Shorter paybacks, subsidy reforms create a strong business case for Concentrated Solar Heat in industrial processes
Concentrated Solar Power Collectors for District Heat in Northern Europe
Concentrated solar power systems have until recently focused on bulk electricity production, with the main focus on solar towers and trough type collectors. Recent developments have focused on smaller units to supplement thermal power stations and to provide heat for industrial processes. Collectors based on the linear Fresnel reflector design are leading the pack.
There is a gap in the market between non-concentrating rooftop collectors used for solar heating and large scale systems used for bulk electricity generation. This gap is being filled by systems which use linear instead of circular focusing. Two main systems are the solar trough and the linear Fresnel (LFR) based collector. Although the trough based system has proven itself over many years of operation in different applications, the Fresnel system is emerging as an alternative with several advantages.
LFR plant is highly modular, ranging from a few hundred kW to several MW in size, and offers the lowest land occupancy compared to other CSP technologies. Parabolic troughs represent the optimal solution for achievable concentration ratio and achievable energy yield per aperture area and, hence, the best overall plant efficiency in line-focussing mirror systems. For that reason CSP development efforts have concentrated on parabolic trough geometry.
Nevertheless, in the last decade LFR systems have aroused an increasing interest. The main reason for this is the search for cheaper solar field solutions. The considerable economic advantages of Fresnel collectors are principally related to their constructive simplicity. In addition, Fresnel solar fields permit higher land use efficiency than any other type of solar fields. These advantages can offset the lower solar-to-heat efficiency, and LFR power plants represent an interesting alternative to parabolic trough power plants .
The main advantage of LFR systems is that their simple design of flat or flexibly bent mirrors and fixed receivers requires lower investment costs and offers a wide range of configurations. Originally designed for low and medium power applications, LFRs are now being designed for higher temperatures which facilitate direct steam generation (DSG) which can be used efficiently in the industrial or power generation sector.
Fresnel systems can be configured to operate over a wide range of temperatures, from 200 to 500°C, although systems with temperatures as high as 550°C are under development. Applications range from industrial process heat, distributed power generation using the organic Rankin cycle to steam turbine systems.
Developments in energy efficiency in both industry and power generation have focused attention on medium and high temperature solar thermal systems. LFRs have great potential in southern Africa due to the low cost and high percentage of local manufacture inherent in the technology.
The linear Fresnel reflector technology receives its name from the Fresnel lens, which was developed by the French physicist Augustin-Jean Fresnel for lighthouses in the 18th century. The principle of this lens is the breaking of the continuous surface of a standard lens into a set of surfaces with discontinuities between them. This allows a substantial reduction in thickness (and thus weight and volume) of the lens, at the expense of reducing the imaging quality of the lens. Where the purpose is to focus a source of light this impact on the image quality is not of major importance .
The principle of dividing an optical element into segments which have the same (or a very similar) optical effect as the original optical element can also be applied to mirrors. It is possible to divide a parabolic mirror into annular segments, forming a circular Fresnel mirror which focuses the light that arrives in rays parallel to the optical axis onto the focal point of the paraboloid mirror.
In an analogous way, a linear Fresnel mirror can be constructed substituting a parabolic trough by linear segments that focus the radiation that arrives in a plane parallel to the symmetry plane of the parabolic trough onto the focal line of the parabolic trough. A LFR has a similar effect to a parabolic trough, when considering the concentration of the radiation in a focal line i.e. a LFR behaves like a parabolic trough with the same focal length and the same aperture .
Fresnel mirror system
The mirrors focus the sun onto a receiver which contains the heat transfer medium which could be water, oil or even molten salt in some designs. The heat transfer medium used will depend on the operating temperature of the system. The main difference between the two systems lies in the way that the sun’s rays are tracked, and this is what gives rise to the cheaper cost of Fresnel.
In the trough system the whole structure rotates about an axis coincident with the focal point of the trough. This means that the mirrors and the collector are connected mechanically, requiring bearings through which the collector tube must pass. In the Fresnel system the individual mirrors rotate to track the sun. There is no mechanical connection between the mirrors and the collector.
