The US Department of Energy has recently released a study titled “The Solar Futures Study” which explores the role of solar in decarbonizing the grid. Through state-of-the-art modeling, the study envisions deep grid decarbonisation by 2035, as driven by a required emissions-reduction target.

The study uses a suite of detailed power-sector models to develop and evaluate three core scenarios. The “Reference” scenario outlines a business-as-usual future, which includes existing state and federal clean energy policies but lacks a comprehensive effort to decarbonize the grid. The “Decarbonisation” scenario assumes policies drive a 95 per cent reduction (from 2005 levels) in the grid’s carbon dioxide emissions by 2035 and a 100 per cent reduction by 2050. The “Decarbonisation with Electrification (Decarb+E)” scenario goes further by including large-scale electrification of end uses. REGlobal presents the key findings from the report…

Key Findings:

  • Achieving the decarbonisation scenarios requires significant acceleration of clean energy deployment. Compared with the approximately 15 GW of solar capacity deployed in 2020, annual solar deployment doubles in the early 2020s and quadruples by the end of the decade in the Decarb+E scenario. Similarly, substantial solar deployment rates continue in the 2030s and beyond.
  • Continued technological progress in solar is critical to achieving cost-effective grid decarbonisation and greater economy-wide decarbonisation. Research and development can play an important role in keeping these technologies on current or accelerated cost-reduction trajectories. For example, a 60 per cent reduction in PV energy costs by 2030 could be achieved via improvements in photovoltaic efficiency, lifetime energy yield, and cost. Higher-temperature, higher-efficiency concentrating solar power technologies also promise cost and performance improvements. Further advances are also needed in areas including energy storage, load flexibility, generation flexibility, and inverter-based resource capabilities for grid services.
  • Solar can facilitate deep decarbonisation of the U.S. electric grid by 2035 without increasing projected 2035 electricity prices if targeted technological advances are achieved. In the Decarb and Decarb+E scenarios, 95 per cent decarbonisation is achieved in 2035 without increasing electricity prices because decarbonisation and electrification costs are fully offset by savings from technological improvements and enhanced demand flexibility.
  • For the 2020–2050 study period, the benefits of achieving the decarbonisation scenarios far outweigh additional costs incurred. Cumulative (2020–2050) power-system costs are one measure of the long-term economics of the decarbonisation scenarios, helping to capture the impact of long-lived generating technologies. These costs are about $225 billion higher in the Decarb scenario than in the Reference scenario, reflecting the added cost of capital investments in clean generation, energy storage, and transmission; operations and maintenance of these assets; and the reduced fuel and other expenditures for fossil fuel technologies. Avoided climate damages and improved air quality more than offset additional costs, resulting in net savings of $1.1 trillion in the Decarb scenario and $1.7 trillion in the Decarb+E scenario.
  • The envisioned solar growth will yield broad economic benefits in the form of jobs and workforce development. The solar industry already employs around 230,000 people in the United States, and with the level of growth envisioned in the Solar Futures Study’s scenarios, it could employ 500,000–1,500,000 people by 2035.
  • Challenges must be addressed so that solar costs and benefits are distributed equitably. Low and medium income communities and communities of color have been disproportionately harmed by the fossil-fuel-based energy system, and the clean energy transition presents opportunities to mitigate these energy justice problems by implementing measures focused on equity.
  • Solar can help decarbonize the buildings, transportation, and industrial sectors. In the Decarb+E scenario, electrification of fuel-based end uses enables solar electricity to power about 30 per cent of all building end uses and 14 per cent of transportation end uses by 2050. For buildings, rooftop solar can increase the value of batteries and investments in load automation systems; distributed batteries and load automation can, in turn, increase the grid value of solar. For transportation, rooftop solar could increase the value of electric vehicle adoption to consumers through a combination of low-marginal-cost electricity and managed charging.
  • Diurnal energy storage enables high levels of decarbonisation, but additional clean firm capacity is needed to achieve full grid decarbonisation. In the Decarb+E scenario, storage with 12 hours or less of energy capacity expands by up to 70-fold, from 24 GW in 2019 to more than 1,600 GW in 2050. This diurnal storage complements renewable energy deployment by storing energy when it is less useful to the grid and releasing it when it is more useful. However, because solar and wind occasionally provide insufficient supply for several days, advances in technologies that can provide clean firm capacity at any time are needed to reliably meet demand as full decarbonisation is approached.
  • Maintaining reliability in a grid powered primarily by renewable energy requires careful power system planning. In the decarbonisation scenarios, the grid becomes increasingly reliant on weather-dependent inverter-based resources (IBRs) such as PV, representing a dramatic change from the current grid based primarily on synchronous electricity generators. A grid dominated by IBRs will require new approaches to maintain system reliability and exploit the ability of IBRs to respond quickly to system changes. 
  • Demand flexibility plays a critical role by providing firm capacity and reducing the cost of decarbonisation. Demand flexibility shifts demand from end uses, such as electric vehicles, to better utilize solar generation. In the Decarb+E scenario, demand flexibility provides 80–120 GW of firm capacity by 2050 and reduces decarbonisation costs by about 10 per cent.
  • Developing U.S. solar manufacturing could mitigate supply chain challenges, but different labor standards and regulations abroad create cost-competitiveness challenges. Global PV supply chains can be constrained by production disruptions, competing demand from other industries or countries, and political disputes. A resilient supply chain would be diversified and not over reliant on any single supply avenue. To enhance the domestic supply chain, American solar technology manufacturers may improve competitiveness by increasing automation and exploiting the advantages of domestically manufacturing certain components. Policies can help promote domestic solar manufacturing.
  • Although land acquisition poses challenges, land availability does not constrain solar deployment in the decarbonisation scenarios. In 2050, ground-based solar technologies require a maximum land area equivalent to 0.5 per cent of the contiguous U.S. surface area. This requirement could be met in numerous ways including use of disturbed lands. The maximum solar land area required is equivalent to less than 10 per cent of potentially suitable disturbed lands, thus avoiding conflicts with high-value lands in current use.
  • Water withdrawals decline by about 90 per cent by 2050 in the decarbonisation scenarios. The water savings result from the low water use of solar and other clean energy generation technologies, compared with fossil fuel and nuclear generators.

