Intermittent Generation

Description

Solar and wind power have seen historic growth over the last two decades with installed capacity expanding from less than 1 percent of the U.S. generation fleet to 14 percent by 2021.i. While the “fuel” for wind and solar is free and the electricity produced competitive with traditional generation, the power is intermittent, as the quantity of power produced at any time is dependent upon time of day, season, and local weather.

With U.S. commitments to net-zero electricity by 2035 and net-zero greenhouse gas (GHG) emissions by 2050¹, our dependence on these cheap, zero-carbon energy sources will continue to grow. The recent passage of the Inflation Reduction Act (IRA)² extends and expands the tax and other federal government incentives for these technologies creating an immediate boost. The increased reliance on solar and wind energy, however, exacerbates the intermittency challenge. How can we deploy increased amounts of wind and solar energy to decarbonize the US grid and still ensure power to homes and businesses 24 hours a day, 365 days a year?

Key Technologies

Wind power is typically deployed on a large-scale, with the latest wind towers taller than the Statute of Liberty supporting blades longer than a football field. In contrast, solar power installations come in all sizes; from a few square yards on the roof of a house, to over a thousand acres — creating enough energy to light a town.

Solar

Solar panels, composed of Photovoltaic (PV) cells are the primary method for harnessing the sun’s energy. Solar panels integrate multiple solar cells where the photons in sunlight are absorbed by semiconducting materials, such as silicon, creating an electrical current that is collected.

Beyond the Solar Panel, other key components of a solar energy system include:

An Inverter that converts DC current that the panels produce to AC, which is used by the grid.
Racking systems to hold the Solar Panels, sometimes including tracking systems that optimize generation by aligning the panel surface with the sun’s location.
Energy Control Systems to manage integration into the grid.
For large solar farms, a substation to manage the interconnect to the distribution system, including transformers to assure proper output voltage and frequency.

Wind

Wind power harnesses the wind’s kinetic energy by using air flow over the over mounted propeller-like blades to create rotation, which in turn drives an electric generator. Key components of a wind turbine include:

The tower, which supports the wind turbine and blades and average over 300 feet high to reach steadier, less turbulent wind flows.
The hub and blades (typically 3), that can range from 50 meters to more than 100 meters in length.
The hub, drive shaft, gearbox, and generator, the system which converts the low-speed, high-torque rotation from the wind energy to spin a turbine to generate electricity.
The nacelle (the cover for the generating components of the turbine).
A substation to manage the interconnect to the distribution system, including transformers to assure proper output voltage and frequency.

The average capacity of newly installed wind turbines has increased 9 percent since 2020 and 319 percent since 1999. Wind turbines are growing in generation capacity through increases in hub height and blade length.³

Offshore wind turbines are exposed to more consistent winds of higher speeds, typically able to generate more energy than onshore turbines. Still onshore wind is one of the most cost-effective renewable energy sources. On average onshore wind is 50% the cost of offshore wind, and 25% the cost of solar PV. Offshore turbines are typically larger and more difficult to access, creating increased maintenance and infrastructure costs.

Potential Market Size & Timing

As the economy grows and the temperature increases, the demand for clean energy will continue to increase over time. The U.S. is expected to see its highest record of power consumption this year, with projected power demand climbing to 4,029 billion kWh in 2022, surpassing the previous all-time high of 4,004 billion kWh in 2018.⁴ In the first half of the year, 24% of electricity in the United States was produced by renewable energy.⁵ In addition, if the U.S. keeps to an “electrify everything” decarbonization strategy where all building, cars, trucks, and even most factories run on electricity, this could create as much as a 50% increase in U.S. electricity demand over the next 20 years. So, rapid acceleration of clean energy generation is needed to meet this increasing demand while simultaneously decreasing GHG emissions.

FIGURE 1. SHARE OF PRIMARY ENERGY FROM RENEWABLE SOURCES IN THE U.S. FROM 1965-2021.⁶

Future Market Size

Wind and solar have been the fastest growing categories of power of the last two decades. If the U.S. continues to embrace the national goal of 100% carbon-free electricity by 2035, it will need to add thousands of additional megawatts of clean wind and solar power. For example:

An NREL report calls for a massive increase in renewable capacity to achieve 100% clean electricity in the U.S. by 2035.⁷ In least cost scenarios for electrification, solar and wind provide 60-80% of the generation mix for all scenarios analyzed. See Figure 2 for illustrated growth in solar and wind energy.
The same NREL study calculates that to achieve those levels would require an additional 40–90 GW of solar on the grid per year and 70–150 GW of wind per year through 2030.

