CSP-Beam Down Tower

The Beam Down Tower






When "beam-down" solar power the first thing that popped to mind was a Japanese plan which would involve solar panels in space which would generate power which would be transmitted to the Earth's surface via microwaves. This next post isn't about that, it is still about scientists in Japan and it is about solar, but that's pretty much where the similarities stop.

Researchers at the Tokyo Institute of Technology are reporting that they have developed a new Beam-Down solar thermal technology which they say could reduce the cost of solar thermal power. So how
 does this differ from your garden variety solar thermal power plant?




image: SENER

Sunlight Bounced Twice

This new method works somewhat like solar thermal systems which use sun-tracking mirrors (heliostats) to bounce sunlight onto a central tower to heat a liquid which is used to generate power. The difference is that instead of the light being bounced directly onto the tower, in the Beam-Down System it is first bounced on to a central reflector and then down onto a receiving unit on the ground. From there a liquid is heated, steam is generated, which drives a turbine and voila, you have electricity.

The researchers are claiming that the total cost of the Beam-Down System will be 8.37 US cents/kWh and that this system has the highest megawatt potential of any solar power generation method.


The Beam Down Tower at Masdar is a step forward in concentrated solar power (CSP). Unlike other plants, the system reflects sunlight twice, once from the heliostats to the central tower and once from the tower down to a collection platform at the system’s base. Because scientists can focus the sunlight at a very small area, they can achieve great heat. They recently concentrated solar energy to 1,100 degrees. The plant is currently only 100 kW, but designers say it could scale up easily.



Concentrate the Sun

Thirty-three heliostats—mirrors arranged in the shape of a parabola—circle the 66-foot tower in three concentric rings. Motors adjust the elevation and angle of the heliostats throughout the day to track the sun and direct the reflected light toward the underside of the tower.

Beam It down

An array of 45 mirrors made to reflect as much solar radiation as possible, also arranged in concentric circles, lines the underside of the central tower. Each ring corresponds to a specific ring of heliostats. When the reflected sun from the heliostats reaches the tower array, the mirrors redirect the light down toward the base of the tower.

Generate power

A ceramic receiver at the base of the tower absorbs the radiation. Researchers at the Masdar Institute measure only radiation at their plant, but in commercial models—like Planta Solar 10 in Spain—the radiation heats a tank filled with molten salt, air, or water. The medium then heats water to produce steam and drive a turbine.
 

Conventional large-scale desalination is cost-prohibitive and energy-intensive, and not viable for poor countries in the MENA region due to increasing costs of fossil fuels. In addition, the environmental impacts of desalination are considered critical on account of GHG emissions from energy consumption and discharge of brine into the sea. The negative effects of desalination can be minimized, to some extent, by using renewable energy to power the plants.

 

What is Concentrated Solar Power

 

The core element of Concentrated Solar Power Plant is a field of large mirrors reflecting captured rays of sun to a small receiver element, thus concentrating the solar radiation intensity by several 100 times and generating very high temperature (more than 1000 °C). This resultant heat can be either used directly in a thermal power cycle based on steam turbines, gas turbines or Stirling engines, or stored in molten salt, concrete or phase-change material to be delivered later to the power cycle for night-time operation. CSP plants also have the capability alternative hybrid operation with fossil fuels, allowing them to provide firm power capacity on demand. The capacity of CSP plants can range from 5 MW to several hundred MW.

Three types of solar collectors are utilized for large-scale CSP power generation – Parabolic Trough, Fresnel and Central Receiver Systems. Parabolic trough systems use parabolic mirrors to concentrate solar radiation on linear receivers which moves with the parabolic mirror to track the sun from east to west. In a Fresnel system, the parabolic shape of the trough is split into several smaller, relatively flat mirror segments which are connected at different angles to a rod-bar that moves them simultaneously to track the sun. Central Receiver Systems consists of two-axis tracking mirrors, or heliostats, which reflect direct solar radiation onto a receiver located at the top of a tower.

 

Schematic of a typical Parabolic Trough-based CSP Plant

Theoretically, all CSP systems can be used to generate electricity and heat.  All are suited to be combined with membrane and thermal desalination systems. However, the only commercially available CSP plants today are linear concentrating parabolic trough systems because of lower cost, simple construction, and high efficiency

 

CSP-Powered Desalination Prospects in MENA

 

 

A recent study by International Energy Agency found that the six biggest users of desalination in MENA––Algeria, Kuwait, Libya, Qatar, Saudi Arabia, and United Arab Emirates––use approximately 10 percent of the primary energy for desalination. Infact, desalination accounted for more than 4 percent of the total electricity generated in the MENA region in 2010. With growing desalination demand, the major impact will be on those countries that currently use only a small proportion of their energy for desalination, such as Jordan and Algeria.

 

The MENA region has tremendous wind and solar energy potential which can be effectively utilized in desalination processes. Concentrating solar power (CSP) offers an attractive option to power industrial-scale desalination plants that require both high temperature fluids and electricity.  CSP can provide stable energy supply for continuous operation of desalination plants based on thermal or membrane processes. Infact, several countries in the region, such as Jordan, Egypt, Tunisia and Morocco are already developing large CSP solar power projects.

 

Concentrating solar power offers an attractive option to run industrial-scale desalination plants that require both high temperature fluids and electricity.  Such plants can provide stable energy supply for continuous operation of desalination plants based on thermal or membrane processes. The MENA region has tremendous solar energy potential that can facilitate generation of energy required to offset the alarming freshwater deficit. The virtually unlimited solar irradiance in the region will ensure large-scale deployment of eco-friendly desalination systems, thereby saving energy and reducing greenhouse gas emissions.  

CSP plants can provide stable energy supply for continuous operation of desalination plants

Several countries in the MENA region – Algeria, Egypt, Jordan, Morocco and Tunisia – have joined together to expedite the deployment of concentrated solar power (CSP) and exploit the region's vast solar energy resources. One of those projects is a series of massive solar farms spanning the Middle East and North Africa. Two projects under this Desertec umbrella are Morocco’s Ouarzazate Concentrated Solar Power plant, which was approved in late 2011, and Tunisia’s TuNur Concentrated Solar Power Plant, which was approved in January 2012. The Moroccan plant will have a 500-MW capacity, while the Tunisia plant will have a 2 GW capacity. Jordan is also making rapid strides with several mega CSP projects under development in Maa’n Development Area. 

 

Seawater desalination powered by concentrated solar power offers an attractive opportunity for MENA countries to ensure affordable, sustainable and secure freshwater supply. The growing water deficit in the MENA region is fuelling regional conflicts, political instability and environmental degradation. It is expected that the energy demand for seawater desalination for urban centres and mega-cities will be met by ensuring mass deployment of CSP-powered systems across the region. Considering the severe consequence of looming water crisis in the MENA region it is responsibility of all regional governments to devise a forward-looking regional water policy to facilitate rapid deployment and expansion of CSP and other clean energy resources for seawater desalination.