Coastal protection, beach accretion, breakwaters, marinas, offshore support facilities
 
 
 
 
Ocean Energy Development
So far we do not know any successfully commercialised technology converting ocean wave energy into electricity. We can give you a long list of wave energy projects based on the different conepts. But let to cut long story short and talk only about most promising designs.

Please, note we review only ocean wave energy converters and exclude designs using tidal or any other form of energy coming from ocean.
Also we exclude from review any designs of submerged devices that suppose to convert wave energy into electricity. We do not believe that submerged ocean wave energy converter can be commercially valuable. Our concerns:

  1. The cost of any submerged devise in times dearer than cost of the device with the similar power output located above water level. Even when alternator located at shore it does not make the cost of installation less expensive.
  2. The cost of installation and maintenance is higher as well.
  3. Ability to interact with waves and absorb energy from large ocean surface is limited.
  4. Most of known submerged devices use drag force. That is very inefficient approach.

While all wave energy technologies are intended to be installed at or near the water's surface, they differ in their orientation to the waves with which they are interacting and in the manner in which they convert the energy of the waves into other energy forms, usually electricity. The following wave technologies have been the target of recent development.

Terminator devices extend perpendicular to the direction of wave travel and capture or reflect the power of the wave. These devices are typically onshore or nearshore; however, floating versions have been designed for offshore applications. The oscillating water column (OWC) is a form of terminator in which water enters through a subsurface opening into a chamber with air trapped above it. The wave action causes the captured water column to move up and down like a piston to force the air though an opening connected to a turbine.

A point absorber is a floating structure with components that move relative to each other due to wave action (e.g., a floating buoy inside a fixed cylinder). The relative motion is used to drive electromechanical or hydraulic energy converters.

All designs above have common disadvantage. They interact with wave crest and idle with wave trough. Theoretical limit of wave stability approximated by a wave height to wavelength ratio of 1/7 [1]

If wave period is 7 seconds ideal device will work only 1 second and will idle rest of the time. Real device will provide useful work only 0.5 – 0.7 sec. As you can see – low efficiency is perfectly embedded into all these designs. We are talking about single OWC, floating buoy etc.

We believe that the lack of ability to produce useful work constantly during the all wave period is one of the major reasons that make all previous wave energy projects unsuccessful.

There is only one solution to make wave farm generate electricity constantly – array of devices deployed along the wave length. But is it a good idea – to build array of generators where each of them works only 1 second and idles another 6 seconds? Obviously, it will increase capital and operational expenditures in arithmetical progression and make the cost of power completely uncompetitive on electricity market. And we are not sure that even magical carbon credits can save that sort of projects from failure.

We consider oscillating water column (OWC) as most promising concept for ocean wave energy conversion. OWC does not need any mechanical parts and it can be inexpensive in mass production.

What is main advantage of OWC against the other concepts, such as a float or buoy? OWC pumps air out and sucks it back. That means OWC converts wave motion into the high velocity stream of working fluid (air in our case). Basically OWC is a regular air pump where water inside of OWC plays role of the piston in the cylinder of regular reciprocating pump or engine. To be able to maintain energy conversion during the all wave period we have to deploy line of OWC’s along the all wave length.

But as we detailed above – we cannot install generator inside each OWC – because it will make device very expensive. But what is the solution?

As soon as we realised that air stream from OWC has a similar cycle as a gas exchange in the reciprocating pump/engine we found the solution how to make large array of OWC inexpensive for mass production. We apply concept of reciprocating pump/engine to our design. We just put inlet and outlet flaps inside each OWC and connect all OWC’s to each other within inlet and outlet ducts. Please, welcome the Wave Mill!

Heat Engines
The efficiency of various heat engines proposed or used today ranges from 3 percent (97 percent waste heat) for the OTEC ocean power proposal through 25 percent for most automotive engines, to 45 percent for a supercritical coal plant, to about 60 percent for a steam-cooled combined cycle gas turbine.
All of these processes gain their efficiency (or lack thereof) due to the temperature drop across them.

