
A non-renewable fuel source that is formed in the earth from plant or animal remains. Fossil fuels include oil, natural gas, propane, and coal.
Greenhouse Gas (GHG) Emissions
A gas that traps heat in Earth’s atmosphere. Carbon dioxide and methane are examples of greenhouse gases.
Heat Load Calculation
A calculation done to determine a building’s heating and cooling capacity needed for a heating and cooling unit under design conditions. The size, orientation, and amount of weatherization, doors, windows and thickness of walls, windows, and doors is used to determine a building’s heat load calculation.
Heat Pump
Equipment that transfers heat from a colder area to a hotter area by absorbing heat from a cold space and transferring it to a warmer space using the refrigeration cycle.
Manual J
A methodology developed by the Air Conditioning Contractors of America (ACCA) to do a heat load calculation.
Net Zero Emissions
When the total amount of greenhouse gas emissions is equal to or less than the amount of carbon dioxide or its equivalent that is removed from the atmosphere and stored in Earth’s systems annually. The Commonwealth aims to be net zero emissions by 2050.
Refrigeration Cycle
The process of moving refrigerants through a loop to transfer heat from one place to another. Refrigeration cycles can work to move heat in a home in the winter and also move heat out of a home in the summer.
Thermal Storage
A system that stores thermal energy for use in supplementing or offsetting heating system output.
Ground-Source Heat Pumps
Closed Loop
A type of vertical loop-ground source heat pump system where the loop field system circulates an anti-freeze solution through underground pipes. The anti-freeze solution inside the pipes is never mixed with groundwater underground.
Geothermal
A common term used to describe ground-source heat pumps. This term can also refer to energy obtained by tapping underground reservoirs of heat, usually near volcanoes or other hot spots on the surface of the Earth.
Horizontal Loop
A type of ground-source heat pump system where the outdoor heat exchanger is a loop field laid out horizontally, typically at a depth of around eight to ten feet underground.
Loop Field
A loop field is the system of pipes that are run underground to act as the heat exchanger for a ground-source heat pump system. The constant temperature of the ground is used to warm the loop fluid in the winter and cool the loop fluid in the summer to increase the efficiency of the heating and cooling system. The loop field can be at a depth of eight feet in a horizontal loop or hundreds of feet deep in a vertical loop.
Open Loop
A type of vertical loop ground-source heat pump system where the loop field system exchanges water directly with an underground well. Ground water is returned to the well after passing through the heat pump.
Vertical Loop
A type of ground-source heat pump system where the outdoor heat exchanger is an underground loop field drilled hundreds of feet into the group in one or more boreholes.
Organizations
DOER
The Massachusetts Department of Energy Resources (DOER) is a state agency that develops and implements policies and programs aimed at ensuring the adequacy, security, diversity, and cost-effectiveness of the Commonwealth’s energy supply to create a clean, affordable, and resilient energy future.
Energy New England (ENE)
A municipal light plant cooperative owned by light departments of Braintree, Taunton, Concord, Hingham, and Wellesley, Massachusetts that serves as a wholesale risk management and energy trading organization serving the needs of municipal utilities in the northeast, including managing their power supplies and promoting conservation, efficiency, and environmental stewardship.
Energy Star
The federal government-backed symbol for energy efficiency.
Executive Office of Energy and Environmental Affairs (EEA)
A cabinet-level office that oversees Massachusetts’ environmental and energy agencies.
Green Energy Consumers Alliance
A non-profit that serves Massachusetts and Rhode Island residents with a mission to harness the power of consumers to speed the transition to a low-carbon future.
MassCEC
The Massachusetts Clean Energy Center (MassCEC) is a state economic development agency dedicated to accelerating the growth of the clean energy sector to meet the Commonwealth’s clean energy, climate, and economic development goals.
Mass Save
Collaborative of Massachusetts’ natural gas, electric utilities, and energy efficiency service providers to help Massachusetts’ residents save money and energy through energy efficiency measures.
MMWEC
The Joint Action Agency for Massachusetts municipal utilities, delivering the wholesale power supply, financial, risk management and other services needed by municipal utilities to participate effectively in today’s electric utility industry.
