Concentrating Solar Power (CSP) technology involving the use of mirrors to focus sunlight onto a receiver that captures and converts the solar energy into heat for electricity generation has been in use since 1980s. The CSP technology has, however, re-emerged as a promising new green power technology during recent years with new innovations in different CSP systems and the invention of new solar thermal storage solutions such as molten salt technology.
The CSP systems currently in use are broadly of three types namely, the trough system, power tower system and the dish/engine system. The trough system comprises of U-shaped reflectors focussing sunlight onto oil-filled pipes running along their centre with the hot oil boiling water to generate steam for electricity generation. The power tower CSP system uses large flat mirrors called heliostats to focus sunrays onto a receiver sitting atop a tower in which fluid such as molten salt can absorb the heat to make steam for immediate electricity generation or store it for later use.
The dish/engine systems use mirrored dishes to focus and concentrate sunlight onto a receiver mounted at the focal point of the dish. The receiver is integrated with an external combustion engine which generates electricity as the concentrated sun light heats up expanding hydrogen or helium gas contained in its thin tubes driving the piston of the engine.
Global CSP installed capacity at the beginning of 2013 stood at 2.5GW with the United States followed by Spain accounting for the majority of it. The recently opened 320MW Ivanpah solar energy project based on the power tower system in California’s Mojave Desert in the US is the world’s biggest CSP plant. The 280MW Solana solar project located in Arizona, United States, entered into service in October 2013 becoming the world’s biggest trough system-based CSP plant. The Solana facility also offers six hours of molten storage capacity to produce electricity during evening.
Many more CSP plants are currently under development across the world. The long term probability of success of the CSP technology is evident from the use of improved thermal energy storage solutions to avoid solar power’s most common problem of intermittency and the fact that the equipment used for conventional fossil fuelled power plants can be used for large scale CSP plants.
Floating wind turbines
The commercial operation of floating wind turbines could hold the key to unlocking the offshore wind power potential of deeper waters where winds are often stronger and steadier. Unlike conventional offshore wind turbines that require erection of concrete bases in the seabed, floating wind turbines, based on floating oil and gas offshore platform technology, are anchored into the seabed with the use of just a few cables at sites as deep as 700m. Deeper waters also offer the advantage of less obtrusive installations.
The successful demonstration of several prototype floating wind turbines since 2009, has generated interest for commercial deployment floating wind turbines. Some of the best examples include the Dutch floating-turbine developer Blue H Technologies’ test turbine off the coast of southern Italy, the oil and gas company Statoil’s experimental floating wind turbine Hywind off the coast of Norway, and the Fukushima prototype floating wind turbine off the coast of Japan.
Interest for wind power generation from floating turbines is especially noticeable in countries like Japan which has been striving for alternate power following the nuclear disaster in 2011 but does not have enough shallow coastal waters to support conventional wind farms.
Japan has proposed building a 1GW floating wind farm by 2020 around 20km off the coast of the damaged Fukushima Daiichi nuclear plant. The government has invested $226m for the installation of the first prototype turbine and two additional 7MW wind turbines. Following successful testing of the initial turbines, the Fukushima wind power project with 140 additional turbines will be developed by a private coalition including Marubeni, Mitsubishi, Hitachi and others. The Fukushima project uses semisubmersible turbine platform with three buoyancy tanks arranged in a triangle around the turbine and the world’s first floating substation containing the electrical equipment needed to transfer power from turbines to shore.
Floating offshore wind power generation technology is also gaining momentum in the UK. The country’s first floating wind power project Buchan Deep received approval from the Crown Estate in November 2013. The 30MW wind farm comprising six floating turbines will be developed by Statoil off the coast of Aberdeenshire, Scotland, at a water depth of 100m.
Printable organic solar cells
Printable and flexible solar cells could revolutionise photovoltaic solar power generation using semiconducting inks printed directly onto flexible stretchable thin plastic or steel, that will not only reduce the cost of solar cells but also open up a myriad of new installation options.
These extremely light weight organic solar cells can be laminated onto building walls or any other irregular surfaces exposed to sun light as well as be built into construction materials directly. Solar cells comprised of plastic polymers are also considered to perform better in low light conditions.
A group of Australian scientists produced paper-thin solar cells the size of an A3 piece of paper using a purpose-built printing machine installed at Australia’s national scientific research agency CSIRO in the beginning of 2014. The solar cell printer could produce up to ten metres of solar panel per minute. One square metre of the solar panel is expected to produce 10 to 50 watts.
