• Pranav Gupta

Overview of Concentrated Solar Power Technology in the USA, Spain, and Israel

This is a report I wrote with my partner Dhroovaa Khannan for my graduate class Energy Conversion & Supply at Carnegie Mellon University. This report addresses an overview of CSP technology, implementation in countries with the highest penetration of CSP, and policy recommendations for the country that we had to focus on for the report - Israel.


Introduction

This report is an overview of concentrated solar power (CSP) technologies across the globe, with a specific focus on the United States, Spain, and Israel. The report itself is split into four main parts: Energy Resource Overview, Resource Conversion Technology, Resource Utilization Impacts, and Resource Utilization Policy. The “Energy Resources Overview” section provides a brief introduction into solar energy basics and the sun’s function as a primary energy source. This is followed by the current distribution of CSP plants across the world. The “Resource Conversion Technology” section explains the basic science behind the conversion of solar energy into electricity, and the different types of CSP technology used in commercial plants. This section also includes a detailed description of a recently deployed large scale CSP plant in Israel.


The “Resource Utilization Impacts” section briefly summarizes the political, economic, social, and environmental benefits of and concerns with CSP technology. Additionally, this section includes a forecasted growth outlook of CSP globally and in Israel. Finally, the “Resource Utilization Policy” section revisits the benefits of and concerns with CSP implementation specifically in Israel, and discusses possible policy measures that could contribute to an improved use of solar power.

Energy Resource Overview

Solar Energy Basics

Everyday the sun rises and radiates more energy in an hour than the world uses in one year via a process called nuclear fusion.[1] The sun is mostly made up of hydrogen and helium atoms in the plasma state (negatively charged electrons are separated from positively charged atomic nuclei). At the sun’s core, high temperature and pressure cause the nuclei of two kinds of hydrogen isotopes (tritium and deuterium) to fuse together to form helium nuclei. Additionally, the reaction releases neutrons and high energy photons (gamma rays) as byproducts.[2] These high energy photons are radiated outwards into space and solar technologies on Earth capture and convert them into electricity (photovoltaics) or into thermal energy (concentrated solar power).


Figure 1: Nuclear fusion.[3]

Global Solar Energy Access


In 2019, global capacity of concentrated solar power grew by 9.6% to 6.2GW. Spain leads the world with 2.3GW capacity followed by the United States with 1.7GW capacity. The two countries account for approximately 65% of installed global CSP capacity.[4] However, CSP generation in other countries is on the rise as Israel, China, South Africa, Kuwait and France have a combined 1.1GW under construction.[5]


Figure 2: CSP Global Capacity 2009-2019.[5]


Israel added 242MW in 2019 through the construction of two new power plants – the 121MW Megalim tower plant with no thermal energy storage, and the 121MW Negev parabolic trough plant with 4.5hr/495MWh of molten salt storage.[5]


However, when it comes to cumulative capacity in operation, Spain and the U.S. are global leaders. The fact that Spain and the U.S. are global leaders despite having no new additions since 2013 and 2015 respectively[5] shows that the CSP industry is still in its infancy and has potential for growth.


Figure 3: Two maps showing the solar intensity above the United States and Spain.[6][7]


Resource Conversion Technology


This section discusses the basic science behind the conversion of solar energy into electricity using concentrated solar power. The concepts of solar energy and sunlight capture build upon the ideas discussed in the prior section. Although solar photovoltaic (PV) systems and CSP systems share the same primary energy source (sunlight), the manner in which they each convert sunlight to electricity is different. Solar PV uses solar panels created from the combination of different materials (usually silicon) to directly convert the light energy from sunlight into electricity.[8] CSP systems are defined by their use of reflective mirrors to first concentrate solar thermal energy, then convert that thermal energy into electricity.


Conversion of Sunlight to Electricity


There are three main types of CSP systems: parabolic trough systems, dish engine or point focus systems, and power tower systems.[9] The common feature between these three systems is the use of mirrors to concentrate sunlight and convert it into heat, which is then used to create steam that drives power generating turbines. The difference between these systems is in the shape and positioning of the mirrors, the focal point (receiver) of concentrated solar energy, and the process used to convert that solar thermal energy into electricity.


