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Clean Energy

What Are the Five Major Types of Renewable Energy?



The Renewable Energy Age

This was originally published on June 8, 2022, on Elements.

Awareness around climate change is shaping the future of the global economy in several ways.

Governments are planning how to reduce emissions, investors are scrutinizing companies’ environmental performance, and consumers are becoming conscious of their carbon footprints. But no matter the stakeholder, energy generation and consumption from fossil fuels is one of the biggest contributors to emissions.

Therefore, renewable energy sources have never been more top-of-mind than they are today.

The Five Types of Renewable Energy

Renewable energy technologies harness the power of the sun, wind, and heat from the Earth’s core, and then transforms it into usable forms of energy like heat, electricity, and fuel.

The above infographic uses data from Lazard, Ember, and other sources to outline everything you need to know about the five key types of renewable energy:

Energy Source% of 2021 Global Electricity GenerationAvg. levelized cost of energy per MWh
Hydro 💧 15.3%$64
Wind 🌬 6.6%$38
Solar ☀️ 3.7%$36
Biomass 🌱 2.3%$114
Geothermal ♨️ <1%$75

Editor’s note: We have excluded nuclear from the mix here, because although it is often defined as a sustainable energy source, it is not technically renewable (i.e. there are finite amounts of uranium).

Though often out of the limelight, hydro is the largest renewable electricity source, followed by wind and then solar.

Together, the five main sources combined for roughly 28% of global electricity generation in 2021, with wind and solar collectively breaking the 10% share barrier for the first time.

The levelized cost of energy (LCOE) measures the lifetime costs of a new utility-scale plant divided by total electricity generation. The LCOE of solar and wind is almost one-fifth that of coal ($167/MWh), meaning that new solar and wind plants are now much cheaper to build and operate than new coal plants over a longer time horizon.

With this in mind, here’s a closer look at the five types of renewable energy and how they work.

1. Wind

Wind turbines use large rotor blades, mounted at tall heights on both land and sea, to capture the kinetic energy created by wind.

When wind flows across the blade, the air pressure on one side of the blade decreases, pulling it down with a force described as the lift. The difference in air pressure across the two sides causes the blades to rotate, spinning the rotor.

The rotor is connected to a turbine generator, which spins to convert the wind’s kinetic energy into electricity.

2. Solar (Photovoltaic)

Solar technologies capture light or electromagnetic radiation from the sun and convert it into electricity.

Photovoltaic (PV) solar cells contain a semiconductor wafer, positive on one side and negative on the other, forming an electric field. When light hits the cell, the semiconductor absorbs the sunlight and transfers the energy in the form of electrons. These electrons are captured by the electric field in the form of an electric current.

A solar system’s ability to generate electricity depends on the semiconductor material, along with environmental conditions like heat, dirt, and shade.

3. Geothermal

Geothermal energy originates straight from the Earth’s core—heat from the core boils underground reservoirs of water, known as geothermal resources.

Geothermal plants typically use wells to pump hot water from geothermal resources and convert it into steam for a turbine generator. The extracted water and steam can then be reinjected, making it a renewable energy source.

4. Hydropower

Similar to wind turbines, hydropower plants channel the kinetic energy from flowing water into electricity by using a turbine generator.

Hydro plants are typically situated near bodies of water and use diversion structures like dams to change the flow of water. Power generation depends on the volume and change in elevation or head of the flowing water.

Greater water volumes and higher heads produce more energy and electricity, and vice versa.

5. Biomass

Humans have likely used energy from biomass or bioenergy for heat ever since our ancestors learned how to build fires.

Biomass—organic material like wood, dry leaves, and agricultural waste—is typically burned but considered renewable because it can be regrown or replenished. Burning biomass in a boiler produces high-pressure steam, which rotates a turbine generator to produce electricity.

Biomass is also converted into liquid or gaseous fuels for transportation. However, emissions from biomass vary with the material combusted and are often higher than other clean sources.

