Wave-generated power can be more reliable and consistent than other forms of alternative energy. Here, we look at how they work.
By Josh Cosford, Contributing Editor
The need to address climate change by creating and implementing alternative energy projects remains the most critical objective of our generation. Traditional sources of energy, especially those producing electrical power, range from non-renewable coal and oil and gas to infinitely renewable nuclear and hydro sources. However, nuclear energy has experienced contentious support due to safety concerns over spent radioactive material or potential meltdowns. Hydroelectric power comes with its own restrictions, of course, since it’s limited to locations with flowing water potential.
Buoyant floaters convert incoming wave action into hydraulic cylinder motion, which produces high-pressure fluid that powers a hydraulic motor and generator. Courtesy of Eco Wave Power
Alternative energy explores renewable sources outside the venerable options we inherited from our well-intended ancestors. Although hydroelectric power is an ancient technology and still relevant today, nuclear power is beginning to make a comeback as the establishment’s initially ephemeral caution is sidelined in favor of clean energy.
The two most common alternative energy sources are wind and solar, which highlight the challenge experienced by most alternative energy machinery — intermittent operation. Wind requires moving air, which, luckily for us, stems from our incessantly rotating planet, albeit with calm days producing little or no power. There are fluid power systems used in wind turbines, although we’ve covered those systems in the past. Believe it or not, solar power arrays often use compact hydraulic systems to power guidance systems that track the sun for the highest possible exposure.
The power of water
Stepping outside the ordinary, we can find hydraulics in many new alternative energy projects. Wave power, biomass energy and geothermal projects all use fluid power systems to some degree. The most intriguing, in my opinion, are the methods collecting energy from waves, currents, and tides using powerful hydraulic systems. It’s just not possible for competing power transmission technologies to absorb and control the powerful movement of waves in such harsh conditions.
Harnessing power from water makes much sense since it covers 70% of our planet, and we have a propensity to find settlements near shorelines. In fact, only 10% of the world’s population lives more than 6 miles (10 km) from water, so it makes sense to generate power closer to where we turn on our TVs at night. And where there is water, you’ll likely find it move or wave.
Also, water packs a punch compared to air – energy density is orders of magnitude higher, and mass is hundreds of times greater per volume. If you’ve ever stuck your arm deep into water from the side of a small boat, you understand the vigor at which currents can act upon a surface area.
There are nearly as many methods to harness moving water as companies are creating them. Various turbine systems, reciprocating methods, and myriad unique methods exist that use flow, gravity or bladders, and each method has a unique and ingenious take on collecting energy.
Reciprocating cylinders at work
The point absorber buoy is a floating station converting the crests and troughs into energy via lin–ear generators. With the buoy fixed to the sea floor using a cable (or rod for shallow water), the up and down motion reciprocates either a series of hydraulic cylinders or a rack and pinion system. If you picture toy cars with the pinion zip cord you’d pull through the center to spin up the wheels before release, you’re on the right track.
During operation, buoyant “floaters” harvest energy by converting the rising and falling motion of incoming waves. Floater motion extends and retracts hydraulic cylinder pistons which, in essence, act as linear pumps. Courtesy of Eco Wave Power
The reciprocating cylinders act as hydraulic pumps and use a series of check, pressure, and flow control valves alongside accumulators to smooth out the flow rate. The output flow turns hydraulic motors, which in turn drive electric generators. In some cases, the hydraulic motor first turns a heavy flywheel to store energy as inertia, which in turn powers the generator.
Prime choice components for converting mechanical energy into hydraulic energy and back again should only apply. The decades of efficient operational potential mean a piston motor easily covers the spread against its investment cost. By most calculations, wave energy converters are not cheap, so acting penny-wise would prove to be pound-foolish in the long run.
Other point absorber buoys may use a sophisticated rack-and-pinion system to rotate a hydraulic pump instead of reciprocating cylinders. As expected, the hydraulic pump transforms the energy and sends it to the motor-driven generator. The net effect is generally the same as with cylinders, although perhaps more energy is lost through a gear-driven pump than the highly efficient cylinders.
Eco Wave Power is an onshore wave-energy technology company that has developed a cost-efficient system for turning the motion of ocean and sea waves into electricity. The company has taken the next step towards commercialization by finalizing the assembly of the hydraulic energy conversion unit for its Jaffa Port project.