Parabolic trough systems use rows of small mirrors to focus incident sunlight on a nearby pipe with a heating fluid inside. The hot fluid heated by the concentrated solar energy is used to increase the temperature of a working fluid in a heat exchanger, which is then passed through a turbine. This turbine powers a generator that generates electricity as part of a standard Rankine cycle. After exiting the turbine, the working fluid passes through a radiator where it is cooled by either flowing water or a coolant fluid. Then, the working fluid passes through a compressor so that it may again be heated up by the heating fluid (by way of the solar reflectors) to continue the Rankine cycle.[10] Pumps are typically used to pump both the heating fluid between the solar collector and heat exchanger, and the coolant fluid through the radiator. One variation of the parabolic trough system is the Linear Fresnel Reflector system, which uses rows of flat mirrors to concentrate sunlight on pipes of heating fluid that are suspended above the mirrors, as opposed to the parabolic mirrors and ground-level solar collectors used in parabolic trough systems. Overall, these systems have peak plant efficiencies ranging between 14%-20%, with capacity factors ranging from 25%-28%, and 29%-43% with thermal energy storage.[11]


Figure 4: Close-up of a row of parabolic trough mirrors and solar collector pipe with heating fluid.[10]


Dish Engine systems utilize large, curved, dish-shaped mirrors that reflect incident sunlight onto a receiver strategically placed in the foci of the parabola created by the dish. Once again, a heating fluid contained inside the receiver is used to start a similar Rankine cycle that generates electricity. The differences between the parabolic dish model and the previously defined parabolic trough model are the size of the mirrors and that the dishes themselves are typically mounted on structures with multi-axis solar tracking systems that enable them to follow the sun.[12] Overall, these systems have peak plant efficiencies around 30%, with capacity factors ranging from 25-28%.[11]


Figure 5: Close-up of a dish engine system highlighting the large, parabolic mirrors and solar collector.[12]


Power Tower designs rely on a large field with multiple rows of smaller, individual mirrors that concentrate the incident sunlight onto a single solar collector, placed atop a tower in the middle or at one end of the field.[9] Similar to the previous two systems, a heating fluid contained inside the receiver is used to start a Rankine cycle that generates electricity. Although earlier iterations of power towers mostly utilized steam as the heating transfer fluid, some current designs often use molten salts due to their superior heat transfer and energy storage capabilities.[13] Overall, these systems have peak plant efficiencies ranging between 25%-35%, with capacity factors around 55%.[11]


Figure 6: Aerial view of Solar Two, a 10MW power tower facility in CA with molten salt storage.[12]


Historical Look at CSP Plants in the US and Spain


To understand the designs and capabilities of modern CSP plants, we will examine the historical development of CSP specifically in the United States and Spain, where the first commercial CSP technologies were implemented.


In the United States, CSP development is concentrated in the continental southwest, as this region has the highest annual sum of direct solar irradiation–it is the sunniest region of the US and therefore the most viable for solar power plants. The first commercial CSP plants in the world were built in the Mojave Desert, California by Luz International Ltd. This group of plants, known as the SEGS plants, are still operational today and consist of nine separate parabolic trough systems with a total capacity of around 354MW.[6] Between 2013 and 2015 five new utility-scale power tower systems went online in the US, totalling around 1.25GW in capacity. The largest of these facilities is Ivanpah Solar Electric Generating System (ISEGS) tower built by Brightsource in 2014, with a net capacity of 377MW. The latest CSP project to come online in the US is the 110MW Crescent Dunes facility in Tonopah, Nevada.[14] As of 2020, the US has a total of 1.7GW in installed CSP capacity, making it the second largest generator of CSP in the world, behind Spain.


Spain’s CSP development began in 2002, with the introduction of policy measures to make concentrated solar more economical and attractive to investors, via a feed-in tariff. The country’s first commercial CSP plant came online in 2007–the PS10 solar power tower developed by Abengoa Solar with an installed capacity of 283MW.[7] Since the installation of PS10, there have been 49 new additions to the country’s CSP facilities, bringing the grand total to 50 CSP plants. These 50 plants have an aggregate total of 2.3GW installed capacity, making up more than one-third of the world’s total CSP capacity.[14]


Detailed Look at Modern CSP Plants in Israel


Israel has two commercial CSP plants, each with an installed capacity of 121MW. The first of these plants is the Ashalim Plot-B Solar Thermal Power Plant which uses power tower technology and is located in the Negev Desert region of Israel. The second plant is the Negev Energy Solar Thermal Power Plant, which uses parabolic trough technology and is located in the same plot in the Negev Desert. Despite having the same installed capacity and both being built in 2019, these two plants use different CSP technologies and are developed by different groups.[14] We will take a detailed look at the Ashalim Plot-B Plant developed by Megalim to better understand modern CSP technology in Israel.


