September 01, 2026

It’s Clean Energy Month – Here is Your Necessary Terminology

Celebrating "Clean Energy Month" With a Dozen Terms to Get You Started

By Tom McFeeley, Media Relations Specialist

September is National Clean Energy Week. At ELPC, we figured, why stop at a week? So we’re calling this Clean Energy Month, though if we’re being honest, every month is clean energy month around here. 

Through the month, we’ll be digging into the clean energy issues at play across our nine-state footprint, including the biggest topic around clean energy, data centers. But before we get into any of that, it’s worth building an understanding of key terms in the clean energy arena. A lot of these get used in news coverage, utility filings, and political ads without much explanation, so consider this your cheat sheet for expanding your knowledge of clean energy concepts. 

1. Watts, Kilowatts, Megawatts, and Gigawatts

When discussing the power grid or data centers, the terms gigawatts and megawatts and kilowatts are dropped in the conversation, but we thought it was worthwhile to provide clarity and context to their scale.  

A watt is a unit of power. A watt-hour is a measure of energy. Electric bills are paid on kilowatt-hours. 

These are the units that measure power.  

• A watt, the base unit, is tiny on its own: an LED bulb uses about 8 to 10 watts.  

• A kilowatt (1,000 watts) is appliance-scale.  A vacuum or hair dryer draws around 1 to 1.5 kilowatts, and a whole house peaks around 3 to 5 kilowatts on a hot afternoon with the air conditioner running.  

• A megawatt (1,000 kilowatts) is where power generation numbers start, a single utility-scale wind turbine produces about 2 to 3 megawatts, and as a rule of thumb, 1 megawatt is roughly enough to power 750 to 1,000 average homes at once. 

• A gigawatt (1,000 megawatts) is large power plant territory. A solar project in Northwest Indiana will use 2.8 million solar panels and provide almost 1.4 GW when fully built out in 2027. 

2. Renewable Energy

Renewable energy comes from sources that naturally replenish themselves, wind, sunlight, and moving water are the big three. It’s often used interchangeably with “clean energy,” but they’re not identical: nuclear power is carbon-free, so it is often considered clean energy, but it isn’t renewable, since it relies on mined fuel and creates nuclear waste, rather than a naturally replenishing source. 

3. Fossil Fuels

Fossil fuels, coal, oil, and natural gas, are the substances burned to generate most of the country’s electricity today, and burning them is exactly what releases the greenhouse gases clean energy is defined against. They’ve powered the grid for over a century and still supply a large share of it, which is a big part of why the shift to clean energy is slow and complicated rather than a quick swap. 

4. Generation Mix

At any moment, the electricity flowing through the grid is a blend of whatever sources happen to be running, called the generation mix. That mix shifts throughout the day and various sources ramp up or down to fill the gap. 

5. Clean Energy Standard

A clean energy standard is a law requiring utilities to get a rising percentage of their electricity from clean sources by specific dates, essentially a legal deadline for cleaning up the generation mix. Illinois’s Climate and Equitable Jobs Act (CEJA) is a real example, setting benchmarks of 40% renewable energy by 2030 and 50% by 2040, on the way to 100% carbon-free electricity by 2045. 

6.Battery Storage 

Battery storage refers to technology, most commonly large-scale lithium-ion systems, that stores electricity for later use, allowing power generated at one time to be discharged when it’s needed most. This is especially critical for balancing renewable energy sources like wind and solar, which don’t generate power on demand, by storing excess generation during high-output periods and releasing it during peak demand or when generation dips. Battery storage also helps stabilize the grid, delay the need for costly transmission upgrades, and provide backup power during outages. Illinois recently moved to scale this up significantly, with a state mandate for 3 gigawatts of grid-scale battery storage by 2030. 

7. Virtual Power Plants (VPPs)

A virtual power plant is a network of many small, customer-owned devices, home batteries, smart thermostats, EV chargers that act together like one large power plant. Illinois’s ComEd Scheduled Dispatch Virtual Power Plant, approved in June 2026, is a live example. 

8. Peak Demand

Peak demand is the highest point of electricity use in a given day or season, typically a hot summer afternoon or a frigid winter day. It matters because the grid has to be built to handle that single worst hour, not the average hour, which is a big part of why so much grid spending is really about managing a few dozen hours a year rather than the other 8,700. 

9. Load Growth

Load growth simply means how much total electricity demand is increasing over time. For most of the last two decades, load growth in the U.S. was nearly flat, but data centers and electrification have driven the fastest projected increase in decades, which is the underlying force behind almost every grid, rate, and clean energy debate happening right now. 

10. Demand Response

Demand response pays you to use less electricity during a short window, not overall, usually an hour or two on the hottest summer afternoons when the grid is most strained. It’s the concept behind smart thermostat programs that let your utility nudge your air conditioning up a couple degrees during peak hours in exchange for a bill credit. Multiply that by thousands of homes participating at once, and the utility can avoid firing up one of its most expensive backup power plants. 

11. Distributed Energy 

Distributed energy refers to smaller-scale power generation and storage resources located close to where electricity is used, rather than centralized at a large power plant. This includes rooftop solar, community solar arrays, small-scale wind, and on-site battery systems installed at homes, businesses, or local substations. Because these resources are spread across the grid instead of concentrated in one location, they can reduce strain on transmission infrastructure, improve grid resilience during outages, and give customers more direct control over their energy costs. Illinois, largely through ComEd’s territory, has become a Midwest leader in distributed energy, with well over a gigawatt of interconnected rooftop and community solar systems. 

12. Behind-the-Meter 

“Behind the meter” refers to power generated and used on-site, like rooftop solar, without crossing the utility’s meter or touching the shared grid. It’s worth remembering this phrase carefully, since it gets used very differently when large electricity users generate power on-site using gas instead, a distinction that matters a lot once you start reading about data centers. 

That’s your starting vocabulary. Keep it handy, because we’ll be building on many terms this month and beyond.