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Solar chemical reactor demonstration and Optimization for Long-term Availability of Renewable JET fuel

Final Report Summary - SOLAR-JET (Solar chemical reactor demonstration and Optimization for Long-term Availability of Renewable JET fuel)

Executive Summary:
With the first-ever production of synthesized “solar” jet fuel, the SOLAR-JET project has successfully demonstrated the entire production chain for renewable kerosene obtained directly from sunlight, water and carbon dioxide (CO2), therein potentially revolutionizing the future of aviation. The project demonstrated an innovative process technology using concentrated sunlight to convert carbon dioxide and water to a so-called synthesis gas (syngas). This is accomplished by means of a redox cycle with metal-oxide based materials at high temperatures. The syngas, a mixture of hydrogen and carbon monoxide, is finally converted into kerosene by using commercial Fischer-Tropsch technology.
In the ETH laboratories, the reactive material was developed over the project period to obtain a dual-scale porosity which allows enhanced heat and mass transfer. It was also shown that the H2/CO-ratio can be chosen to have the desired value for the Fischer-Tropsch conversion which obviates further species adjustments. A record solar thermochemical energy conversion efficiency of 1.7% was achieved with the first generation of the reactors used in the project. In a further development, a second generation of the reactor features a different geometry with improved temperature distribution in the reactive material and achieves an even higher energy conversion efficiency of unprecedented 2.7%.
Accompanying the experimental demonstration, a computational model was created at DLR which is able to describe accurately the behavior of the solar reactor. The model was validated with actual experimental data from the laboratory and provides a valuable tool to gain further insight into the heat and mass transfer characteristics. It is further used to model a scale-up of the reactor to a power input of 50 kWth.

In a dedicated analysis, the ecological and economic performance of the SOLAR-JET fuel pathway was assessed. It was found that for a baseline case plant with a capacity of 1000 barrels per day (bpd) of jet fuel and 865 bpd of naphtha, greenhouse gas emissions of 0.5 kg CO2-equivalent/L jet fuel at production costs of 2.2 €/L jet fuel are to be expected. Important drivers for both the ecological and economic performance were identified to be the thermochemical energy conversion efficiency and the solar resource. Further, a significant reduction of greenhouse gas emissions can only be expected if CO2 is captured from a renewable, non-fossil source such as the atmosphere. Equally, using renewable instead of grid electricity is essential to achieve an excellent ecological performance due to its impact on life-cycle emissions.
A technological assessment revealed that most process steps are already used on an industrial scale, such as water desalination, concentration of solar energy, gas storage, and Fischer-Tropsch conversion. Further research and development is foremost required for the thermochemical conversion and CO2 capture from air. For the developed process steps, primarily cost targets apply, while for the other processes efficiency and/or cost targets have to be considered.

Project Context and Objectives:
The EU Directive 2009/28/EC requires a 10% share of renewable energy in the transport sector in every Member State by 2020 and the EU energy roadmap for 2050 aims at a 75% share of renewables in the gross energy consumption. Achieving these targets requires a significant share of alternative transportation fuels, including a 40% target share of low carbon sustainable fuels in aviation . Current biofuel technologies do not meet sustainability and availability requirements at the scale of future global fuel demand .
Converting solar energy into fuels has the potential of adding significant renewable capacity to the European transport fuel mix. Solar energy utilization is undisputedly scalable to any future demand and is already utilized at large scale to produce heat and electricity via solar-thermal and photovoltaic installations. Solar energy may also be used to produce hydrogen. However, specific transportation sectors cannot easily replace hydrocarbon fuels, with aviation being the most notable example. All current aircraft developments are designed for conventional jet fuel, since liquid hydrocarbons are ideal energy carriers with exceptionally high energy density and most convenient handling properties, and also because of the existing massive global infrastructure and because of the compatibility with conventional aircraft fuel systems. Due to long design and service times of aircrafts the aviation sector will critically depend on the availability of liquid hydrocarbons for decades to come . Heavy duty trucks, maritime and road transportation are also expected to rely strongly on liquid hydrocarbon fuels . Thus, the large volume availability of ‘drop-in’ capable renewable fuels is of great importance for decarbonizing the transport sector.

Project Results:
Please refer to the attached document (PDF) as this section contains many equations, tables, graphs and illustrations, this was not possible to copy here only plain text without strongly damaging its quality.

