How is Solar Energy Produced Why Will a Space Probe Continue at the Same Velo

Economic and Reliability Benefits of Large-Scale Solar Plants

Udi Helman , in Renewable Energy Integration, 2014

2.2 CSP

CSP plants use mirrors or other reflective surfaces to heat a working fluid, which then heats steam to operate a conventional generation power block with a steam turbine. Unlike PV plants, CSP plants need high direct normal insolation (DNI) to achieve desirable operating efficiencies; hence, they are, with a few exceptions, only built in such regions. There are several different CSP plant designs, which are surveyed in [6] and other sources. ⁷ The studies reviewed in this chapter evaluate the economic benefits of the two primary commercialized designs: the parabolic trough and the tower. In terms of production profiles, for different types of CSP plants without thermal storage (or hybridization with other fuels), production is differentiated primarily in terms of seasonal capability. The positioning of parabolic troughs is optimized to maximize production during the summer months; power towers with tracking heliostats are better able to shape production smoothly across the year. Both types of plants tend to ramp up and down fairly rapidly when there is sufficient DNI, partly as a function of other operational characteristics, such as some degree of natural gas augmentation to manage heat transfer fluid temperatures for start-up or during transient cloud conditions. During periods of transient clouds, CSP designs also provide some degree of inertia.

Thermal energy storage can be directly or indirectly integrated into any of the CSP designs, and the CSP-TES design may affect the operational flexibility of the plant. A key feature of CSP-TES is that in current designs, the storage system charges entirely from the solar field; hence, the plant appears to the system operator as a conventional, dispatchable thermal generator with limited energy, which must be forecast daily. Thus, the simulation models used for economic valuation of either of these design approaches must be able to simulate the hourly conversion of potential thermal energy from the solar field into the state of charge in the energy storage system, and then for operations of the steam turbine to jointly provide energy and ancillary services. In addition, depending on the simulation model, the plant representation can include a detailed range of operational attributes of the power block [7].

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Economic and Reliability Benefits of Solar Plants

Udi Helman , in Renewable Energy Integration (Second Edition), 2017

2.2 Concentrating solar power

CSP plants use mirrors or other reflective surfaces to heat a working fluid, which then heats steam to operate a conventional generation power block with a steam turbine. Unlike PV plants, CSP plants need high direct normal insolation (DNI) to achieve desirable operating efficiencies and hence are, with a few exceptions, only built in such regions. There are several different CSP plant designs (e.g., Refs.[5,6]). ⁵ The studies reviewed in this chapter evaluate the economic benefits of the two primary commercialized designs: the parabolic trough and the tower. In terms of production profiles, for different types of CSP plants without thermal storage (or hybridization with other fuels), production is differentiated primarily in terms of seasonal capability. The positioning of parabolic troughs is optimized to maximize production during the summer months; power towers with tracking heliostats are better able to shape production smoothly across the year. Both types of plants tend to ramp up and down fairly rapidly when there is sufficient DNI, partly as a function of other operational characteristics, such as some degree of natural gas augmentation to manage heat transfer fluid temperatures for start-up or during transient cloud conditions. During periods of transient clouds, CSP designs also provide some degree of inertia, which contributes to frequency control.

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Energy systems

Ibrahim Dincer , Azzam Abu-Rayash , in Energy Sustainability, 2020

3.2.4 Solar power plants

Solar power plants utilize thermal energy from the sun, which is abundant, available, intermittent, yet cheap. This thermal energy is further transformed into electrical energy using photovoltaic panels. This is one type of solar power plants. Simply, a large number of panels are installed in an optimal configuration and harvest light energy from the sun and convert it into electrical energy which feeds into the grid. Another type of solar power plant is the concentrated solar power plant, which composed of mirrors or lenses that are stationed in an organized way to concentrate collected heat to one specific position. This heat is further utilized to power a steam turbine that generates electricity. However, the most common solar power plant is the traditional photovoltaic (PV) option. Solar capacity for each country varies depending on the solar irradiance as well as the available land. This type of power plant is considered a renewable option as the energy source is the sun, which is a clean, renewable, abundant, and cheap source. Solar PV farms can be ground mounted or roof mounted. Additionally, the ground-mounted systems can be fixed arrays, or installed with a single or a dual axis tracker. The modules are usually oriented toward the equator, with a tilt angle that is slightly lower than the site's latitude. Different tilt angles can be explored to find the optimal power production. Axis trackers are used to optimize performance as they allow for panels to track the sun as it moves position throughout the day. Fig. 3.19 shows an illustration that depicts a solar power plant. Once the thermal energy is harvested, solar panels convert it into direct current (DC) electricity. To convert this to alternating current (AC) electricity, another component becomes essential in the solar power plant, which is the inverter. There are different types of inverters including centralized and string inverters. Centralized inverters have higher capacity, in the order of 1 MW, while string inverters are significantly lower in capacity, normally in the order of 10 kW. Fig. 3.19 depicts a solar power plant with its main features and components.