The ultra low cost printable solar cell technology complemented with a range of other related technologies, currently in research phase, to improve the power output of printable photovoltaic cells – such as dye-sensitised solar cell (DSC) technology and the use of dye-coated plastic can to absorb light coming from different angles – holds the promise of raising the economy and efficiency of photovoltaic solar power generation to the next level.
Biomass gasification technology for power generation
Converting biomass into combustible gas and using it for power generation has emerged as means of converting abundantly available biomass wastes into clean and efficient electrical energy.
An advanced biomass gasification power plant typically involves a gasifier system converting solid biomass into clean combustible gas by thermo-chemical processes involving the stages of drying, pyrolysis and gasification. The non-combustible ash produced in the process migrates to the grate at the base of the gasifier and is removed from time to time with grate-shaking mechanism.
The produced syngas is burned in the oxidiser at temperature up to 700°F with the produced hot flue gas passing through a boiler to produce high-pressure steam that drives the turbine for producing electricity. Electrostatic precipitators are used to capture the remaining particulates present in the flue gas released into air.
The 10.3MW Birmingham Bio Power project being developed at Tyseley, Birmingham, UK, is one of the major recently launched commercial scale power projects using advanced biomass gasification technology. The biomass gasification based power generation technology also holds significant potential especially in developing countries where the enormous amount of biomass wastes heading for landfill can be used for clean power generation.
Tidal energy technologies
Tidal power generation technology is at a nascent stage compared to other renewable power technologies but the rate of innovation and new demonstrations of technology is a good that tidal energy could emerge as a viable commercial scale green power technology in the long term.
A range of devices including offshore floats, buoys or pitching devices, oscillating water column (OWC) devices and under water turbines have been developed to produce electricity from waves and tides of the ocean. An innovative under water floating device called Deep Green equipped with hydrodynamic wing and a gearless turbine anchored to the ocean bed with a tether was developed by the Swedish marine energy technology company Minesto in 2013 to harness low velocity tidal current for power generation.
While many different devices have been tested, the use of underwater tidal turbines has emerged as the most promising model of tidal power generation. The world’s first commercial-scale tidal turbine was commissioned in Northern Ireland’s Strangford Lough in July 2008. Other notable tidal power projects using under water tidal turbines include the Sound of Islay and West Islay wind farms being developed off the coast of Scotland.
Tidal lagoons are also emerging as another promising model for tidal power generation. The world’s first tidal lagoon power project has been proposed at Swansea Bay in the UK. The project scheduled for ground breaking in 2015 and commissioning in 2018 will involve the construction of a 9.5km-long sea wall or breakwater facility to create a harbour like structure cordoning off 11.5km2 of sea area.
As the sea level outside the wall rises, the sluice gates are opened to allow the water to pass through installed bulb hydro turbines to generate electricity. Similarly when the outside sea level falls, water is released from the lagoon again driving the turbines. The six megawatt demonstration phase of the proposed 320MW Swansea Bay project is targeted for completion by 2016.
Microbial Fuel Cell (MFC) technology
Microbial Fuel Cell (MFC) technology has the potential to generate power from a range of organic waste materials including waste water and human urine. The technology uses bacteria to generate electricity from waste by converting chemical energy into electrical energy by the catalytic reaction of microorganisms. The technology also simultaneously helps sanitise the waste material used.
The MFC technology utilises naturally-abundant microbes in the anode compartment of the cell that work as a bio-catalyst. When the organic waste is fed into the cell the microbes generate electrons by consuming the waste as part of their natural metabolic process. When connected to the cathode, electricity is generated with the movement of electrodes. A group of UK scientists with backing from Bill Gates are developing a MFC device specially designed to generate electricity from human urine.
In a separate development, researchers at the Georgia Institute of Technology, in the beginning of 2014, developed a hybrid fuel cell that can directly convert a wide range of soluble biomass to electricity with the use of a catalyst that can be activated by solar or thermal energy. Biomass is ground up and mixed with a photochemical and thermochemical catalyst called polyoxometalate (POM) in solution.
The POM oxidises the biomass under photo or thermal irradiation and carries charge to the cathode. The technology combines the photochemical and solar-thermal biomass degradation in a single chemical process to generate electricity without using expensive metal catalysts. The POM catalyst can also be re-used without further treatment.