When Will Renewable Energy Take Over?

Despite the recent growth of renewables, fossil fuels still dominate the global energy mix.

Most countries are in the early stages of the energy transition, and only a handful get significant portions of their electricity from clean sources. However, the ongoing decade might see even more growth than recent record-breaking years.

The IEA forecasts that, by 2026, global renewable electricity capacity is set to grow by 60% from 2020 levels to over 4,800 gigawatts—equal to the current power output of fossil fuels and nuclear combined. So, regardless of when renewables will take over, it’s clear that the global energy economy will continue changing.

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Clean Energy

Gridlock: Visualizing the U.S. Clean Energy Backlog

The U.S. has almost 2 million megawatts of clean energy capacity on hold in interconnection queues, seeking connection to the grid.



u.s. clean energy backlog

Gridlock: Visualizing the U.S. Clean Energy Backlog

The U.S. has almost 2 million megawatts (MW) of solar, wind, and storage capacity on hold in interconnection queues, seeking connection to the electrical grid.

However, the lack of transmission infrastructure, in addition to a lengthy permitting process, has resulted in a bottleneck of clean energy projects awaiting approval before they can be plugged into the grid.

This infographic sponsored by the National Public Utilities Council maps U.S. clean energy capacity in interconnection queues by transmission region, based on data from the Berkeley Lab.

But before we dive into the data, let’s fully understand what interconnection queues mean.

What are Interconnection Queues?

Before new power plants can be built and connected to the grid, they go through a series of impact assessments to ensure safety and reliability. The projects in this process form grid interconnection queues, which are essentially waitlists of proposed power plants seeking grid connection.

Here are some of the problems associated with U.S. interconnection queues:

  • Wait times: The average time projects spend in the queue is up from 2.1 years in 2000 to 3.7 years in 2021, according to the Energy Transitions Commission. 
  • Withdrawal rates: Historically, most projects have withdrawn from the queue, with just 21% of projects seeking connection from 2000–2017 reaching commercial operation.
  • Aging transmission: The U.S. grid is aging, and queued-up projects can end up facing large fees from the updates required to transmission infrastructure.

Although the backlog is alarming, the interconnection queues also show that project developers are invested in the clean energy transition. In fact, the amount of clean energy capacity in interconnection queues exceeds the amount needed to get to 90% zero-carbon electricity by 2035, according to Berkeley Lab.

U.S. Clean Energy in Queues

Solar and battery storage projects account for the majority of capacity in interconnection queues, followed by wind.

Energy SourceCapacity in Interconnection Queues (MW)% of Total
Battery Storage682,78235%
Offshore Wind114,0066%

Data as of the end of 2022.

Notably, 48% of all solar capacity in the queues is proposed as a “hybrid plant” that combines generation with battery storage. Similarly, over half of all battery storage capacity is proposed with some amount of generation.

The large number of hybrid and storage configurations show that project developers are addressing the intermittent nature of renewables by combining generation with storage.

Interconnection queues are managed by Independent System Operators (ISOs) and Regional Transmission Organizations (RTOs) that operate the grid and wholesale electricity markets in different regions. Here’s a look at the clean energy capacity in queues grouped by major transmission regions and ISOs:

ISO/Transmission RegionClean Energy Capacity in
Interconnection Queues (MW)
% of Total
West (non-ISO)578,93730%
Midcontinent ISO (MISO)321,72317%
PJM (RTO)284,38415%
Electric Reliability Council Of Texas (ERCOT)207,80811%
California ISO (CAISO)196,79210%
New York ISO (NYISO)108,1636%
Southern Power Pool (SPP)105,3985%
Southeast (Non-ISO)92,9565%
New England ISO (ISO-NE)34,2232%

Data as of the end of 2022. Percentages may not add up to 100 due to rounding. 

Overall, the West (non-ISO) region has the most solar (254 GW), battery (262 GW), and onshore wind (63 GW) capacity in interconnection queues. Offshore wind capacity is highest in New York (63 GW), managed by the NYISO.

