Energy storage systems can be highly beneficial – particularly in stabilizing the output of wind turbines – but the utility industry seems slow on the uptake. Are we ready to embrace this technology?

Candida Jones, Carbon International, UK

A new type of energy storage technology could allow far greater amounts of wind to be used on small and large-scale power networks. As well as providing grid management back-up and boosting security of supply, the new technology is able to transform the intermittent output of wind power into one of firm, reliable supply. Indeed, according to John Ward, an independent wind developer and consultant, the technology could enable “100 per cent of power to come from wind in many areas of the world”.

The technology – the VRB Energy Storage System (VRB-ESS) – developed by Vancouver-based VRB Power Systems Inc., is already storing energy in Australia, Japan and the USA, and systems will shortly be installed in Germany and Denmark. Since it is able to increase wind penetration on any energy grid, it could lead to a marked reduction in dependency on fossil fuels and help cut harmful emissions.

Firm, reliable output

Opponents of wind traditionally complain that wind energy cannot be controlled or predicted. Indeed, without power storage, Ward describes wind farms as “power stations out of control”. 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 impact its performance, so power stored during a windy day can be released an hour later, a day later or three weeks later, bringing the ‘power station’ back under control.

The value the VRB-ESS can bring to large-scale wind farms has already been demonstrated, most notably at the 32 MW Tomamae wind farm on Hokkaido, northern Japan. Here, a 6 MWh VRB-ESS, installed by power company Sumitomo has been successfully smoothing wind output for over 12 months, enabling the supply of firm power to the grid.

Of course VRB’s technology is not the first to store power, lead-acid batteries are able to do this, as are fuel cells and a range of other relatively new technologies, however the VRB-ESS’s environmental credentials and its scalability mean it is a fully flexible carbon neutral alternative.

Renewable storage

The VRB-ESS is effectively a large, environmentally-benign version of a rechargeable battery. Uniquely, VRB uses a solution of vanadium – an abundant natural resource used in steel production – as its key ingredient and storage medium, or electrolyte. Vanadium is a transition metal so can be oxidized and reduced, charged and discharged, time and time again. This gives the electrolyte, and therefore the storage capacity of the battery, an almost indefinite life-span.

Unlike lead-acid batteries, the amount of energy that can be stored by the VRB-ESS is entirely independent of its power output rating. In other words this technology is uniquely scalable and could be used for a large wind farm with a capacity of 100 MW, or a single house using a small wind turbine.

Figure 1. Countries such as Denmark have recognised the benefits of using energy storage systems alongside wind energy
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The VRB-ESS can be sized for any amount of power in 5 kW or 50 kW increments, and can store any number of determined hours of energy by simply adding additional litres of electrolyte. If you need longer hours of storage, you add more electrolyte, if you need greater output you just add more cell-stacks. It also has far greater efficiency than other storage solutions – in the region of 75 per cent depending on its application and use. Unlike lead acid batteries, which typically have a 20-25 per cent depth of discharge, 100 per cent of the power stored in the ESS can be used, and it recharges as quickly as it discharges.

Reducing emissions

The impact that the VRB-ESS can have on emissions is already being demonstrated in places such as King Island in the Bass Strait off southern Australia, where a 200 kW (400 kW peak) system has been installed alongside a wind farm of five turbines to reduce dependence on diesel generation. Until the installation of wind turbines and the VRB-ESS, King Island relied solely on diesel but now it benefits from a 40 per cent wind penetration on its grid and will see a reduction in diesel costs and an estimated payback of less than four years. It is also estimated that there will be a 46 per cent reduction in emissions.

According to Simon Clarke, executive vice president, corporate development of VRB Power: “In small islanded communities you can typically show close to a three-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 per cent and by reducing maintenance costs. You also typically cut emissions by over 50 per cent. Depending on the exact location, it is now cheaper to generate through wind with the VRB-ESS than by adding additional diesel generation or by adding a gas fired power station, and even adding coal generation in certain areas is now more expensive than wind and a VRB-ESS.”

A 40 per cent wind penetration is certainly not the maximum achievable with the VRB-ESS, as Clarke explains: “We are involved in projects which, if implemented, would result in wind penetration of over 60 per cent, and if the wind regime and economics makes sense you could go higher still”.

Ireland is a perfect example of a country that could benefit hugely from energy storage. According to Ward, “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 and especially if combined with storage technology. For an economy to have that certainty is very valuable indeed.”

Figure 2. The VRB-ESS uses vanadium as an electrolyte and is both highly scalable and efficient
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According to Clarke, Ireland’s only workable wide-scale renewable resource is wind: “Even with the current levels of approximately five per cent of Ireland’s electricity generation coming from wind the need for storage to stablilize the wind output is being recognised”.

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 €90 ($115) 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, paybacks in five years are achievable. When other benefits are factored in the business case becomes stronger still.”

Bringing stability to the grid also enables wind power to be maximized. Clarke stresses that the VRB-ESS actually helps the connection to the grid, “especially where this is weak or the renewable resource is constrained by the connection. The VRB-ESS regulates the release of electricity such that the amount of electricity never goes over the size of the connection and will enable the wind operator to maximize their connection.”

Mainland storage

Even well-connected countries, like Denmark, have recognized the potential of energy storage systems. Approximately 20 per cent of Danish electricity consumption comes from wind-generated power, the highest percentage of any country in the world. Denmark is also a highly interconnected country.

In June, VRB Power announced it had sold a 120 kWh 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, 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.

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.”

Figure 3. VRB-ESS systems have been installed in Australia, Japan and the USA, and will shortly be installed in Germany and Denmark
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Tim Hennessy, CEO of VRB Power believes that the “successful demonstration of the VRB-ESS will help show how storage will alleviate issues of intermittency and curtailment which arise when there is a high penetration of wind generation”.

Indeed, Clarke believes that with the VRB-ESS, a significant portion of the power on Europe’s large grids could come from renewable sources. “Storage would certainly make this viable in certain areas,” says Clarke. “It depends on the country and the renewable resources. Most countries are initially talking about a 20 per cent penetration rate by 2020 with others such as Denmark and Sweden aiming higher still”.

Attitude shift

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. Ward believes he has the answer. “We’re talking about a paradigm shift. Until now the networks have believed that energy couldn’t be stored, but they’re wrong”. Clarke agrees. “One of the barriers we come up against is a lack of understanding that full acceptance of storage is needed. In Europe this is becoming accepted in certain territories but we have yet to find full technical acceptance of the VRB-ESS.

“As we introduce more systems in the field in high profile areas, we will achieve this acceptance and hope that, as we deliver on sales, we will be able to demonstrate that a small company in Vancouver really can execute and deliver these large systems.”

Hugh Sharman, director of Incoteco, an international consultancy and energy broker, echoes these sentiments: “The VRB-ESS is a relatively new development working in an industry that is fanatically conservative. A reluctance to embrace new solutions, on behalf of electricity system operators, means that change is happening at a slow rate,” Sharman believes.

Given the Kyoto targets we must meet, the need for improved security of energy supply and the finite nature of fossil-based alternatives, change will, however, have to come.