Separation of the mirrors and the receiver allows high temperature heat transfer mediums to be used, and also a much wider scope in the design of the receiver. The Fresnel system also allows individual control of each mirror, effectively changing the configuration of the reflector to optimise its function.
The mirror aperture is the area of the reflector mirrors in the horizontal position, and defines the amount of solar radiation collected by the LFR. Aperture is usually quoted on a module or single mirror length basis. Increasing the mirror aperture increases the amount of solar radiation reflected to the receiver module. Typical aperture widths for large systems are of the order of 15 m.
The receiver aperture is the area of the receiver per mirror or module length, and varies according to the design of the system. Receiver width is close to the mirror width, but may be less if curved mirrors are used, or wider if other focusing methods are used.
Mirrors may be flat or elastically curved and are generally constructed of glass with a composite/metal backing, although other materials are finding their way into the sector. Adding curvature to the mirror increases the concentration ratio and makes the design of the receiver simpler. Mirror width and length will depend on the design. The mirrors are mounted in the tracking system in several different ways. A typical mounting would be a circular loop driven by a tracking motor (Fig. 4).
The receiver generally consists of a secondary reflector mounted above the receiver tube which contains the heat transfer fluid. The receiver may consist of a single tube or several tubes, which may be contained in a vacuum glass tube enclosure. Typical designs are shown in Fig. 5.
The LFR system alone cannot reach the same radiation concentration as a parabolic trough. The sun changes its position in relation to the optical axis plane of the system. It is theoretically impossible to design the curvature of the individual mirror strips in such a way that there is always a sharp focal line for parallel radiation, and it is necessary to mitigate the unavoidable optical inaccuracy of the Fresnel collector. This can be done by a secondary concentrator that is located above the receiver tubes.
The collector concentration ratio is the ratio of mirror aperture to receiver aperture. The low-profile setting of LFR collectors maximises the concentration ratio, which enables high temperature output.
Fundamentally, increasing the mirror aperture allows more sunlight to be reflected onto the receiver. Because the low-profile architecture provides for great flexibility in the selection of length and concentration ratio, linear Fresnel collectors can be readily tailored for different target temperatures to meet varying application needs, thus providing practical versatility of usage. As an example, the Fresdemo system has a primary mirror field width of 21 m and a receiver width of 0,5 m, giving a concentration ratio of 42 .
Heat transfer fluids
The fixed design of the receiver gives a wide choice of heat transfer fluids. Water is used as the transfer fluid at low temperatures, oil as temperatures increase, steam for much higher temperatures and molten salt for the highest ranges. In addition, pressurised CO2 or air are being considered for higher temperature operation .
LFR exhibit optical conversion efficiency in the region of 65%. Conversion efficiency depends on the angle of incidence of the sun, and thus average efficiency will vary with latitude. Thermal peak output of 562 W/m2 in terms of primary reflector aperture area, and 375 W/m2 in terms of installation area usage, is claimed for a typical commercially available system .
Medium heat generation
Medium heat systems for industrial applications or supplementary power systems operate in the temperature range 100 to 250°C and may use water or oil as the heat transfer medium. There are numerous systems of this type in operation.
Direct steam generation
Thanks to the fixed absorber tubes, direct steam generation (DSG) is easier in LFR power plants than in parabolic trough power plants. DSG has several advantages over oil heat transfer:
Water is less corrosive than salt. Its freezing temperature is much lower than the freezing temperature of salt and even slightly lower than of thermo oil. The effort required to ensure adequate anti-freeze protection is reduced significantly.
There are several systems on the market that use DSG. In this system water is fed through pipes in the receiver where it is converted to steam and then to superheated steam. Steam is used to drive turbines directly or as supplementary heating for thermal power plants. Steam is also used for industrial purposes.
Molten salt systems
High temperature systems (≈550°C) using molten salt as the heat transfer medium have been developed. Such systems incorporate heat storage systems for prolonged operation. Fig. 6 shows a high temperature plant using salt as the heat transfer medium .
Because of the simplicity of design and the high operating temperatures now possible, LFR are being considered as alternatives to tower and heliostat based CSP systems. In addition, the short optical path between mirror and receiver eliminates many of the tracking problems as well as environmental objections associated with tower/heliostat based systems. In addition LFR salt based systems are able to recover from “salt freezing”.
