The Promise of Parabolic Dish CSP Technology

Parabolic dishes are commonly understood to be the most efficient concentrating solar power (CSP) technology[1]. As such, the promise of parabolic dish technology has long been recognized. Solarflux is realizing that promise through the FOCUS, a parabolic dish concentrator designed to deliver low-cost, zero emission heat energy for a variety of applications including industrial process heat, water desalination and purification, space heating and cooling, hot water, and electricity generation.

CSP has faced challenges as an industry in the past decade, with the most mature CSP technologies – parabolic trough systems and power towers – struggling to compete against the continually falling price of photovoltaic (PV) panels. A third, linear fresnel, has seen only niche applications, whereas the fourth - parabolic dish - has in recent times primarily been used in conjunction with stirling engines for electricity generation purposes and has struggled with cost and complexity. To date, the prime use case for CSP has been utility-scale electricity generation, with massive installations dedicated to generating heat to produce steam which then powers a turbine and makes electricity. With PV prices tumbling, and some of the large scale CSP projects (such as the Ivanpah Solar Power Facility in the California desert) struggling to meet production targets, the perceived attractiveness of CSP has waned.

However, the Solarflux team believes CSP - particularly parabolic dish - holds significant potential, particularly as a distributed solar thermal (vs. electrical) energy technology. According to the IEA, heat is the largest energy end-use, accounting for over 50% of energy consumption[2]. Half of this is used by industry, for process heat, drying and industrial hot water applications. The balance is used for space and water heating and cooking in homes and buildings, as well as in agriculture. Only around 10% of heat is provided by renewable technologies. Additionally, air conditioning is another huge energy consumer, accounting for up to 27% of home energy consumption in parts of the U.S. and 12% nationally.[3] Typically electrically powered, air conditioning can be provided far more energy efficiently using a thermal energy source coupled with an absorption chiller.

In suitably sunny regions (such as southwest United States), CSP provides a way to sustainably meet this significant need for thermal energy. Because thermal energy does not transport well, locating the CSP generation equipment close to the point of use is important. Of the available CSP technologies, parabolic trough and parabolic dish are best suited to distributed applications, offering more modular deployment than larger scale power tower systems. Parabolic trough is the most mature CSP technology, offering a relatively simple design with solar-to-steam conversion efficiencies in the range of 43-59%[4]. Parabolic trough systems have been deployed on rooftops in many countries, including Mexico, for distributed solar thermal applications, including providing process heat to dairies and factories.

Parabolic dish systems, on the other hand, offer far higher solar-to-steam conversion efficiencies than parabolic trough – in the 70-80% range or higher. This is because they use dual-axis tracking (vs. single-axis for trough), so are always facing the sun, and use a more efficient cavity receiver (vs. evacuated tube receiver for trough). Additionally, parabolic dish systems can be mounted on a mast, so can be placed almost anywhere with sufficient clearance, including on rocky or hilly terrain, or attached to a roof support column (dispensing with the expensive rooftop support structure required for parabolic trough or PV panels). In contrast, parabolic trough systems require clear, level ground for mounting. Because of their much higher energy conversion performance, parabolic dish systems also deliver much higher energy per unit of land devoted to their installation relative to parabolic trough systems.

Historically, a key challenge with parabolic dish has been the perceived greater complexity of a system requiring curved reflectors and a two-axis tracking system relative to the simpler curvature of the parabolic trough reflector and single-axis tracking system. However, the Solarflux team believes this complexity and cost can be engineered out through design and volume manufacturing approaches. If it’s possible to volume produce and market something as complex as the 2020 Chevy Spark for less than $15,000, while meeting automotive reliability standards, it must also be possible to produce something as simple as a dual-axis tracking solar concentrator (less complex than a refrigerator) while also delivering excellent reliability. If this can be accomplished, the superior efficiency performance of the parabolic dish can be captured in a flexible, reliable, and low-cost product.

The Solarflux engineering team, led by former Bell Labs distinguished engineer John Fangman, has pursued this approach with the FOCUS. The result is a parabolic dish concentrator designed from the inception to minimize cost per unit of energy generated ($/kWh) through a careful focus on cost/benefit. Costly support structure has been eliminated through the use of aluminum petals and a monocoque design for the dish. Mature volume manufacturing approaches have been adopted for all of the key components making up the FOCUS. Reliable, commercially available parts have been used where available. The result is a device that, despite a strong emphasis on cost reduction, has demonstrated well in excess of 70% energy conversion during an extended field trial at a Penn State University campus in Pennsylvania.

Whereas past attempts at parabolic dish typically optimized for performance vs. performance at minimum cost, the FOCUS is the first truly productized parabolic dish concentrator designed specifically for low-cost volume production. The Solarflux team has to date shipped 15 demonstration units to various parties worldwide, and recently won a $340,000 grant from the Met-Ed Penelec Sustainable Energy Fund to implement a volume production method for the FOCUS aluminum reflector petals.

CSP can be an important part of helping countries with significant solar resource, such as the United States, Mexico, Chile, Spain, Australia, South Africa, China, India, Israel, and others around the world, to both increase energy resiliency and meet their CO2 emission reduction targets. High performing CSP systems such as the FOCUS can serve as part of a diversified energy mix, complementing PV and other sustainable energy sources to efficiently meet the often significant thermal energy requirements of industry and buildings.

For more information about the FOCUS, please reach out to us at contact@solarflux.co.

[1] Coventry, J. and Andraka, C.: “Dish Systems for CSP” (2017); https://www.osti.gov/servlets/purl/1356835.

[2] https://www.iea.org/fuels-and-technologies/heating

[3] https://www.eia.gov/todayinenergy/detail.php?id=36692

[4] Tambaya, M., Enaburekhan, J. S. and Rufa I. A.: “Experimental performance evaluation of parabolic trough solar concentrator for steam generation”, Fudma Journal of Science vol.3 no.3 (September 2019) pp 248-257