The move towards CSP yield optimisation has a number of causes and a number of solutions – and the opportunity now exists to give the technology long-term viability.

In the build-up to the CSP Yield Optimisation Europe Conference & Expo (31 May – 1 June, Seville), Solar Millennium explained to CSP Today exactly how the company is making optimisation a driving strategy for their business.

According to Solar Millennium, the optimisation of CSP plants goes hand-in-hand with the progression of the industry: “CSP is the only commercially available renewable energy which contributes to security of supply and grid stability. It can cover specific load curves and peak/average loads using thermal storage units like in the Andasol plants. Due to the thermal storage the electricity production is up to a certain extent independent of the momentary solar irradiation; thus electricity can also be provided when the sun does not shine which allows a stable electricity supply.” How does this link to optimisation? “Today parabolic trough power plants constitute the most efficient proven large scale technology for converting solar energy into electricity. The more power plants are built, the greater the cost reductions through technical innovations, serial production, as well as construction and operational experience,” according to Solar Millennium.  “This in turn achieves an on-going reduction in the need for state subsidies or support.”  

To support the drive towards optimisation, Solar Millennium highlights the study Solar Thermal Electricity 2025 by A.T. Kearney and ESTELA (2010), which “predicts that within the next ten years, there will be an opportunity to generate solar-thermal electricity (STE) economically and free of subsidies. In doing so, it will compete with fossil fuels.”  In Spain, the situation is determined by the royal decree Real Decreto 661/2007, which Solar Millennium believes made the country an “attractive market, as a consequence of having one of the most advanced subsidisation programs.  The subsidisation of solar-thermal power plants is explicitly designed for a nominal capacity of up to 50MW per power plant.”  

At the end of 2010, the new Royal Decree 1640/2010 “secures predictability of future returns from the production of electricity in solar thermal power plants. A main topic of the RD 1640/210 is that the maximum number of operating hours p.a. reimbursed according to feed-in tariff is limited to e.g. 4,000 for plants including 9 hours storage.”  Does this affect the output of Solar Millennium’s solar thermal power plants?  “The new decree has no negative impact on the profitability of Solar Millennium’s plants – as expected operating hours for plants such as Ibersol with 8 hours storage in a “standard year” amount to 3,400”.

Solar Millennium sees the biggest gains for CSP optimization in two areas: collector design and expansion into hybridisation.  In the former, specific gains can be made by “testing alternatives to current heat transfer fluids in the absorber tubes of parabolic trough power plants to increase temperature and therefore efficiency, or molten salts replacing the oil/salt heat exchanger.”  The company’s Helio Trough collector design, awarded the CSP Innovation prize at the 2010 CSP Today USA awards, aimed to meet the twin challenges of higher collector efficiency and specific cost reduction.
It is clear that there are many areas in which yield optimisation can be achieved in CSP.  Solar Millennium work actively in various fields in order to achieve the maximum megawatts for a plant, starting as early as location assessment.   “In order to appropriately assess a potential location, Solar Millennium takes its own meteorological measurements on site in the scope of a feasibility study. These measurements are taken with the help of a meteo station, which has been developed by the company itself and works automatically. The main function, in addition to recording other data, is to record the direct normal irradiation over the duration of at least one year and to synchronise this with years of satellite data.”  Is direct solar radiation the decisive factor to site selection? “Precise measurements of direct solar radiation play an important role for a solar power plant, and not just in the selection of the site. A permanent flow of information on the direct radiation during the operation of solar-thermal power plants is also required. Taking these measurements as a basis, the efficiency of the plant is monitored on the one hand, while the operating strategy is optimised on the other.”

There is one other key area that Solar Millennium, and its subsidiaries, work to optimise CSP plants: technology. Engineers from the Solar Millennium Group’s Technology and Construction segments, namely the subsidy Flagsol GmbH, develop the collector design, calculate the required size of the solar field and align the collectors in the field. They also render engineering services for the heat transfer system, energy storage and the power block with its ancillary systems (Engineering).  Considerations for yield are crucial at this stage: “during the construction period, the engineers monitor the quality of the high-precision optical collectors. A subsidiary supplies the control of the solar field, which is a key component for the operation of the entire plant, and is in charge of component procurement (Procurement).” Being the technology provider, the Solar Millennium Group is also involved in the construction phase and operation of the power plant.

There is one other source of optimisation that Solar Millennium believes is “little used” but still very important – and that is operation and maintenance planning combined with weather forecasts.  These can then be converted into “power generation forecasts”.  The benefits of taking this approach to O&M are clear: “High accuracy short-term weather forecasts can help power plant operators to constantly operate the power plant at maximum performance level. Solar Millennium, together with scientific researchers from DLR, is developing an integrated weather and power generation forecast tool to exploit this potential.”

To hear more on successful planning for CSP plants, the project development subsidiary of Solar Millennium, Milenio Solar, will be tackling land use and permitting issues at the CSP Yield Optimisation Conference & Expo Europe (31 May – 1 June, Seville).  The objective of the conference is to show how to maximise CSP plant output through improved balance of plant engineering.