Muni HELPS
An MMWEC program that delivers free home energy audits and innovative energy technology to MMWEC customers.
Northeast Energy Efficiency Partnership
Northeast Energy Efficiency Partnership (NEEP) is a non-profit accelerating energy efficiency in the Northeast and Mid-Atlantic states. It is one of six Regional Energy Efficiency Organizations (REEOs) funded, in part, by US Department of Energy to support state efficiency policies and programs.
Solar Hot Water
Evacuated Tube
Solar collectors with thin, copper tubes filled with fluid, inside a vacuum-sealed clear glass plastic tube. Evaporated tube collectors typically perform better during the winter than flat plate collectors, but they are not as efficient at warmer temperatures. View Image
Flat Plate
Solar collectors with a clear glass or plastic casing over a dark metal collector with embedded copper tubes with fluid inside. Flat plate collectors traps heat like a greenhouse.
Flat plate collectors can operate at a wide range of temperatures. View Image
Ground Mounted
Solar collectors mounted on the ground often near a building. Collectors are tilted on the ground to optimize solar exposure. View Image
Roof Mounted
Solar collectors mounted on the roof of a building. Collectors are generally mounted directly to the roof, but sometimes they are tilted up at a different angle (especially on flat roofs) to optimize their solar exposure. View Image
Solar Collectors
Solar collectors are devices that collect solar radiation from the sun. These devices are primarily used for heating water for personal use. These collectors are often mounted on the roof, although they can also be mounted on the ground or on the side of a building. View Image
Wall Mounted
Solar collectors mounted on the side of a building. Collectors can be mounted flush to the wall or tilted at a different angle to optimize solar exposure (sometimes called an awning mount). View Image
Solar Photovoltaics (PV)
Alternating Current (AC)
Alternating current (AC) is an electrical current that can flow in both directions. This is the type of electricity supplied by electric utilities in the United States.
Community Solar
Community solar makes it possible for households who can’t install solar panels where they live to benefit from solar energy and avoid the large up-front costs associated with installing solar. It is ideal for homes without sufficient roof space or sun exposure, renters, condo owners, or homeowners who want electricity at a low cost. By subscribing to a community solar project or buying a portion of the panels, these customers can power their homes with low-cost clean energy and support clean energy deployment. They can also receive net metering credits or offsets towards their electric bill.
Direct Current (DC)
Direct current (DC) is an electrical current that flows in one direction. This is the kind of power that solar panels produce, and it needs to be converted into Alternating Current (AC) before being used in homes and buildings.
Direct Ownership
Direct ownership is where a customer pays an installer upfront to install a solar energy system on the customer’s property. This option requires upfront cash or a loan, and a quality project site with appropriate solar access. With direct ownership, the customer owns, operates, and is typically responsible for maintaining the system. The customer also typically retains sole ownership over the energy, environmental incentives, and tax credits that the system generates.
Distribution
The delivery of electricity from the high-voltage transmission network to individual homes and businesses through local substations and powerlines.
Electrical Panel
The electrical panel is where electricity enters a building – from either the solar panels or the utility grid. The electrical panel will automatically draw additional power from the utility when the solar PV system is unable to meet the building’s electricity demand. If the solar electric system is producing more electricity than needed, the electrical panel will send the excess electricity to the utility grid through a device called a net meter.
Grid Connection
In a grid-connected solar electric system, a building’s solar panels are connected to the local utility’s electrical grid. The building can continue to get some or all of its electricity from the grid. It can also “export” energy from its PV system to the grid when the PV produces more than the building needs.
Interconnection
Interconnection is when a solar system is connected to the electric grid. Interconnection may depend on utility inspection of the solar setup to ensure that it meets technical, performance, and safety standards, as well as a wiring inspection.
Inverter
The inverter converts the direct current (DC) electricity produced by the panels into alternating current (AC) electricity, which is the form that can be used in the building. Inverters include a range of technologies, from central inverters that convert the electricity from many solar panels, to microinverters that are attached to each individual panel in a system. In grid-connected systems, inverters are designed so that if power from the utility goes down, the PV system will shut down, too – a critical safety precaution for utility workers and public safety personnel.
