Most research within the renewable energy industry itself (apart from improving panel efficiencies in solar PV) appears to have been in the development of electrochemical storage methods, such as batteries using different types of technology. Whilst in my opinion that is important and significant progress has been made, when it comes to actually costing our renewable developments to include batteries, it emerges that the capital spend (CAPEX) associated with battery storage can often make the envisaged project uneconomic, particularly in this 'post-incentive era' (although please recall my comments on use of cheap batteries with short shelf lives which are replaced every 3-5 years). 

Developers like my companies have therefore sought other means by which to store energy (essential to making renewable energy generation profitable and hence of interest to investors) and have turned to some other areas. I see storage of electricity through 2 particular methods as offering potentially cost-effective solutions to the storage of (particularly solar PV-produced) electricity (reflecting the 'production versus demand problem' within our societies), and these are in the areas of thermal and chemical storage. For thermal storage we have a partner : and we may explore that route further but the area of greatest interest to me at the moment is the Chemical means of energy storage. This includes the following areas which are of interest:

  • Hydrogen from water electrolysis/electrolytic water splitting

  • Thermochemical Energy Storage (chemical reactions)

  • Power-to-Gas

  • Electrocatalysis/Photocatalysis

  • Electrofuels/biofuels

I find the comments of ARPA-E, the US government agency, particularly interesting for the latter category in terms of defining a direction some of us could follow in terms of research:

High efficiency routes to energy-dense, infrastructure compatible liquid fuels for transportation from sunlight and CO2 are urgently required. Although photosynthetic routes show promise, overall efficiencies remain low and the ability to deploy many possible configurations remains unclear. Progress has been made in the direct inorganic conversion of photosynthetic energy to reduced chemical species; however, the ability to form carbon-carbon bonds in a high-yielding predictable approach remains limited. 

In addition ARPA-E states that their objectives include:

  • The direct use of electric current to produce energy-dense, infrastructure compatible liquid fuels directly from CO2 as the only carbon source;

  • The use of reversibly reducible earth abundant metal ions or of cheap, readily available redox active organic materials as intermediaries, transferring reducing equivalents into a cell, which produces energy-dense, infrastructure compatible liquid fuels directly from CO2 as the only carbon source;

  • The development of Calvin cycles variants that accepts reducing equivalents from regenerable agents other than Photosystems I and II or directly from solar current;

  • The development of organisms that assimilate solar hydrogen with high affinity to produce energy-dense, infrastructure compatible liquid fuels directly from CO2 as the only carbon source.

There are also other pathways to solar fuels, using the Fischer Tropsch Process :

In order to reduce carbon dioxide emissions from fossil-fuel-based power plants, CO2 can be captured and further processed to obtain fuels that readily integrate into the current transportation infrastructure. This upgrading of CO2 can be accomplished in a solar refinery, which uses sunlight as a renewable energy source to drive catalytic reactions as shown below (Herron et al., 2015).

The two main methods for CO2 conversion include: (1) catalytic conversion using solar-derived hydrogen, and (2) direct reduction of CO2 using H2O and solar energy. Solar utilities can be utilised in the form of heat (e.g., in thermolysis and thermochemistry), electricity (e.g., in electrocatalysis), and as a photon source (e.g., in photo-chemical reactions).

We are performing systems-level, techno-economic and conceptual design and operational analyses of different process configurations for the available power-to-fuel chemical routes. In particular, we assess the energetic and economic feasibility of each process by quantifying the impact of key areas, such as solar energy capture and conversion, CO2 capture, catalytic conversion processes, and chemical storage (Kim et al., 2011; Kim et al., 2012; Herron & Maravelias, 2016).


  • Kim, J., Henao, C. A., Johnson, T. A., Dedrick, D. E., Miller, J. E., Stechel, E. B., & Maravelias, C. T. (2011). Methanol Production from CO2 Using Solar-Thermal Energy: Process Development and Techno-Economic Analysis. Energy & Environmental Science, 4(9), 3122–3132.

  • Kim, J., Johnson, T. A., Miller, J. E., Stechel, E. B., & Maravelias, C. T. (2012). Fuel Production from CO2Using Solar-Thermal Energy: System Level Analysis. Energy & Environmental Science, 5(9), 8417–8429.

  • Herron, J. A., Kim, J., Upadhye, A. A., Huber, G. W., & Maravelias, C. T. (2015). A General Framework for the Assessment of Solar Fuel Technologies. Energy & Environmental Science, 8(1), 126–157.

  • Herron, J. A., & Maravelias, C. T. (2016). A General Framework for the Assessment of Solar Fuel Technologies. Energy Technology, 4(11), 1369–1391.

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