LightSail’s Mission to Cut Costs of Compressed Air Energy Storage

by Katy Schaefer

LightSail, an energy storage company based out of Berkeley California, is attempting to change the way we approach energy conservation. Not only is the method dramatically more efficient, but the costs that have the potential to be cut is game changing. Lightsail’s aim is to create a more economical storage system through compressing air to create heat energy, which before was just wasted energy. It seems that there is something to their system, as some of the country’s most prominent tech billionaires have backed the plan. Unfortunately LightSail and its leader, Danielle Fong, the 27 year old co-founder and chief scientist, are not releasing the details of the plan just yet. However, here’s what we do know. Continue reading

Is Diesel Made from Air and Water be a Green?

by Jesse Crabtree

Audi is teaming up with German energy company Sunfire to make fuel for internal-combustion engines and it is literally pulling the fuel out of thin air. This diesel-like substance, called “Blue Crude,” is a string of hydrocarbons formed by combining atmospheric CO2 with hydrogen atoms obtained by water electrolysis. According to Audi, the process produces fuel at an overall efficiency of 70% and is meant to be powered by renewable energy. Furthermore, one of its main draws is that, with the exception of the electrolysis, all of the infrastructure for production and consumption of this product has already been tried and tested. Although it only releases the CO2 initially reclaimed from the atmosphere, the fact that Blue Crude does not totally sequester any emissions gives it a shaky hold on the term ‘green.’ Thus, Blue Crude’s ‘green’ status depends on renewable energies being used to power its electrolysis step. Either way, Blue Crude relies on several important factors—namely low energy prices and new legislation—in order to even be feasible.

Continue reading

A Tesla Battery for Your Home?

by Nour Bundogji

With the emerging energy storage market, Tesla Motors Inc., best known for their Model S all-electric sedan, announces plans to release a lithium-ion battery to power your home. Elon Musk, Chief Executive Officer of Tesla Motors, stated in an earnings conference call, “We are going to unveil the Tesla home battery, a consumer battery that would be for use in people’s houses or businesses fairly soon.”

What is this battery?

Well, Musk said that it “will be like the Model S pack: something flat, 5 inches off the all wall, mounted, with a beautiful cover, an integrated bi-directional inverter, and plug and play.” Continue reading

Of the many Energy Storage Systems, Integrated Hydrogen-Oxygen Storage Stands Out

by Tim Storer

Wind power comes with the disadvantage of intermittent gaps in energy production and instances of excess supply. This variability puts strain on the electric grid and is the primary barrier to large-scale wind power integration. In order to combat this issue, various forms of energy storage have been considered to bridge the gap between supply and demand of wind power. Gao et al. 2014 conduct a brief literature review on all existing energy storage systems (ESS) for wind power. Each method comes with drawbacks associated with scale, cost, or safety, but hydrogen-oxygen storage was seen here as the best future option. By improving storage technologies, wind energy will become more viable in the market and help to reduce the share of energy coming from fossil fuels that contribute to climate change. In addition to the literature review, this study examined a possible hydrogen-oxygen ESS in Jiangsu Province, China and saw that such an operation could be profitable in the current market.

While there are some operational forms of ESS, there is a variety of issues preventing ESS –and subsequently, wind power– from becoming widespread energy sources. For example, battery power is too costly and difficult to build at a large scale, systems that involve pumping water upward for energy storage have geographical limitations, and magnetic energy storage has low storage time. In the case of hydrogen generation from electrolysis, the costs are simply too high to be competitive in the energy market with capital costs of 1000-2500$/kW (when they need to be near 400 $/kW).

Hydrogen-oxygen combined storage consists of electrolyzers that break water down into hydrogen and oxygen. The hydrogen and oxygen are combusted to form super-heated steam that powers turbines. The system is closed, and uses water as a recycled fuel. Gao and colleagues examined three variants of hydrogen-oxygen ESS: simple integrated ESS, integrated ESS with a feed water heater, and an integrated ESS with both a feed water heater and a steam reheater. In simple terms, these systems each contain an additional measure to capture heat from the steam turbines and use that heat elsewhere in the process, thus improving efficiency. All of these integrated systems contain a complex web of mechanisms that can be adjusted alongside price fluctuations in the power market to minimize costs. The former two had roughly equivalent efficiencies of 49%, but the latter system had efficiency of up to 54.6%, thus demonstrating the benefits of feed water heaters and steam reheaters.

While the 54.6% efficiency of the fully integrated system is marginally below that of some other ESS technologies, hydrogen-oxygen systems come with certain advantages. They can be implemented on a large scale, are fully eco-friendly, not limited by geographical and material restraints, and can be adjusted rapidly based on demand changes. The system was analyzed under two extreme scenarios: an “intermittent operation mode” simulating an extremely variable wind supply, and “continuous operation mode” simulating a perfectly steady supply. Because of how effectively the system dealt with times of low wind, it was actually more profitable under the intermittent scenario with annual income of $13 million per year. Real wind conditions lie somewhere between these extremes, and efficiencies of approximately 50% and prices of 0.03–0.05$/kWh were estimated.

Dan Gao, Dongfang Jiang, Pei Liu, Zheng Li, Sangao Hu, Hong Xu, 2014. An integrated energy storage system based on hydrogen storage: Process configuration and case studies with wind power. Energy, Vol. 66: 332–341.