Investor-Owned Utility
An Investor-Owned Utility (IOU) is a private company that provides utility services—such as electricity, natural gas, or water—with the primary goal of generating profits for its shareholders. Unlike municipal or cooperative utilities, IOUs are for-profit corporations and are regulated by the Department of Public Utilities (DPU) in Massachusetts. The investor-owned electric and gas utilities in MA are National Grid, Eversource, Unitil, Liberty Utilities and Berkshire Gas.
Kilowatt (kW)
A kilowatt (kW) is a unit of electrical power equal to 1,000 watts. It is commonly used to measure a solar system’s maximum output or capacity. For example, a 5 kW solar panel system can produce up to 5 kilowatts of power under ideal conditions.
Kilowatt Hour (kWh)
A kilowatt hour (kWh) measures energy usage over time. It represents the energy produced or consumed at a rate of one kilowatt over one hour. In the context of solar, kWh describes how much energy a solar system produces or how much energy your home consumes over time.
Megawatt (MW)
A megawatt (MW) is a unit of electrical power equal to one million watts. It is commonly used to measure a solar system’s maximum output or capacity, especially for larger projects, like solar farms.
Municipal Light Plant (MLP)
Municipalities may own, maintain and operate a municipal light plant (MLP) in order to provide electric and/or gas services to their citizens. The MLP provides both distribution and supply services to its customers. Generally, MLPs are run by municipal light boards or commissions in a municipality, or by the mayor/select board. The Department of Public Utilities’ role in regulating MLPs is limited since MLP’s rates are set by municipal officials.
Net Metering
A billing mechanism that credits solar energy system owners for the electricity they add to the grid. If the solar electric system is under 10 kW and generates extra power beyond what the system owner can use, the owner can sell the excess back to the utility through net metering. The owner will then get credit on their bill for this excess power. They are billed for the difference between the amount of the electricity used and the amount created, also called the “net.” When the system owner creates more than they use, it’s documented on their electric bill as net metering credits and applied towards future bills.
Panel
Panels are made up of a series of individual solar cells that convert sunlight into direct current (DC) electricity. The higher the intensity of the sunlight striking the panels, the more electricity they produce. Once the electricity is produced, it flows to the inverter.
Payback Period
The payback period of a solar system represents how many years it takes for the system’s savings to match the initial costs. After the payback period, the customer fully owns the system. They can continue to receive earn-as-you-produce incentives and use the electricity generated by the system to power their home.
Photovoltaic (PV)
Photovoltaics (PV) gets its name from the process of converting light (photons) to electricity (voltage), which is called the photovoltaic effect. “Solar cells” may also be called “photovoltaic cells,” and they convert sunlight directly into electricity.
Power Purchase Agreement (PPA)
A PPA is similar to a solar lease, in that the solar company will own and operate the system on the homeowner’s roof. Rather than a fixed monthly payment, however, the homeowner agrees to purchase the electricity generated by the system at an agreed-upon per-kilowatt-hour price, often lower than typical utility rates. Like a solar lease, a PPA allows a homeowner to begin saving money immediately, with little or no up-front cost. When considering a solar lease or PPA, review the contract carefully to understand all terms and conditions.
Solar Massachusetts Renewable Target (SMART)
SMART is an earn-as-you-produce incentive that is paid directly by investor-owned utilities in Massachusetts to solar electric system owners. If eligible, customers can receive incentive payments for the solar electricity produced by their panels for 20 years after installation. SMART was launched by the Department of Energy Resources (DOER) in conjunction with investor-owned utilities. The selected Solar Program Administrator, CLEAResult, accepts and processes applications. The customer’s installer will apply to the SMART program on their behalf and should help navigate obtaining incentives through the program. Please see the DOER SMART website and the program administrator’s SMART website for more information. Residents of towns with a Municipal Light Plant (MLP) are unable to participate in SMART.
Solar Lease
Under a solar lease, a property owner agrees to pay a pre-determined monthly bill to a solar company, which installs, owns and operates the solar electric system. The property owner then has access to the electricity generated by the system, lowering their monthly utility bill. A solar lease provides the opportunity for a homeowner to benefit from solar electricity with little or no up-front cost.