Normally, solar power plants are constructed on wide-open spaces, constructing a solar farm, which produces a significant amount of electricity. This type of power plant fulfills the peaking demand, as it is a limited and intermittent source. Unless the storage option becomes sustainable and durable, this type of power plants will remain limited to peaking demand and not the base load demand. The performance of solar power plants is a function of climatic circumstances along with the quality of the equipment used in the system. Furthermore, locations with higher solar insolation yield higher electric production. Besides, solar systems' efficiencies also vary depending on the type of panels used. This conversion efficiency is critical as it impacts the overall efficiency of the system. Moreover, other system losses include losses between the DC output and the AC input.

Concentrated solar power (CSP) is another method to generate power using solar energy. After concentrating great amount of light into one source, heat is used to generate a steam turbine, which is connected to a generator to generate electricity. CSP is less common than PV plants, primarily because PV plants can still operate with cloud cover, while CSP is crucially impacted by any cloud cover. Furthermore, PV plant operating cost and production are much higher than that of CSP's. Moreover, the price per Watt from solar PV has significantly decreased, while system efficiency has increased, making power generation through this source somewhat lucrative. CSP uses various types of concentrators to yield different peak temperatures, which subsequently impact thermodynamic efficiencies. Fig. 3.20 shows different types of concentrators used for CSP.

Power generation through solar means has survived economically through various governmental incentives and grants such as feed in tariff, net metering programs, tax credits, and loan guarantees. The solar system's financial performance is a function of income and costs. Income is associated with the electrical output and the rate at which electricity is purchased. Although electricity prices may vary at times, support programs such as the ones aforementioned allow for sale rates to remain competitive and stable. As for the costs, the capital costs associated with solar power plants make up the dominant cost. Operating and maintenance costs are also considered when it comes to costs associated with this type of power generation.

Solar power plants can be off-grid and stand-alone systems or they can be connected to the grid in some capacity. Furthermore, these systems differ in size as some are simply for residential use and range between 6 and 10 kW while other solar farms may be massive in capacity ranging in MWs. Moreover, battery storage solutions are still underway with these types of power plants and could influence the market greatly if developed to the point of commercial competitiveness.

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The long-term market potential of concentrating solar power systems

Luis Crespo , in Concentrating Solar Power Technology (Second Edition), 2021

13.3.1 Natural geographical areas for CSP deployment

CSP plants are most likely to be deployed in Sunbelt countries where DNI exceeds 1800 kWh/m²/year. Although the cost and corresponding competitiveness level of CSP will depend on the DNI level, climate change mitigation actions will push to encourage CSP plants in countries with DNI levels close to the minimum threshold as there will not be any better renewable choice in many of the areas.

Fig. 13.3 shows an assessment of the attractiveness of CSP that can be expected in different geographical areas along with a DNI world map (Crespo, 2019).

The United States (South West) and Northern part of Mexico are perhaps the areas in which the installed capacity of CSP plants could be the greatest by 2050. DNI levels above 2500 kWh/m²/year, relatively easy site development along with high electricity demand could place this region as number one in the ranking if overall greenhouse gas reduction policies are accelerated. The northern Mexican states will benefit on grid stability issues when the solar deployment in this part of the country is more balanced between PV and CSP.

In spite of the outstanding DNI levels and site development opportunities in the Northern part of Chile and the Southern part of Peru the market potential in South America is presented as 'two stars' as the electricity demand in these areas is not that big. Some regions in Argentina and even in Brazil are also good in terms of DNI and land characteristics but again the electricity demand in those areas is moderate. Long high voltage DC transmission lines could help in increasing the shares of CSP, particularly in the case of Chile.

