TODAY’S STUDY: MIT ASSESSES SOLAR’S FUTURE
The Future of Solar Energy
Schmalensee, et. al., May 2015 (Massachusetts Institute of Technology)
Solar electricity generation is one of very few low-carbon energy technologies with the potential to grow to very large scale. As a consequence, massive expansion of global solar generating capacity to multi-terawatt scale is very likely an essential component of a workable strategy to mitigate climate change risk. Recent years have seen rapid growth in installed solar generating capacity, great improvements in technology, price, and performance, and the development of creative business models that have spurred investment in residential solar systems. Nonetheless, further advances are needed to enable a dramatic increase in the solar contribution at socially acceptable costs. Achieving this role for solar energy will ultimately require that solar technologies become cost-competitive with fossil generation, appropriately penalized for carbon dioxide (CO2) emissions, with — most likely — substantially reduced subsidies.
This study examines the current state of U.S. solar electricity generation, the several technological approaches that have been and could be followed to convert sunlight to electricity, and the market and policy environments the solar industry has faced. Our objective is to assess solar energy’s current and potential competitive position and to identify changes in U.S. government policies that could more effi ciently and effectively support the industry’s robust, long-term growth. We focus in particular on three preeminent challenges for solar generation: reducing the cost of installed solar capacity, ensuring the availability of technologies that can support expansion to very large scale at low cost, and easing the integration of solar generation into existing electric systems. Progress on these fronts will contribute to greenhouse-gas reduction efforts, not only in the United States but also in other nations with developed electric systems. It will also help bring light and power to the more than one billion people worldwide who now live without access to electricity.
This study considers grid-connected electricity generation by photovoltaic (PV) and concentrated solar (or solar thermal) power (CSP) systems. These two technologies differ in important ways. A CSP plant is a single largescale installation, typically with a generating capacity of 100 megawatts (MW) or more, that can be designed to store thermal energy and use it to generate power in hours with little or no sunshine. PV systems, by contrast, can be installed at many scales — from utility plants with capacity in excess of 1 MW to residential rooftop installations with capacities under 10 kilowatts (kW) — and their output responds rapidly to changes in solar radiation. In addition, PV can use all incident solar radiation while CSP uses only direct irradiance and is therefore more sensitive to the scattering effects of clouds, haze, and dust.
Realizing Solar Energy’s
Photovoltaic Modules The cost of installed PV is conventionally divided into two parts: the cost of the solar module and so-called balance-of-system (BOS) costs, which include costs for inverters, racking and installation hardware, design and installation labor, and marketing, as well as various regulatory and fi nancing costs. PV technology choices infl uence both module and BOS costs. After decades of development, supported by substantial federal research and development (R&D) investments, today’s leading solar PV technology, wafer-based crystalline silicon (c-Si), is technologically mature and large-scale c-Si module manufacturing capacity is in place. For these reasons, c-Si systems likely will dominate the solar energy market for the next few decades and perhaps beyond. Moreover, if the industry can substantially reduce its reliance on silver for electrical contacts, material inputs for c-Si PV generation are available in suffi cient quantity to support expansion to terawatt scale.
However, current c-Si technologies also have inherent technical limitations — most importantly, their high processing complexity and low intrinsic light absorption (which requires a thick silicon wafer). The resulting rigidity and weight of glass-enclosed c-Si modules contribute to BOS cost. Firms that manufacture c-Si modules and their component cells and input materials have the means and the incentive to pursue remaining opportunities to make this technology more competitive through improvements in effi ciency and reductions in manufacturing cost and materials use. Thus there is not a good case for government support of R&D on current c-Si technology.
