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Direct Solar Energy - page 30 / 68





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Direct Solar Energy

Scaling up thermochemical processes for hydrogen production to the 100-kWth power level is reported for a medium-temperature mixed iron oxide cycle (800°C to 1,200°C) (Roeb et al., 2006, 2009) and for the high-temperature zinc oxide (ZnO) dissociation reaction at above 1,700°C (Schunk et al., 2008, 2009). Pilot plants in the power range of 300 to 500 kWth have been built for the carbothermic reduction of ZnO (Epstein et al., 2008), the steam reforming of methane (Möller et al.,

  • 2006)

    , and the steam gasification of petcoke (Z’Graggen and Steinfeld,

  • 2008)

    . Solar-to-gas has been demonstrated at a 30-kW scale to drive

a commercial natural gas vehicle, applying a nickel catalyst (Specht et al., 2010). Demonstration at the MW scale should be warranted before erecting commercial solar chemical plants for fuels production, which are expected to be available only after 2020 (Pregger et al., 2009).

Direct conversion of solar energy to fuel is not yet widely demonstrated or commercialized. But two options appear commercially feasible in the near to medium term: 1) the solar hybrid fuel production system (includ- ing solar methane reforming and solar biomass reforming), and 2) solar

PV or CSP electrolysis.

Australia’s Commonwealth





Organisation is running a 250-kWth reactor and plans to build a MW-scale demonstration plant using solar steam-reforming technology, with an eventual move to CO2 reforming for higher performance and less water usage. With such a system, liquid solar fuels can be produced in sunbelts such as Australia and solar energy shipped on a commercial basis to Asia and beyond.

Oxygen gas produced by solar (PV or CSP) electrolysis can be used for coal gasification and partial oxidation of natural gas.With the combined process of solar electrolysis and partial oxidation of coal or methane, theoretically 10 to 15% of solar energy is incorporated into the metha- nol or DME. Also, the production cost of the solar hybrid fuel can be lower than the solar hydrogen produced by the solar electrolysis process only.


Industry capacity and supply chain

This subsection discusses the industry capacity and supply chain within the five technology areas of passive solar, active solar heating and cool- ing, PV electricity generation, CSP electricity generation and solar fuel production.

In passive solar technologies, people make up part of the industry capacity and the supply chain: namely, the engineers and architects who collaborate to produce passively heated buildings. Close collabo- ration between the two disciplines has often been missing in the past, but the dissemination of systematic design methodologies issued by


Chapter 3

different countries has improved the design capabilities (Athienitis and Santamouris, 2002).

The integration of passive solar systems with the active heating/cool- ing air-conditioning systems both in the design and operation stages of the building is essential to achieve good comfort conditions while saving energy. However, this is often overlooked because of inadequate collaboration for integrating building design between architects and engineers. Thus, the architect often designs the building envelope based solely on qualitative passive solar design principles, and the engineer often designs the heating-ventilation-air-conditioning system based on extreme design conditions without factoring in the benefits due to solar gains and natural cooling. The result may be an oversized system and inappropriate controls incompatible with the passive system and that can cause overheating and discomfort (Athienitis and Santamouris, 2002). Collaboration between the disciplines involved in building design is now improving with the adoption of computer tools for integrated analysis and design.

The design of high-mass buildings with significant near-equatorial-facing window areas is common in some areas of the world such as Southern Europe. However, a systematic approach to designing such buildings is still not widely employed. This is changing with the introduction of the passive house standard in Germany and other countries (PHPP, 2004), the deployment of the European Directives, and new national laws such as China’s standard based on the German one.

Glazing and window technologies have made substantial progress in the last 20 years (Hollands et al., 2001). New-generation windows result in low energy losses, high daylight efficiency, solar shading, and noise reduction. New technologies such as transparent PV and electrochromic and thermochromic windows provide many possibilities for designing solar houses and offices with abundant daylight. The change from regu- lar double-glazed to double-glazed low-emissivity argon windows is presently occurring in Canada and is accelerated by the rapid drop in prices of these windows.

The primary materials for low-temperature thermal storage in passive solar systems are concrete, bricks and water. A review of thermal stor- age materials is given by Hadorn (2008) under IEA SHC Task 32, focusing on a comparison of the different technologies. Phase-change material (PCM) thermal storage (Mehling and Cabeza, 2008) is particularly promising in the design, control and load management of solar build- ings because it reduces the need for structural reinforcement required for heavier traditional sensible storage in concrete-type construction. Recent developments facilitating integration include microencapsulated PCM that can be mixed with plaster and applied to interior surfaces (Schossig et al., 2005). PCM in microencapsulated polymers is now on the market and can be added to plaster, gypsum or concrete to enhance

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