Solar Futures Scenarios

The Solar Futures scenarios are modeled using the Regional Energy Deployment System (ReEDS) capacity-expansion and dispatch model of the U.S. electricity sector. ReEDS identifies the optimal power system portfolio from a mix of renewable and non-renewable generation technologies, bulk energy storage options, and transmission expansion.

The study compares the electricity generation mix of the U.S. grid in 2020 to the grid mix envisioned in the Decarb+E scenario in 2035. It illustrates two key mechanisms for decarbonisation: grid decarbonisation and electrification. Grid decarbonisation is depicted by the significant reduction in carbon-emitting fossil fuel flows in the Decarb+E grid mix in 2035.

In 2020, about 60 per cent of electricity came from carbon-emitting fossil fuel combustion in more than 1,000 coal and natural gas plants. By 2035, solar accounts for about 37 per cent in the Decarb+E scenario, and the remainder is met largely by other zero-carbon resources, including wind (36 per cent), nuclear (11-13 per cent), hydroelectric (5-6 per cent), and bio power and geothermal (1 per cent) sources. The impact of electrification is illustrated by the overall growth of the grid: electricity demand grows by about 30 per cent from 2020 to 2035 in the Decarb+E scenario, owing in part to the electrification of fuel-based building loads, vehicles, and some industrial processes.


Curtailment is the practice of foregoing available RE output due to transmission congestion constraining RE delivery, other system inflexibilities such as minimum generation limits, and mismatches between generation and demand profiles. The study estimates the annual curtailment through 2050 under the core scenarios.

Annual curtailment reaches 274 TWh (8 per cent of available PV and wind generation) in 2035 and grows to 398 TWh (9.2 per cent) by 2050 under the Decarb scenario. With electrification and decarbonisation, curtailment is greater in absolute and relative terms by 2050; 2035 and 2050 annual curtailment are 298 TWh (7 per cent) and 826 TWh (13 per cent) under the Decarb+E scenario.

