Storing the sun and wind

Imagine what would happen if we could not store water, wheat or oil for when we needed them. It hardly bears thinking about. Electricity, however, is one essential commodity we cannot keep - at least in large quantities. We have to use what we produce at the time. Yet, in future, this could change. Growth in renewable energies is driving an unprecedented amount of research into electric storage technologies that can compensate for the intermittent nature of the sun and wind. ACCIONA is taking part in this effort with pioneering initiatives and projects.

The electricity grid only supplies the energy it consumes at any moment. That fact calls for complex technical procedures for which so-called system operators have responsibility and in Spain this is taken care of by the Spanish Electricity Grid (REE, Red Eléctrica de España).

In a conventional system, the balance is maintained mainly by manageable power stations, such as natural gas combined cycle and hydroelectric, which can be regulated to adapt to the electricity production required by demand at any moment.

But the large-scale incorporation of renewable energies - which are non-manageable - such as wind or solar power, variable by nature and difficult to predict, have led to a shift in scenario: all the players responsible for electricity generation and supply are now involved in a huge technological effort aimed at maintaining the stability of the grid and security of supply.

So far, this effort has focused mainly on improving the technology of wind turbine generators, as well as developing operational and control centers. ACCIONA, with its Renewables Control Center (CECOER), was a pioneer in that respect. Thanks to such initiatives, the wind in Spain covers over 60% of total electricity demand at some moments, unthinkable just a few years back.

But our capacity for innovation allows us to be yet more ambitious. Now we have the emergence of electrical storage systems which are coming to the fore as an indispensable ally for renewables. If we can store the sun and wind - or, strictly speaking, the electricity produced from these sources - and use them as a function of demand, then the penetration of clean energies in the grid system will be facilitated enormously, to previously unimaginable levels.

Now new technologies are maturing fast to commercialization. The challenge is to make storage efficient and profitable. ACCIONA is taking very important steps forward in this field (see the ILIS project) and is alert to the evolution of these technologies so it can apply them to improve the efficiency and profitability of its facilities.

Why store?

Storing electricity generated from solar or wind power could be incredibly useful, by:

• Improving the technical integration of photovoltaic and wind power into the grid.
• Guaranteeing power despite sudden changes in wind or solar radiation.
• Moving electricity supply to where consumption is high.
• Allowing renewables to provide complementary services to the grid (currently only performed by conventional energies).
• Advancing us towards a more decentralized (distributed), intelligent and renewable electrical system.
• Avoiding network saturation and increasing efficiency.
• Increasing the quality and security of electricity supply.

Storage pioneers

ACCIONA Energy has carried out the first experiment in Europe to incorporate batteries into the operation of an industrial-size photovoltaic plant. It did so in the framework of the ILIS (Innovative Lithium-Ion System, to manage multi-MW solar plants) project.

The accumulators used allowed engineers to smooth power fluctuations in photovoltaic production, storing, or complementing, the electricity being drawn from fields of solar panels. This also makes it possible for the plant to respond to instructions from grid operators to regulate power output, thus facilitating management of the electrical system.

The new facility is operating satisfactorily in ACCIONA's photovoltaic plant at Tudela in Navarre, northeastern Spain. It includes a system of latest-generation lithium-ion batteries of 1.1MW power and 560kWh of electricity, supplied by the French hi-tech battery manufacturer, Saft Groupe.

ACCIONA has developed efficiency strategies for managing the photovoltaic plants with storage, using batteries both to modulate the plant's output and provide complementary services to the electrical system.

The success of the initiative, which forms part of the European low-carbon network, Eurogia+, allows ACCIONA to take the lead in photovoltaic projects which must comply with advanced connection requirements. It positions the Company as a reference for large photovoltaic facilities, as the technology is readied for worldwide expansion.

The next challenge for ACCIONA is to incorporate the results of the project in the Company's commercial offering for photovoltaic while also transferring the acquired know-how to the wind power sector.p>

Other fields of innovation

ACCIONA is also researching other fields related to storage and incorporation of renewables into the grid, such as:

Wind power

Analytical, simulation and decisionmaking help is being developed to allow optimum storage systems to be applied to wind farms in different conditions and markets, from both economic and energy perspective.

REserviceS project

European consortium, in which ACCIONA participates, analyzing technical and economic aspects of complementary services provided to the grid by wind and photovoltaic facilities, with the aim of establishing a reference base and recommendations for regulatory policies.

Grid issues stricter connection requirements

The growing penetration of wind and solar energy has seen grid operators increase the technical requirements to integrate these technologies into the system. This they do to guarantee the stability of the systems and security of supply.

This is not just the case for countries with a high renewables quota - such as Denmark and Germany - but also for others with less interconnected networks - the United Kingdom and Ireland - and emerging markets such as South Africa, and other countries including the US, Mexico, Australia, Croatia and Poland.

A new version of the Spanish grid's operational procedures is being drawn up (REE PO12.2) to place special emphasis on wind power generation. ACCIONA has taken an active part in its preparation.

We are also participating in a project to draft network codes proposed by the operators via the European Network of Transmission System Operators for Electricity (ENTSO-E). Compliance with the new codes will be compulsory in all European electricity systems.

The new requirements generally refer to very technical aspects, such as overcoming voltage fluctuations, back-up for subsequently recovering the system, and frequency control.