Supplementary heat or steam generation for power plants
Fresnel mirrors are being considered as a means to supplement heat in thermal power stations. Parts of the cycle such as preheating of the boiler feed water use low to medium temperature heat sources, and solar thermal systems can provide this heat. Typical applications are to substitute the bleed steam used for preheating boiler feedwater as shown in Fig. 7.
The solar heat source is connected in parallel with the bled steam source and when available provides the heat normally used from the steam. The increased steam output then enables additional power generation from the turbine (solar boosting mode) or fuel consumption can be reduced (fuel saver mode).
More complex systems use several stages of regeneration with heat substitution at each stage. Heat may be stored for periods when the solar resource is low, or the plant may be operated in a two shift mode. Using solar power may have two effects:
The integration of solar thermal collectors into conventional fossil plants, or solar aided power generation (SAPG), has proven a viable solution to address the intermittency of power generation and combines the environmental benefits of solar power plants with the efficiency and reliability of fossil power plants. In SAPG technology, thermal oil can be used as solar heat carrier and no solar steam needs to be generated, therefore the pressure of solar system can be much lower than that of the solar collector using water/steam as the heat carrier. Newer developments make use of the higher heat content of solar steam directly, provided from DSG plants.
The temperature of the heat source is one of the major defining factors of a power plant – higher temperature results in higher overall power plant efficiency. With SAPG, the heat source temperature is not limited by the solar input temperature and is therefore an effective means of utilising low or medium solar heat (250°C) for power generation. However, internationally the adoption of the technology has been slow, despite it being a viable and quick means of CO2 emission reduction.
A study was conducted on a simulated SAPG power plant at Lephalale, which was based on a generic 600 MW subcritical fossil power plant with a reheater and regenerative Rankine cycle with two low pressure feedwater heaters (FWH) downstream of the deaerator and three high-pressure FWHs upstream .
This study showed that integrating solar thermal with steam plant is approximately 1,5 times as efficient at converting solar energy to electricity as a CSP stand-alone generating plant. Therefore, a solar assisted high pressure feedwater heater system at an existing coal-fired power station is 1,8 times more cost-effective than a stand-alone CSP plant. The conversion efficiency is claimed to be of the same order as solar PV .
The Fresnel mirror solution is gaining popularity because of cost and simplicity advantages over the parabolic trough solution for SAPG systems. Costs of the Fresnel based system are estimated to be approximately 70% of the equivalent parabolic trough system .
 M Gunter: “Linear Fresnel Technology”, DLR, www.energy-science.org/bibliotheque/cours/1361468614Chapter%2006%20Fresnel.pdf M J Montes, et al: “A comparative analysis of configurations of linear Fresnel collectors for concentrating solar power”, Energy, 2014. Novatec: “Concentrated solar power by Novatec solar”, Brochure. E Hu, et al: “Solar Aided Power Generation: Generating Green Power from Conventional Fossil Fuelled Power Stations”, Intech open science. W Pierce, et al: “A comparison of solar aided power generation (SAPG) and stand-alone concentrating solar power (CSP): A South African case study”, Applied Thermal Engineering, 2013. Areva: “Areva integrates energy storage in solar CFLR design at Sandia national labs”, http://us.areva.com/EN/home-1977/areva-solar-power-salt-storage.html S Benmarraz: “Linear Fresnel Reflectors Concentrated Solar Power: cost reduction and performance improvement trends”, IRENA Workshop, March 2015. Industrial solar: “Industrial Solar linear Fresnel collector LF-11”, Technical brochure.
Mike Rycroft, features editor, EE Publishers
More than 500 industrial manufacturers trust solar heat worldwide. SHIP is the acronym for Solar Heat for Industrial Processes and describes systems which provide solar heat in a factory. A collector field heats a process fluid by means of solar radiation and a heat exchanger transfers this heat to a supply system or production process in the factory as hot water, air flow or steam. Storage units make it possible to use the generated heat at night-time
Renewable power generation is on the rise worldwide, and in 2015, renewables were, for the first time, responsible for more than 50% of added capacity globally, exceeding fossil fuels and nuclear (1). The heating market lags behind in the adaptation of renewables in general, and this trend holds especially true for industrial process heating. Renewable solutions can reduce fossil fuel consumption and carbon dioxide (CO2) emissions in process heating. In pharmaceutical manufacturing, process heating represents a significant opportunity for improvement, because the process heating supply accounts for approximately two-thirds of the total final energy demand from a manufacturing site (2). Major pharmaceutical companies around the world have announced ambitious targets for their future energy use (3), and an increased uptake of solar process heating is expected in this sector.
