Don't chase the wind - capture it

Wind power is emerging as the mainstream path to cutting carbon emissions, but as extra energy cannot be stored much green electricity goes to waste when the wind blows hardest. David Hopkins outlines a way around this problem - an energy storage solution that can turn wind farm output into a steady source and dramatically increase average output at the same time, he argues.

New energy storage that boosts wind farm efficiency

Wind energy has often been seen as an inefficient source of power due to its intermittency and lack of reliable output. Now, a commercially available technology is reversing that view and showing that power can still flow, even when the wind won't blow.

A study initiated in September this year by Sustainable Energy Ireland (SEI), the statutory body charged with promoting and assisting the development of sustainable energy, could radically alter the view of renewables in the energy landscape, and give them a far more prominent role in supplying the country's energy needs.

The study will evaluate the economic feasibility of using an innovative electricity storage system developed and marketed by Canadian Company, VRB Power Systems ("VRB Power") to guarantee an uninterrupted, reliable, supply of wind-generated electricity to the national grid.

It follows the purchase, in August this year, of a 12MWH VRB Energy Storage System ("VRB-ESS") from VRB Power, by Tapbury Management Ltd, the company overseeing the 32MW Sorne Hill Windfarm in Inishowen, County Donegal.

This VRB-ESS, will be coupled to the second phase of the Sorne project, due for completion next autumn, when an additional 6.9MW of wind power capacity will be brought on-line. The VRB system will be able to supply 12 MW hours of power, or 1.5MW over eight hours, enough to meet all the electricity requirements of up to 400 homes.

If the results of the study are successful, Tapbury has already announced that it may expand the energy storage elements of the system to cover the existing 32MWs of wind power at Sorne, which would need approximately 50MWhs of additional VRB storage. In short, the VRB-ESS is a commercial system which has the potential to ensure the uninterrupted provision of significant amounts of power to a large number of homes and businesses and, in so doing, demonstrate that renewable energy really can provide the same kind of stability as coal, oil or gas-generated power.

According to Tim Hennessey, VRB's CEO and Chairman: "This will be one of the largest flow batteries to be coupled to a wind farm and it will be the first large scale system of this type to be installed in Europe. The project will provide high-level visibility and credibility for our technology for wind applications in what is a fully commercial project."

Once expanded, Sorne, at 38MW, will become one of the largest windfarms in Ireland. With the VRB Energy Storage System (VRB-ESS"), Sorne will be uniquely able to provide steady, unbroken power whether or not the wind is blowing. Indeed, John Ward, Director and shareholder in Tapbury and Sorne Wind Energy Limited, believes that VRB's technology could revolutionise Ireland's power supply.

"This purchase is a significant milestone in the development of a real and credible alternative to fossil generation in Ireland and Europe," Ward said. "With the VRB system, we will be able to significantly expand and develop the substantial wind energy resources which the country has."

David Taylor, CEO of Sustainable Energy Ireland agrees: "Given the rapid growth and potential for wind power in Ireland and the Government's commitment to the greater use of renewable energy in our electricity mix, it is critical that we begin now to examine technologies which will help us realise our full potential."

This type of power storage could not only lead to a marked reduction in dependency on fossil fuels and help cut harmful emissions by allowing far greater amounts of wind to be used on small and large-scale power networks, it also provides grid management back-up and boosts security of supply.

Because of this range of advantages, the VRB-ESS is already storing energy from Australia and Japan to the US and, as well as Ireland, systems will shortly be installed in South Africa and Denmark.

Renewable Storage for Renewable Energy

Opponents of wind traditionally complain that such an intermittent source cannot be controlled or predicted. However, the VRB-ESS can store power when the wind is blowing and release it again when it drops, as well as being able to discharge continuous power while simultaneously charging. Crucially, time does not materially impact its performance, so power stored during a windy day can be released an hour later or three weeks later, when the blades stop turning.

Of course, VRB's technology is not the first to store power. However, the VRB-ESS's environmental credentials and its scalability make it a fully flexible carbon neutral alternative. Its long life, coupled to the fact that it is not cycle constrained are key differentiators over the competition, especially in wind applications where storage devices need to be able to cycle as much as 600 times per day.

According to Hennessy: "The VRB-ESS is the most advanced wind coupled storage system in the world The repeated deep cycling in wind applications makes it virtually impossible for conventional batteries or even advanced batteries to compete with the VRB-ESS."

Unlike lead acid batteries, which typically have a 20-25% depth of discharge, 100% of the power stored in the VRB-ESS can be used, and it recharges as quickly as it discharges.

The VRB-ESS, is effectively a larger version of a rechargeable battery. Uniquely, VRB uses a solution of vanadium - an abundant natural resource used in steel production - as its key ingredient or electrolyte. Vanadium is a transition metal and can be oxidized and reduced, charged and discharged, time and time again, enabling the storage and release of energy.

