Tag Archives: clean energy

Salinity gradient power rising as a realistic renewable energy source

Estuaries are the locations where river water mixes with seawater. They are found along coastlines throughout the world, but what most people don’t realize is the significant potential to produce clean energy from these mixing water streams. The salinity gradient between the two streams of water contains a large amount of osmotic power, which can be thought of as the available energy (or chemical potential) from the differences in salt concentration between the fresh water and seawater. The enormous amounts of energy released where freshwater and seawater meet “can be utilized for the generation of power through osmosis”, which is “defined as the transport of water through a semi-permeable membrane.” [1]

The idea of obtaining energy from osmosis, or salinity gradient power, has been studied for decades, but in early 2009 two teams were racing to be the first to build a working prototype power plant making salinity gradient power a feasible method for renewable energy generation. Both teams have been working on the development and implementation of a membrane based osmotic process, but their approaches for generating the electricity are very different [2]. Westus (The Centre for Sustainable Water Technology), located in the Netherlands, is focusing on the Reverse Electrodialysis (RED) method to produce electricity. They claim that they will utilize fresh water from the Rhine river and saltwater from the North Sea to construct a type of battery by employing two membranes permeable to ions, but not to water. Utilizing the saltwater, one membrane will allow the passage of positively charged sodium ions into a stream of fresh water and the other membrane will allow the passage of negatively charged chloride ions into another channel of freshwater. The separated charged particles with electrodes placed in both streams makes up the chemical battery, which directly produces electricity. [2] Statkraft, a leading renewable energy group located in Norway, is focusing on Pressure Retarded Osmosis (PRO) as their method to extract electricity from salinity gradients. This method utilizes a membrane, permeable to water, to draw fresh water into the concentrated salt water, thus increasing the pressure in the salt water chamber. The resulting pressure can then be used to drive a turbine to produce electricity. In November of 2009, Statkraft opened the world’s first prototype osmotic power plant in Tofte Norway. [3] This facility had a limited production capacity (of around 4 kW) and is mainly used for testing and validation of data, hopefully leading to the construction of a large commercial power plant by 2015.

While the idea of harvesting free energy from estuaries and salinity gradients may seem like a flawless idea, it comes with both pros and cons. On one side, the technology is considered “as green as it gets”, with the only waste product being brackish water, which flows into the sea mixing with the sea water [2].  It is a constantly flowing source of renewable energy, unlike the intermittent energy provided by sources such as solar or wind power. It can also easily be combined with existing power plants and industries and can be built underground, thus reducing costs and visual pollution [2]. On the other side, the membrane technology still has a long way to go. The membranes are prone to bio-fouling from algae and silt, which reduce the membrane’s lifetime and efficiency. Salinity gradient power is mainly suitable only for places where there is an abundant supply of freshwater meeting saltwater, which clearly favors countries with a large coastline [2]. Also, the environmental impact and environmental policy should be considered for future plants of this type. First off, there are many species of aquatic life that are adapted to survive in waters with a specific range of salinity concentrations, and these power plants could affect the salinity of an area of water. It has been found that large salinity changes in aquatic environments can result in low densities of plants and animals [4]. Then one must consider the environmental policy and impact of structures that intake such large volumes of river water and sea water. These power plants must conform to strict construction permits and environmental regulations.

While many issues dealing with the viability of salinity gradient power as a renewable energy source are still being addressed, advancements in the technology are constantly being made. In June of 2012, Statkraft’s head of osmotic power said “We see that the development of technology is accelerating and that an industry is emerging. The membranes we are testing at Tofte this summer are ten times more efficient than the ones we installed during the opening of the prototype in the autumn of 2009” [5]. Earlier this year, researchers discovered a new more efficient way to harness osmotic power utilizing Boron nitride nano tubes [6]. They claim that a 1 meter-squared membrane using this technology could have the same 4 kW capacity as the whole Statkraft prototype power plant. This experimental device, which is three orders of magnitude more efficient than the current system, could significantly enhance the commercial viability of salinity gradient power as a realistic source of energy [6]. While the ultimate future of salinity gradient power is unknown, it has the potential to be one of the prominent renewable energy sources on the planet.