The limitations of c-Si have led to research into thin-fi lm PV alternatives. Commercial thin-fi lm PV technologies, primarily cadmium telluride (CdTe) and copper indium gallium diselenide (CIGS) solar cells, constitute roughly 10% of the U.S. PV market today and are already cost-competitive with silicon. Unfortunately, some commercial thin-fi lm technologies are based on scarce elements, which makes it unlikely that they will be able to achieve terawatt-scale deployment at reasonable cost. The abundance of tellurium in Earth’s crust, for example, is estimated to be only one-quarter that of gold.
A number of emerging thin-fi lm technologies that are in the research stage today use novel material systems and device structures and have the potential to provide superior performance with lower manufacturing complexity and module cost. Several of these technologies use Earth-abundant materials (even silicon in some cases). Other properties of some new thin-fi lm technologies, such as low weight and compatibility with installation in fl exible formats, offer promise for enabling reductions in BOS costs along with lower module costs.
Though these emerging technologies are not nearly competitive with c-Si today, they have the potential to signifi cantly reduce the cost of PV-generated electricity in the future. And while the private sector is likely to view R&D investments in these technologies as risky, the payoff could be enormous. Therefore, to increase the contribution of solar energy to long-term climate change mitigation, we strongly recommend that a large fraction of federal resources available for solar research and development focus on environmentally benign, emerging thin-fi lm technologies that are based on Earth-abundant materials. The recent shift of federal dollars for solar R&D away from fundamental research of this sort to focus on near-term cost reductions in c-Si technology should be reversed.
Concentrated Solar Power
CSP systems could be deployed on a large scale without encountering bottlenecks in materials supply. Also, the ability to include thermal energy storage in these systems means that CSP can be a source of dispatchable electricity. The best prospects for improving CSP economics are likely found in higher operating temperatures and more effi cient solar energy collection. Therefore R&D and demonstration expenditures on CSP technology should focus on advances in system design, including singlefocus systems such as solar towers, and in the underlying materials science, that would allow for higher-temperature operations, and on the development of improved systems for collecting and receiving solar energy.
Historically, U.S. federal government support for CSP technology has included loan guarantees for commercial-scale installations. CSP plants only make economic sense at large scale and, given the technical and fi nancial risks, investors in these large installations are naturally conservative in their selection of system designs and component technologies. Missing in federal efforts to promote CSP technology has been support for pilot-scale plants, like those common in the chemical industry, that are small enough to allow for affordable higher-risk experimentation, but large enough to shed light on problems likely to be encountered at commercial scale. Therefore we recommend that the U.S. Department of Energy establish a program to support pilot-scale CSP systems in order to accelerate progress toward new CSP system designs and materials.
The Path To Cost Competitiveness
As of the end of 2014, PV systems accounted for over 90% of installed U.S. solar capacity, with about half of this capacity in utility-scale plants and the balance spread between residential and commercial installations. The industry has changed rapidly. In the past half-dozen years, U.S. PV capacity has expanded from less than 1,000 MW to more than 18,000 MW. Recent growth has been aided in part by a 50%–70% drop in reported PV prices (without federal subsidies) per installed peak watt. (The peak watt rating of a PV module or system refl ects its output under standard test conditions of irradiance and temperature.) Almost all of this improvement has refl ected falling prices for modules and inverters. In addition, the market structure for solar energy is changing, particularly at the residential level, with the evolution of new business models, the introduction of new fi nancing mechanisms, and impending reductions in federal subsidies.
Currently, the estimated installed cost per peak watt for a residential PV system is approximately 80% greater than that for a utility-scale plant, with costs for a typical commercial-scale installation falling somewhere in between. Module costs do not differ signifi cantly across sectors, so the major driver of cost differences in different market segments is in the BOS component, which accounts for 65% of estimated costs for utility-scale PV systems, but 85% of installed cost for residential units. Experience in Germany suggests that several components of BOS cost, such as the cost of customer acquisition and installation labor, should come down as the market matures. Costs associated with permitting, interconnection, and inspection (PII) may be more diffi cult to control: across the United States, thousands of municipal and state authorities and 3,200 organizations that distribute electricity to retail customers are involved in setting and enforcing PII requirements. A national or regional effort to establish common rules and procedures for permitting, interconnection, and inspection could help lower the PII component of installed system cost, particularly in the residential sector and perhaps in commercial installations as well.