Carbon Emissions

The study combines the estimated power-sector emissions with emissions from U.S. end-use sectors – residential and commercial buildings, industry, and transportation, to estimate total energy-related CO2 emissions.

In the Reference scenario, reduced power-sector emissions are offset in part by increased emissions in the end-use sectors. As a result, annual energy-related CO2 emissions are 21 per cent below 2005 levels in 2035, declining only slightly to 24 per cent below in 2050. In contrast, the Decarb scenario, which has the same end-use sector emissions as the Reference scenario, reduces energy-related emissions to 42 per cent below 2005 levels in 2035. The rate of energy-related CO2 reductions between 2020 and 2035 is similar to reductions experienced during the prior 15 years. Energy-related emissions rise slightly between 2035 and 2050 as increased emissions from end uses outpace power-sector emissions reductions.

Combining grid decarbonisation with electrification provides larger emissions reductions. The Decarb+E scenario shows that increasing use of low-carbon electricity in the end-use sectors can lower energy-related CO2 emissions to 2,950 Mt by the mid-2030s (51 per cent below 2005 levels) and 2,280 Mt by 2050 (62 per cent below 2005 levels).

The Three R’s for Deployment of Solar Power

Reliability of solar power encompasses many factors, which can be expressed as the three Rs: resource adequacy (RA), operational reliability, and resilience. RA represents planning for the system’s ability to supply enough electricity at the right locations to keep the lights on, even during extreme-weather days and when “reasonable” outages occur. The second component, operational reliability, ensures the lights stay on even when unexpected things happen. RA is intended to ensure sufficient capacity is available during events such as an outage. Operational reliability enables the system to operate in the seconds during an abnormal event and minutes after the event. Resilience is “the ability to withstand and reduce the magnitude and/or duration of disruptive events, which includes the capability to anticipate, absorb, adapt to, and/or rapidly recover from such an event”. Resilience also typically includes more extreme events that go excluded from RA and traditional operational reliability.

Cybersecurity in the Future Grid

Modern grids measure and collect large amounts of data and use a variety of advanced control systems in the information technology and operational technology spaces, but each innovation opens doors for new vulnerabilities and cyber threats that could disrupt grid operation. Addressing cybersecurity concerns requires all energy stakeholders—electric utilities, aggregators, grid operators, vendors, and state and federal government agencies.

 “Game-changing” technologies are needed to enable a fully distributed grid while protecting national security. These include Name data networking, which enables secure end-to-end communications without dependence on the security or topology of underlying channels; Zero-trust networks for grid operations and management, which recognize the information, devices, applications, and frameworks that must be protected with the assumption that the network is potentially compromised; Quantum-resistant cryptographic algorithms which requires development of cryptographic schemes resistant to the impacts of quantum computers; and, Use of fifth-generation (5G) cellular technology in the modern grid for power communications to provide significantly higher throughput, better coverage, and better reliability.

Synergies for energy decarbonisation in buildings

One of the key challenges in the grid integration of solar is the temporal mismatch between solar output peaks (midday) and grid demand peaks (early evening). Instead of ramping up a flexible generator or storing and shifting solar output through batteries, grid peak demand can be shifted from the evening to the midday by shifting flexible loads. Leveraging building load flexibility could be a key measure for integrating solar faster and more cost-effectively.

Building energy technology automation, coordination, and aggregation can significantly enhance the role of solar in building energy decarbonisation.

The Role of Solar by End-Use Sector

The energy system exists to generate and deliver power for end-use activities. These end uses are often categorized into three sectors: residential and commercial buildings, transportation, and industry. Solar plays the most immediate role in the buildings sector, which is characterized by a relatively large share of electrified loads, good prospects for near-term electrification, and the potential for near- universal electrification by 2050. Solar plays more limited near-term roles in transportation and industry because of the reliance of these sectors on direct fuel combustion.

The study analyses the role of solar in decarbonizing each of these end uses.

By 2050, using the assumptions of the Decarb+E scenario, the study estimates that solar electricity powers around 37 per cent of building energy, 28 per cent of transportation energy, and 13 per cent of industrial energy.

The complete report can be accessed here