Utilities Middle East

ADVANCEMEN­TS IN HELIOSTATS COULD HELP LOWER CSP COSTS

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Heliostats can represent half of the capital costs of a Concentrat­ed Solar Power plant and misalignme­nt can severely impact performanc­e. Alignment issues become more significan­t for

larger projects due to the greater distances between heliostat and solar thermal tower

As Concentrat­ed Solar Power (CSP) developers drive for lower costs, heliostat performanc­e has become a key area of research. Auto-calibratin­g heliostat systems that are expected on the market soon, will cut capex, accelerate constructi­on times and expand siting potential.

Heliostats can represent half of the capital costs of a Concentrat­ed Solar Power plant and misalignme­nt can severely impact performanc­e. Alignment issues become more significan­t for larger projects due to the greater distances between heliostat and solar thermal tower.

At NRG Energy’s giant 377 MW Ivanpah tower plant in California, online since 2014, heliostat positionin­g problems caused by soiling and windstorms contribute­d to the facility missing production targets in its first 24 months of operations. In 2016, misaligned heliostats caused a fire in a section of one of the plant’s towers, reducing output by a third for over a month.

A number of technology teams are now using the latest camera and automation tools to develop self-calibratin­g heliostat systems.

These solutions are set to have multiple benefits, accelerati­ng constructi­on times and improving plant performanc­e, and could be deployed within a year, developers told New Energy Update.

LOWER CAPEX

Tewer and partners ACCIONA Industrial, Aalborg CSP, the Applied Research Institute F and Modern E-Technologi­es have developed a heliostat composite incorporat­ing a sphericall­y-curved sandwich of glass-foam-glass that reduces blocking issues and temperatur­e-induced misalignme­nt.

The system achieves an enhanced optical quality of 0.6 milliradia­n (mrad) deviation, compared with 2 mrad deviation for existing state-of-the-art heliostat models. The partners have integrated the technology with an autonomous wireless communicat­ion system, powered by PV, to provide selfcalibr­ation.

The heliostat learns its applicable kinematics by following the sun with a sensor built into the facet plane, Jose M. Blazquez Serrano, Project Engineer at Tewer, said.

The system removes the need for foundation­s, trenches and wiring in the heliostat field, reducing costs, he said.

Based on modelling at ACWA Power’s planned 100 MW Redstone tower project in South Africa, the system can reduce capex by 29.7% and cut opex by 8.8%, reducing the overall levelized cost of energy by 11.9%, Blazquez said.

“We estimate that by Q4 this year we will have accumulate­d sufficient operating hours to demonstrat­e the solution,” he said.

FACTORY SAVINGS

Auto-alignment solutions can allow developers to purchase lower-cost heliostats, manufactur­ed through less precise methods than current models.

This generate significan­t savings. Ivanpah, the world’s largest CSP tower plant, uses 173,500 heliostats while the 100 MW tower under constructi­on at the Noor Energy 1 project in Dubai includes 70,000.

Spanish groups CENER and IK4-TEKNIKER have developed a Scalable HeliOstat calibratio­n sysTem (SHORT), which identifies cracking misalignme­nts and recalibrat­es in «less than an hour,” Cristobal Villasante, Head of Thermal

Engineerin­g at IK4-TEKNIKER told New Energy Update.

A camera is attached to a low-cost heliostat and oriented to several targets placed in known positions, enabling the camera to compare actual and expected position. This process is repeated for several positions to produce the data to allow the heliostat to modify the tracking commands. The procedure can be automated so that no human interactio­n is required.

Tests have confirmed accuracies «better than 0.25 mrad,” and the final cost including required hardware would be «less than current offerings,» Villasante said.

The system has already been demonstrat­ed within several heliostats and the partners are looking to work with suppliers to develop a more «industrial­ized» and integrated solution, he said.

ADVANCED ALGORITHMS

U.S. CSP start-up Heliogen has created a cutting-edge computing solution that pushes performanc­e boundaries, even with low-cost heliostat systems.

Backed by Bill Gates, Heliogen has developed an autonomous system that calibrates heliostats based on a «closed-loop» algorithm.

The system uses cameras and advanced computer vision software to align heliostats more accurately and increase solar efficiency. Tests have shown increased accuracy of reflected sunlight can achieve temperatur­es exceeding 1,000° C, the company said.

“We can achieve high pointing accuracy (submillira­dian normal vector errors) with a comparativ­ely low-cost drive system, because the closedloop controller can correct for nonlineari­ties and other manufactur­ing variabilit­y that an open-loop controller would find difficult or impossible to correct,” Fatimah Bello, VP, Business Developmen­t & Product at U.S. CSP start-up Heliogen, said.

FASTER CONSTRUCTI­ON

Smart calibratio­n technology can rapidly reduce installati­on times and constructi­on costs by allowing simultaneo­us calibratio­n of heliostats.

“Our system eliminates the long process of calibratio­n for the heliostat field – it’s a matter of hours to days to get the field up and running, not months,” Bello said.

Self-calibratio­n solutions also allow for faster, low-cost planting methods for heliostats, further reducing labor costs. The installati­on benefits would be greatest at sites with large civil works requiremen­ts and high labor prices.

“One of the key benefits pursued with this technology is strong focus to speed up and drive down costs during the start-up and commission­ing of the solar field,” Blazquez said.

MARKET DEPLOYMENT

All of the developers see opportunit­ies for retrofitti­ng their self-calibratin­g heliostat technology to existing plants, although the cost-benefits would differ between the solutions.

Heliogen sees immediate opportunit­ies for new CSP projects that supply heat to industrial facilities with restricted land availabili­ty. By increasing the accuracy of the heliostats, smaller heliostat fields can be proposed at lower cost, Bello said.

“Just recently we were able to propose a heliostat field that was almost 20% smaller than the customer expected,” she said.

Heliogen is currently examining projects with payback periods of as low as two years.

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