Clean Energy Technology

A key attribute of the very high temperature reactor (VHTR) concept is its ability to produce the higher temperatures (up to 1 000 °C) needed for large scale hydrogen production using thermo-chemical cycles and some high temperature process heat applications. Also, the high temperatures allow for very high efficiencies together with a Brayton cycle. However, VHTRs would not permit use of a closed fuel cycle. Reference designs are for around 250 MW of electricity, or 600 MW of heat, with a helium coolant and a graphite-moderated thermal neutron spectrum. Fuel would be in the form of coated particles, formed either into rods or pebbles according to the core design adopted. VHTR designs are based on prototype high-temperature gas-cooled reactors built and operated in the United States and Germany, and much R&D has been completed. Key challenges for the VHTR (temperature 1 000 °C) include developing improved high temperature-resistant materials, and the fuel design and manufacture. In the meantime, the technology exists to build and operate High Temperature Reactors (with outlet temperatures up to 750-900 °C). China has constructed the HTR-PM (750 °C, with Rankine cycle) to be connected to the grid in 2021. Japan has a test reactor (HTTR) which operated for several hours with 950 °C outlet temperatures and was shutdown after the great earthquake in 2011. The reactor was restarted in 2021.

Several sodium-cooled fast reactors (SFRs) have already been built and operated in several countries, making it one of the best established Generation IV technologies. SFRs feature a fast neutron spectrum, liquid sodium coolant, and a closed fuel cycle. Full-sized designs (up to 1 500 MW) mostly use mixed uranium plutonium oxide fuel, as part of future closed nuclear fuel cycles with multi-recycling of nuclear materials. France operated for a number of years the 1200 MWe Superphenix industrial prototype that demonstrated the operational performance of the technology with MOX fuel at industrial scale. Russia has operated commercial SFRs for many years. The 600 MW BN-600 has been operating since 1980, and the 800 MW BN-800 was connected to the grid in 2015. Small designs in the 100 MW range are also being considered. SFRs have a higher (550C) outlet temperature than light water reactors, increasing the range of possible non-electricity applications. Reducing capital costs and increasing passive safety are important R&D aims, together with the industrial deployment of advanced fuel reprocessing technologies.

Wave Energy Converters (WECs) harness the energy contained in the movement of the waves. WEC placement is flexible; WECs can be deployed on or near the shoreline, or at a distance of over 100 metres from the shore. Wave technology remains at an earlier stage of development than tidal stream technology, with novel device prototypes undergoing testing in real sea conditions. A range of innovative wave device design concepts are in testing globally; wave energy is comparatively further from technological convergence. Successful design convergence may not resemble that of tidal technology; instead, a wider variety of different designs may be successful, given the broad spectrum of feasible ways to harness energy from the waves. Wave prototypes are currently found in four main forms. The point absorber is a floating structure that absorbs energy through the movement of the waves at the water's surface. The attenuator sits across the wave front, capturing energy by selectively constraining the movement caused by the passing wave. The hinged flap is mounted on the seabed in shallower water, and harnesses energy through an oscillating flap. Finally, the Oscillating Water Column (OWC) is a partially-submerged, hollow structure open to the sea water below the surface, trapping air above the water. The rising and falling waves compress and decompress this air, which is channelled through an air turbine. WEC technology developers are seeking to improve the power rating of their devices through design optimisation. This will allow for proving of the technology at higher TRLs, and proceeding to commercialisation.