The MENA Region—from Morocco to Jordan—has relatively high DNI levels and easy site development. The atmosphere is clear in most of the potential locations and, due to the latitude—heliostat fields and trough mirror fields can be deployed with similar optical performance. Water might be an issue in many places and therefore dry cooling system is likely to dominate. In these countries an optimal blend of PV and CSP plants could meet the bulk of the electricity demand on a 24/7 basis most of the year.

Gulf countries have high global radiation levels but the DNI figures are relatively moderate, due to dust levels, in most of the area and particularly in the Arab Emirates. That is why the expectations in the 2030 horizon are somewhat more modest than for the MENA countries. However, the night demand is very high and the complementary role to PV generation in these countries—especially in the Arab Emirates—is clear. Climate change mitigation measures could push for an earlier substitution of the gas backup after daytime.

The South Africa cone, including Namibia and Botswana, are especially privileged regarding DNI levels and CSP should play a very important role in the long term. The penetration of CSP in RSA will mainly depend on the decarbonization policies as coal is an abundant resource. Another important barrier is the transmission infrastructure, which must be reinforced. Namibia, Botswana, Zambia, and Zimbabwe to a certain extent, have also good conditions for deployment but the demand is much lower due to the reduced population and industrial activity. Nevertheless, the possibilities to export to Central African countries, where the share of PV will be relevant, provides additional potential for installing CSP plants in these countries. PV can be also deployed.

China has started recently a strong policy driven support program for CSP plants based on feed-in-tariffs, although the possibilities for a large contribution of CSP plants to meet its own demand is limited as good quality resources exist in the interior western desert regions, while the majority of the load is in the east. The PV industry reference, with the great export success of modules could be behind the current commitment with this sector. CSP components are not as easily exported but export of EPC services could be an additional goal of the Chinese industry policy.

Central Asia is not ranked very high as DNI resources are not as good as in other regions and the demand is also moderate in those areas where CSP plants could be deployed.

India—and its neighbouring countries—area big question mark for this industry. There are not many places where DNI exceeds 1800 kWh/m²/year but the demand growth is high and there will not be many choices to provide the necessary backup to PV after daytime. Another drawback is the monsoon season when CSP plants would be stopped for a couple of months. Hybrid concepts, either with biomass or with the decoupled solar—gas combined cycle concept, described in Section 13.2.5 could be a proper solution. In such big country all technologies will definitely find their own niche.

Australia is a continent with excellent DNI resources. Climate change mitigation measures along with the aging of the fleet, should progressively result in the decommissioning of coal plants, which should be substituted by renewable and dispatchable synchronous generation (e.g. CSP plants), which besides the complementary role to PV plants—as advocated for the rest of the world—could also contribute here during day time as well. Very high capacity factor CSP plants could be required by the Australian electrical system, which could help to bring down the cost of energy, compensating to some extent other country specific factors that would make cost higher in Australia than in other places.

Finally, Europe holds a great opportunity for STE/CSP deployment in the Southern countries, not just based on their own country needs but in the renewable backup requirements after sun sets in central and northern European countries. There will not be any other cheaper possibility for dispatchable renewable electricity in these countries. In addition, the new Renewable European Directive asks for 15% cross border exchanges of renewable electricity by 2030. The issue of site availability for large plants—over 500 hectares—could be a strong bottle neck in countries like Italy or Greece while in Portugal and Spain it could be easier to manage.

The International Energy Agency published in 2014 simultaneously two roadmaps on the expected role of solar electricity in the 2050 horizon. One was the Solar Thermal Electricity Technology Roadmap and the other for PV (IEA, 2014a, 2014b). The IEA envisaged a significant contribution from CSP plants by 2030. By 2050 the IEA vision was that CSP will play even a larger role than PV in the Middle East and Africa countries, Fig. 13.4 shows the expected levels of generation by region.

When putting together the PV and the STE/CSP roadmaps, as shown in Fig. 13.5, a total contribution of solar technologies of more than 25% was envisaged in 2050 becoming the single largest source of electricity production at world level at that time.