Solar Loan
Many homeowners opt to take out a loan to finance a solar electric system purchase. Financing a solar electric installation through loans provides the system owner with many of the benefits of a direct purchase with a lower up-front investment, though interest payments and other fees may apply. In recent years, loans dedicated to solar installations have become popular in Massachusetts.
Solar Renewable Energy Certificate (SREC)
A Solar Renewable Energy Certificate (SREC) is a type of Renewable Energy Certificate (REC) that is specifically designated for energy output from eligible solar photovoltaic (PV) systems. The SREC program was replaced by SMART in 2018. To learn more about SRECs, visit MassCEC’s website.
Third Party Ownership
Third-party ownership is where a third-party installs, owns, operates, and maintains the system on a customer’s home or business. Third-party ownership can be a good option for customers who don’t choose to or are unable to pay up front for a solar energy system. There are two types of third-party ownership: solar leases and power purchase agreements (PPAs). You can learn more about each of these models through their definitions in this glossary.
Transmission
The process of transporting electricity from any source, including solar electric systems, to consumers through high-voltage power lines and substations.
Watt
A unit of electrical power measuring the rate at which energy is transferred or consumed, equivalent to one joule of energy per second.
A
Air Sealing
The process of ensuring that there are as few gaps in a building’s envelope as possible for conditioned indoor air to escape and unconditioned outdoor air to get in. Air leakage in buildings can represent 5%-40% of space conditioning costs. Air sealing often involves sealing gaps in attics, crawl-spaces, and floor joists; re-sealing windows; replacing broken or jammed vents; and replacing the rubber seals around door frames.
Air-Source Heat Pump
A heating and cooling system that transfers heat between the indoor and outdoor air to heat your home in the winter and cool your home in the summer. Air-source heat pumps run on electricity instead of burning fossil fuels. Colloquially they are also referred to as “mini-split” or “ductless,” although these terms refer to a specific kind of air-source heat pump. View Image
Air-to-water heat pumps
A type of air-source heat pump that uses water, instead of air, in the distribution system and provides heat through a radiator or baseboard. View Image
Alternating Current (AC)
Alternating current (AC) is an electrical current that can flow in both directions. This is the type of electricity supplied by electric utilities in the United States.
B
Battery Storage
A device that stores energy in the form of chemical energy for use at a later time as electrical energy.
Boiler
A fuel-burning apparatus or container for heating water, typically used for home heating and/or hot water.
C
Carbon Footprint
The total greenhouse gas (GHG) emissions caused by an individual, event, organization, service, or product.
Clean Energy
Technologies that significantly reduce or eliminate the use of energy from non-renewable sources through efficiency or conservation or by producing energy from the sun, wind, water, biomass, or any renewable, non-depletable or recyclable fuel.
Closed Loop
A type of vertical loop-ground source heat pump system where the loop field system circulates an anti-freeze solution through underground pipes. The anti-freeze solution inside the pipes is never mixed with groundwater underground.
Community Solar
Community solar makes it possible for households who can’t install solar panels where they live to benefit from solar energy and avoid the large up-front costs associated with installing solar. It is ideal for homes without sufficient roof space or sun exposure, renters, condo owners, or homeowners who want electricity at a low cost. By subscribing to a community solar project or buying a portion of the panels, these customers can power their homes with low-cost clean energy and support clean energy deployment. They can also receive net metering credits or offsets towards their electric bill.
D
Direct Current (DC)
Direct current (DC) is an electrical current that flows in one direction. This is the kind of power that solar panels produce, and it needs to be converted into Alternating Current (AC) before being used in homes and buildings.
Direct Ownership
Direct ownership is where a customer pays an installer upfront to install a solar energy system on the customer’s property. This option requires upfront cash or a loan, and a quality project site with appropriate solar access. With direct ownership, the customer owns, operates, and is typically responsible for maintaining the system. The customer also typically retains sole ownership over the energy, environmental incentives, and tax credits that the system generates.
Distribution
The delivery of electricity from the high-voltage transmission network to individual homes and businesses through local substations and powerlines.