Potential Impact:
The socio-economic impact of large-scale production of SOLAR-JET fuel is expected to be two-fold, energy supply security and wealth from local fuel production. The potential to reduce the dependency of oil producing countries for the supply of hydrocarbon fuels and thus to establish supply security is a strong driver for high-insolation regions such as in southern Europe, Africa and Australia. Due to the large solar resource and the wide availability of the resources water and CO2, single countries have the potential to cover their own demand of jet fuel and some of them even the global demand.
The SOLAR-JET technology requires a large solar resource of direct normal insolation (DNI) which is typically found in countries with vast areas of arid non-arable land. The construction of large-scale production facilities could therefore bring wealth to economically challenged regions and help to develop local industries and economies. As this is a new technology, it would not replace an existing industry but would be complementary and therefore create new jobs and opportunities. It is conceivable that the construction of a SOLAR-JET plant with its necessary water provision could supply a surplus of fresh water to the local population and agriculture with a profound and sustainable positive socio-economic impact.
An economic model is used for the estimation of jet fuel production costs. A baseline case with a plant size of 1000 bpd of jet fuel production is chosen. At the same time, 865 bpd of naphtha are produced from the same facility. The solar-stand alone facility, i.e. without external sources of heat or electricity, is publicly financed and located in a region with 2500 kWh/(m² a) of direct normal irradiation with a tower system as concentrator. Thermochemical energy conversion efficiency is assumed to be 20%. Carbon dioxide is provided by an air capture unit located onsite and water by seawater desalination located at 500 km distance and 500 m altitude difference. The produced fuels are transported over 500 km via pipeline.
For the calculation of jet fuel production costs from the baseline plant, investment costs and operation and maintenance costs (O&M) are estimated. The total investment costs are 880 million € for the fuel production plant, where 74% are for the heliostat field, 11% for the thermochemical reactors including the reactive material ceria, 8% for the solar tower, 5% for the Fischer-Tropsch conversion unit, and smaller contributions for buildings and other technical equipment. The O&M costs are 123 million € per year, where 37% are for operation and maintenance of the heliostat field, 32% for CSP electricity, 27% for CO2, and minor contributions for the operation and maintenance of the Fischer-Tropsch unit, water provision, mirror replacement, and fuel distribution.
The annuity method is used for the derivation of production costs of jet fuel. At first, the present value of the O&M costs are calculated as the annual O&M costs multiplied with the annuity factor, where the O&M costs are in constant currency and the annuity factor is calculated with the real interest rate. Naphtha is sold at a fixed price of 80% with respect to the jet fuel production costs. The lifetime of the publicly supported plant is 25 years and the interest rate is nominal 6% for the baseline case. Public funding could be the case if such a facility is supported by the government in order to secure supply security of liquid hydrocarbon fuels.
Production costs of 2.2 € per liter of jet fuel are estimated. For the present case, the economics of the plant are ruled by the accumulated O&M costs which have about twice the impact with respect to the investment costs. However, plant economics are also strongly driven by investment costs, as the concentration of the solar resource requires an expensive infrastructure.
In order to study the influence of a set of variables, a sensitivity study is performed for the level of solar irradiation, thermochemical efficiency, life time of the plant, specific investment costs of reflective area, and costs of CO2 provision. An improved plant location that increases the level of solar irradiation by 10% reduces the production costs by 4.7%. Similarly, a reduction in solar irradiation by 10% increases production costs by 5.8%. These values are not identical because the increase by 10% of solar irradiation diminishes the heliostat field by 9%, while its decrease requires a larger reflective surface area of 11%. The same is true for the variation of thermochemical efficiency that defines the required size of the heliostat field: an increase of efficiency by 10% reduces the production costs by 6.1%, while a similar decrease in efficiency leads to an increase by 7.5%. As for the concentration of dilute solar energy a large field of mirrors is needed, investment costs for solar concentration play a major role. A variation of ±10% of the unit cost of heliostat area leads to a variation of production costs of ±2.4%. The 10%-reduction in lifetime of the plant increases the production costs by 5.0%, while a 10% longer lifetime reduces the costs by 4.0%. Finally, the costs of CO2 provision have the smallest influence of ±1.8% on the production costs. Solar irradiation, thermochemical efficiency, and plant lifetime are thus identified to have the largest influence on plant economics and are consequently the main cost drivers of the process.
Climate impact
A life-cycle analysis is performed for a baseline case of a fuel production plant of 1000 bpd output of jet fuel to estimate the global warming potential associated to jet fuel and naphtha. The functional unit is 1 L of jet fuel, where 0.87 L naphtha is produced as by-product. A well-to-wake boundary is chosen that includes resource provision, concentration of solar energy, thermochemistry, and Fischer-Tropsch conversion, as well as final combustion of the fuel. As CO2 is captured from the air, the amount of CO2 in the atmosphere is reduced in the capture process which counts negatively in the overall CO2 balance. The plant operates in a solar stand-alone configuration, i.e. all heat and electricity requirements are covered by the local conversion of solar primary energy.
Life cycle greenhouse gas emissions are 0.49 kgCO₂-eq. per liter jet fuel and 0.55 kgCO₂-eq. per liter naphtha. Largest influences on the positive emissions have fuel combustion with 65%, FT conversion with 16%, and construction, use and decommissioning of the solar concentration facility with 12%. Emissions of the FT conversion originate from the combustion of the light hydrocarbon fraction in a combined heat and power plant, as well as fugitive emissions. Emissions of the solar concentrator are almost completely associated to its construction and deconstruction, while its use has only a small influence. Only small contributions are due to the thermochemical reactors, electricity, and fuel transportation. Greenhouse gas emissions could be reduced by about 80% through the use of solar jet fuel compared to conventional jet fuel. This significant savings potential is well below current reduction threshold of 35% and even the stricter emissions reductions targets set by the EU for the use of biofuels.
The solar stand-alone configuration has low greenhouse gas emissions because heat and electricity is provided by conversion of solar primary energy. Grid electricity that is partly based on fossil energy carriers is thus not used. Also capture of carbon dioxide from the air significantly reduces the emissions compared to the capture from fossil sources if the fossil emissions are included into the system boundaries. Different plant configurations are possible, where also the heat and power from the combined heat and power plant is supplied by renewable energy conversion, thereby further reducing the emissions.
A sensitivity study is performed on the variables solar irradiation level, thermochemical efficiency, lifetime of the plant, and emissions from the construction, use and deconstruction of the concentration infrastructure, in which selected variables are varied by ±10% at constant output of the plant. The results indicate that a variation of the plant lifetime, of thermochemical efficiency, or of solar irradiation have a similar influence on the overall greenhouse gas emissions: a reduction by 10% of the variables leads to higher emissions by 10-12%, while a 10% increased value deminishes the costs by 8-10%. A longer lifetime distributes the environmental burdens associated with the infrastructure and operation of the plant over a different number of years and thus the specific emissions per unit fuel produced are altered. Solar irradiation and thermochemical efficiency define the required mirror area and thus the emissions associated with their production. The rather large number of mirrors for the concentration of sunlight has an impact also through the associated emission factor per unit of mirror area. A change by ±10% varies the life cycle GHG emissions by ±8.6%. Thus, there is a possible improvement through a decrease of the material intensity of the heliostats, an interesting topic also for economic reasons.
If CO2 capture from fossil sources were introduced, it would dominate the emissions and show a different sensitivity with respect to the chosen variables. An improvement of the climate impact of solar jet fuel production could therefore be achieved through the choice of a highly irradiated plant location, the enhancement of the thermochemical conversion step, a prolongation of the lifetime of the plant components, and a reduction of the material intensity of the mirrors and the solar tower.