In the past few years, the nature of the residential solar business in the United States has changed appreciably. A third-party ownership model, which is currently allowed in half the states, is displacing direct sales of residential PV systems by enabling homeowners to avoid up-front capital costs. The development of the third-party ownership model has been a boon to residential PV development in the United States, and residential solar would expand more rapidly if third-party ownership were allowed in more states.
Today the estimated cost for a utility-scale PV installation closely matches the average reported price per peak watt, indicating active competition in the utility segment of the PV market. However, a large difference exists between contemporary reported prices and estimated costs for residential PV systems, indicating that competition is less intense in this market segment.
Two influences on PV pricing are peculiar to the U.S. residential market and to the thirdparty ownership model. One is the effect of current federal tax subsidies for solar generation: a 30% investment tax credit (ITC) and accelera ted depreciation for solar assets under the Modifi ed Accelerated Cost Recovery System (MACRS). Third-party owners of PV systems generally need to operate on a large scale to realize the value of these provisions, which creates a barrier to entry. In addition, because there is generally little price competition between third-party installers, PV developers often are not competing with one another to gain residential customers, but with the rates charged by the local electric distribution company.
Some of the largest third-party solar providers operate as vertically integrated businesses, and their systems are not bought and sold in “arm’s-length” transactions. Instead, for purposes of calculating federal subsidies they typically can choose to estimate their units’ fair market value based on the total income these units will yield. In a less than fully competitive market, this estimation approach can result in fair market values that exceed system costs and thus lead to higher federal subsidies than under a direct sale model. Where competition is not intense, subsidies are not necessarily passed on to the residential customer.
Over time, more intense competition in the residential PV market (as a natural consequence of market growth and the entry of additional suppliers) should direct more of the available subsidy to the residential customer by driving down both power purchase rates under third-party contracts and prices in direct sales. And these pressures will also intensify industry efforts to reduce the BOS component of installation cost.
Even with greater competition, however, an inherent ineffi ciency in the current, investmentbased federal subsidy system will remain. Because residential solar has a higher investment cost per peak watt, and because the magnitude of the federal subsidy is based on a provider-generated calculation of fair market value, residential solar receives far higher subsidies per watt of deployed capacity than utility-scale solar. Moreover, because third-party contracts are infl uenced by local utility rates, which vary considerably across the country, the per-watt subsidy for identical residential or commercial installations can differ substantially from region to region.
Solar Economics…Residential Solar…Integration Into Existing Electric Systems…Distributed Solar…Wholesale Markets…Deployment of Current Technology…
A Closing Thought
In the face of the global warming challenge, solar energy holds massive potential for meeting humanity’s energy needs over the long term while cutting greenhouse gas emissions. Solar energy has recently become a rapidly growing source of electricity worldwide, its advancement aided by federal, state, and local policies in the United States as well as by government support in Europe, China, and elsewhere. As a result the solar industry has become global in important respects.
Nevertheless, while costs have declined substantially in recent years and market penetration has grown, major scale-up in the decades ahead will depend on the solar industry’s ability to overcome several major hurdles with respect to cost, the availability of technology and materials to support very large-scale expansion, and successful integration at large scale into existing electric systems. Without government policies to help overcome these challenges, it is likely that solar energy will continue to supply only a small percentage of world electricity needs and that the cost of reducing carbon emissions will be higher than it could be.
A policy of pricing CO2 emissions will reduce those emissions at least cost. But until Congress is willing to adopt a serious carbon pricing regime, the risks and challenges posed by global climate change, combined with solar energy’s potential to play a major role in managing those risks and challenges, create a powerful rationale for sustaining and refining government efforts to support solar energy technology using the most efficient available policies.