Small-scale solar systems with large-scale potential
Buildings consume about 40 % of global energy and emit approximately a third of greenhouse gas emissions, making them a key target for actions to enhance energy efficiency and reduce emissions. The EU-funded Innova MicroSolar project has delivered a high-performance, cost-effective concentrating solar power (CSP) system for small-scale, onsite electricity and heat generation.
CSP for the world’s smallest organic Rankine cycle turbine
Photovoltaic (PV) systems use sunlight to generate electricity directly via semiconductor-based PV cells. CSP systems use reflective devices like mirrors to harness the sun’s heat. Linear Fresnel reflectors are less complex and more cost-effective and efficient than other systems. Mirrors focus the sunlight onto a linear receiver tube. The heated working fluid generates vapour directly, eliminating the need for complex and expensive heat exchangers. The vapour is then used to spin a turbine that drives a generator to produce electricity. “Innova MicroSolar developed a novel, lightweight linear Fresnel reflector solar concentrating field using Therminol 62, a high-performance synthetic heat transfer fluid. The system was operated at modest temperatures of between 220 ⁰C and 280 ⁰C,” explains Khamid Mahkamov of Northumbria University and project coordinator. This system was coupled with a micro-organic Rankine cycle turbine using an organic working fluid with a low boiling point, making it possible to generate vapour with low-temperature heat. “Innova MicroSolar’s 2-kilowatt-electric organic Rankine cycle turbine is the smallest in the world,” adds Mahkamov.
Innovative thermal energy storage for CSP
CSP can be combined with thermal energy storage (TES) via phase change materials (PCMs) to make efficient use of the sun’s heat when the it is not shining. “We developed a novel PCM-TES design with reversible heat pipes to transfer thermal energy from the Therminol 62 to the PCM and vice versa, ensuring compact dimensions and high efficiency. A new PCM was developed based on solar salt (a molten salt mixture) and expandable graphite, which enhances the thermal conductivity of solar salt by a factor of 20,” explains Mahkamov. The TES can run the organic Rankine cycle turbine up to 4 hours without sunlight.
Small-scale, solar-powered electricity and heat with reduced emissions
The 2-kilowatt-electric/18-kilowatt-thermal Innova MicroSolar plant was field tested in Spain, demonstrating it can achieve target output throughout the spring-summer-autumn period. In winter, thermal energy generated by the solar field was used directly to heat water for domestic use. Mahkamov adds, “The system provides the highest energy savings in southern EU countries, covering all electricity demand in some. Elsewhere, it provides between 20 % and 60 % of demand. When used in a single-family dwelling, it reduces CO2 emissions by 70 % to 95 % in southern locations and about 30 % less on average in other countries.” A techno-economic and environmental analysis confirmed the solution’s highly competitive position with respect to other advanced renewable energy technologies. Commercial and governmental organisations in the Gulf Region, India, Italy, Latin America and Nigeria are in discussions to adopt the technology. The next stop is Sardinia where the Innova Microsolar system’s performance will be optimised while providing energy to local schools and a training facility for a technical college. Reliable, cost-effective and independent renewables-powered electricity and heat production is coming to small buildings around the world.
Keywords
Innova Microsolar, solar, CSP, emissions, TES, linear Fresnel reflector, organic Rankine cycle, thermal energy storage, Therminol 62, concentrating solar power