CO2 reduction potential for complete substitution of jet fuel
The associated CO2 reduction potential is estimated from the specific greenhouse gas emissions of the SOLAR-JET fuel and the market size of aviation fuel which is currently 254 Mt (2012). If the complete jet fuel demand is supplied by SOLAR-JET fuel, about 805 Mt of CO2 could be saved.

Benefit for countries with large solar resource
For the production of solar thermochemical fuels, a high direct solar irradiation is required which is mainly found in countries of the Mediterranean region, the Middle East, Australia, and the Southwest of the United States. The implementation of a fuel production infrastructure could therefore lead to significant investments and job creation opportunities in these regions which could help to develop the local and regional economy. In the following, the investments and the number of jobs created are estimated for the establishment of solar thermochemical fuel production.
Future investment opportunities:
Similar to most renewable energy technologies solar thermochemical fuel production has high upfront cost and relatively low annual maintenance and operation cost. The development of production capacity is therefore accompanied by large capital expenditure. A coarse estimate on capital requirement may be derived from the size of the solar field area of 1.3*1010 m2, and the specific investment costs of the solar plant. Projected heliostat costs range significantly below
200 $/m2, where this latter value may serve as an upper bound estimate of the total specific financial investment in the n-th solar fuel plant. Multiplying the required collector area with the specific investment cost yields a total investment of 2600 billion $ for the complete substitution of aviation fuel. This number can be compared to the world’s gross domestic product (GDP) of about 74,000 billion $ in 2013 (CIA, 2014). Thus less than 1% of the global GDP is required for a capacity roll-out time of one decade.
Future job creation opportunities:
A large scale roll-out of solar thermochemical fuel production capacity would take place in regions with favourable solar resource. It is estimated that 1.3*1010 m2 of mirror area are required for a 100% substitution of conventional jet fuel. Assuming an installation period equal to a plant life time of 30 years equates to an annual installation of 4.3*108 m2 mirror area. The US National Renewable Energy Laboratory lists construction job years and mirror areas for existing CSP solar tower facilities, including Gemasolar (800 job years for 304,750 m2), Ivanpah (1896 job years for 2,600,000 m2) and Crescent Dunes (1500 job years for 1,071,361 m2) (NREL, 2014). The installed mirror area per construction job year varies widely from 381 m2 for Gemasolar (Spain) to 1370 m2 for Ivanpah (US). Assuming the larger value of 1370 m2 per job year, an annual addition of 4.3*108 m2 mirror area requires 314.000 job years for construction. Although this represents a major work force especially in scarcely populated areas, this work force does not appear as a show-stopper. It may also be expected that the installed mirror area per construction job year will increase due to automation. The required work force for operation and maintenance of concentrated solar thermal facilities is much smaller than for plant construction. In 2010, 446 people were employed for operation and maintenance of Spanish CSP electricity generation, while 23,398 people have been employed for construction (Deloitte, 2011).

List of Websites:

Dr. Andreas Sizmann, Project Coordinator
Bauhaus Luftfahrt e.V.
Willy-Messerschmitt-Straße 1
85521 Ottobrunn
+49 (0)89 307 4849-38