Wind power is one of the most tangible displays of new investment in renewables, low-carbon, or “green”, energy technologies with lines of tall towers in prime locations and, possibly far from the eye, many offshore developments are proposed.

What is generally less apparent to the public, although increasingly recognised in national and international power sectors, and by governments and investors, however, is the hidden challenge that intermittent generation from such highly visible, wind assets brings to electricity transmission networks. Variable output from solar power adds to the challenges.

To meet the calls for fast-response inputs, and so help bridge the gaps in available supplies to meet the dynamic demands of a grid, both large-scale generation capacity and capability of rapid reaction are needed. The hydropower sector has advantage in both counts and is increasingly being called upon, not least its pumped storage facilities which can, in effect, reuse the same water. The latter is also a way to effectively “charge” an electrical system with additional potential energy, like a battery, when wind and solar are producing more than is needed by the grid.

Hydro, then, has significant potential to benefit from under- and over-production by the two types of renewables undergoing major expansion – wind and solar photovoltaics (PV). But sufficient hydro storage is not always nearby, or even naturally available in sufficient quantity, to serve those needs and take advantage of the opportunities. A key factor in this aspect of the current boom in hydro and pumped storage, therefore, is construction of more transmission links – cables – between regional and national grids.

Studies have been underway to examine the benefits that the massive presence of Norwegian hydro at the edge of Continental Europe could afford the region’s proposed shift to significant renewables generation, especially in Germany. Investigators from Germany and Norway have been probing a host of scenarios that assess the possibilities, benefits and needs to deliver such expanded systems, especially construction of new interconnections between their grids; the studies also go much wider, to assess how extra grid links at strategic points across Europe could help achieve balanced grid performance for even more countries.

The challenges brought by rapid wind power expansion has also been a subject of study, and some argument, in the west coast of the US, especially the Pacific Northwest. Earlier this year, a confluence of high winds and rain brought a dilemma that had not been addressed before: which to pick over the other? The system hadn’t been running to strategically anticipate possible overproduction by wind and employ pumped storage to take-up the energy; instead there were already high storage volumes and discharge needed, also to help manage water quality for fisheries in the Columbia River basin, and so hydro production was picked over wind.

In recent months, however, the construction of new interconnections with California has widened the possibilities for take-up of production when the wind blows well. This also brings into play greater possibilities for support that hydropower can offer a wider region, though the question of prioritising local wind and hydro generation in the Northwest will be important to have been sorted to prevent future disputes.

The Pacific Northwest experience can offer lessons to other regions, including Europe, where, although the strategic perspective is that Norwegian hydro is geographically distinct from wind and solar in the likes of Germany, like many places there is a local co-existence of hydro resources. If, and until, greater and wider interconnections are weaved to bind together region grids, for all local hydro and wind assets there will remain the questions of planning to avoid generation clashes and claims of losses.

Europe: Linking Germany and Norway

The ability to call upon ensured power, or demand, within seconds is of major importance for the local and wider balance of transmission networks.

Beyond its core strength of generating electricity from the basic flow of water, the hydropower sector has long been at the forefront of providing fast power to the grid in many regions, although competing often with gas-fired generation despite being a non-carbon option. And, though pumped storage, the sector has assets to create sudden demand to soak up some of the overproduction on networks at short notice, to classically “time-shift” by taking advantage of cheap prices at forecast quiet periods in the market, and provide ancillary services (frequency regulation, black starts, etc) to further support grid stabilisation.

Possibilities for hydro and pumped storage schemes are investigated on case-by-case basis but their cost-benefit scenarios look to be increasing set in wider market environments, and there may also be examination of neighbouring schemes – existing and planned – in hydro-rich regions.

One such hydro-rich region, which also has abundant long-term storage in lakes, is Norway and it has been involved in a variety of studies to investigate how this concentration of resource might help meet large peak power needs far from its borders, in Continental Europe, but also offer balancing support to the introduction of wind and solar power schemes.

Norwegian perspective

In October, a workshop on the potential for Norway’s hydro storage to be a, if not “the”, renewable energy battery of Europe, many of the potential benefits to help Continental Europe’s pursuit of increased renewable generation capacity, and the challenges, were discussed. The workshop was held in Trondheim and co-hosted by Technoport, a science-business forum, and the country’s Centre for Environmental Design of Renewable Energy (Cedren), which involves research body Sintef, the Norwegian Institute for Nature Research (Nina) and the Norwegian University of Science and Technology (NTNU).

