Green energy refers to electricity made from renewable resources, such as sunlight or wind. These types of energy sources emit little-to-no emissions, making them a clean option for energy supply.
Brown energy refers to power generated from fossil fuels such as oil or coal. These resources are known for being heavy polluters, causing large amounts of greenhouse gas emissions that seep into the atmosphere and contribute to climate change.
For some, utilizing green energy might mean installing a few solar panels on their rooftop or placing a small-scale wind turbine in their backyard. But you don't have to make such a big investment to get green energy. In fact, you probably already use some alternative energy in your normal electricity supply.
That's because many retail energy suppliers and utilities purchase large quantities of renewable energy to place on the power grid. In most states, legislation requires utilities to purchase a set amount of green energy and add it to their normal power supply. So there's typically a small amount of green energy on the grid in most areas.
If you live in a deregulated energy market, you have the option to kick up your green energy use by purchasing a renewable energy supply from a retail energy supplier. Some energy companies even sell 100 percent green plans, which can help you offset your home's total energy consumption each month.
It's important to note that when you buy green energy, the power that comes into your home isn't guaranteed to be 100 percent green. Instead your provider will purchase enough green energy to power your home and place it on the electric grid on your behalf. The green energy mixes with the brown energy already on the grid before power is delivered to your home. However, by purchasing a green energy supply you essentially offset the energy you consume. Some companies may refer to this process as purchasing renewable energy credits, whereby you purchase green power and get credit for the energy placed on the grid.
Like renewable energy credits, carbon offsets can help compensate for your energy consumption and emissions caused by brown energy. However, when you purchase a carbon offset you pay for the destruction or reduction of carbon emissions in the atmosphere, not green energy. For example, your money might go toward eliminating the methane emitted from decaying manure at a dairy farm. In return, you get to offset an equivalent amount of emissions caused by your energy use. Carbon offsets are most often used by businesses because each offset is worth a large amount—typically a metric ton—of greenhouse gas emissions. These companies often use offsets to reach and promote carbon neutrality.
Solar energy is generated by utilizing the power from the sun. It's a powerful resource because every hour that the sun beams down on the Earth, it provides enough energy to power the entire world for a year. Plus, it's free. Today, this energy source is harnessed through the use of solar panels. These panels, also called photovoltaic cells, are made of semiconductors such as silicon. When sunlight strikes the panels it's absorbed through the semiconductor material and electrons are knocked loose. Then the energy created from the moving electrons can be harnessed to create renewable electricity.
For centuries mankind has harnessed the powerful energy from the wind to do everything from flying kites to sailing ships. But recently, people have used the free resource to generate electricity. Wind energy is most commonly harnessed through wind turbines, which resemble giant pinwheels. These structures can stretch more than 400 feet in the air with blades the circumference of a Ferris wheel. As the wind blows, it pushes the blades around, creating kinetic energy. That energy is then converted into usable electricity and sent to the power grid.
Wind energy is quickly picking up speed. In 2012, wind energy became the number one source of new energy generation capacity in the U.S., representing 43 percent of all new electricity additions. However, the renewable commodity only supplied about 3 percent of the nation's energy needs in 2011.
The movement of water is another powerful and free resource that can be harnessed to generate electricity. Hydroelectric plants produce electricity by forcing water, often held at a dam, through a turbine. As the water turns the turbine, an attached generator converts the water's kinetic energy into electricity. This process is considered renewable because the water used in this process isn't wasted or contaminated. In fact, as soon as it's pushed through the turbine it simply returns to a body of water below the dam.
Hydroelectric power is one of the oldest forms of energy generation. In fact, in the 1920s hydroelectric plants supplied nearly 40 percent of the electricity produced in the United States. But as the population grew and fossil fuel resources gained widespread use, the percentage of hydroelectric power in the nation's energy mix dwindled. As of 2011, the renewable resource made up 7.6 percent of electricity generated in the United States.
Deep in the core of the Earth is a layer of molten hot magma, but there are areas, often called hot spots, where this magma creeps up toward the surface. That's why there are natural phenomena such as volcanoes or hot springs. These extreme temperatures radiating from the Earth can be converted into energy with geothermal technologies. To harness this energy, geothermal power plants drill near geological hot spots. The steam or hot water that comes up at the drilling site pushes a turbine, which then converts the resource into electricity.
The United States produces more geothermal energy than any other nation, with more than 3,000 megawatts of renewable energy generated across eight states. While that's certainly a major accomplishment, geothermal energy only supplies about .04 percent of the nation's energy needs.
Biomass energy is created by utilizing plant waste, such as corn stalks, walnut shells or forest residue. Because these plant materials capture and store the sun's energy as they grow, they are full of energy that can be harnessed. When the plant waste is burned, it releases the energy which can then be captured and converted into electricity. Biomass can also encompass other forms of renewable energy. For example, plants can be fermented to produce ethanol for vehicles.
Every year in the United States, farmers and foresters produce roughly 39 million tons of crop residues. Though only some on the material is put to use through energy generation, biomass makes up 1.4 percent of the total electricity mix.
The process of generating biogas is perhaps the smelliest version of recycling. Biogas is created by converting animal manure into energy. When bacteria decomposes manure anaerobically—without oxygen—it turns the waste into methane gas. The gas can then be used to generate heat for hot water or electricity. And the leftover manure is often used as a fertilizer. More often than not, this energy is used on the farms where it's created, so you're not very likely to get any biogas energy in your electricity supply.
Because there are so many renewable solutions, you might wonder why the United States isn't running off of 100 percent green power. What's holding renewable energy back?
A major part of the problem is that renewable resources aren't reliable. The sun can't shine 24 hours a day and the wind doesn’t always blow. Using only green energy would make it very challenging to power a country that uses electricity all the time. Fossil fuels, while harmful for the environment, are a more reliable option. Power plants can operate day and night to provide a constant steam of power for the energy demand of the nation.
And for the most part, the electricity infrastructure in the United States was built to run off fossil fuel-generated power. Power plants are connected to the grid and make getting electricity from point A to point B an easy task. It's more difficult to connect renewable energy resources to the grid. Wind energy for example, is created through dozens of Speaking of expenses, the cost to generate green energy has also hindered its growth. Installing solar panels or wind turbines can cost thousands or even millions of dollars depending on their size. However, in recent years the cost of manufacturing has gone down significantly and renewable energy has grown in popularity, driving down the cost of green energy development. Prices are expected to continue to drop and investments in renewable energy are projected to rise. At some point in the future, expense may no longer stand as a barrier to renewable energy generation.