Hybrid Solar Technologies

Patented hybrid energy system

At the CET, we understand the need for step change and that’s why we specialise in hybrid energy systems, which give the ability to produce energy from renewable sources but with fossil fuels as a back-up or supplementary fuel source.

About the system

The HSRC’s fossil fuel source is gas, which means that users can manage short and long term variability of the renewable energy source by maximising renewable energy use when it is available, and using gas at other times – all in a single unit.

The unit can provide a firm supply of hot air at up to 800°C around the clock and maximise penetration of renewables into a network. The HSRC reduces CO2 emissions, compared to a standalone combustion system, because of its faster start up time and it has a much greater solar share than conventional, concentrated solar thermal systems. The economic benefits of the HSRC have already been assessed.

We expect:

• a 24% reduction in levelised cost of electricity (LCOE)
• 4-45% reduction in net fuel consumption
• 51% reduction in overall power plant capital cost, as compared to a system with a standalone solar and combustion systems.

Applications

The HSRC can be fitted to industrial process heat and electricity generation systems.

In industrial settings, the thermal energy from the unit could provide firm supply at the exact temperature needed, to reduce dependency on natural gas and CO2 emissions. This would apply to smelters and limestone, alumina, and magnesium calcining as well as in other industrial settings.

For electricity generation, the HSRC could be integrated with current concentrating solar power (CSP) towers to provide steady, continuous energy supply.

The HSRC could also supply energy for solar gasification of biomass and for liquid fuel manufacturing from biomass in remote settings such as mine sites or in the Upper Spencer Gulf region.

The system will help us to transition to a renewable future by increasing solar share and hybridising methane or syngas with solar thermal as it will be able to supply baseload power from a single unit rather than from solar with gas back-up generation

What’s happening now?

The HSRC is currently at Technology Readiness Level (TRL) 4 after being awarded ARC Linkage funding in 2012.

The first HSRC unit (12 kWth) was built and successful demonstrated in 2017 by Dr Alfonso Chinnici, Prof. Bassam Dally and Prof. Gus Nathan. The key outcomes of this investigation are:

• Efficient operation in all three modes (combustion-only, solar-only and mixed-mode, including operations under MILD combustion) with thermal efficiency of 88%;
• Low NOx (<5 ppm) and CO (<100 ppm) emissions;
• CFD models validated by experimental data;
• Confidence to design and build on-sun HSRC at large scale.

Other research activities include:

• Development of a sealing gas system to minimise convective heat losses during solar-only and mixed-mode operations;
• Experimental (Particle Image Velocimetry) and numerical investigation of the isothermal flow-fields within a HSRC prototype (acrylic).

The CET team is now looking for project and partnership opportunities to:

• Demonstrate the HSRC at pilot, small and large scales;
• Integrate the HSRC into a solar cavity receiver to reduce infrastructure costs and heat losses.

People

	Professor Gus Nathan		Professor Bassam Dally
	Dr Alfonso Chinnici

Solar thermal power offers low net greenhouse emissions but the intermittent nature of solar radiation makes it a high cost technology. Fossil fuels offer continuous power and are more economical, but carbon dioxide (CO2) emissions are high.

Dr Mehdi Jafarian has developed a new, integrated system to reduce the costs of solar technology by combining it with chemical looping combustion (CLC) technology in power plants.

Patented hybrid energy system

The hybrid solar chemical looping combustion (Hy-Sol-CLC) system is a world-first, with the potential to contribute to step change in integrating renewable energy technologies into conventional power generation systems. The system can manage the inherent variability of solar power and significantly reduce costs.
Applications

Chemical looping combustion technology was originally developed to provide industrially-pressurised CO2 streams for sequestration or reuse. Using CLC process components, CET researchers designed the novel hybrid solar CLC (Hy-Sol-CLC) power plant that can provide steady power generation despite variations in solar thermal energy input. In addition to storing solar energy, the Hy-Sol-CLC system could also be run as a conventional CLC system during extended periods of low solar radiation.

What’s happening now?

The researchers have developed mathematical models to compare the Hy-Sol-CLC system with other solar technologies. While current generation hybrids operate at around 3–10% solar share, the Hy-Sol-CLC power plant can achieve a solar share of 60% while maintaining base load power generation.

The thermodynamic performance of two configurations is also being examined – with and without an after-burner. Without the after-burner the hybrid system achieved a first law efficiency of 44% with a solar share of 60% and produced pressurised and industrially-pure CO2 ready for reuse or storage. With the after-burner the first law efficiency increased to 50% with a reduction in solar share. Sensitivity analyses indicated that further improvements to the performance of the cycle are possible.

Key references

• Jafarian M, Arjomandi M and Nathan GJ (2014) The energetic performance of a novel hybrid solar thermal & chemical looping combustion plant. Applied Energy 132, 74-85.
• Jafarian M, Arjomandi M and Nathan GJ (2014) A hybrid solar chemical looping combustion system with a high solar share. Applied Energy 126, 69-77.

Proposed hybrid solar-CLC combined cycle

Text description of image.

• Reservoirs R1 and R2 are used to store the hot and cold particles from the solar fuel and air reactors, respectively.
• A direct air-particle heat ex-changer is employed to further cool the particles to the OC particle storage temperature in reservoir R1.
• An after-burner is optionally used to increase the temperature to the gas turbine inlet using valve V2 and V3.

Low cost, low carbon jet fuel and diesel possible with unique SDFB gasification process

A novel solar hybridised dual fluidised bed (SDFB) gasifier developed by CET scientists offers sensible thermal storage of bed material, use of inert particles in the solar receiver, and a process that delivers a constant rate of syngas production despite solar variability. This technology combined with low cost biomass residues can offer low cost path to low carbon jet fuel and diesel.

About Solar Hybridised Dual Fluidised Bed (SDFB) gasification

Solid carbonaceous fuel is fed to a bubbling fluidised bed gasifier, where it is reacted with a fluidising agent – steam – to produce syngas, a gaseous mixture comprising mostly H2 and CO. The heat required by the endothermic gasification reactions is provided by hot bed material transferred from combusting residual char and additional fuel with air or directly heated by concentrated solar thermal. A steady syngas output can be achieved when the hot bed material is maintained at a constant temperature, through adjusting fuel input to the combustion process according to the variation in solar radiation.

Applications

The syngas generated from this technology is a valuable general-purpose fuel, suitable either as a feedstock for liquid fuels and petro-chemicals or as industrial fuel in its own right.

What’s happening now?

The research team, led by Professor Gus Nathan, have performed a series of process modelling to optimise the technical and economic performance of this concept. The team will also undertake a study to understand the interaction between the bed material and ash generated from low cost biomass residues as well as to understand the hydrodynamics of the SDFB.