DOER
The Massachusetts Department of Energy Resources (DOER) is a state agency that develops and implements policies and programs aimed at ensuring the adequacy, security, diversity, and cost-effectiveness of the Commonwealth’s energy supply to create a clean, affordable, and resilient energy future.
Ducted
A heat pump that uses ductwork (connected to an indoor air-handling unit) as the indoor distribution. View Image
Ductless
Heat pumps that use refrigerant pipes as the indoor distribution. Small copper refrigerant pipes are connected to indoor units that each have their own heat exchanger and fan for circulating conditioned air. View Image
Ductwork Upgrades
Air sealing and insulating ductwork to improve the efficiency of a heating and cooling system by ensuring that more of the heated or cooled air gets delivered to where it is needed.
E
Electrical Panel
The electrical panel is where electricity enters a building – from either the solar panels or the utility grid. The electrical panel will automatically draw additional power from the utility when the solar PV system is unable to meet the building’s electricity demand. If the solar electric system is producing more electricity than needed, the electrical panel will send the excess electricity to the utility grid through a device called a net meter.
Electric Resistance Heating
Heating systems which produce thermal energy by passing an electric current through a high resistance material, converting electrical energy into heat. Electric resistance heating is not as efficient as heat pumps, another heating solution that runs on electricity.
Electrical Service
The amount of ampage that your electrical panel can handle, or the amount of electricity your electric panel is able to distribute. A fully electrified home typically needs 200-amp electrical service.
Electric Vehicle (EV)
A vehicle that uses electricity to charge a battery, which then discharges its energy to propel the vehicle. View Image
Energy Efficiency
The concept of using less energy to perform the same work. Weatherization is an important type of residential energy efficiency. Other examples include using more efficient lighting and appliances.
Energy New England (ENE)
A municipal light plant cooperative owned by light departments of Braintree, Taunton, Concord, Hingham, and Wellesley, Massachusetts that serves as a wholesale risk management and energy trading organization serving the needs of municipal utilities in the northeast, including managing their power supplies and promoting conservation, efficiency, and environmental stewardship.
Energy Star
The federal government-backed symbol for energy efficiency.
Evacuated Tube
Solar collectors with thin, copper tubes filled with fluid, inside a vacuum-sealed clear glass plastic tube. Evaporated tube collectors typically perform better during the winter than flat plate collectors, but they are not as efficient at warmer temperatures. View Image
Executive Office of Energy and Environmental Affairs (EEA)
A cabinet-level office that oversees Massachusetts’ environmental and energy agencies.
F
Flat Plate
Solar collectors with a clear glass or plastic casing over a dark metal collector with embedded copper tubes with fluid inside. Flat plat collectors traps heat like a greenhouse. Flat plate collectors can operate at a wide range of temperatures. View Image
Fossil Fuels
A non-renewable fuel source that is formed in the earth from plant or animal remains. Fossil fuels include oil, natural gas, propane, and coal.
G
Geothermal
A common term used to describe ground-source heat pumps. This term can also refer to energy obtained by tapping underground reservoirs of heat, usually near volcanoes or other hot spots on the surface of the Earth.
Green Energy Consumers Alliance
A non-profit that serves Massachusetts and Rhode Island residents with a mission to harness the power of consumers to speed the transition to a low-carbon future.
Greenhouse Gas (GHG) Emissions
A gas that traps heat in Earth’s atmosphere. Carbon dioxide and methane are examples of greenhouse gases.
Grid Connection
In a grid-connected solar electric system, a building’s solar panels are connected to the local utility’s electrical grid. The building can continue to get some or all of its electricity from the grid. It can also “export” energy from its PV system to the grid when the PV produces more than the building needs.
Ground Mounted
Solar collectors mounted on the ground often near a building. Collectors are tilted on the ground to optimize solar exposure. View Image
Ground-Source Heat Pump
A heating and cooling system that transfers heat between the earth and the indoors to heat your home in the winter and cool your home in the summer. Ground-source heat pumps run on electricity instead of burning fossil fuels. Also called “Geothermal.” View Image
H
Heat Load Calculation
A calculation done to determine a building’s heating and cooling capacity needed for a heating and cooling unit under design conditions. The size, orientation, and amount of weatherization, doors, windows and thickness of walls, windows, and doors is used to determine a building’s heat load calculation.