In addition to energy collected by solar collectors, biomass and geothermal sources can be used for process heating; however, they are ultimately limited. Despite being in its infancy today, industrial process heating is predicted by the International Energy Agency to be the largest application of solar thermal technologies in the future (4). Solar thermal technologies are applied by pharmaceutical companies around the world today, as the three case studies in this article illustrate.
Developing solar process heating projects requires both cost-effective generation of solar heat and an efficient integration into the existing heat supply. Thus, a profound understanding of the heat supply as well as the various processes, their specific temperatures, and the load profile(s) are important. Two different integration approaches for solar process—supply level and process level—can be used, as shown in Figure 1.
Figure 1: Solar thermal energy can be integrated directly as process heat or indirectly as supply heat. Figures are courtesy of the author.Both need to be further specified by the heat carrier and type of heat exchange applied, for example. The two approaches differ mainly in respect to the temperature and flow rate of the heat carrier, which results in different plant designs and yields. Six major criteria for selecting an integration approach and an indicative evaluation are depicted in Table I.
Defining an integration concept is inevitably linked to the choice of the collector technology–most importantly, the selection between non-concentrating and concentrating solar thermal collectors. In the first, the heat carrier circulates through the collector and is heated directly by the solar irradiation. The earliest type was the flat plate collector, in which pipes are placed in isolated boxes with a glass cover on top. More common today are evacuated tube collectors, in which the heat carrier circulates through pipes covered by an evacuated glass to reduce the heat losses. Both concepts are simple in design, but because their efficiency drops with increasing temperatures, a cost-effective application is limited to temperatures below 100 °C. Concentrating collectors, on the other hand, concentrate the sunlight with reflective surfaces on smaller absorbers and thereby can achieve temperatures even above 300 °C. This technology is more complex, especially as the collectors need to be moved to track the sun, and its application is spatially limited to regions with a reasonable share of direct (non-diffuse) irradiation. The following three examples show that solar process heating is already applied in the pharmaceutical sector, using different collector technologies and integration concepts.
Sunil Healthcare, the second largest Indian manufacturer of capsule shells, located in Alwar, Rajasthan, uses flat-plate collector solar thermal energy for hot water generation. For capsule production, the company needs to prepare a gel at approximately 75 °C. Previously, the heat was provided by a diesel boiler. To reduce carbon emissions, the company installed 70 flat-plate collectors with a total aperture area of 147 m², a thermal capacity of 100 kW, and a hot water storage with 6.5-m³ capacity. Because the solar heat is only fed to the gel preparation, the integration is process linked. During sunny days, this system can cover the largest share of heat demand, while the boiler provides the remaining, when needed.
Another approach was taken by RAM Pharma in Sahab, Jordan. Flexibility in respect to the use of the solar thermal energy was important, and because Jordan has a high share of direct solar irradiation, the company decided to install concentrating solar collectors, which provide heat at the supply level. A Fresnel collector system with an aperture area of 400 m² and a capacity of 230 kWth for direct steam generation was installed on the warehouse roof. Fresnel collectors use uniaxially tracked mirrors to concentrate sunlight on an absorber tube in which the heat transfer medium can reach temperatures of up to 400 °C. The installation at RAM Pharma uses direct solar steam generation, which means that no additional heat exchangers are used. The water partly evaporates in the absorber tube and is fed to buffer storage from which steam at 160 °C is directly released to the company steam grid. Such a steam drum offers further benefits to its users. It increases the capacity (because during peak demand the boiler and drum work in parallel) and smooths the pressure fluctuations within the steam supply, because the control valve can react more quickly than most fuel-fired boilers.
