The need for big Vertical Axis Wind Turbines

Global electricity demand is expected to grow from 21,400TWh in 2010 to 73,000TWh in 2050.

Moving transport away from fossil fuels towards electric power is is just one example of adding demand for electricity, which may be stored in batteries. Using the batteries of these vehicles as a buffer is currently being tested on the island of Porto Santo.

Electricity demand grew 4% in 2018 to 26,700TWh but wind accounted for only 12.8% of the change in generation by source. Generation by coal and gas power plants increased considerably driving up CO2 emissions from the sector by 2.5% and nuclear power grew by 87TWh

Comparing carbon footprint in CO2 equivalent per Kilowatt hour generated by sources:

Coal combustion . . . . . . . . . . . . . . . . . . . . . . 1000

Coal with gasification plant . . . . . . . . . . . <800

Biomass low density material . . . . . . . . . . 93

Biomass high density wood chip . . . . . . . 25

Photovoltaics (PV) in UK . . . . . . . . . . . . . . 58

(PV) in south of Europe . . . . . . . . . . . . . . . . 35

Marine (wave & tidal) . . . . . . . . . . . . . . . . . 25 to 50

Hydro (storage systems) . . . . . . . . . . . . . . 10 to 30

Hydro ( river run-off) . . . . . . . . . . . . . . . . <5

Wind Onshore . . . . . . . . . . . . . . . . . . . . . . . . 4.6

Wind Offshore . . . . . . . . . . . . . . . . . . . . . . . . 5.25

Nuclear ( with high grade ore ) . . . . . . . . . 5

Nuclear ( with lower grade ore ) . . . . . . . . 6.8

This growth in production of electricity needs to be with the lowest possible carbon footprint:

While nuclear power has a marginally lower CO2 footprint than offshore wind it is noted that as capacity is increased high grade uranium ore deposits could deplete and there are other risks attached to nuclear power. River run-off hydro schemes can have the lowest footprint but the availability of sites are limited. Onshore wind deployment is limited by competing demands for land. That leaves offshore Wind as the best area to develop backed up by hydro (storage systems).

The bigger a plant is the lower the operational running costs per unit of power generated tend to be. This has driven the manufacturers of wind turbines to develop increasingly larger units. GE Renewable Energy is developing a 12 MW 220 meter diameter turbine designed to capture more energy at low wind speeds for a higher capacity rating pro rata to its generator. Due to tip speed limitations the time gap between blades increases with size allowing more air to freely pass though the turbine. It is approaching a realm of diminishing returns. Bigger HAWTs can capture more energy but their efficiency decreases.

Sandia National Laboratories, a federally funded research and development centre, clearly show in their reports that in the offshore environment where the depths are such that floating support structures are required that VAWTs have some advantage over HAWTs. VAWTs due to their lower centre of gravity and smaller turning moments from the forces on the aerofoils are more stable and require smaller floating support structures.

Energy Research Centre of the Netherlands coordinated the S4VAWT consortium demonstrating the improvements in VAWT performance that can be achieved with active pitch control on a 6MW design combining the VAWT on a semi submersible floating support.

Unlike HAWTs the efficiency of VAWTs could be improved with scaling up particularly by increasing diameters. Unfortunately while showing some advantages none of the current VAWT designs are able to be scaled up dramatically.

No wind turbine (HAWT or VAWT) of current designs can harvest energy levels above the capacity rating of their generator. A lot of available wind energy is not harvested, because the wind would be too strong for the turbine.

To minimise carbon emissions an alternative approach is required to enable making better use of the energy that is available in the wind .

By the nature of its design the novel VAWT, which is a flywheel driven by the wind, overcomes the limitations of current wind turbine designs and can be scaled to virtually any size allowing for improved efficiency. Most significantly it has the inherent capability of kinetic energy storage and for that the bigger the better. Feathering is still a safety feature but at a level such that when the wind energy is greater than the generators capacity, the flywheel speeds up to store the excess energy. The nominal operational tip speed range does not vary greatly with size but the mass and the resulting kinetic energy storage capability can increase by the cube ratio of size. The potential for a massive increase in scale with the capability of using a buffer of kinetic energy results a massive increase in power production per generator capacity compared to any current system. It also results in a dramatic increase in the potential power that can be harvested per unit area in a wind farm. For a grid system external energy storage may still be required but the integrated flywheel buffer system reduces the capacity requirements for such systems.

The design allows the system to be installed where water depths are much greater than current designs allow for increasing its deployment potential. It also includes a combination of features which existing VAWTs do not have. It does not rely on electronic controls for pitch control allowing for maximum power harvesting capability but making it much better suited for offshore environments which can have potentially adverse conditions. The system also enables the aerofoils to be fully feathered for safety during maintenance.