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Integrated Design of Communities

Moncef Krarti , in Optimal Design and Retrofit of Energy Efficient Buildings, Communities, and Urban Centers, 2018

7.3.4.3 Solar Radiation Requirements

Actual CSP plant power generation and economic feasibility are highly dependent on the availability of direct solar irradiation. Therefore, only locations with high solar direct normal irradiation (DNI) levels are suitable for CSP plants. Indeed, only direct solar radiation can be used to maintain operating temperatures sufficiently high for CSP plants to generate electricity (IRENA,2012). Various references suggest threshold values for the minimum DNI requirements for CSP plants as summarized for select locations in Table7.9. Solar resource data are not readily available for all locations throughout the world. Generally, datasets collected by organizations such as NASA and NREL are used to perform preliminary analysis and assess potential sites for CSP plants in a specific country (Fluri,2009). Typically, CSP analysis tools require hourly data for solar irradiation. However, only monthly extraterrestrial solar radiation is generally available for remote locations using mostly satellite data. The extraterrestrial radiation data obtained using satellite imaging are usually specific to large areas rather than specific locations. For example, data available from NREL for most African countries are spread over a 40×40km area and that from NASA covers 80×110km area. Models to convert monthly satellite-based extraterrestrial solar radiation to hourly DNI data do exist and typically require hourly cloud cover or clearness index values (Corral etal.,2012). Fig.7.20 provides the annual average DNI values for countries where CSP plants have been constructed and operated.

Table 7.9. Desired Threshold Values for Direct Normal Irradiation at Various Countries

Country/reference/report	Annual DNI (kWh/m²/yr)	Notes
Any location (IRENA,2012)	2,000	A general value for achieving attractive LCOE values.
Chile (Corral etal.,2012)	2,190	This DNI value is for northern Chile where a CSP is proposed.
Turkey (Kaygusuz,2011)	1,800	This DNI value is considered for economic feasibility in Turkey. Some locations have as high as 9 kWh/m²/day average DNI.
Qatar (Weber,2013)	2,200	Assume for CSP economic feasibility.
India (Jain etal.,2013)	2,100	This DNI value is specific to Jodhpur City.
South Africa (Fluri,2009)	2,100	Only sites having DNI above this value are considered suitable for CSP plants.
Australia (Hinkley etal., 2013)	2,564	At hypothetical plant location in Longreach, Queensland.
Cyprus (Poullikkas,2009)	2,000	This DNI is assumed for analysis.
Jordan (Al-Soud and Hrayshat,2009)	2,400	This DNI value is specific for Kharana. Economic viability is assumed to be above 2000kWh/m²/yr
Egypt (Blanco etal.,2013)	2,496	This DNI value is specific to Port Safaga, on the west side of Red Sea.
Algeria (Boukelia and Mecibah,2013)	1,800	Sites with as high as 2650kWh/m²/yr DNI values are available.
Serbia (Pavlović etal.,2012)	1,400	This DNI value represents the mean of 3.3–4.3kWh/m²/day.

Fig.7.21 presents the US solar resources suitable for CSP pants. Specifically, Fig.7.21 shows a map that provides the daily average normal direct solar irradiation expressed in kW/m²/day¹ for all continental US locations (NREL,2016c). The direct solar irradiation values are estimated based on data obtained for the 1998–2015 period. Similar to the solar resources shown for PV applications, the map of Fig.7.21 indicates that the southwest of the United States has the highest solar resources suitable for generating electricity cost-effectively from CSP plants.

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Introduction

Zhifeng Wang , in Design of Solar Thermal Power Plants, 2019

1.1.1 Constitution of the Solar Thermal Power Plant

An CSP plant consists of three major units: solar energy collection, thermal energy storage, and a thermal power generation unit. The first two mainly include the irradiation concentrator, the receiver, thermal storage, and the evaporator, whereas the last mainly includes the turbine, the power generator, control of the power cycle, the electricity system, water treatment, and the supply system.

Capacity of an CSP plant shall be determined according to the capacity of the generator unit, which is irrelevant to solar irradiation resources, environmental and meteorological conditions and concentrator power. Power plants of equivalent capacity may correspond to concentration fields (mirror fields) of different sizes.

An CSP plant can be constructed economically by using combined heating and electricity based on solar direct normal irradiation (DNI) resources, the current status of the local power load, and thermal load.

CSP can be complemented by coal, petroleum, or natural gas in a mixed-fuel power plant constructed according to circumstances in areas with an abundant solar resource and coal or petroleum resources.