Heat Pump
A heat pump is an electric appliance that can replace both your traditional air conditioner and home heating system (like a furnace or boiler). Heat pumps use electricity to move heat from one place to another, rather than creating it. That makes heat pumps much more energy efficient than their fossil fuel counterparts.
Heat Pump Clothes Dryer
A clothes dryer that reuses the heat used to dry clothing instead of venting it to the outdoors. All heat pump components are located inside the dryer and no connection to the outdoors, not even a vent, is needed. Heat pump clothes dryers run on electricity instead of burning fossil fuels.
Heat Pump Water Heater
A hot water heating system that transfers heat from the air (often in a basement or mechanical room) to a hot water tank to heat hot water. Heat pump water heaters run on electricity instead of burning fossil fuels. View Image
Horizontal Loop
A type of ground-source heat pump system where the outdoor heat exchanger is a loop field laid out horizontally, typically at a depth of around eight to ten feet underground.
I
Indoor Unit
The part of an air-source heat pump that release hot air in the winter and cold air in the summer into a home. Indoor units can be ducted or ductless. Ductless options include wall, ceiling, or floor mounted units. View Image
Induction Stove
An electric stovetop that uses magnetic fields to generate heat in cookware instead of generating heat from an electric resistance coil. Induction stoves are more efficient and offer more temperature control precision than traditional stoves. View Image
Insulation
The material used to slow heat transfer through the building envelope (walls, roof, floors, etc.). Common types of insulation include fiberglass, cellulose, and foam board.
Integrated Controls
The use of one system to control two separate heating systems. Integrated controls can be a single thermostat or multiple connected thermostats. Integrated controls are sometimes used when air-source heat pumps are used in conjunction with a backup heating system such as an oil or propane boiler.
Interconnection
Interconnection is when a solar system is connected to the electric grid. Interconnection may depend on utility inspection of the solar setup to ensure that it meets technical, performance, and safety standards, as well as a wiring inspection.
Inverter
The inverter converts the direct current (DC) electricity produced by the panels into alternating current (AC) electricity, which is the form that can be used in the building. Inverters include a range of technologies, from central inverters that convert the electricity from many solar panels, to microinverters that are attached to each individual panel in a system. In grid-connected systems, inverters are designed so that if power from the utility goes down, the PV system will shut down, too – a critical safety precaution for utility workers and public safety personnel.
Investor-Owned Utility
An Investor-Owned Utility (IOU) is a private company that provides utility services—such as electricity, natural gas, or water—with the primary goal of generating profits for its shareholders. Unlike municipal or cooperative utilities, IOUs are for-profit corporations and are regulated by the Department of Public Utilities (DPU) in Massachusetts. The investor-owned electric and gas utilities in MA are National Grid, Eversource, Unitil, Liberty Utilities and Berkshire Gas.
Islanding Capability
Islanding capability allows your solar and battery storage system to power critical loads in your home in the event of a grid electricity power outage. For the safety of utility line workers, solar and battery storage systems are designed by default to stop feeding electricity into your home during power outages. Islanding capability changes this while still protecting utility workers and allows you to isolate your home from the grid during a power outage. You can then power critical loads with your solar and battery system.
K
Kilowatt (kW)
A kilowatt (kW) is a unit of electrical power equal to 1,000 watts. It is commonly used to measure a solar system’s maximum output or capacity. For example, a 5 kW solar panel system can produce up to 5 kilowatts of power under ideal conditions.
Kilowatt Hour (kWh)
A kilowatt hour (kWh) measures energy usage over time. It represents the energy produced or consumed at a rate of one kilowatt over one hour. In the context of solar, kWh describes how much energy a solar system produces or how much energy your home consumes over time.
L
Loop Field
A loop field is the system of pipes that are run underground to act as the heat exchanger for a ground-source heat pump system. The constant temperature of the ground is used to warm the loop fluid in the winter and cool the loop fluid in the summer to increase the efficiency of the heating and cooling system. The loop field can be at a depth of eight feet in a horizontal loop or hundreds of feet deep in a vertical loop.