Atle Harby, director of Cedren, told delegates that a preliminary study by the organisation has looked at the technical potential of building more hydropower infrastructure in southern Norway to develop an extra 20GW – but without construction of new reservoirs or dramatic changes in lake levels, limiting the rate of rise or fall to 100mm/hour to minimise drawing attention to the movement. Cedren concluded this could be achieved by 2030-35, and would also lead to much construction and equipment procurement activity.

Other aspects of its studies on the expansion of the hydropower system in Norway, though, has considered potential barriers or resistance, such as: impacts on the environment and wildlife from more access road and transmission line construction; the variation in lake levels on shorelines and fisheries; and, safety matters where water level lowers below ice-covered reservoirs. There is also the question of possible risk to biodiversity from water carrying foreign species into neighbouring, or higher, catchments.

Harby noted there is also debate over the proposals for increased power line construction – important to wind power as well as hydro, and the potential benefits to be secured from expanded and inter-linked transmission networks.

Separately, Sintef itself has been looking into cross-border “balance management” in a study since 2007 and due to complete soon. It has noted that a system-wide approach would be preferred over a control area approach to help reduce the total cost of having reserve capacity available for transmission networks.

Harby added that ‘if we want to do a massive investment to develop Norwegian hydropower for balancing power for Europe we need a lot more connection lines, a lot more cables, to the Continent and UK’.

Eivind Heloe, a senior vice president with energy company Statkraft, told delegates: ‘We are now in the early stages of formidable growth in renewable energy in Europe,’ adding that there is ‘still has a long way to go’ to hit the target of 20% renewable energy by 2020.

To meet the goal, he said that approximately 600TWh/year of new renewable energy needs to be brought onto the market within nine years – ‘that is around five times the current production of Norway’. Heloe added: ‘And, even then, they have barely started on the journey towards the 80% renewable energy society they are aiming for in 2050.’

The bulk of the new renewable capacity, he notes, will come from wind and solar power: his data show Europe with 79GW of wind power capacity and 16GW in 2009, and projected to increase to 180GW-230GW and 150GW, respectively, by 2020. In Germany the capacities of wind and solar power are to rise from 26GW to 46GW and 10GW to 52GW, respectively.

The rise in renewables will ‘need huge amounts of balancing power,’ Heloe said, to meet daily, weekly and annual cyclic, fluctuating and peak demands. Coincidentally, the Nordic area is expected to have significant power surplus in the next 10-15 years, partly contributed by the rise in renewables as well as new capacity, refurbishment and upgrades, improved efficiency, and introduction next year of the electricity certificate market between Norway and Sweden which itself would introduce more than 26TWh/year across the two countries, it is expected.

‘So, it is imperative that we get a meaningful use of this power surplus in a way that does not include deflated prices, over-consumption and waste,’ he added.

Building interconnections between grids to mop up and balance out extra production over short and longer periods is vital to improving security, stability, regional and wider uses of energy resources, and helping to mitigate climate issues.

Interconnectors help preserve water in dry years by enabling energy imports, and provides for exports in wet years – ‘we have just experienced the wettest August in recorded history’ – to avoid flooding. Despite the wet August, Norway’s last two winters were very cold and dry, and interconnectors ‘saved the day,’ Heloe added. ‘Without the interconnectors we would have to develop many more hydro reservoirs to have enough power reservoirs, entailing unacceptable environmental impacts.’

Yet, Norway’s existing reservoirs and hydro network hold the key to the extra storage that Germany needs.

German perspective

Studies undertaken by the German Advisory Council on the Environment (SRU) conclude that periods of overproduction by the ambitious investment in wind and solar capacity in the country would, in linked grids, enable Norwegian reservoirs to be filled higher and, eventually, wholesale electricity prices to be lower for their Nordic neighbours. Future prices under the suggested linked grids have been a concern for energy-intensive industries, such as aluminium production.

With such hydropower and pumped storage storage available – Germany has ‘little puddles’ to Norway’s ‘big lakes’, says Prof Olav Hohmeyer, of the University of Flensburg, and who has been leading SRU’s studies – it would be possible for 100% renewable electricity supply in the country and Europe to be achieved by 2050. It could be done by 2030, he adds, ‘if in a hurry.’

In October, a major summary report of its studies was published, marking the substantive end to examining the merits and challenges of a stronger German-Norwegian grid axis. It was concluded that pumped storage and transmission links ‘will be absolutely crucial’, and any other storage solution would be less efficient and more expensive.