As mentioned above, the Megalim plant uses solar power tower technology to achieve its capacity of 121MW. The USD $840 million plant was developed by Megalim Solar Power Ltd. and is currently operated by General Electric.[14] The plant consists of a solar field filled with heliostats (mirrors), a central power tower where the solar collector rests, and a steam turbine for power generation. The solar field itself has an area of 3.15 km2, with over 50,000 individual heliostats. Each heliostat has an aperture of 20.8m2, and is computer-controlled to ensure that it is positioned at the optimal angle to receive maximum solar irradiation. The sunlight from these mirrors is reflected onto the solar collector, placed at the top of a 240m tower, making it the tallest CSP power tower in the world. The superheated steam inside the solar collector is then pushed through a steam rankine cycle to generate electricity, from which the plant generates 3.2GWh annually.[14] This plant has no thermal storage capacity, unlike its sister parabolic trough plant which has molten salt thermal storage capabilities.


Figure 7: A wide-angle view of the Megalim Solar Thermal Power Plant in Negev, Israel.[15]


Resource Utilization Impacts


CSP Benefits and Concerns


As with any power generation technology, CSP has its strengths and weaknesses which can be categorized into environmental, economic, political, and social categories. From an environmental perspective, CSP is far more viable than fossil fuel (coal, natural gas, etc.) which are widely used for power generation across the world. CSP plants use approximately five acres of land per MW of installed capacity, with no further land use requirements for resource extraction or processing. There is enough CSP-suitable land in the southwestern United States to generate six times the current national demand for energy.[9] CSP plants are also completely non-emitting, meaning that no greenhouse gases or toxic chemicals are emitted in the power generation process. The only GHGs associated with CSP plants are those emitted from the manufacturing of the plant materials and plant construction. Even so, CSP plants have an average energy payback time of five months, i.e. they generate enough electricity to recoup the energy consumed in the manufacturing of the plant within this time.[9] Additionally, CSP has higher control capabilities, as the rate at which steam is pushed through the Rankine cycle to produce electricity can be manipulated. This allows for greater control of electricity during peak hours when compared to solar PV, where generation is dependent only on the solar intensity. Some drawbacks of CSP include high capital cost and low capital recovery factors. In some cases, as with Spain in the early 2000s, these high costs and low returns on investment can stifle CSP development plans.[7] For CSP to become more price competitive, advancements in R&D and increased production are needed. Additionally, CSP can only provide generation during sunlight hours, making it impossible for CSP plants to be the sole generator for communities without large scale storage options. Although daytime capacity factors and plant efficiency numbers are higher than even some fossil fuel plants, CSP cannot provide around the clock reliable power to communities by itself. CSP also requires access to water supply as water is used both to cool the high-pressure steam used in the Rankine cycles, and to clean solar reflectors. However, it should be noted that almost all power plants require access to water supplies, some at much higher quantities than CSP.


Forecasting Future Trends in CSP


Recent trends indicate that CSP is gaining traction across the world with construction underway in Asia (China and India), the Middle East (U.A.E., Saudi Arabia, and Israel) and Latin America (Chile). This is in sharp contrast to 2015, when most projects were aggregated in Spain and the US. Due to the spread of markets, broadening of supply chains and industry experience, costs have fallen remarkably. The weighted average levelized cost of electricity (estimated revenue required to build and operate a generator over a specified cost recovery period) has fallen by 47% between 2010 and 2019.[5] These costs are expected to fall further with increased R&D and construction of CSP plants across the world.


