Solar and wind energy farms are becoming common, but current energy systems by themselves will not be able to meet entire requirements of the world, considering the limitations of these sources as also those of energy storage systems. These may not be sufficient to reach goal of pollution free energy, and there is scope for some new additional technologies, if the goal to make fossil fuels extinct has to be achieved in good time. There have been efforts by a number of researchers and organisations to develop newer sources and methods of energy generation and storage.
New technologies are being used in heat pumps, electronic equipment as also in solar and wind systems to improve their efficiencies and output. Following technologies are being added to the cart in energy development systems:
Tidal energy
Tidal energy is one of the major renewable sources in the world, but as yet in infant stages. Motion of natural water currents and rivers can be used to run mechanical devices to produce power. This can be done in number of ways.
- Tidal stream generators use kinetic energy of running water to power tidal turbines, similar to wind turbines. This method is preferred due to its lower cost and least ecological impact. Dynamic tidal power uses both the kinetic and potential energy of moving water. This is done by creating very long dams across coasts right into the sea, without specifically enclosing an area. This method has a downside in that it can have adverse effects on natural habitat and ecology.
- Tidal barrages are built across full width at mouth of an estuary. Water is stored in barrages on high tide. Difference in levels during low tides is used for generating electricity similar to hydropower plants. This method has limitations due to lack of enough available sites worldwide, and may also affect the ecology of river system.
iii. Oscillating water column uses waves to compress air in a closed chamber to generate wind and run turbine. Wind is created when water enters and recedes from chamber. Turbine is designed so that its direction does not depend on wind direction. One such plant of 500 KW capacity is in operation since 2000 in Scotland at Islay island.
- Tapered channel (TAPCHAN) devices use waves to pump seawater to an elevated reservoir. By energy conservation principle, as the wave width decreases, the amplitude increases, enabling the wave travel up a ramp and pour into the reservoir. Trapped water is then released back to run a turbine for generating electricity.
Benefits of tidal energy
- Tidal power is not much vulnerable to weather and season, and power is uniform all the year (since tides are predictable), with only minor variations.
- No fuel needed to operate, and no waste products.
iii. Long term and operating costs are low compared with conventional energy sources.
Gestation periods for these plants are quite long, and no power can be generated till they are complete. Payback periods are therefore longer. Batteries cannot be placed near them in sea. Though a new technology, it has high potential. UK is looking forward to 200-300 MW tidal wave generation capacity by 2020, and see a potential of up to 27 GW by 2050. This will be enough to meet 12% of current UK demand.
Blue Shark Power System, France has signed an MoU with the Republic of Djibouti for supply of 495 of River Tidal Turbines, with a capacity of 240 kW each, making a total capacity of 120 MW. They have planned to test one turbine in the first half of 2019. First 80 machines are scheduled for the first half of 2020. The country will become energy independent once the project is completed.
Credit for the largest tidal project in the world goes to South Korea at the Sihwa Lake Tidal Power Station, with an installed capacity of 254MW. Built in 2011, this also used a 12.5 km long seawall built in 1994 to protect the coast against flooding and to support agricultural irrigation.
Orbital Marine Power, UK, is developing a tidal turbine system, which is claimed to be the most powerful tidal generating platform in the world. They plan to deploy their 2MW Orbital O2 turbine at the European Marine Energy Centre, in Orkney, in 2020. This will be 73 m long floating structure having two turbines of 1 MW each, with 20 m rotor diameter. The capacity is rated for wave speed of 2.5 m per second, and adds up to generation of 48,000 KWH per day at full load.
Geothermal Energy
Geothermal energy from hot springs and geysers has been historically used for cooking, bathing and heat. Civilizations have used it throughout past 10,000 years, as is known from history. Number of places on earth use it today, mainly for heating and cooking purpose. At many places, hot water comes naturally to surface, and its use is easy. Sources for geothermal energy can be from shallow hot water springs and rocks, to few kilometers down the earth surface as extremely hot molten rock.
Efforts are on to pump water deep into rocks in dry land areas, and circulate the water to get heat to surface. Direct use of geothermal energy applications give heat at 50 -150°C, and can be used for room or space heating, and some low temperature applications. In Iceland and New Zealand, among others, buildings are heated by this hot water, and about 50 per cent energy approximately gets trapped this way. This system has problems of salts and impurities, which need to be returned to earth.