M
Manual J
A methodology developed by the Air Conditioning Contractors of America (ACCA) to do a heat load calculation.
MassCEC
The Massachusetts Clean Energy Center (MassCEC) is a state economic development agency dedicated to accelerating the growth of the clean energy sector to meet the Commonwealth’s clean energy, climate, and economic development goals.
Mass Save
Collaborative of Massachusetts’ natural gas, electric utilities, and energy efficiency service providers to help Massachusetts’ residents save money and energy through energy efficiency measures.
Megawatt (MW)
A megawatt (MW) is a unit of electrical power equal to one million watts. It is commonly used to measure a solar system’s maximum output or capacity, especially for larger projects, like solar farms.
Mini-splits
A common term used to describe a ductless air-source heat pump.
MMWEC
The Joint Action Agency for Massachusetts municipal utilities, delivering the wholesale power supply, financial, risk management and other services needed by municipal utilities to participate effectively in today’s electric utility industry.
Multi-Zone
A heat pump where one outdoor unit connects to more than one indoor units. Multi-zone indoor units can include a mix of ducted and ductless units.
Muni HELPS
An MMWEC program that delivers free home energy audits and innovative energy technology to MMWEC customers.
Municipal Light Plant (MLP)
Municipalities may own, maintain and operate a municipal light plant (MLP) in order to provide electric and/or gas services to their citizens. The MLP provides both distribution and supply services to its customers. Generally, MLPs are run by municipal light boards or commissions in a municipality, or by the mayor/select board. The Department of Public Utilities’ role in regulating MLPs is limited since MLP’s rates are set by municipal officials.
N
Net Metering
A billing mechanism that credits solar energy system owners for the electricity they add to the grid. If the solar electric system is under 10 kW and generates extra power beyond what the system owner can use, the owner can sell the excess back to the utility through net metering. The owner will then get credit on their bill for this excess power. They are billed for the difference between the amount of the electricity used and the amount created, also called the “net.” When the system owner creates more than they use, it’s documented on their electric bill as net metering credits and applied towards future bills.
Net Zero Emissions
When the total amount of greenhouse gas emissions is equal to or less than the amount of carbon dioxide or its equivalent that is removed from the atmosphere and stored in Earth’s systems annually. The Commonwealth aims to be net zero emissions by 2050.
Northeast Energy Efficiency Partnership
Northeast Energy Efficiency Partnership (NEEP) is a non-profit accelerating energy efficiency in the Northeast and Mid-Atlantic states. It is one of six Regional Energy Efficiency Organizations (REEOs) funded, in part, by US Department of Energy to support state efficiency policies and programs.
O
Open Loop
A type of vertical loop ground-source heat pump system where the loop field system exchanges water directly with an underground well. Ground water is returned to the well after passing through the heat pump.
Outdoor Unit
The part of an air-source heat pump that is outside where the refrigerant absorbs heat in the winter and rejects heat in the summer to transfer heat between the indoors and the outdoors and condition the home.
P
Panel
Panels are made up of a series of individual solar cells that convert sunlight into direct current (DC) electricity. The higher the intensity of the sunlight striking the panels, the more electricity they produce. Once the electricity is produced, it flows to the inverter.
Payback Period
The payback period of a solar system represents how many years it takes for the system’s savings to match the initial costs. After the payback period, the customer fully owns the system. They can continue to receive earn-as-you-produce incentives and use the electricity generated by the system to power their home.
Photovoltaic (PV)
Photovoltaics (PV) gets its name from the process of converting light (photons) to electricity (voltage), which is called the photovoltaic effect. “Solar cells” may also be called “photovoltaic cells,” and they convert sunlight directly into electricity.
Power Purchase Agreement (PPA)
A PPA is similar to a solar lease, in that the solar company will own and operate the system on the homeowner’s roof. Rather than a fixed monthly payment, however, the homeowner agrees to purchase the electricity generated by the system at an agreed-upon per-kilowatt-hour price, often lower than typical utility rates. Like a solar lease, a PPA allows a homeowner to begin saving money immediately, with little or no up-front cost. When considering a solar lease or PPA, review the contract carefully to understand all terms and conditions.