One such project under construction is the Noor 1 project in U.A.E. which will include 700MW of CSP capacity, consisting of three 200MW parabolic trough plants and a 100MW tower plant.[16] The Cerro Dominador project in Chile has 110MW of capacity, and China has 250MW of both parabolic trough and tower capacity under construction.[5] Additionally, Spain has announced plans to increase its installed CSP capacity to 5GW by 2030.[17]


2019 has also seen a range of R&D activities. EDF (French utility) and Shoughang (Chinese CSP company) are working together to improve the technology to be capable of working at higher operating temperatures.[18] In the U.S., the Department of Energy has announced $30 million for 13 research projects that are aimed at improving the economics of CSP by reducing manufacturing costs, developing new storage technologies, and increasing autonomous system operations.[19]


Israel in particular wants to add another 15GW by 2030 and increase the proportion of its total electricity generation from renewables from 17% to 30%.[20] Since Israel lacks any substantial hydro, wind or geothermal resources, solar energy will be the primary source of this growth. However, between PV and CSP, rooftop PV seem to be the path going forward as the high land use requirements and capital costs make CSP less viable in the long term.[21][22]


Resource Utilization Policy


Benefits and Concerns with CSP in Israel


Israel has a solar power-conducive geography, as much of its land receives large amounts of solar radiation each year. Most of the environmental benefits of CSP mentioned above apply to Israel as well, which is a key reason why the Ashalim plants were built in the first place. However, the largest challenge Israel faces with respect to CSP is land use. CSP is a relatively land-intensive power generation technology, requiring approximately five acres of land per MW generated. At this rate there is not enough land in the Negev desert region, the most suitable region in Israel for CSP, to produce 100% of the nation’s annual electricity demand. This is of little concern in the short term, as Israel only sought to meet 10% of its total generation from renewable energy sources by 2020. Long term however, the land use intensity and high capital costs of concentrated solar makes it less viable for Israel than solar PV.


Figure 8: A map showing the intensity of sunlight above Israel.[23]


Policy Recommendation for Improved CSP in Israel


The constraints facing CSP development in Israel are both unique to the nation’s geography and faced globally as well. CSP’s high land-use requirements prove difficult for Israel in the long term, as the Negev desert region (Israel’s hottest and least populated region) would not be able to meet the entirety of the nation’s electricity needs even if it were 100% full of CSP plants.


Diversifying renewable energy supply in Israel is difficult since it lacks any major hydro, wind or geothermal resources. Although nuclear energy has been discussed as an option in the past, it is difficult for Israel to go through that route because Israel is not a signatory to the Nuclear Non-proliferation Treaty. As a result, Israel cannot conduct business with international suppliers of nuclear technology.[24]


It is however a country with 330 sunny days and thus, Israel’s renewable energy plan going forward is focused mostly on solar and rightly so.[25][26] Israel’s Energy Minister - Mr. Yuval Steinitz announced four months ago that the Energy Ministry will mobilize $23 billion in government and private funding to increase solar capacity to 16GW by 2030 which will provide 30% of the country’s power demand.[27] Additionally, Israel is already encouraging the expansion of solar PV through net metering and feed in tariffs.[28] Although Israel’s goals regarding the deployment of renewables are commendable, the future of CSP in the country remains relatively uncertain.


In order to improve CSP outlooks in Israel, two concerns must be addressed: the high capital cost requirement for bringing commercial CSP plants online and the intensive land use requirement of CSP technology. For this, we suggest a two-step policy measure to ensure reliable solar power at an economical price for both consumers and developers. In order to ensure a steady capital recovery factor, Israel should look to extending its solar PV feed-in tariff to concentrated solar power as well. Allowing developers and generators a reasonable, guaranteed return on initial investment would incentivize CSP development and implementation. For modeling this policy, they could look to either Israel’s own feed-in tariff structure for rooftop solar PV or to Spain’s previous successes with implementation of similar policies.[28][7]


Addressing land-use requirements for CSP development in Israel is a bigger task, as large-scale implementation would require either drastic improvements in plant land-use efficiency or an increase in Israel’s available land resources. Instead, what we suggest is that future CSP development be complemented with thermal storage and solar PV. For example, Ashalim’s Negev solar thermal power plant has both molten salt storage and solar PV generation in addition to its CSP generation.[15] The combination of solar PV and CSP will allow Israel to maximize the share of renewable energy it generates from sunlight, and optimize its generation on an hourly basis to meet customer demand.

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