In 2022, California ISO did not accept any new interconnection requests due to the backlog from 2021. Meanwhile, the PJM announced that it would not review any new requests until 2025. Despite these slowdowns, over 700 GW of capacity was added to U.S. interconnection queues in 2022.

Unlocking the Gridlock

Given the current backlog, along with the incentives for new clean energy projects in the Inflation Reduction Act, clearing the gridlock is now more important than ever.

The large backlog, long wait times, and high withdrawal rates highlight the growing challenges in interconnection and transmission. Among other longer-term solutions, there are two ways to alleviate the gridlock:

  • Expanding high-voltage transmission lines: Many solar and wind projects are located in remote areas and require high-voltage transmission lines to carry electricity to cities. Expanding the transmission network can allow more projects to connect to the grid.
  • Streamlined permitting: Interconnection processes and the reviews involved are long and costly for project developers. Reforming processes and streamlining permits can help in shortening the wait times for projects in queues.

To address this problem, some grid operators have already made changes to their interconnection processes. Additionally, the Department of Energy has launched the Interconnection Innovation Exchange (i2X) in an effort to improve collaboration and transparency in interconnection.

History shows that most of the projects in interconnection queues will ultimately not be built. However, what’s clear is that the U.S. is on the road to decarbonization, and energy project developers are focusing on clean energy sources for the future.

Learn more about how electric utilities and the power sector can lead on the path toward decarbonization here.

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Clean Energy

Visualizing Clean Energy and Emissions Goals by State

An overview of each U.S. state’s ultimate clean energy or GHG emission reduction goal, broken down by goal type and target year.



Visualized: Clean Energy and Emissions Goals by State

In its Nationally Determined Contribution to the Paris Agreement, the U.S. set a target of reducing its greenhouse gas (GHG) emissions by 50-52% below 2005 levels by 2030, as well as achieving 100% carbon-free electricity by 2035.

To discover how each state is contributing to these goals, this graphic sponsored by the National Public Utilities Council provides an overview of each state’s ultimate clean energy or GHG emission reduction goal.

Varying Commitments

An analysis of the aggregated data by S&P Commodity Insights reveals a broad spectrum of clean energy and emission reduction goals in the United States.

While some states have more ambitious goals of attaining 100% clean energy by 2040, others, such as Ohio, have opted for more modest and short-term targets, aiming to achieve 8.5% renewable electricity by 2026.

Eleven states, or 22%, have never set clean energy or emission reduction goals. These states include Alabama, Florida, Georgia, Mississippi, Tennessee, and West Virginia.

Similarly, another ten states (20%) have expired goals with target dates as far back as 2015. These ten states, including the Dakotas, Missouri, Kansas, Montana, and Oklahoma, have not reset their goals since.

Shares of Clean Energy by State

To get a glimpse into how far each state has to go in achieving its goal, a snapshot of the use of clean electricity in each state is shown below.

Using data from the Nuclear Energy Insitute, the bars show each state’s 2021 share of emission-free electricity broken down by nuclear and various renewables.

While clean electricity made up 70% or more of the electricity mix in several states, nuclear and renewable energy sources comprised approximately 40% of total U.S. electricity generation in 2021.

To hit its 100% carbon-free electricity goal, therefore, the U.S. needs a minimum 4.3% annual increase in clean electricity generation through 2035. For context, an average annual growth of 2.4% was observed in the last five years.

On the GHG reduction side of things, emissions were 17% below 2005 levels in 2021, showing the need for an additional 35% reduction by 2030.

As these figures show, achieving the ambitious clean energy and emissions reduction goals in the U.S. will require a significant ramp-up of clean electricity generation in the upcoming years, along with accelerated decarbonization efforts across all sectors.

Click here to learn more about how electric utilities and the power sector can lead on the path toward decarbonization.

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National Public Utilities Council