Within the scope of a rearrangement of processes and the implementation of continuous production, Pfizer Manufacturing Deutschland GmbH in Freiburg (Germany) installed a solar drying system for air-conditioning in the production facilities. Unlike most solar thermal installations, which use water or a water-glycol mix, the Solar Thermal Air Regeneration (STAR) 2 system uses air as a heat carrier. Four collector fields with (in total) 20 collectors and an aperture area of 110 m² were installed on the roof of the factory. The humid air from the production area streams through a sorption wheel where the humidity is dissipated to a desiccant. The sorption wheel is comprised of a wavelike fiberglass structure that contains the desiccant. It turns slowly, passing through a separated area where heated air, needed for regeneration, streams through the wheel. The humidity collected in the desiccant is removed (i.e., regeneration), the wet air is released to the outside, and the process starts again. The energy required for regeneration is fully or partially provided by the solar thermal collectors. In total, the STAR 2 system reduces CO2 emissions by 36 tons of CO2 annually, which is approximately as much as the combustion of 9000 L of diesel fuel.
Vol. 41, No. 4
Pages: 64–65, 67
When referring to this article, please cite it as M. Haagen, ” Using Solar Energy for Process Heating,” Pharmaceutical Technology 41 (4) 2017.
About the Author
Martin Haagen is business development manager at Industrial Solar, Freiburg, Germany, Tel: 49.761.767111.24. firstname.lastname@example.org.
Rioglass Solar, leading manufacturer of HCE receivers and mirrors used for Solar Thermal Energy (STE) and Concentrated Photovoltaic (CPV) technologies, has signed an agreemente with Schott Solar CSP GmbH (Schott Solar), for the acquisition of its receiver business, including the company in Spain and the assets in Germany.
PRESS RELEASE: https://www.slideshare.net/slideshow/embed_code/key/c9F0jSyRFPIDDz
CONCENTRATED SOLAR Technology Platform organized within the First Symposium on Concentrated Solar Thermal Technology held on 3 and 4 November a round table for medium temperature.
These are the conclusions:
Petroleum Development Oman (PDO) and GlassPoint Solar have broken ground on their landmark solar project ‘Miraah’. The site preparation and grading for the project, located at Amal oil field in southern Oman, began one month ahead of schedule.
Miraah, which means mirror in Arabic, will harness the sun’s energy to produce steam used in heavy oil production. In July, the two companies announced a deal to build one of the world’s largest solar plants, which at its peak will be able to generate in excess of one gigawatt of solar thermal energy.
Raoul Restucci, managing director of PDO, said, “The ground breaking is a significant milestone for PDO and GlassPoint as we progress towards the safe and efficient delivery of Miraah. I commend the project team and our local contractors for their tireless efforts to not only stay on track, but pushing forward ahead of schedule.”
“PDO is proud to lead the industry in deploying innovative solutions that allow us to develop our heavy oil while at the same time reduce our energy consumption and our costs. Miraah will provide a substantial amount of the steam demand at Amal, reducing our reliance on natural gas to make steam. The gas saved can be used by other industries to support Oman’s diversification and economic growth strategies,” Restucci added.
The site grading is being performed by a Local Community Contractor (LCC) owned and operated by Omanis that live in the communities surrounding Amal field. Developing a local Omani workforce and job opportunities for local contractors and small business is part of PDO’s and GlassPoint’s joint commitment to In-country Value.
Rod MacGregor, president and CEO of GlassPoint, added, “Miraah will be 100 times larger than our solar pilot at Amal, which has been operating successfully for nearly three years now. The pilot was built safely, on time and on budget, providing invaluable experience to ensure we achieve this same success with Miraah at commercial-scale.”
“Miraah will generate significant value for the Sultanate by creating new opportunities in supply chain development, manufacturing capacity, employment and training. We are committed to working with local contractors throughout the value chain, from construction to the sourcing of local materials,” MacGregor emphasized.
Once complete, Miraah will generate an average of 6,000 tons of solar steam daily for oil production. The use of solar for oil recovery is a long-term strategy to develop PDO’s viscous oil portfolio and reduce consumption of natural gas. Miraah will save 5.6 trillion British Thermal Units (BTUs) of natural gas each year, the amount of gas that could be used to provide residential electricity to 209,000 people in Oman.