Geothermal heat pumps at shallow depths can be used to heat buildings or houses. At these depths of under 6 meters, temperatures are more or less stable all the time, and direct heat exchangers can be used to cool or warm the rooms depending upon season and location, and also by circulating air from house through underground pipe system. This takes all the load of air conditioning.
Another method collects rising steam from depths by pumping water in, and use it to run turbines in power generation plant. Pressurized high temperature water is drawn from deep under the earth, and subject it to sudden decrease in pressure to vaporise it. Steam is then used for power plant. It is also possible to circulate heat exchanger fluids to these depths to heat water into high pressure steam for use in power plants.
Geothermal power plants have been in operation in New Zealand, California since 1960s, and today over 80 countries are using geothermal energy. Leaders in the field are China, Turkey. Hungary, U.S.A. and Iceland. Worldwide installed geothermal electrical power plant capacity in 2017 was about 14,000 MW, producing about 84.8 TWh. Waste heat from these plants can be used for low temperature applications before recirculating the heat exchanger fluids through earth. Largest power plant complex is operating at Geysers, USA, consisting of 22 plants, with 1.5 GW capacity.
Geothermal plants can be normally used for 20-30 years, and energy output may decrease with time. Environmental effect of geothermal heat extraction is minimum.
Artificial Photosynthesis
Artificial photosynthesis is a chemical process mimicking natural photosynthesis process to use CO2, water and sunlight to generate carbohydrates and oxygen. Plants use sunlight and perform huge conversion of over 1000 billion tons of CO2 into organic matter and oxygen every year. They do this using only 3 per cent of sunlight reaching the earth. Artificial photosynthesis system or photo-electrochemical cells mimicking the plants can create endless source of inexpensive never-ending source of gas and electricity, that too, in storable form.
Joint Center for Artificial Photosynthesis, US, came up with an artificial leaf, which uses sunlight to convert energy from sunlight to isolate hydrogen from water. They made prototypes with 3D printers, and in 2015 created system to separate CO2 before it is released into atmosphere, and convert to fuels and other products. Efficiency is claimed at 3 per cent, and they feel it will be viable when the efficiency goes up to 10 per cent.
Most water-splitting devices are made of a stack of light-absorbing materials. Each layer absorbs different wavelengths of full solar spectrum from infrared light to visible or ultraviolet light and generates voltage. These individual voltages together give enough one voltage to split water into oxygen and hydrogen fuel. The problem with this is performance potential of silicon cells that is compromised in this system.
Converting seawater into jet fuel
US is the largest consumer of fuel in the world, with jet fuel accounting for over 70 per cent of petroleum products. Though submarines can run on nuclear power, jet fuel for aircraft is still needed in large quantities. They were looking for development a process for synthesizing fuel on board, so that dependence on oil tankers to fuel jets could be eliminated. Material science and technology division of Naval Research Laboratory, US has reported developing a way to separate CO2 and hydrogen from seawater and convert these into liquid fuel.
NRL has filed a patent for a process to produce fuel from sea water. They claimed success with 92 per cent efficiency in CO2 removal, and used the fuel to power a remote-controlled sustained flight. The process involves conversion of carbonates and bicarbonates to CO2, with simultaneous production of hydrogen using metal catalyst in reactor and convert the gases into liquid hydrocarbons. Sea contains over 140 times the concentration of CO2 compared to air.
Sea water is first acidified through ion exchange reaction to pH of 6.5 or lower by exchanging H+ ions for Na+ ions. It is then degassed to obtain CO2, and fed to a reactor to produce jet hydrocarbons. The carbon dioxide obtained by degassing is fed to a reactor with hydrogen to produce hydrocarbons, such as jet fuels. Hydrogen for reactor is also produced from sea water. Cost of jet fuel with this process is claimed to be $3-6 per gallon.
