MAMMOET WORLD Issue 17 | 201748 Issue 17 | 2017 MAMMOET WORLD 49

Sun

Heater TransferFluid

HX2

HX1

Generator

Greenelectricity

Heliostats

Steamcondenser

Inside a ceramic molten salt capsule

Solar heat storage with solar ceramic capsules

Coating material

Salts with nano-scale infrared absorbers

Pellet wall

Void

SolarReceiver

Superheatedsteam

Steam Turbine

a tank. Provided enough heat is cap-tured during daytime, it can be used to power the steam turbines and generate electricity for a number of hours after darkness sets in.Dr Goswami expects he can halve the costs of generating electricity with this technology by solving a couple of issues with current molten salt technology: “First of all, the tanks and pipes of the system need to be made of high-quality materials to be able to withstand the highly corrosive effects of the salts. This effect is greater when salts are molten at

high temperatures. Second, the system is fairly expensive because it requires two storage tanks, one for cold and one for hot salts. If the two mix, the hot salts cool down before heat can be efficiently converted into electricity.”

Salt capsulesIn the concept developed by Dr Goswami and his team, the salts are enclosed in capsules, roughly the size of tennis balls. This prevents corrosive contact between salts and the system. The pipes and storage tank can then be

constructed of lower-cost materials. The capsules are suspended in a single tank with a fluid flowing around them to extract heat. Only one tank is required since fluids of different temperatures are separated by stratification, natural layer-ing of the fluid, with the warmest layers at the top and the coldest at the bottom.Salt capsules have been a focal area for researchers for a longer time, but they always ran into certain difficulties. “The main issue for encapsulation is that salt requires 25 to 40 percent room for expansion to go from a solid to a liquid

In every hour of every day, the amount of sunlight that strikes the earth is more than enough to meet the world’s yearly energy consump-

tion. But we have yet to harness the full potential of this form of clean energy. In the past decades, solar power plants have been built employing two different techniques. The first type uses photo-voltaic solar panels to directly convert sunlight into electricity. The second, Concentrated Solar Power plants, use mirrors to concentrate sunlight and cre-ate heat. This is used to generate steam that drives a turbine coupled to an elec-trical generator. Although we have the technology to turn sunlight into electric-

ity, the output drops when the sun goes down. The challenge is how to make solar power as reliable as a fossil fuel or nuclear power plant.“To generate a reliable and continuous flow of electricity we need cheap stor-age systems for large amounts of solar energy”, says Dr Yogi Goswami. “Then it can be stored during daytime and released during nighttime or bad weather when output is low. Photovol-taic solar panels have the problem that storing electricity in batteries is very expensive. But by improving thermal energy storage systems, Concentrated Solar Power plants can become the major part of our energy supply. Fuels, including fossil, will only act as a backup energy source.”

Reducing costsGoswami is seeking to improve the ther-mal energy storage system used in Concentrated Solar Power (CSP) plants. Most of the CSP plants built today use so-called molten salt technology: the concentrated sunlight heats and melts the salts into a liquid, which is stored in

Unlocking the vast potentialof

Salt capsules the size of tennis balls could spark an energy revolution. The brainchild of Dr Dharendra Yogi Goswami, this cost effective method could turn solar power into our most dominant form of energy.

solar power

MAMMOET WORLD Issue 17 | 201750 Issue 17 | 2017 MAMMOET WORLD 51

Sun

Heater TransferFluid

HX2

HX1

Generator

Greenelectricity

Heliostats

Steamcondenser

Inside a ceramic molten salt capsule

Solar heat storage with solar ceramic capsules

Coating material

Salts with nano-scale infrared absorbers

Pellet wall

Void

SolarReceiver

Superheatedsteam

Steam Turbine

Sun

Heater TransferFluid

HX2

HX1

Generator

Greenelectricity

Heliostats

Steamcondenser

Inside a ceramic molten salt capsule

Solar heat storage with solar ceramic capsules

Coating material

Salts with nano-scale infrared absorbers

Pellet wall

Void

SolarReceiver

Superheatedsteam

Steam Turbine

Sun

Heater TransferFluid

HX2

HX1

Generator

Greenelectricity

Heliostats

Steamcondenser

Inside a ceramic molten salt capsule

Solar heat storage with solar ceramic capsules

Coating material

Salts with nano-scale infrared absorbers

Pellet wall

Void

SolarReceiver

Superheatedsteam

Steam Turbine

Concentrated Solar Power plants can

become the major part

of our energy supply

state. If you don’t have this room for expansion the capsules will fail. We were able to combat this problem com-pletely by creating a void, or vacuum, in the center of the capsule, that fills as the salt expands”, says Goswami.Goswami and his team have also man-aged to overcome a second problem: transferring heat to the salts. When the salts are cold and solid, they conduct heat very slowly. Various ideas have been tried in the past to overcome this, for example, putting fins on the salt cap-sules to transfer heat or using materials with a high thermal conductivity for the capsules. “We came up with a very sim-ple solution,” says Goswami, “and here my age helps. I remembered a study by NASA from 40 years ago where they looked into the transparency of salts to infrared radiation. By adding nano-scale infrared absorbers to the salts, infrared radiation from the system can heat salts at the core almost as fast as at the walls of the capsule.”Using this salt mixture, Goswami and his team developed low-cost capsules with a non-corrosive outer shell, made of polymer or ceramics, that is transpar-ent to infrared radiation.