[1] http://www.statkraft.com/energy-sources/osmotic-power/

[2] http://www.gizmag.com/salinity-power-renewable-energy-osmosis/11206/

[3] http://www.gizmag.com/statkraft-osmotic-power/13451/

[4] Montague, C., Ley, J. A Possible Effect of Salinity Fluctuation on Abundance of Benthic Vegetation and Associated Fauna in Northeastern Florida Bay. Estuaries and Coasts. 1993. Springer New York. Vol. 15 No. 4. Pg. 703-717

[5] http://www.statkraft.com/presscentre/news/statkraft-considering-osmotic-power-pilot-facility-at%20sunndalsora.aspx

[6] http://www.gizmag.com/osmotic-salinity-gradient-power-nanotubes/26623/

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Bloom Energy and the Energy Server

This morning, the new company Bloom Energy, headed by founder and CEO KR Sridhar, Ph.D, launched their new business based on their new patented energy generation technology with hopes of revolutionizing the energy market.  Dubbed the “bloom box”, the bloom box is composed of a patented solid oxide fuel cell technology developed by Dr. Sridhar and Bloom Energy. To gain a better understanding of this technology, let’s first discuss solid oxide fuel cells (source).

Solid Oxide Fuel Cells

Fuel cells have been around for the last century. Early forms of fuel cells including proton exchange membranes, phosphoric acid fuel cells, and molten carbonate fuel cells have all been too inefficient to consider as all require expensive precious metals, corrosive acids or hard to contain molten materials. These materials are all expensive and with the amount of gain compared to the other options on the market, they have never been economically viable. Fuel cells also produce a large amount of heat energy as a byproduct. Researchers started to try to harness this wasted heat energy by developing combined heat and power (CHP) schemes however these to seemed to prove economically inefficient in the majority of cases.

Solid Oxide fuel cells, however, use low-cost ceramics and highly efficient electrical material to increase their economic efficiency. Because they operate at such high temperatures (800 deg C), this allows for the solid oxide fuel cell to no longer need the precious metals required by other forms of fuel cells. The fuel cell is composed of three layers; an anode, electrolyte, and a cathode. A fuel source is then pumped into the anode layer and air into the cathode layer. In the electrolyte, a chemical reaction takes place and electrons are moved, generating an electric current. Byproducts are also expelled from the other two layers. These fuel cells have estimated efficiencies of 50-60% and when the waste heat is reused, the efficiency reaches ranges of 80-85% (source)

Diagram: How a Solid Oxide Fuel Cell (SOFC) works. An AFC consists of a non-porous metal oxide electrolyte (typically zirconium oxide) sandwiched between an anode (negatively charged electrode) and a cathode (positively charged electrode). The processes that take place in the fuel cell are as follows: 1. Hydrogen fuel is channeled through field flow plates to the anode on one side of the fuel cell, while oxygen from the air is channeled to the cathode on the other side of the cell.  2. At the cathode, a catalyst causes electrons from the electrical circuit to combine with oxygen to create negatively charged oxygen ions. 3. The negatively charged oxygen ions flow through the electrolyte to the anode. 4. At the anode, the catalyst causes the hydrogen to react with the oxygen ions forming water and free electrons. 5. The negatively charged electrons cannot flow through the electrolyte to reach the positively charged cathode, so they must flow through an external circuit, forming an electrical current. 6. At the cathode, the electrons combine with oxygen to create negatively charged oxygen ions, and the process repeats.


Bloom Energy’s Design

Bloom Energy, through research in materials sciences and engineering, has developed a patented new solid oxide fuel cell. The anode and cathode layers are comprised of specially formulated inks where as the electrolyte is a thin sheet of ceramic created from beach sand. Fuel enters on the anode side and then combines with steam to form the another type of fuel that is then applied to the anode. On the other side, heated air, more importantly, heated oxygen is placed on the cathode side. When the heated oxygen and fuel meet at the electrolyte, a chemical reaction takes place. In Bloom Energy’s case, the reaction is stated to be:

CH4 + 2O2 —› CO2 + 2H2O + e- + heat

The electrons then flow from the oxygen molecules through the electrolyte and generate electricity. The CO2 is released on the anode side and the water is then reused to form the steam required to mix with the fuel. The heat generated from the reaction is also reused to heat the incoming oxygen for the process to take place. As long as there is fuel, air, and heat, the process will continuously take place. To see an animated version of the process along with an explanation please click here.