According to the needs of thermal and power load development in corporate planning, construction of a self-contained heating-type CSP plant with an appropriate scale is suggested.

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INTRODUCTION TO THERMOCHEMICAL AND THERMAL ENERGY STORAGE PANEL

Chairman:N. KurtiPlenary Speaker:G. WettermarkPARTICIPANTST. Bramlette A. Berlad H. Büchner D. Eissenberg M. Furrer P.V. Gilli I. Glendenning W. Masica B. Mathey C. Meyer U. Plantikow R. Rigopoulus S.K. Sharma S. Stillesgö C.F. Tsang D. Van Velzen J. Wortman J . Würtz , in Energy Storage, 1980

LARGE POWER GENERATION SYSTEMS

Mr. Ian Glendenning of the United Kingdom initiated the discussion on utility applications by stating that thermal energy storage can save energy within the framework of the present utility structure only when it permits the replacement of a limited energy source (e.g., fossil fuels) by an unlimited source (e.g., solar energy). Storage does, however, provide a mechanism for reducing the need for additional power plants.

Storage is highly dependent on the particular utility's technology mix (e.g., gas turbine, nuclear), operating characteristics, and growth rate among other variables. Mr. Glendenning postulated that the use of thermal energy storage with fossil plants, gas turbines, or low-cost baseload plants (e.g., nuclear) will not be economically viable until the late 1990s (see Exhibit T.1). However, when and if a surplus of nuclear capacity develops and nuclear plants begin to be used to meet peak or intermediate demands, thermal storage may become economical.

Professor P. V. Gilli of Austria then described specific cases where thermal energy storage will play a crucial role, based on the results of a comprehensive study he conducted of thermal energy storage in power generation. In an electric grid, demand and production must be balanced at all times. Load balance can be achieved either by adapting production to current demand or by controlling demand based on production. Adapting production to demand requires energy storage either in the power plant or elsewhere in the grid.

"Internal" thermal energy storage (i.e., associated with the power station) represents one of the most promising possibilities for achieving continuous operation of the nuclear reactor while covering daily demand peaks. Continuous operation of the reactor minimizes temperature cycling of the fuel, thus maximizing efficiency, safety, and cost-effectiveness. Using the plant for peaking by means of energy storage also eliminates the need for a separate peak load plant, and thus the need to use scarce and expensive peak load fuel (e.g., light oil, kerosene, natural gas).

Solar power plants have several features that make integrated thermal energy storage even more necessary:

○: Fuel storage is not possible
○: Primary energy input changes daily and annually, and also depends on weather conditions
○: Storage system will increase the load factor of all plant components
○: In many cases, not only the power input but also the waste heat disposal system exhibit cyclic or stochastic behavior
○: Sudden meteorological changes can affect plant control.

Professor Gilli emphasized the importance of the Prestressed Cast Iron Vessel (PCIV) developed by Siempelkamp of Krefeld, Federal Republic of Germany, which introduces new prospects for thermal energy storage. The PCIV consists of cast iron blocks that are prestressed by circumferential as well as axial high-strength tendons. Its main advantages are the possibilities of use at high pressures and large unit sizes, without transportation or site welding problems, and outstanding safety features resulting from the prestressed design.

Professor Gilli then reviewed in detail the various modes of energy storage using water and steam and how they might be applied to nuclear, solar, and fossil-fired power stations.

Next, Dr. William Masica of the United States described an ongoing study to investigate electric utility applications for thermal energy storage. Three specific potential applications have been identified: peaking power generation; process heat for in-plant and industrial use; and advanced power systems. The study is emphasizing near to mid-term applications that reduce oil consumption and focus on new power plants. Of the numerous systems identified, four have been selected for in-depth evaluation and comparison:

○: Large power swing coal plant: peaking turbine with dual media storage (oil rock)
○: Large power swing coal plant: peaking turbine with underground hot water
○: Nuclear/feedwater with prestressed cast iron vessels
○: Nuclear/feedwater with dual media storage.

The results of the comparative cost/benefit analyses (see Exhibit T.2 and T.3) indicate that a coal cycling plant (the selected reference system) is not only more economical than the four options, but consumes less scarce fuel. Thus, this study concluded that thermal storage systems are unattractive for utility applications. Future efforts will focus on further developing and applying compressed air, pumped hydro, and electrochemical systems for utility applications.