Examples of heat engines It is important to note that although some cycles have a typical combustion location (internal or external), they often can be implemented as the other combustion cycle. In addition, the externally heated engines can often be implemented in open or closed cycles. What this boils down to is there are thermodynamic cycles and a large number of ways of implementing them with mechanical devices called engines.

Phase change cycles In these cycles and engines, the working fluids are gases and liquids. The engine converts the working fluid from a gas to a liquid, from liquid to gas, or both, generating work from the fluid expansion or compression.

Engine Type Efficiency
Automobiles: Otto cycle 15-20%
Trucks: Diesel cycle 20% - 35%
Power plants: Rankine cycle 40-50%
Gas turbines: Brayton cycle 50-60%

Most of the heat engines can maintain pick of efficiency only within certain conditions, such as RPM, load etc.
Real engines have many departures from ideal behavior that waste energy, reducing actual efficiencies far below the theoretical values given above. Examples are:

  • friction of moving parts
  • inefficient combustion
  • heat loss from the combustion chamber
  • departure of the working fluid from the thermodynamic properties of an ideal gas
  • aerodynamic drag of air moving through the engine
  • energy used by auxiliary equipment like oil and water pumps
  • inefficient compressors and turbines
  • imperfect valve timing

Another source of inefficiency is that engines must be optimized for other goals besides efficiency, such as low pollution. The requirements for vehicle engines are particularly stringent: they must be designed for low emissions, adequate acceleration, fast starting, light weight, low noise, etc. These require compromises in design (such as altered valve timing) that reduce efficiency. The average automobile engine is only about 35% efficient, and must also be kept idling at stoplights, wasting an additional 17% of the energy, resulting in an overall efficiency of 18%. Large stationary electric generating plants have fewer of these competing requirements as well as more efficient Rankine cycles, so they are significantly more efficient than vehicle engines, around 50% Therefore, replacing internal combustion vehicles with electric vehicles, which run on a battery that is charged with electricity generated by burning fuel in a power plant, has the theoretical potential to increase the thermal efficiency of energy use in transportation, thus decreasing the demand for fossil fuels, although practical problems of energy losses from long transmission lines and the additional multiple energy conversions required between the power plant and the vehicle driving wheels will reduce any potential fuel saving and may even require increased fuel consumption compared to local use of fuel in the more directly coupled power trains of traditionally engined vehicles.

Therefore we have to find efficient and compact engine - generator that can be used as a power supply for vehicles, thus decreasing the demand for large and heavy battery on board. Assume its efficiency is 50%, the same as a large stationary power plant can have. Average electric motor efficiency is 50%. In this case our vehicle will have stable and continuous 25% from heat to wheels.

Energy Efficiency of heat exchangers
A counter flow heat exchanger is generally, effectively 100% efficient in transferring heat energy from one circuit to the other, albeit at a slight loss in temperature.

Ideal Heat Engine
Ideal heat engine must to convert all heat into useful work.
The conceptual design of internal combustion engine has embedded limitations that will not let to improve its thermal efficiency. Basically design is based on “Heat Out” concept. When we burn something – we have to be quick enough to catch the portion of heat and convert it into useful work.
Why we cannot use “Heat In” concept? Why we cannot concentrate heat in some perfectly insulated space and convert it portion by portion as much as we need it and add more heat into our heat container when we want to?
A heat pipe is a heat transfer mechanism that combines the principles of both thermal conductivity and phase transition to efficiently manage the transfer of heat between two solid interfaces.

Assume that hot solid interface is the wall inside the cylinder (see image below). We can perfectly perform phase transition inside pre-heated cylinder. During the phase change the working fluid turns itself into gas that occupies significantly more of its original volume. The pressure inside our cylinder jumps up. The motion of piston transfers some portion of heat into useful work.
Assume we pre-heat our cylinder up to 400˚C and injected small portion of water inside cylinder. When liquid water changes state from a liquid to a gas it occupies ~1600 times its original volume at atmospheric pressure. The portion of injected water immediately absorbs portion of heat from the cylinder walls by changing its phase from liquid to gas (vapour). The pressure inside cylinder pushes piston up.

Injection of a small portion of water Exhaust

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