Programmable Thermostat
A thermostat that can be set to adjust the temperature of a home based on the time of day and week, in order to use less energy when it is not needed.
R
Refrigeration Cycle
The process of moving refrigerants through a loop to transfer heat from one place to another. Refrigeration cycles can work to move heat in a home in the winter and also move heat out of a home in the summer.
Roof Mounted
Solar collectors mounted on the roof of a building. Collectors are generally mounted directly to the roof, but sometimes they are tilted up at a different angle (especially on flat roofs) to optimize their solar exposure. View Image
S
Single-Zone
A heat pump where one outdoor unit connects to one indoor unit, which could be either a ducted air-handling unit or a ductless indoor unit. A home can have multiple single-zone systems.
Solar Collectors
Solar collectors are devices that collect solar radiation from the sun. These devices are primarily used for heating water for personal use. These collectors are often mounted on the roof, although they can also be mounted on the ground or on the side of a building. View Image
Solar Hot Water
A hot water system that uses heat from the sun to heat a fluid in solar collectors that is then circulated to a hot water tank where the fluid transfers heat for domestic hot water use (e.g., showers, washing dishes). Also called “Solar Thermal.” View Image
Solar Lease
Under a solar lease, a property owner agrees to pay a pre-determined monthly bill to a solar company, which installs, owns and operates the solar electric system. The property owner then has access to the electricity generated by the system, lowering their monthly utility bill. A solar lease provides the opportunity for a homeowner to benefit from solar electricity with little or no up-front cost.
Solar Loan
Many homeowners opt to take out a loan to finance a solar electric system purchase. Financing a solar electric installation through loans provides the system owner with many of the benefits of a direct purchase with a lower up-front investment, though interest payments and other fees may apply. In recent years, loans dedicated to solar installations have become popular in Massachusetts.
Solar Massachusetts Renewable Target (SMART)
SMART is an earn-as-you-produce incentive that is paid directly by investor-owned utilities in Massachusetts to solar electric system owners. If eligible, customers can receive incentive payments for the solar electricity produced by their panels for 20 years after installation. SMART was launched by the Department of Energy Resources (DOER) in conjunction with investor-owned utilities. The selected Solar Program Administrator, CLEAResult, accepts and processes applications. The customer’s installer will apply to the SMART program on their behalf and should help navigate obtaining incentives through the program. Please see the DOER SMART website and the program administrator’s SMART website for more information. Residents of towns with a Municipal Light Plant (MLP) are unable to participate in SMART.
Solar Photovoltaics (PV)
Solar panels that use the sun’s radiation to generate electricity. View Image
Solar Renewable Energy Certificate (SREC)
A Solar Renewable Energy Certificate (SREC) is a type of Renewable Energy Certificate (REC) that is specifically designated for energy output from eligible solar photovoltaic (PV) systems. The SREC program was replaced by SMART in 2018. To learn more about SRECs, visit MassCEC’s website.
T
Thermal Storage
A system that stores thermal energy for use in supplementing or offsetting heating system output.
Third Party Ownership
Third-party ownership is where a third-party installs, owns, operates, and maintains the system on a customer’s home or business. Third-party ownership can be a good option for customers who don’t choose to or are unable to pay up front for a solar energy system. There are two types of third-party ownership: solar leases and power purchase agreements (PPAs). You can learn more about each of these models through their definitions in this glossary.
Transmission
The process of transporting electricity from any source, including solar electric systems, to consumers through high-voltage power lines and substations.
V
Vertical Loop
A type of ground-source heat pump system where the outdoor heat exchanger is an underground loop field drilled hundreds of feet into the group in one or more boreholes.
W
Wall Mounted
Solar collectors mounted on the side of a building. Collectors can be mounted flush to the wall or tilted at a different angle to optimize solar exposure (sometimes called an awning mount). View Image
Watt
A unit of electrical power measuring the rate at which energy is transferred or consumed, equivalent to one joule of energy per second.
Weatherization
The process of making a home better protected from extreme weather, which often involves sealing up air leaks and adding insulation in your home.
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