Unlike lead-acid batteries, the amount of energy that can be stored by the VRB-ESS is entirely independent of its power output rating. If you need longer hours of storage, you add more electrolyte, if you need greater output you just add more cell-stacks.

This scalability means the system could be used for a large wind farm or a single house using a small wind turbine.

Reducing Emissions

The value the VRB-ESS can bring in terms of emissions reductions is already being demonstrated in places such as King Island in the Bass Strait off Southern Australia, where a 200kW (400kW peak) VRB-ESS has been installed alongside a wind farm of 5 turbines to reduce dependence on installed diesel generation. Until the installation of wind turbines and the VRB-ESS, King Island relied solely on costly and polluting diesel. It is now benefiting from a 40% wind penetration on its grid and will see a significant reduction in diesel costs resulting in a fast payback as well as a large reduction in diesel emissions.

According to Simon Clarke, Executive Vice President Corporate Development of VRB Power: "In small islanded communities you can typically show close to a 3-year payback on the costs of integrating wind and a VRB-ESS into the generating system. The payback is based on cutting the diesel bill by about 50% and by reducing maintenance costs. You also typically cut emissions by over 50%. Depending on the exact location, it is now cheaper to generate through wind with the VRB-ESS than by adding additional diesel generation."

Ireland is a perfect example of a country which will benefit hugely from the installation of the VRB-ESS, as Ward explains. "In the case of Ireland, the windiest parts of the country are those which are least well-connected to the national grid. Wind represents a huge opportunity to provide a very cheap source of energy in these locations once the capital costs are paid off, especially if combined with storage technology. For an economy to have that certainty is very valuable indeed."

According to Clarke, Ireland's only workable wide-scale renewable resource is wind: "Even with the current levels of wind penetration in Ireland the need for storage to stabilise the wind output in certain regions is becoming necessary, and with close to 4,000MW of additional wind under contract or in the application process intermittency and curtailment issues are only going to increase."

So, too are the financial benefits of storing night-time energy for sale during the day, Clarke says. "Power pricing depends on the time of day and time of year and exactly where you are, but it is not unusual in Ireland for example, to see a spread of up to Euro 90 per MWh between peak and off-peak pricing, and in the winter it can be even higher. At this kind of spread and on this value stream alone, fast paybacks are achievable. When other benefits are factored in the business case becomes stronger still."

How it works

The VRB storage system works on the principle of a venadium rechargeable fuel cell (centre) that converts energy between electrical and chemical forms, coupled with an electrolyte contained in two tanks (left and right). Chemical energy is stored in different ionic forms of vanadium in the dilute sulphuric electrolyte liquid. A detailed explanation of how the system works is available here.


Mainland storage

Even well-connected countries, like Denmark, have recognized the potential of energy storage systems. Approximately 20% of Danish electricity consumption currently comes from wind-generated power and although this is the highest percentage of any country in the world, the government has stated that it wishes this figure to rise to 35%.

In June, VRB Power announced it had sold a 120kWh energy storage system for use on the Danish grid. The VRB-ESS has been sold to Riso National Laboratory, as part of a project supported by Energinet.dk, the Danish Transmission System Operator. The VRB-ESS will be evaluated by Riso and its partners with a view to using it in a number of wind power applications, both on and off the grid and help the government reach its ambitious targets.

Henrik Binder, Senior Scientist and project manager of Riso commented; "We see the VRB-ESS as one of the technologies with a potential of being the glue that binds together a power system with a high penetration of wind energy and distributed generation. We are looking forward to testing a unit in our SYSLAB - a distributed energy system facility - and characterizing the unit for use in a Danish context".

Attitude shift required

Given the tremendous benefits that the VRB-ESS can bring, it is perhaps puzzling why more grid operators, utilities and wind generators are not using it.

"One of the barriers we come up against is a lack of acceptance that storage is needed and a lack of knowledge as to the full benefits of storage, however, we are focusing on those countries and territories where wind penetration is highest and where issues from the intermittent nature of the resource are already being felt" Clarke says. "As we introduce more systems in the field in high profile areas, we will achieve this acceptance and prove our ability to enable firm delivery of electricity from renewable resources and to maximize the economic and other benefits of these resources."

The Tapbury windfarm and the SEI study - due to be completed by the end of 2006 - should show working proof of the benefits of energy storage, and it cannot be long before this approach becomes part of wind-farm development across Ireland and beyond.

For more information on wind power in Ireland see Sustainable Energy Ireland

For more details on the energy storage systems see VRB Power.

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| renewables | wind energy

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Energy efficiency & low-carbon
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