An Upcoming Method of Energy Storage

by Alex Elder

California is currently in the forefront of clean energy production, not only in the United States, but in the world. Although their rising production of wind and solar energy yields many benefits for the state and its residents, it also produces some unprecedented problems. Specifically, the increase in energy generation results in complications for managing the electric grid which has to maintain the balance of energy supply and demand. The strain on the grid has resulted in a technological movement to improve energy storage systems which would help relieve some of the issues associated with increased energy production. Because energy storage systems are designed to store and then quickly release energy onto the grid, they are able to prevent a potential supply imbalance which can sometimes be caused by the sporadic influx of solar and wind energy. Battery-based storage systems in particular can store energy from the grid when electric rates are low and discharge it for use during the day. This kind of system is especially useful for banking solar energy, which can then be used at night or when power from the grid is more expensive at certain times of the day. Continue reading

Undersea Ocean Renewable Energy Storage

Ocean Energy Storage

by Allison Kerley

Slocum et al. (2013) propose a new design for an energy storage and generation unit composed of underwater concrete spheres and offshore wind turbines. The proposed design utilizes pumped storage hydraulics (PSH). During times of low energy demand from the grid, the cylinder would contain water at equal pressure with the surrounding ocean. In the proposed design, the floating wind turbines generate energy and the excess energy is used to pump water out of the storage sphere, creating a vacuum. When energy is needed from the sphere, the turbine would open, allowing water to pass through into the sphere. The proposed sphere design would have an inside diameter of 25 m, and would retain a 1/20th-atm environment when fully discharged. The proposed design could be used without alteration in depths between 200 and 700 m, and would continue to be economically feasible to a depth of approximately 1500 m. The authors tested a small-scale dry version of the proposed design, with the test sphere having an inner chamber diameter of 75 cm, with a ten meter height difference from the top of the pump and wind turbine to the top of the sphere. The test unit was found to have a low round-trip efficiency of 11%, which the authors attribute to their inability to use the most efficient pump and turbine technology due to the small size of their test model. They calculated that in a full scale model, the lowest round-trip efficiency would be 70%. Continue reading

Wearable Supercapacitors: Making Devices More Flexible

Flexible supercapacitor


by Emil Morhardt

Maybe someday you will be able to recharge your gadgets by plugging them into your jacket, which you charged up in a few seconds from a convenient wall plug. I wrote earlier about storing energy in wires that were configured to be capacitors. Now Yu et al. (2014), at the School of Chemistry and Chemical Engineering, Nanjing University, in China, have fabricated experimental sheets of flexible layered conductive and non-conductive materials (diagram above is from their paper) that they envision as eventually wearable. We all get tired of waiting around for batteries to charge, but supercapacitors charge almost instantly. They don’t usually have much energy storage capacity though—you don’t get as much energy storage per unit weight or volume as you presently can from batteries—but if they are built into something that you need to carry around with you anyway, that might not be so important. A good example is the plug-in electric boat I wrote about on October 11. Boats don’t care much about how large or heavy something is, but they need to be fueled rapidly. So if you could store all the energy you need quickly in your jacket, your battery-powered devices could recharge in your pocket, wherever you are. Continue reading

Flywheel Versus Supercapacitor for Running a Small Electric Ferry

by Emil Morhardt

When we think of all-electric cars, we think lithium-ion batteries because they are lightweight and have a high power density. For ships, light-weight doesn’t matter so much, and it turns out there are types of shipping routes that don’t need very much energy storage: think ferries, specifically the plug-in ferry Ar Vag Tredan (the “electric boat” in Breton), a zero-emission passenger ferry crossing the Lorient roadstead 56 times a day. When parked between trips it can recharge its supercapacitor more-or-less instantly (that’s a main feature of supercapacitors—that and their ability to discharge their power equally quickly to meet any need for power the ship may have.) How would a flywheel energy storage system work compared to the existing supercapacitor? That’s the question asked in a new paper by Olivier et al. (2014). Continue reading

Membrane-Free Lithium/Polysulfide Semi-Liquid Battery for Large-Scale Energy Storage

by Allison Kerley

Yang et al. (2013) discussed their new proof-of-concept lithium/polysulfide semi-liquid battery as a potential solution to large-scale energy storage. The lithium/polysulfide (Li/PS) battery uses a simplified version flow battery system, with one pump system instead of the traditional two. The Li/PS battery was found to have a higher energy density than traditional redox flow batteries, with the 5 M polysulfide solution catholyte cell reaching an energy density of 149 W h L–1 (133 W h kg –1), about five times that of traditional vanadium redox battery. The Li/PS battery cells were also found to have a high coulomb efficiency peak around 99% before stabilizing at around 95%, even after 500 cycles. The authors conclude that the Li/PS cells maintain a steady rate of performance after 2000 cycles, and Continue reading

How to Maximize Renewable Energy in California

by Emil Morhardt

The looming problem with renewable energy—especially in California where there is potential for a great deal of solar energy—is finding the right balance between attractive new, but intermittent, solar and wind power plants, and some other source of generation large enough that dispatching it will meet any energy demand, even if the wind isn’t blowing and the sun isn’t shining. A new paper by Abebe Solomon, Dan Kammen, and Duncan Callaway, researchers in the Energy & Resources Group at the University of California Berkeley, calculates that if energy dumping doesn’t occur, the best we can hope for in California without energy storage, is meeting 29% of our energy needs with solar and Continue reading