Bloom Energy has created fuel cells that are small in size, yet are capable of producing around 25 watts of power, which is enough to power a light bulb. When these fuel cells are combined into stacks with metal layers, they form what is called a “bloom box”. A bloom box is capable of producing one kilowatt of power. It is enough to where two bloom boxes alone could be enough to power an average American home at its base load. Groups of these bloom boxes are then combined into a large unit called and energy server. These energy servers are capable of producing 100 kW of power. Bloom Energy posted a spec sheet for one of their patented energy servers and it is given below.

Technical Highlights
Fuels Natural Gas, Directed Biogas
Input fuel pressure 15 psig
Fuel required @ rated power 0.661 MMBtu/hr of natural gas
Water required (for startup only) 120 gallons municipal water
Rated power output (AC) 100 kW
Electrical efficiency (LHV net AC) > 50%
Electrical connection 480V @ 60 Hz, 4-wire 3 phase
Weight 10 tons
Size 224″ x 84″ x 81″
NOx < 0.07 lbs/MW-hr
SOx negligible
CO < 0.10 lbs/MW-hr
VOCs < 0.02 lbs/MW-hr
CO2 @ specified efficiency 773 lbs/MW-hr on natural gas,
carbon neutral on Directed Biogas
Standard temperature range 0° to 40° C (extreme weather kit available)
Max altitude at rated power 6,000 ft. MSL
Humidity 20% – 95%
Seismic Vibration IBC 2003: Site Class D
Location Outdoor
Noise @ rated power < 70 DB @ 6 feet
Codes and Standards
Complies with Rule 21 interconnection standards
Exempt from CA Air District permitting; meets stringent CARB 2007 emissions standards
Product Listed by Underwriters Laboratories (UL) to the FC-1 standard
Additional Notes
Operates in a grid parallel configuration
Includes a secure website for you to showcase performance & environmental benefits
Remotely managed and monitored by Bloom Energy
Capable of emergency stop based on input from your facility


Layout of the ES-5000


These energy servers as can be seen above are very large yet have the capability of producing large amounts of power. They are capable of running on either natural gas or bio gas as can be read from the spec sheet.  These are ideal for large corporations who have many large buildings to power. In fact, Bloom Energy has already deployed test units to customers who have been secretly trying the systems. Some of these big name companies include Google, Staples, Wal-Mart and eBay. In an interview with an eBay official done by CBS’ 60 Minutes, he claimed that int he past nine months, a handful of these energy servers saved a campus of eBay buildings in California over $100,000 alone. Similar results have been found by the other major companies. (To view the CBS interview video, please click here)

Perhaps the greatest aspect of these revolutionary energy servers is that they produce little to no pollution or green house gases. When used with natural gas, a slight amount of carbon is emitted. However, when used with bio gases, the carbon is simply recycled and therefor no carbon emissions occur or it is carbon neutral. Also, Bloom Energy is attacking the transmission sector. A large amount of energy is lost in the transmission from the power plant to the home and business sectors. With the energy server, electricity is generated on sight and therefore the transmission of the electricity is completely eliminated along with the inefficiencies that it brings with it. Bloom Energy hopes to one day replace the entire energy grid with on site electricity generation. As also can be seen from the 60 Minutes stories, many big names have stated their support in Bloom Energy’s energy severs. Colin Powell stated his views in the story as saying that though it may not be an absolute answer to our energy needs, it is defiantly a viable solution to aid in the change over to clean energy technologies (source).

Bloom Energy’s energy server is a brand new technology and like all new technologies, it  shows promise. However, I am still personally skeptical at this new innovation.  Only time will tell if this new revolutionary technology is efficient enough to be a leading aid in our transition to cleaner energy.


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