The hydraulic conversion unit is an integral part of the Eco Wave Power system as it transforms pressure (created by the waves) into clean electricity. During operation, buoyant “floaters” harvest energy by converting the rising and falling motion of incoming waves. Floater motion extends and retracts hydraulic cylinder pistons which, in essence, act as linear pumps. Cylinder action transmits high-pressure biodegradable fluid to accumulators that are mounted onshore. Pressurized fluid is stored in the accumulators and subsequently routed to a hydraulic motor. The motor turns a connected electrical generator which supplies electricity into the grid via an inverter. The fluid, after decompression, flows back to the hydraulic tank where it is then reused by the pistons, thus creating a closed-circuit system.
Rugged and reliable
Using the bobbing effect of waves, other systems use a series of floating segments, looking like a gigantic toy snake. Each segment pivots relative to the next as the waves oscillate, which strokes the cylinders mounted to the opposing segment. As with the absorber buoy, the reciprocating cylinders create flow and, with the help of similar accoutrement, create the flow that powers the hydraulically driven generators.
On the topic of hydraulically driven generators, if you had asked me in the past about choosing hydraulics to transfer energy for energy production, I’d have told you not to waste your time. Even the best combination of pump and motor running at ideal pressure and flow rates is lucky to achieve 90% efficiency.
Infographic demonstrates how tidal power is converted to on-shore power generation.
However, due to the formidable conditions of oceans and seas, which exert a powerful influence on anything within their realm, all-electrical technology simply doesn’t suffice. It’s not just the corrosive effects of salt water but also the forces from pounding waves at the surface and crushing pressure below. A failure or breach to the hull or body of a hydraulically actuated wave converter won’t result in a catastrophic write-off of the entire apparatus, as could be possible with electric-only actuators.
Near-shore oscillations
Continuing with cylinder-operated wave energy generators, my favorite is the oscillating wave surge converter. These units look like giant paddles attached to the sea floor, which capture energy from the to-and-fro movement of waves around 20-30 feet below sea level. Working best near shore, wave generators use the same hydraulic components as other reciprocating systems to create flow that subsequently powers generators.
Also known as oscillating wave surge converters, these individual generators may constitute a farm many miles long, installed end-to-end. Unlike wind farms, where the net energy removed from the passing wind does little to affect generators downwind, wave converters do poorly when tiered row by row. Because of the energy density of water waves and the harvesting capacity of the wave converters, these units create a significant energy shadow shoreward of their installed location. There’s simply not enough wave energy left to power a second converter closer to land, although the principle may affect some deep-water versions less.
Easy to scale
Although it’s been shown that deep water wave energy generators benefit from more consistent average power output, the near-shore generators have some advantages. Instead of installing generators at each station, some pumps send their output flow to nearby onshore hydroelectric power plants. Imagine sending high-pressure sea water from many collectors to a single plant to power larger electric generators with the benefits of dry land maintenance, repair and distribution.
Wave power devices for alternative electricity production. Pictured are floating segments used in oscillating projects.
Although wave energy generators are enormous, I feel they offer the most potential for homemade or portable units for low capital investment. A couple of hydraulic cylinders mounted to a flap atop a heavy base could be installed on a beach, where cresting waves oscillate the converter to pump water or oil with fair energy potential. Any reciprocating cylinder can be turned into a pump with a handful of check valves, and output flow is sent to a hydraulic motor turning a heavy flywheel. The flywheel helps maintain the constant and desired speed for the generator to which it is attached.
These small generators could power communities disconnected from any power grid and offer an easily maintained power source compared to wind and solar plants, which are more specialized and complex to maintain. Wave generators of all types can be made small enough for portable operation, making them perfect for emergency response teams working with shore-side communities after a natural disaster.
That hydraulics are so prominent in the various methods of wave energy converters provides reassurance to my theory that hydraulics will never die. Fluid power is fundamentally simple, powerful and easily accessible as a technology. Rather than become obsolete, we continue to dream up creative methods to adopt technology to take advantage of the inherent strengths of hydraulics.
For extreme, demanding applications that require smooth yet powerful conversion of energy, hydraulics are hard to beat. Inherently robust and environmentally resilient, hydraulics are the power transmission method of choice for wet and watery conditions.
As a prominent and growing alternative energy source, wave energy conversion will continue to expand beyond the already dozens of technologies to provide one of the power-dense sources of renewable electricity in years to come, and expect hydraulics to be there every step of the way.
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