The ability to mechanically liquify, store, and transport air on a global scale provides baseload from wind for the first time. Solar and wind energy are making considerable inroads to help correct this situation. Unfortunately, they are both intermittent and cannot supply firm capacity (baseload) electricity. There is a need to develop sources of renewable energy that can be stored in large quantities and for extended periods of time. We believe this can only be done using the tremendous energy of far offshore wind and ocean transport.
Keuka Energy has chosen liquid air as a stored energy option
Keuka Energy proposes to use liquid air produced by floating offshore wind farms as a large-scale energy solution to wind and solar intermittency while increasing mass flow to the utilities gas turbines. The challenge faced by all gas turbines is that as ambient temperature or elevation rises, the density of the air naturally decreases, reducing the mass flow into the gas turbine. This reduced mass flow results in reducing the fuel flow proportionately to hold turbine inlet temperatures constant, resulting in lower output.
Liquid air restores the mass flow that is naturally missing by injecting cold air into the compressor intake and adding heat to the liquid air re-gas system to warm the incoming air, producing more energy for the generator section. The gas turbine control system reacts naturally and adds a proportionate amount of fuel to account for the increase air mass flow, resulting in constant combustion and turbine inlet temperatures. The increased mass flow through the turbine section increases the mechanical torque to the compressor and generator producing electricity.
Mature cryogenics
To produce liquid air, Keuka Energy is employing its novel wind machine using both the patented RimDrive™ turbine and floating “V” platform. The liquid air system is based on the science that air can be turned into a liquid by cooling it to around -196° C using standard industrial equipment. Around 700 m3 of ambient air becomes 1 m3 of liquid air, which can be stored in an insulated vessel. When heat (including ambient or low-grade waste heat) is reintroduced to liquid air it boils and re-gasifies, expanding 700 times in volume and under high pressures. This expansion and pressure drive a turbine/generator to produce electricity, thereby making it a viable large-scale energy storage solution.
Fortunately, cryogenic liquid production, its distribution infrastructure and equipment supply chain are already mature. LNG (liquid natural gas) is the largest user of cryogenic systems and the only “end to end” system proven on a large scale. There are over 300 LNG tankers, most with a storage capacity exceeding 125,000 m3 plying the world’s oceans at any given hour. In addition, liquid air having no fuel combustion, or high-pressure risks would make shipping and handling cost 5 to 15% less than that of shipping and handling LNG. Since a typical LNG tanker holds about 125,000 cubic metres of liquid and 10 cubic metres of liquid air produces about 1 MWh of electricity, imagine the comfort level a utility would have if they had 12,500 MWh of renewable stored energy at their beck and call. That would be 17.3 MW’s every hour for one month (732 hours) that they could use as needed. All renewable and all wind. Each 35,000 hp wind farm should produce about 46,120 m3/month of liquid air.
RimDrive turbine
The single largest cost of producing liquid air is the electricity used to power the electric motors doing the work. When wind machines mechanically drive the liquefaction equipment, most of the costs of producing liquid air are eliminated. The RimDrive™ wind machines take power from the outer rim and not the central shaft, thus requiring no gearbox. The US DOE (U.S. Department of Energy) finds that the gearbox is 25% of the 30-year cost of conventional wind machines.
Taking energy from the rim’s lowest point also keeps a considerable amount of the weight down low. This lends to less stress being placed on the tower and a much lower operation and maintenance (O&M) costs. Additional cost is avoided by not needing large cranes to install or service the machines since the blades of the rim driven machines lower on their own power when needed. Much higher speeds are achieved at the outer rim and the machines have eight shafts being driven simultaneously so that a combination of work can be achieved at the same time, (Ex: compressors, turboexpanders, etc.).
The blades are made of marine grade aluminium, are totally recyclable, have over 100-year service life expectancy, and cost less than 10% of composite blades. NREL (National Renewable Energy Lab) tests show the RimDrive™ to be more powerful per square metre of blade swept area than existing three bladed machines. The outer rim gives a flywheel effect that eliminates most wind gusting and turbulence problems and improves their scalability to multimegawatt size. The semi-open centre produces less downstream turbulence and lends to placing more units per given area.
Minimised cost
Production costs are minimised with numerous turbines stationed on each of Keuka Energy’s “V” platforms. Offshore floating wind farms using one support platform that doubles as cryogenic storage cost less than USD 1 m/MW. Keuka’s “V” platform has no need for costly yaw mechanisms since the entire support structure weathervanes into the wind as it is anchored to the sea floor using a single anchor line. It is dry-docked at sea eliminating the need to be brought back to land for maintenance and the support structure will stock all parts needed to maintain the wind machines. The V shape of the flotation platform produces a calm water environment within the structure needed for berthing LNG class tankers to load the liquid air.
A floating offshore rim driven wind farm mechanically producing liquid air without the need for electricity has an LCoE (Levelized Cost of Energy) of USD 0.04/KWh. The LCoE of natural gas is around USD 0.048/KWh.
For more information about the mission and vision of Keuka Energy, visit www.keukaenergy.com.