Energy 101: Alternative Energy

Updated: July 10, 2024

By Drew Schiavone

Renewable energy sources are those that are naturally replenishing but flow-limited. These resources are virtually inexhaustible in duration but limited in the amount of energy that is available per unit of time. Renewable energy relies upon ongoing natural cycles (such as solar radiation, rain, or Earth’s internal heat) as opposed to stored fossil energy created over long periods of time. Renewable energy resources include biomass, hydro, geothermal, solar, wind, ocean thermal, wave action, and tidal action.

Maryland's legislature enacted a renewable portfolio standard (RPS) in 2004 and has amended it several times since then. The latest update came in May 2019, when the Maryland legislature required that 50% of the state's electricity retail sales come from renewable sources by 2030, in addition to the existing 20% requirement by 2020. The state will also study the possibility of obtaining 100% of its electricity from renewables by 2040. As part of the updated RPS, 14.5% of an electricity supplier's retail sales must come from solar power by 2030. The RPS also requires that the state's offshore wind generating capacity reach 400 megawatts in 2026 and increase to at least 1,200 megawatts in 2030.

Renewable energy credits in Maryland from 2004 to 2019 chart — Renewable Energy Credits Used to Comply with Maryland's RPS. Solar Renewable Energy Credits (SREC) and RECs retired in Maryland for RPS compliance.

Renewable energy, including small-scale generating facilities and larger utility-scale power plants, currently provides around 14.5% of Maryland's in-state net electricity generation.

Maryland Net Electricity Generation by Source November 2020 Graph

In 2019, the top three renewable energy sources in Maryland in terms of net generation were hydropower (64%), solar (25%), and wind (10%); although other energy sources and their derivatives are used in the state to a lesser extent.

Net Electricity Generation in Maryland for 2001 and 2019

he sun is the ultimate source for all of the energy sources and fuels that we use today. Various technologies have been developed to collect and use solar thermal (heat) energy, as well as to convert solar energy into electricity. Solar thermal energy systems are commonly used to heat water (homes, buildings, or swimming pools), indoor air (homes, greenhouses, and other buildings), and high-temperature fluids (solar thermal power plants). On the other hand, solar photovoltaic (PV) systems convert sunlight into electricity using small PV cells (calculators, watches, and other small electronic devices), PV panels and arrays (electricity for an entire house), or even larger PV power plants that may cover many acres (multiple housing units, commercial/industrial operations).

Solar energy provides about one-fourth of Maryland's renewable electricity generation, and has increased significantly in recent years, nearly tripling from 2016 to 2018. Two-thirds of the state's solar generation came from small-scale solar photovoltaics (PV), such as rooftop solar panels, and the rest of the generation was at larger utility-scale sites like solar farms. By early 2019, Maryland had nearly 1,100 megawatts of solar generating capacity installed. The state's largest solar project—located on the Eastern Shore—came online in 2018 with a generating capacity of 75 megawatts. Several large solar panel arrays also have been installed at commercial buildings in the state.

Wind is caused by uneven heating of the earth's surface by the sun. Because the earth's surface is made up of different types of land and water, it absorbs the sun's heat at different rates. One example of this uneven heating is the daily wind cycle in which air above the land heats up faster than air over water during the day. Warm air over land expands and rises, and heavier, cooler air rushes in to take its place, creating wind. At night, the winds are reversed because air cools more rapidly over land than it does over water. In the same way, the atmospheric winds that circle the earth are created because the land near the earth's equator is hotter than the land near the North Pole and the South Pole. Today, wind energy is mainly used to generate electricity. Water-pumping windmills were once used throughout the United States and some still operate on farms and ranches, mainly to supply water for livestock.

Wind energy provided about 10% of Maryland's renewable electricity generation in 2018. Maryland's most significant onshore wind potential is in its western mountains and along its southern Chesapeake Bay and Atlantic Ocean shorelines. The state's only operating utility-scale wind farms are along Maryland's western Appalachian Mountain crests, where almost 200 megawatts of generating capacity is installed. Maryland's largest wind energy potential is offshore. Two major wind projects are planned off Maryland's Atlantic coastline. One wind project, located about 17 miles offshore, will consist of 23 tall turbines that can generate up to 250 megawatts of electricity and is scheduled to come online in early 2021. A second wind project, expected to be operating in 2022, will be located about 20 miles offshore and have 15 turbines with a generating capacity of 120 megawatts.