Tidal stream turbines harness the flow of ocean currents in the same way that wind turbines harness the flow of wind. Tidal stream turbines can be mounted directly on the seabed, or floating and moored to the seabed. Technologies are approaching commercialisation, with the testing of full-scale devices in real-sea conditions, led by European companies. The design of tidal stream turbines is approaching design convergence. Converging designs generally comprise two- to three-bladed horizontal-axis turbines. Alternative designs include: vertical axis turbines, which work under the same principles as horizontal axis turbines, except the rotor turns on a vertical axis; oscillating hydrofoils, that have a hydrofoil attached to an oscillating arm, which is lifted by the tidal stream to generate power; enclosed tips, or Venturi Effect devices increase the velocity of the tidal stream by funnelling it through a duct; tidal kites, which are tethered to the seabed with a turbine attached below its 'wing', and 'flies' in a figure-of-eight path to exaggerate the speed of the waterflow through the turbine; and Archimedes screws, a helical corkscrew device which draws power from the tidal stream as the water flows up the spiral, turning the turbine. Tidal stream has reached a Technology Readiness Level (TRL) of between 6 and 8, depending on device type. Devices and their auxiliary technology are expected to reach commercialisation following around ten years (estimated) of further research, development and real-sea experience. The rated power of existing tidal technology ranges between smaller-scale devices of 0.1-0.25 MW, and larger scale of 1 and 2 MW, with scope to increase by 50% or more in coming years. The progress of tidal stream in recent years is demonstrated by the operating hours accumulated, capacity deployed and electricity generated, with companies operating at all scales active in Europe and globally. Since 2010, more than 26.8 MW of tidal stream has been deployed in Europe, and more globally. 11.9 MW of this is currently operating, and 14.9 MW has now been decommissioned.

A Generation III nuclear reactor incorporates evolutionary improvements in design developed during the lifetime of the Generation II reactor designs, such as improved fuel technology, superior thermal efficiency, improved safety features including passive and active safety systems and standardised design for reduced maintenance and capital costs. Typically large scale (>1GW) and based on light water reactor technology. Usually operated in baseload but all Generation III designs have the ability to operate flexibly (load following).

Ocean technologies are a broad technology family, encompassing a range of designs to generate electricity from energy in the sea, generally either in wave or tidal form. Tidal power harnesses energy from tides in a similar way to wind power. Ocean thermal energy conversion (OTEC) draws thermal energy from the deep ocean and converts it into electricity or commodities. Salinity gradient power is energy produced from the chemical pressure that results from the difference in salt concentration between fresh water and saltwater. This can therefore be exploited at river mouths where fresh and saline water meet. Two technologies are being developed to convert this energy into electricity: pressure-retarded osmosis (PRO) and reverse electrodialysis (RED). Finally, ocean current technology can harvest energy from sea currents, which always flow in one direction and are driven by wind, water temperature, water salinity and density among other factors; they are part of the thermohaline convection system that moves water around the world.

Salinity gradient exploits the osmotic pressure between seawater and fresh water. While there is significant potential for deployment, salinity gradient technology requires further development before this will be possible. Countries around the world are developing and testing this technology – the Netherlands and Mexico are key participants.

Concentrated PV (CPV) technologies use an optical concentrator system which focuses solar radiation onto a small high-efficiency cell. CPV modules can achieve efficiencies of above 40%.

Small modular reactors are defined as reactors with an electric generating capacity of up to 300 MW. Light water reactor (LWR) SMR designs are based on existing commercial LWR technology but are generally small enough to allow all major reactor components to be placed in a single pressure vessel (i.e. integral designs). The reactor vessel and its components are designed to be assembled in a factory and transported to the plant site for installation, potentially reducing construction time and costs compared to those of large LWRs.

Ocean Thermal Energy Conversion (OTEC), including Sea-Water Air Conditioning (SWAC), exploits temperature differences found at different ocean depths. The technology can also be harnessed to deliver SWAC and desalination. Beyond power production, SWAC is commercially competitive in commercial and data centre cooling in Europe.

Tidal range adopts conventional hydropower principles to harvest energy from the difference in sea level between high and low tides. Tidal range development is focused in the UK, the Netherlands, France and Korea.

Today, the vast majority of PV modules are based on wafer-based crystalline silicon (c-Si). The manufacturing of c-Si modules typically involves growing ingots of silicon, slicing the ingots into wafers to make solar cells, electrically interconnecting the cells, and encapsulating the strings of cells to form a module. Modules currently use silicon in one of two main forms: single- (sc-Si) or multi- (mc-Si) crystalline modules. Current commercial single-crystalline modules have a higher conversion efficiency of around 14 to 20%. Their efficiency is expected to increase up to 25% in the longer term. Multi-crystalline silicon modules have a more disordered atomic structure leading to lower efficiencies, but they are less expensive. Their efficiency is expected to increase up to 21% in the long term.