Flying wind farms
A large number of entrepreneurs are targeting the sky to harvest high amounts of energy in winds there. High up in the sky, ground resistance decreases, and winds blow at very high speeds, exceeding 150 Kmph. NASA is reserving funds of USD 100,000 for research for exploring high altitude wind farms. Idea is to have air borne turbines at 30,000 ft above ground level. At these heights, wind has more power and velocity, can be predictable, and power generated can be 8 to 27 times that produced at ground level. Researchers estimate potential of such high-altitude wind turbines to be over 100 times that needed for the entire planet.
One benefit naturally is it will not take any ground space. Turbines may be housed using kites, or can be kept floating using helium filled balloons. NASA is trying with kite designs. The M.A.R.S. (Magenn Power Air Rotor System, in picture) is a helium filled device capable of harnessing wind energy and transporting it down via 330-meter rope. This 4 KW unit is likely to start production soon, and they expect to have 7 more models in coming years.
One major limitation is airspace restrictions in place so that they do not obstruct or interfere with air traffic. Currently, these limit the heights of turbines to 2000 ft and below. Winds at 2000 feet are 20 times stronger than for land-based turbines at 350 feet high. Theoretically, wind energy grows exponentially with speed.
Sky Windpower, a San Diego is developing a Flying Electric Generator (FEG), a kite-like 1,100-pound air-borne wind turbine expecting to build stable flying wind farms in future. This technology will act like vehicles in air space conforming to strict air traffic monitoring so that it does not become hazardous to other flying objects. There is also a challenge in transporting energy harnessed in skies above the oceans towards land-based power plants.
Solid-Oxide fuel cells (SOFC)
According to developers, solid oxide fuel cell technology would be among the most in demand. Researchers at Harvard School of Engineering and Applied Sciences, headed by Sriram Ramanathan are working on solid oxide fuel cells to replace fossil fuels with pollution-free fuel cells. They use abundant natural resources at low cost to create small devices working at lower temperatures. One major hurdle in current all-ceramic thin-film SOFC fuel cell technology has been in use of very expensive platinum electrodes. Harvard team developed platinum-free low cost and more reliable SOFC. Conventional technology needed very high temperatures between 800-1000°C. New technology SOFC works at 500 °C and efforts are on to reduce the temperature near 300 °C.
These fuel cells will run on methane, abundantly available at low cost, and useable at low temperatures. Hydrogen was found to be costlier than methane for fuel cells. These SOFC may be usable both for stationary as well as transport applications if temperatures are on lower side, and present target of 300 °C may make it possible.
Downside of SOFC is their water emission as waste, which may not be good in a number of applications. Since low temperature operation is a long way, there is no immediate possibility of their use in computers and mobile phones. The drawbacks are expected to be overcome and SOFC technology is likely to be in extensive use in near future.
Portable fusion reactors
Lockheed Martin has been trying to create portable compact fusion reactor (CFR) since past five years. They aim to create a reactor to power a small city. Researchers created a small cylindrical reactor in a space of 1m × 2m and created a confined plasma, heating Deuterium gas with RF energy (a form of non- ionizing electromagnetic radiation). Plasma is kept stable using magnetic field. In May 2016, there were good number of investment proposals, and they expect projects as large as 100 MW in ten years.
Other developments
Recently China has reported creating artificial sun, using fusion reaction and reaching temperatures six time that at the core of the sun. When fully developed, they expect to get energy and light from this high temperature plasma source in earth orbit on continuous basis to cover huge requirements for the country.
Algae is looked upon as a viable perennial source of fuel. Algae are mega oil producers, capable of producing 1000-5000 gallons oil per acre, not possible by any crop. Oil from algae is similar to vegetable oil and can be converted to oil using existing technology. Algae do not compete with food sources for land, can be grown even in salty conditions and they also treat polluted waters. There is still some way to go, but researchers feel this can be promising fuel source of future. If and when the systems are in place, there will be good energy available from algae, which at the same time, helps remover water pollution as well. A German firm Rawlemom has created a spherical sun power prototype, called Beta.ray. The yield is expected twice that of solar panel in a much smaller surface area. Design is fully rotational, and is suitable for inclined surface, walls of buildings, or anywhere where it is open to sky. This can also be used for car charging stations.
There are other developments also going on, and we can expect new exciting technologies in near future forming a part of renewable energies.