The key strength Norway has is that it is, literally, mountainous hydro country with large systems and operating, in effect, cascades through catchment-based approaches. One catchment alone was put under the spotlight – Sira-Kvina, which has 5.6 TWh pf storage capacity and could be expanded without much difficulty or construction of new dams or lakes.

In terms of building transmission links, though, he says the studies suggest that a 100% renewables scenario would require 42GW capacity of cables from Germany to Denmark as part of the inter-connection to Norway by 2050. A phased programme of construction would enable step changes is benefits for reservoir operations and gradual lowering of prices in Norway, he notes. Most cables would be about 1.4GW capacity and some are in planning, although there are some political and social challenges to such major infrastructure projects.

Cedren’s Harby commented, separately that ‘we would also need to develop the market because today’s trading system is not sufficient.’ He does not think that the current market system will allow the large investment needed to be paid back.

‘But there is a large potential,’ he adds. ‘This has to come through intergovernmental agreements. I think politicians have to decide if this is something we want to do or not.’

To further inform the available data, additional work by SRU is examining scenarios where its self-imposed restriction – 100% renewables (85% supplied domestically, 15% export) – is being removed to see what effects there might be on infrastructure decisions on location and timing. The analysis has just started, Hohmeyer says, and is expected to take between six months and year to report.

Separately, Hohmeyer’s team in the energy and natural resource science department at Flensburg is working with Statkraft to modell in detail the entire Norwegian hydro system. More data are needed to help any planning for infrastructure and market operations. The studies are expected to take another couple of years.

Western US: Links and spats

On the other wise of the word, in the western US, recent months have seen more strategic movement on the interplay of wind, hydro and other generation sources and energy storage capabilities.

‘While wind energy makes our grid cleaner,’ said Brad Roberts, director of the Electricity Storage Association (ESA), ‘energy storage makes our grid more flexible and reliable.’

Denise Bode, chief executive of the American Wind Energy Association (AWEA), said: ‘Energy storage can be a valuable resource for the power system in maximising the efficient use’ of wind energy.

They were commenting upon their release, in June, of a statement of joint principles on clean energy, which was welcomed by the national-hydropower-association (nha). It supports regulatory frameworks and operating regimes that, ‘given the growth of variable energy resources’, that value grid services, especially ancillary services.

In mid-November, NHA then welcomed the introduction of a proposed energy storage bill into the legislative process. In a statement, NHA’s director Linda Church Ciocci, said: The expansion of the investment tax credit to incentivise the construction of energy storage technologies, including pumpd storage hydropower, is vital as additional variable energy resources are brought online.’

NHA commented that a study, by Navigant and completed in 2010, concluded that 24GW of pumped storage capacity could be brought online by 2025.

Also in November, Bonneville Power Authority (BPA) announced that arrangement had been made allowing wind generation facilities more frequent opportunities – half hourly rather than hourly – to market output into California. The pilot scheme is to help reduce operational issues and increase market opportunities.

BPA had previously announced, in August, that investment advances were being made on grid connections of its own as well as the California-Oregon Intertie which is jointly owned with Portland General Electric and PacifiCorp. The utility has had increased pressure from the wind sector following the decision, in the second quarter, to briefly pick hydro over wind for operational and environmental reasons during periods of both high wind and high flows at a time of reduced power demand.

As in Europe, the progressive development of inter-connections between grids would create more opportunity, it is recognised, to absorb over-production in the system.

Bigger goal

The heightened pursuit of building renewable power projects, and the challenges and opportunities for grids, connections and hydro, comes in no small measure from concerns over man-made global warming. This is the backdrop against which strategic, regional choices and developments will be undertaken, or not.

As Cedren’s Harby says: ‘Keep in mind, this is not only about markets and benefits, it’s also about mitigating climate change. But I don’t think we can do that, and several studies have shown this as well, if there are no economic incentives either. So this has to go in parallel.’

The key driver, he says, is replacing carbon energy production with more renewables. He says hydro will be in competition with coal-fired generation (‘a little faster these days’ being turned on) and gas-fired (‘Norway is the main source of delivering gas to Europe’).

‘So, ask,’ he continues, ‘is this what we want to do in Norway: to deliver gas or should we be looking at the possibility of using the hydro reservoirs?’

‘I don’t think that hydro reservoirs can do it alone but I think it could be a very good alternative to some of the fossil fuels, but we have to make sure the environment is protected in the best ways, by only using existing reservoirs and looking carefully at where, and where not, to do this.’

Power resources become truly renewable, he argues, when backup is provided by other renewables rather than fossil fuels.