Resources
Illinois Solar & Energy Glossary
Plain-language definitions of the solar, incentive, and home-energy terms Illinois homeowners run into. Program details and incentive amounts change over time, so confirm the current terms before you rely on them, or just ask us.
- Adjustable Block Program (ABP)
- The Illinois state program that supports Illinois Shines. It buys the Renewable Energy Credits a solar system produces through set "blocks" of capacity. Pricing and availability change over time, so confirm the current block terms before you count on them.
- Azimuth
- The compass direction a solar array faces. In the northern hemisphere, south-facing (an azimuth near 180 degrees) usually produces the most energy, though east and west orientations still work.
- Battery storage
- A home battery that stores solar energy so you can use it at night or during an outage instead of sending it back to the grid. Sizing depends on which loads you want to back up. Learn more.
- Bifacial panels
- Solar panels that capture light on both the front and the back, picking up reflected light off the ground or roof. They can add production, especially on ground mounts over light surfaces.
- ComEd
- Commonwealth Edison, the electric utility that serves northern Illinois and the Chicagoland area. Your utility determines your interconnection process and available rebates. Learn more.
- Derate
- The expected real-world loss between a panel’s lab rating and what a full system actually delivers, from wiring, inverter efficiency, heat, and shading. A realistic estimate accounts for it.
- Federal Investment Tax Credit (ITC)
- A federal tax credit for a percentage of the cost of a qualifying solar (and often battery) system. It reduces the federal taxes you owe. Amounts and eligibility are set by federal law, so verify the current rate.
- Geothermal (ground-source heat pump)
- A heating and cooling system that moves heat to and from the ground through buried loops. It is very efficient because ground temperatures stay stable year round. Learn more.
- Ground-mount solar
- A solar array installed on racking in the yard or a field instead of on the roof. Good for shaded roofs, large systems, and farms, and it can use directional boring to run wiring cleanly.
- Heat pump (air-source)
- An electric system that both heats and cools a home by moving heat rather than burning fuel. Modern cold-climate models work well through northern Illinois winters and pair naturally with solar. Learn more.
- Illinois Shines
- The state incentive (delivered through the Adjustable Block Program) that pays a solar owner for the Renewable Energy Credits their system generates over a set period. Program terms change, so confirm the current details.
- Illinois Solar for All (ILSFA)
- A separate Illinois program that makes solar accessible to income-eligible households and certain nonprofits and public facilities, with no upfront cost in qualifying cases. Eligibility rules apply.
- Interconnection
- The utility’s approval process to connect your solar system to the grid. It includes an application, review, and a final inspection before the system can be switched on. Timelines vary by utility.
- Inverter
- The device that converts the direct current (DC) a solar panel makes into the alternating current (AC) a home uses. Systems use a central string inverter or per-panel microinverters.
- Kilowatt (kW) vs kilowatt-hour (kWh)
- A kilowatt is a rate of power (how big the system is). A kilowatt-hour is an amount of energy used or produced over time (what shows up on your electric bill). A 1 kW system running for one hour makes about 1 kWh.
- Net metering
- A billing arrangement where the extra solar energy you send to the grid credits your account, offsetting the energy you pull back later. It is a big driver of solar savings, and the rules can change. Learn more.
- Payback period
- How long it takes for the energy savings and incentives from a system to equal what you paid for it. After payback, the ongoing savings are effectively yours. Learn more.
- Photovoltaic (PV)
- The technology that turns sunlight directly into electricity. A "PV system" is another name for a solar electric system. Learn more.
- Renewable Energy Credit (REC)
- A tradable credit representing the environmental value of one megawatt-hour of clean energy. In Illinois, solar owners are paid for their RECs through Illinois Shines.
- Solar Renewable Energy Credit (SREC)
- A REC specifically from solar generation. Selling SRECs (in Illinois, via Illinois Shines) is one of the main ways a solar system pays for itself.
- Solar panel (module)
- The unit that captures sunlight and produces electricity. Panels are combined into an array sized to your energy use, roof or land, and budget. Learn more.
- Tilt
- The angle of a solar array relative to flat ground. The best tilt balances annual production with roof pitch or ground-mount design.
- U-factor and SHGC
- Two window efficiency ratings. U-factor measures how well a window keeps heat in (lower is better); SHGC measures how much solar heat it lets in. Both matter for comfort and energy bills. Learn more.