Exhibit T.2. Thermal Storage for Peaking Power Generation: Cost Comparison

THERMAL STORAGE FOR PEAKING POWER GENERATION: COST COMPARISON

		THERMAL ENERGY STORAGE SYSTEM
DESCRIPTION	PLANT TOTAL INSTALLED COST ($/KW_E)	TOTAL INSTALLED COST C_T ($/KW_E)	POWER RELATED COST C_P ($/KW_E)	ENERGY RELATED COST C_S ($/KW_E-HR)
BASE PLANTS
COAL (741 MW_E)	875	—	—	—
NUCLEAR POWER (1,072 MW_E)	800	—	—	—
COAL CYCLING PLANTS
1800 PSI, 950/950°F (512 MW_E)	744	—	—	—
2400 PSI, 1000/1000°F (512 MW_E)	877	—	—	—
COAL BASE PLANT/TES
DUAL MEDIA (1,125 MW_E)	762	544	408	23
UNDERGROUND CAVERN (1,148 MW_E)	740	495	308	32
NUCLEAR POWER BASE PLANT/TES
PCIV, FEEDWATER STORAGE (1,221 MW_E)	902	1639	457	198
DUAL MEDIA (1,223 MW_E)	832	1059	982	13

(1): TOTAL INSTALLED COST = BASE COST + COSTS FOR CONSULTANTS, SITE SELECTION, ETC + FEES, PERMITS STATE AND LOCAL TAXES + SPARE PARTS + INTEBEST DURING CONSTRUCTION + CONTINGENCY ALLOWANCE (1976 $, ASSUMING PLANT START-UP IN 1990)
(2): C_T = C_P + C_ST; T = HOURS

Exhibit T.3. THERMAL STORAGE FOR PEAKING POWER GENERATION: SYSTEM COMPARISONS

DESCRIPTION	$HEAT RATE \frac{BTU}{{KW}_{E} - HR}$ (TES TURN AROUND⁽¹⁾ EFFICIENCY - %)	TOTAL INSTALLED COST $/KW_E	- PEAKING -LEVELIZED BUSBAR ENERGY COST⁽²⁾ MILLS/KW_E-HR
BASE PLANTS
COAL (741 MW_E)	9,789	875
NUCLEAR POWER (1,072 MW_E)	10,489	800
COAL CYCLING PLANTS
1800 PSI, 950/950°F (512 MW_E)	10,324	744	120
2400 PSI, 1000/1000°F (512 MW_E)	9,566	877	135
COAL BASE PLANT/TES
DUAL MEDIA (1,125 MW_E)	(66)	762	130
UNDERGROUND CAVERN (1,148 MW_E)	(80)	740	119
NUCLEAR POWER BASE PLANT/TES
PCIV, FEEDWATER STORAGE (1,221 MW_E)	(70)	902	226
DUAL MEDIA (1,223 MW_E)	(43)	832	176

(1) TURN AROUND EFFICIENCY = [ELECTRICITY GENERATED FROM TES ELECTRICITY NOT PRODUCED BECAUSE OF DIVERSION OF THERMAL ENERGY TO STORAGE]

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Heat flux and temperature measurement technologies for concentrating solar power (CSP)

J. Ballestrín , ... J. Cumpston , in Concentrating Solar Power Technology, 2012

18.1 Introduction

CSP plants collect solar radiation using reflective or transmissive optical elements that concentrate the radiation to a focal region where it is directly converted into thermal or electrical energy. Concentrating solar thermal (CST) systems perform the task by collecting the concentrated solar radiation in a high temperature receiver. This receiver should be designed to maximise thermal efficiency, defined as the ratio of the thermal power absorbed by the receiver to the incident radiant power falling on the This is done by minimising thermal losses from the receiver due to conduction, convection, and radiation (further comprising reflection and re-radiation). The basic trough, linear Fresnel, tower and dish concentrator types are covered in detail in Chapters 7,6,8 and 9, respectively. The basic principles around thermal losses and performance are covered in Chapter 2.