The full-scale project will comprise 36 glasshouses, built in succession and commissioned in modules of four. The first module will begin generating steam in 2017. Upon completion, the total project area will span three-square kilometers, an area equivalent to more than 360 football pitches.
PDO and GlassPoint will be exhibiting together at the Abu Dhabi International Petroleum Exhibition (ADIPEC) next week. The booth will feature a 3D virtual reality tour of Miraah, transporting visitors to south Oman to see the scale of the project and technology up-close. PDO and GlassPoint are nominated for an ADIPEC Award in the “Best Oil and Gas Innovation or Technology (Surface)” category.
News published in WORLD OIL
As part of Secretary John Kerry’s Climate and Clean Energy Investment Forum, the Overseas Private Investment Corporation (OPIC) today signed an agreement with U.S. based energy developer SolarReserve and ACWA Power, recognizing OPIC’s $400 million commitment of debt financing to support the development of the Redstone Concentrating Solar Power (CSP) project in Northern Cape, South Africa.
The Redstone project is a 100 megawatt (MW) clean energy facility that will be connected to the South African national grid. Using SolarReserve’s cutting-edge CSP technology, Redstone’s molten salt storage capability will deliver consistent baseload electricity, even after the sun sets. This is a critical development in a country where frequent power outages have been cited as an obstacle to economic growth.
OPIC support to the Redstone project is also a significant milestone for President Obama’s Power Africa initiative, of which OPIC is a key contributor. Power Africa aims to bring new power access to the more than 600 million sub-Saharan Africans currently living without energy access.
“The development of the Redstone project will benefit the South African people, the international clean energy sector, and the role of U.S. leadership in emerging market development,” said Elizabeth Littlefield, OPIC’s President and CEO. “It’s impressive that Redstone brings together the innovative U.S. private sector leadership and technology of SolarReserve, the international experience of ACWA, and large-scale catalytic financing from OPIC. This sort of change-making partnership is at the heart of President Obama’s Power Africa initiative and creates broad, lasting impact in international development.”
“The Redstone project marks an important technology advancement for Africa in clean, renewable power, and a demonstration of U.S. developed technology that is leading the world in large scale solar energy storage,” said SolarReserve’s CEO Kevin Smith. “In addition, the project’s delivered electricity price is the lowest of any CSP project in the country to date,” Smith added. “We appreciate OPIC’s support and look forward to working with our partner ACWA Power and the communities where the project is located to help South Africa at a time when it critically needs new generation to support growth of its economy.”
“The Redstone CSP Project, ACWA Power’s 2nd project in South Africa, delivers dispatchable power at the most competitive tariff offered in its Renewable Energy Independent Power Producer Procurement Programme (REIPPPP) program to date for CSP technology, while maximizing value retention in not only the South African economy, but also within the local economy in the project vicinity. Quite apart from the socio-economic contribution this project will make to South Africa, the first time deployment of CSP Tower technology in the country using a project finance framework, which was made possible by the galvanizing leadership of OPIC financing, will enable this very important clean energy technology to be deployed at scale and at a faster pace than otherwise would have been possible,” said Paddy Padmanathan, President and CEO of ACWA Power.
“We are excited about the progress forged by OPIC and these private sector leaders on the Redstone project,” said Patrick Gaspard, U.S. Ambassador to South Africa. “It’s a priority for South Africa and regional neighbors to diversify their power production beyond traditional energy sources, including a greater share of renewables, efficiency improvements, and energy storage capabilities. The U.S. stands by South Africa as a partner, and working together with agencies like OPIC and great U.S. companies like SolarReserve, we can increase sustainable access to electricity, a foundation linked to overall lasting economic growth.”
OPIC’s financing to the Redstone project helps fulfill both the U.S. commitment to clean energy in the developing world as well as South Africa’s own goals through their Renewable Energy Independent Power Producer Procurement Programme (REIPPPP), which aims to add 3,725 MW of clean power to South Africa’s energy generation mix.
SOLARRESERVE PRESS RELEASE
SOLAR CONCENTRA has just published a document which shows the systematic identification of dependency relationships between
different lines of research R & D in Solar Thermoelectric.
This document is in Spanish.