Broad focus“Our system is easily scalable from a few hundred kilowatt-hours to a few hundred megawatt-hours, using 2, 3 or 4 inch diameter salt capsules, and as many or few in a tank as needed. By scaling up the solar field and the storage units, a lot of additional heat can be stored on sunny days.” Goswami expects the costs of storage to become so low that the system can be scaled up to provide a reliable 24/7 power supply – even on multiple consecutive cloudy days.The benefits of Dr Goswami’s salt cap-sule storage technology are not limited to solar power plants. The technology can also be employed to increase the efficiency of other thermal power plants, including nuclear and fossil fuel. “Our

storage solution can be used to bridge the gap between peak and off-peak demand by storing large amounts of energy. Instead of running less-efficient plants at peak performance, they could have a more steady output. This is also an important issue for nuclear plants. A nuclear reactor cannot be easily switched on and off. Our storage solu-tion could bring the benefit of running the nuclear plant’s reactor at a continu-ous level and, at the same time, storing large amounts of additional heat to sup-plement output during peak demand. People from the nuclear power industry are already looking into this possibility”, says Goswami.

Supercritical CO2 turbinesIn all thermal power plants, including solar, fossil fuel and nuclear, electricity is generated by steam turbines. But

steam can only achieve a maximum temperature of around 400 degrees Celsius, while molten salts can extract much higher temperatures – whether from sunlight, burning of fossil fuels or a nuclear reactor. “Using various salts with different melting points, we can capture temperatures from around 100 to 1,000 degrees Celsius. If we can convert those higher temperatures to electricity that will increase the effi-ciency of the power generation process for any type of thermal power plant.”Getting the most out of the molten salt storage technology will require an addi-tional innovation. Dr Goswami expects that in the near future, besides steam turbines, power plants will get an addi-tional power cycle working at tempera-tures between 600 and 800 degrees Celsius or higher. This could be made possible by turbines running on super-critical carbon dioxide (CO2). These new turbines are currently in develop-ment. Supercritical CO2 is a fluid state of carbon dioxide, held above its critical pressure and temperature to maintain its fluid state. The density of carbon dioxide at that critical point is nearly twice as dense as steam, potentially providing turbines with much more power.

Licensed technologyNo matter which technology will be deployed, Dr Goswami’s salt capsules could be at the heart of a new generation of power plants. “The US Department of Energy is eager to com-mercialize and our university is eager to license our technology. The first license has already been sold to China. I very much hope it will be put to use in a Concentrated Solar Power plant. In any case, the costs of solar power will only continue to go down for a long time to come, whereas other forms of power will only become more and more expensive. This is a very good develop-ment, for the environment and for our global economies.” ■

Dr. Goswami

SMART

INNOVA

TIONS

HOUSE ON STILTSGlobal warming is bringing a higher risk of flooding, increas-ing the area of the world unsuit-able for new housing development. Responding to this, the Larkfleet Group of Companies has applied for planning permission to build an experimental ‘elevating house’ in the UK. The house has a modular steel-frame construc-tion and can be raised up to 1.5 meters above ground level by eight mechanical jacks. Once a flood warning has been issued, a central electric motor, gear-box and drive shafts can jack up the house within five min-utes, well before flood waters arrive. A roof-based solar panel array and battery system ensure that the home maintains power while in its elevated state, while the sewage and water connections would stay active thanks to flexible hoses. People in flood risk areas who are advised to pack up, lock up and take refuge elsewhere, can do so, knowing their house will not be affected by the rising flood water.

ARTIFICIAL BLOWHOLEWave Swell Energy twists the proven concept of the oscillating water column (OSW) to convert wave motion into electricity. An OSW-system con-sists of a large hollow concrete chamber, sitting on the seabed, with one opening below and one above the water line. Wave motion causes the water level inside the chamber to rise and fall, resulting in an oscillating column of air flowing in and out of the upper opening. In other systems, this airflow drives a bi-directional turbine, but this is fairly complex and inefficient. Wave Swell Energy takes a different approach. It vents the outgoing airflow, resulting from the wave crest, through a series of valves. As the water level drops again, the vents close. Air flowing into the chamber drives a turbine spinning in just one direction. This is more efficient than the bi-directional turbine design. The system also uses resonance to amplify the up-and-down motion of the waves, drawing more energy in. Wave Swell Energy aims to deploy its first full-sized unit by mid-2018, generating electricity at a price comparable to a coal-fired power plant.

OCEAN RESEARCH BEHIND THE DESKOceanic researchers are no longer constrained to spending limited research time aboard an expensive ship. Instead, using Saildrone, live data is streamed to their desk computers via satellite. Saildrone is a 6-meter-long trimaran that autonomously navi-gates the oceans, alone or in fleets, powered by a rigid carbon fiber sail. Equipped with a comprehensive package of sensors, the vessels allow for more cost-effective ocean data collecting. Researchers can customize the sensors on-board before departure. Once each Saildrone has reached its study area, they can re-task the sen-sors remotely to zoom in on interesting discoveries. The data will aid oceanographic and climate research, fish stock analysis and environmental monitoring.