The design and characterisation of such receivers involve gathering detailed knowledge on heat transfer pathways into and out of the receiver and the heat transfer fluid (HTF). Firstly, receiver geometry will be determined by the spatial variation and extent of incident solar flux within the region of maximal focus, otherwise known as the focal region, where the receiver will be placed. To do this, it is desirable to obtain accurate and spatially detailed profiles of the solar flux within the focal region. Flux profiles are also important for determining concentrator performance. Optical concentration ratios range from around 80 : 1 for linear systems up to around 20,000 : 1 for high accuracy point focus systems. This translates to flux levels from 80 kW/m² up to 20,000 kW/m².

Radiometers and fluid-heating calorimeters are basic devices that can be used for direct measurement of incident heat flux in a particular location within the focal region, incorporated in ways that depend on the type of concentrator and the level of solar concentration. Alternatively, indirect measurement of solar flux is performed using remote cameras and reflective targets that are placed within the focal region for detailed images of the flux profile, sometimes calibrated using direct flux measurement with radiometers. Ray tracing based on measurements of concentrator surface topology can also be used to create simulated flux distributions, which can be used for further analysis.

Once a receiver is installed, thermometry can provide temperatures that aid in characterising the performance of the receiver. Contact methods have limitations so appropriate pyrometers and infrared cameras are used to determine temperatures and heat losses due to radiation. In advanced applications, receiver temperatures in excess of 1,000 °C are encountered.

These tasks can present significant challenges to the engineer, particularly when working with high solar concentrations and high temperatures that can damage materials placed within the focal region. As such, the objective of this chapter is to provide a summary of techniques and existing technologies that have been used in obtaining flux profiles for different concentrator types.

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Vulnerability of Energy to Climate

M.A. Lange , in Climate Vulnerability, 2013

3.11.5.1 General Principles

Concentrating solar power (CSP) plants represent solar-thermal facilities for electricity generation. They combine the capability of a thermal energy storage medium with alternative hybrid operations employing either solar energy harvested or fossil or biofuels (Figure 8). This enables – at least theoretically – the provision of electrical power on demand, 24 h a day and 365 days a year. The core element of a CSP plant is a field of large mirrors reflecting the captured solar rays to a small receiver element, thus concentrating the solar radiation intensity by about 80 to several 100 times and producing high temperature heat at several 100 to over 1000 °C. This heat can be either used directly in a thermal power cycle based on steam turbines, gas turbines, or Stirling engines, or accumulate in a heat storage medium such as molten salt, concrete, or phase-change material to be delivered at a later point to the power cycle for nighttime operation (see the following).

The principle of operation of a concentrating solar collector and of a CSP plant is given in Figure 8, which illustrates both the hybrid operation option of a CSP plant with solar and other energy and the option of either using the energy harvested directly in the power cycle or to transfer it to the heat storage device. Related to the typical requirements of a grid operator, CSP plants can be considered similar to any conventional fuel-fired power station, but with less or no fuel consumption. Therefore, CSP plants represent important elements for maintaining grid stability and control in future electricity supply systems based mainly on renewable energy sources. CSP plants can have capacities from 5 to several 100 MW of electricity generation (Trieb et al. 2009).

One of the benefits of CSP power plants is the fact that the steam turbines usually used for power generation provide an excellent spinning reserve: Such a reserve is very important for short-time compensation of any failures or outages within the electricity grid. Spinning reserves can only be provided by rotating generators such as steam or gas turbines. Moreover, the flexible design of CSP plants allows them to operate in all load segments from base-load and intermediate-load to peak-load services, just as often required by grid operators (Trieb et al. 2009).

A major advantage of the CSP technology is illustrated in Figure 9 . The figure illustrates a simulated time series of one week of operation of equivalent wind, PV, and CSP systems with 10 MW installed power capacity each at Hurghada, Egypt. As can be seen, whereas wind and photovoltaic power systems deliver fluctuating power and either allow only for intermittent solar operation or require considerable conventional backup, a concentrating solar power plant can deliver stable and constant power capacity because of its thermal energy storage capability and to the possibility of hybrid operation with fuel ( Trieb et al. 2009).

To cover a constant load or to follow a changing load by wind or PV electricity would additionally require the electricity grid and conventional plants for external backup. In both cases, an additional backup capacity would have to be installed and operated for most of the time, generating a relatively small portion of electricity during daytime and wind periods, but full capacity during night and periods without significant wind. In our example, the renewable share provided by CSP is about 90%, that of PV is 25%, and that of wind power is about 35–40%. Depending on varying conditions at different locations, these numbers also can be considered as typical for the average annual renewable share of such systems (Trieb et al. 2009).