The good news is that this growth in clean energy combined with expansion of the grid to electrify transportation and other sectors of the economy would be very good for the economy, creating 462,430 installation jobs in the U.S., in addition to 80,000 manufacturing jobs and 800,000 indirect and induced jobs.

FIGURE 2. U.S. ENERGY AND CAPACITY CONTRIBUTION BY RESOURCE IN MAIN PROJECTION SCENARIOS, 2035.⁸

Barriers

Intermittent renewable power creates challenges for the U.S. grid as customers expect reliable power, no matter whether the wind is blowing, or the sun is shining. Because of this, the future grid must be able to manage the variable output of this generation. This will require investment in “clean, dispatchable” power to augment the intermittent renewable power. In addition, investments into technologies that help the grid manage variable generation, such as advanced grid management tools, automated customer demand management, and energy storage, will help reduce the need for redundant back up generation while ensuring reliable power for homes, offices, and factories.

Major new wind and solar installations will require new transmission lines to move the power to where it is needed. For instance, the Southwest has the best solar resource while the Midwest has the best wind resource. It is estimated that the U.S. will need to build over one million miles of new transmission lines over the next three decades to bring wind from the Midwest and solar from the Southwest to meet distant loads.

General Wind and Solar Barriers:

Current transmission/distribution system not designed for intermittent generation.
Existing U.S. transmission system not designed to move solar and wind from best resource locations to major load zones.
Currently, global supply chain problems delaying projects and increasing prices.
Overreliance on Chinese panel makers now subject to tariffs and human rights concerns.
Critical mineral shortages block production of key components.
Skilled labor shortages.

Distributed Solar Barriers:

Affordability of solar for all homeowners.
Grid stability and integration upgrades as distribution grid changes from centralized, one-way flows to distributed two-way flows.
Policy disputes over who pays for upgrades needed (e.g., the resident adding the solar or the distribution system).
Building ownership: Renters and commercial tenants pay for the energy while building owners typically control roof.

Utility-Scale Solar Barriers:

Land availability and permitting.
Managing massive generation swings between day and night.
Managing smaller, but more frequent generation variances due to weather patterns.

Onshore Wind Barriers:

Land availability.
Extreme weather — disruption of normal wind patterns by climate change.
Local opposition to projects due to noise, traffic, and view concerns.

Offshore Barriers:

Increased capital and operating costs required for construction, operations, and maintenance.
Disruptions to marine wildlife and fishing sites.
Local opposition to siting primarily due to view concerns.

Accelerators

The Infrastructure Investment and Jobs Act and the Inflation Reduction Act extend and expand support for wind and solar energy while making major investments into the grid to enhance flexibility and reliability. The Infrastructure Investment and Jobs Act includes $65 billion for investments to enhance grid reliability, expand transmission lines, improve grid flexibility, and deploy distributed energy resources. The Inflation Reduction Act allocates $369 billion to climate investments, including enhanced tax incentives for wind and solar projects, adding direct tax incentives for storage, and expanding support for domestic manufactures of clean energy components. Implementation of these programs over the next few years will certainly spur additional wind and solar projects, but there are other solutions needed and available to ensure the U.S. reaches its decarbonization goals.

General Wind and Solar Accelerators:

Modernizing the grid, (through enabling technologies such as sensors, distributed intelligence, and communications) is a necessary predicate to adding the volumes of wind and solar resources necessary under almost any scenario to significantly decarbonize the U.S. grid.
Peak shaving solutions such as customer-controlled demand management and dispatchable demand reduction) allow the demand side of the grid to help mitigate renewable generation variability.
Increased clean firm generation, such as hydroelectric, geothermal, and fuel cells, to supplement intermittent renewable generation.
Both utility scale and distributed energy storage to meet the challenge of increased reliance on intermittent energy sources, automated and integrated into the grid.
The price of solar panels decreased 65% between 2010 and 2019, where the average cost declined from $7.34 per watt to $2.53 per watt.⁹ Further panel and balance of system cost reductions will make solar more affordable to more homeowners, commercial businesses and communities, and will accelerate deployment.
Through policies accelerating scaling, off shore wind costs can be reduced to be in line with other generation alternatives. For instance, the Departments of Energy, Interior, Commerce, and Transportation announced an expansion of the Biden administration’s offshore wind efforts on September 15, 2022, through the new Floating Offshore Wind Energy Earthshot program.¹⁰