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UK University models pairing wave with wind, direct to grid

A UK, Birmingham University professor of energy and his team have come up with a shortcut to getting dispatchable energy out of a combination of wind farms and wave power. Professor Xiao-Ping Zhang, Director of Smart Grid, Birmingham Energy Institute at the University of Birmingham explained his new system in detail in a paper delivered to the IEEE which can be read here.

He revealed the research to the world when he gave a speech last week at the 2019 UNESCO International Water Conference, in Paris.

The whole idea is to use wind and wave turbines in sync with one another so that the wind turbine smooths the highly intermittent energy produced by waves, which fluctuate wildly every 5 to 12 seconds. Zhang outlines a method for compensating by smoothing the energy output of a wave turbine using the momentum of a nearby wind turbine, effectively harvesting some of its inertia, almost as if it was a battery.

Most wind farms and solar installations have to be paired with batteries before they can be used at scale with an electrical grid. If more than 30% of the energy on that grid is from intermittent sources, there is not enough energy to stabilize the frequency of the Alternating Current if it varies, which risks brownouts and inertia on the grid. Typically a generating turbine can sense this by the way the frequency varies and respond to it by upping the energy it loads into a grid. Intermittent sources of energy cannot do this, since you have wind when it is blowing, sun when it is shining and wave power only when the water moves strongly in one direction.

This has been used as an argument by fossil fuel suppliers to limit the amount of renewable energy on a grid, and has led to increased investment in fossil fuels and also is the basis of a lot of research into intelligent grids which do not need stabilizing. Batteries are now used routinely in front of renewable resources to enable them to behave more like a gas turbine, which can offer frequency stabilization. But this adds cost to renewable energy turbines which have just broken through the subsidy barriers on price, and should be standing on their own two feet for the first time ever.

Add the cost of a battery to that and you have taken renewable energy out of the reach of parity pricing alongside say gas.

Which is why this paper is so important. What Zhang seems to be claiming is that intelligent control of the wind cycle, can entirely eliminate the fluctuating nature of wave power.

So far he has done the math and then modelled 5 configurations of either a single wind turbine with wave power, or multiple turbines with wave turbines, and used something called Integral Compensation Control to show what outcomes would likely be.

The graphs below shows the electrical energy produced in three instances, 1) using the classical MPPT control, 2) using direct compensation control and 3) Using Integral Compensation Control (ICC).

A key challenge is varying the kinetic energy stored in the rotor leads to a bias of the rotor speed and reduces the wind power capture efficiency. Integral Compensation Control, smooths the total power output of the combined farm with only a marginal loss of the wind efficiency.

Zhang calculates that this type of partnership using ICC, would only lose about 1% of the energy produced on the wind farm, and none of that produced on the wave turbines.

Obviously there is a long way to go here, and the next step would likely be a real world experiment with real turbines, which should work, given that the modelling was carried out with real world data. From there we have to see how it might fail over a long period trial and finally such a set up could be directly connected to a grid and then long term trialed at scale.

But even so this still has the potential to bring the cost of including wave turbines in the energy mix low enough that it may bring the time when wave power can be harnessed efficiently forward by as much as a decade. From there its increased use would accelerate investment in cheaper wave devices.

Professor Zhang said, “There is great potential to integrate wind and wave energy Generation. With one million GW of wind energy available from total land coverage of the earth, just one per cent of this would meet global electricity demand – not forgetting that global wave power potential alone could be up to 10,000 GW.

Professor Zhang then went on to suggest that the Birmingham effort might be harnessed by the China led Global Energy Interconnection Development and Cooperation Organization’s (GEIDCO) and its initiative develop a Global Energy Interconnection (GEI) system – something being pushed as a template to build a new energy template, for Africa in particular.

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