Geothermal energy is heat within the earth. The word geothermal comes from the Greek words geo (earth) and therm (heat). Geothermal energy is a renewable energy source because heat is continuously produced inside the earth. Geothermal heat is used to heat buildings and to generate electricity. Geothermal energy comes from deep inside the earth. The slow decay of radioactive particles in the earth's core, a process that happens in all rocks, produces geothermal energy.

Residential geothermal heating and cooling diagram

Maryland's residential and commercial sectors each account for about one-third of the state's natural gas consumption, and the electric power sector uses nearly one fourth; generating about 33% of Maryland's net electricity generation in 2018. The industrial and transportation sectors account for the remaining amount of the state's gas consumption. Natural gas is most commonly used for heating, with over 40% of Maryland households using natural gas as their primary fuel for home heating. Because natural gas is typically delivered through a pipeline, it is not commonly used in agricultural operations. However, natural gas is used in industrial manufacturing as an input in agriculture-related products, such as nitrogen fertilizers.

Hydropower is one of the oldest sources of energy for producing mechanical and electrical energy and up until 2019, it was the largest source of total annual U.S. renewable electricity generation. Conventional hydroelectric facilities include run-of-the-river systems, where the force of the river's current applies pressure on a turbine. The facilities may have a weir in the water course to divert water flow to hydro turbines. Water typically flows through a pipe, or penstock, then pushes against and turns blades in a turbine to spin a generator to produce electricity. The volume of the water flow (i.e., flow rate) and the change in elevation (i.e., head) from one point to another determine the amount of available energy in moving water. In general, the greater the water flow and the higher the head, the more electricity a hydropower plant can produce. The amount of precipitation that drains into rivers and streams in a geographic area determines the amount of water available for producing hydropower. Seasonal variations in precipitation and long-term changes in precipitation patterns, such as droughts, can have large effects on the availability of hydropower production.

In 2019, hydroelectricity accounted for about 6.6% of total U.S. utility-scale electricity generation and 38% of total utility-scale renewable electricity generation. Hydroelectricity’s share of total U.S. electricity generation has decreased over time, mainly because of increases in electricity generation from other sources. Hydropower currently accounts for more than half of Maryland's renewable electricity generation. The Conowingo hydroelectric generating station, located in northern Maryland on the Susquehanna River, was the largest power plant ever built when it began operating in 1928. The 11 turbines at the power station have a combined summer generating capacity of 572 megawatts. Conowingo provides almost all of Maryland's hydroelectricity and it is one of the five largest electricity producing plants in Maryland based on actual yearly generation.

Biomass is organic material that comes from plants and animals. Solid biomass (e.g., wood, agricultural crops and municipal garbage) can be burned directly to produce heat or converted into biogas or liquid biofuels (e.g., ethanol and biodiesel) that are subsequently burned for energy. Biogas is produced when biomass (e.g., paper, food scraps, and yard waste) decomposes in landfills or by processing sewage and animal manure in special vessels (i.e., digesters). Ethanol is made from the fermenation of some crops (e.g., corn and sugar cane) to produce a fuel ethanol commonly used in vehicles. Biodiesel is produced from vegetable oils and animal fats for use in vehicles or as a heating oil.

Biomass accounts for about 45% of all renewable energy consumption in the U.S. and about 5% of total U.S. energy consumption. Of that 5%, about 47% was from biofuels (mainly ethanol), 44% was from wood and wood-derived biomass, and 10% was from the biomass in municipal waste (sum of percentages is greater than 100% because of independent rounding). Biomass was used to generate about one-tenth of Maryland's renewable electricity in 2018 at facilities that use landfill gas, municipal solid waste, and wood and wood waste. There are many small landfill gas-to-energy facilities in cities around the state, but Maryland's largest biomass electricity-generating capacity—accounting for 80% of the state's total biomass capacity—is found at two facilities that use municipal solid waste: one in Montgomery County in the suburbs of Washington, DC, and the other in Baltimore. The Baltimore facility also generates steam for a downtown piping system that supplies heat to more than 200 businesses.