As a consequence, CSP plants can save more fossil fuel and replace more conventional power capacity compared with other renewable energy sources such as PV and wind power. Theoretically, instead of conventional backup power or fuel, electricity generated by all three systems could be stored in batteries, pump storage, or hydrogen energy storage in order to provide continuous power capacity. In that case, the additional electrical storage capacities needed by CSP would be rather small, whereas significant storage would be required for PV and wind power, prohibitively increasing the overall system cost and energy losses (Trieb et al. 2009).

A reasonable economic performance of concentrating solar power plants is reached at an annual direct solar irradiance of more than 2000 kWh m⁻² year⁻¹. The economic potential of CSP in Europe has been assessed in Trieb et al. (2005). It is limited to Spain, Portugal, Greece, Turkey, and the Mediterranean Islands and amounts to 1580 TWh year⁻¹, of which 1280 TWh year⁻¹ are located in southern Spain. Although there is a relatively large CSP potential in Europe, more attractive sites are located south of the Mediterranean Sea with an annual direct solar irradiance of up to 2800 kWh m⁻² year⁻¹.

For concentration of the incoming sunlight, most systems use curved or flat glass mirrors because of their very high reflectivity. Point focusing and line focusing collector systems are used, as shown in Figure 10. These systems can only use the direct portion of solar radiation, but not its diffuse component, which cannot be concentrated by mirrors. Line focusing systems are easier to handle than point concentrating systems, but have a lower concentration factor and hence achieve lower temperatures than point focusing systems. Therefore, line concentrating systems will typically be connected to steam cycle power stations, whereas point concentrating systems are additionally capable of driving gas turbines or combustion engines (Trieb et al. 2009).

More details to these and additional CSP technologies can be found in Trieb et al. (2009). In the following, I will briefly describe the three technologies depicted in Figure 10 in more detail.

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Solar energy

N. El Bassam , in Distributed Renewable Energies for Off-Grid Communities (Second Edition), 2021

7.6 Concentrating solar thermal power

CSP systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam.

Commercial CSP plants were first developed in the 1980s. The 354-MW SEGS CSP installation is the largest solar power plant in the world, located in the Mojave Desert of California. Other large CSP plants include the Solnova solar power station (150 MW) and the Andasol solar power station (150 MW), both in Spain (Solar Millennium AG, 2011). The 200-MW Golmud Solar Park in China is the world's largest PV plant (Wang, 2011). Many power plants today use fossil fuels as a heat source to boil water. The steam from the boiling water spins a large turbine, which drives a generator to produce electricity. However, a new generation of power plants with CSP systems uses the sun as a heat source. The three main types of CSP systems are linear concentrator, dish/engine, and power tower systems.

Linear concentrator systems collect the sun's energy using long rectangular, curved (U-shaped) mirrors. The mirrors are tilted toward the sun, focusing sunlight on tubes (or receivers) that run the length of the mirrors. The reflected sunlight heats a fluid flowing through the tubes. The hot fluid is then used to boil water in a conventional steam-turbine generator to produce electricity. There are two major types of linear concentrator systems: parabolic trough systems, in which receiver tubes are positioned along the focal line of each parabolic mirror; and linear Fresnel reflector systems, in which one receiver tube is positioned above several mirrors to allow the mirrors greater mobility in tracking the sun.

A dish/engine system uses a mirrored dish similar to a large satellite dish. The dish-shaped surface directs and concentrates sunlight onto a thermal receiver, which absorbs and collects the heat and transfers it to the engine generator. The most common type of heat engine used today in dish/engine systems is the Stirling engine. This system uses fluid heated by the receiver to move pistons and create mechanical power. The mechanical power is then used to run a generator or alternator to produce electricity.

A power tower system uses a large field of flat, sun-tracking mirrors known as heliostats to focus and concentrate sunlight onto a receiver on the top of a tower. A heat-transfer fluid heated in the receiver is used to generate steam, which is then used in a conventional turbine generator to produce electricity. Some power towers use water or steam as the heat-transfer fluid. Other advanced designs are experimenting with molten nitrate salt because of its superior heat-transfer and energy-storage capabilities. The energy-storage capability, or thermal storage, allows the system to continue to dispatch electricity during cloudy weather or at night (Figures 7.11–7.18).