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Trend Report No. 2a: Energy Storage (Part 1) / November 2011
Independent of the vagaries of the weather –
energy revolution requires new electric storage systems
- Tomorrow’s grid electric storage systems
- Ratio of fluctuating power to predictable power is shifting
- Storage in the electricity grid especially in potential energy
Now that the energy transition has moved up the political agenda, the ACHEMA special show on energy generation and storage is more relevant than ever. Innovative storage technologies hold the key to renewable energy utilization and energy-efficient industrial processing.
The world is becoming more plugged in. Energy researchers predict that electricity generation worldwide will rise by two-thirds between now and 2030. Global population growth and the electrification of previously undeveloped regions are not the only factors which are driving the increase in demand. Electricity grids in the industrialized world are expected to supply more and more power. Electromobility is one of the mega issues which are driving this trend. The German government has set a target of 6 million electric cars on German roads by 2030.
The problem is that electricity is a transient form of energy. When electricity is generated, there must be corresponding demand in the grid. If too much electricity is generated, the line frequency increases. Frequency variations can result in major power outages. Increased use of renewables such as solar and wind power makes the problem even more difficult to manage. This became very noticeable last spring when the grid in Eastern Germany threatened to shut down. The turbines in Eastern Germany, driven by strong winds, generated up to 12 gigawatts of electricity which was fed into the grid. Regional demand, however, is only a fraction of that level.
Back in 2006, high electricity output from European wind turbines triggered a chain reaction that had serious consequences. The wind force was strong in Northern Germany late in the evening of November 4th. Shortly after 10P.M., an overhead power line above the Ems River was shut down for safety reasons while a cruise ship was being launched. At the time, the power line was carrying 10GW of wind-generated electricity to Southern and Western Europe. To stabilize the line frequency, part of the grid in Western Germany, Belgium, Northern and Southern France, Northern Italy and Spain were temporarily shut down. Some areas of Spain were affected by a blackout for up to two hours.
Renewable energy is also having a noticeable effect on the electric power markets. At times, payment is offered to customers for using excess wind-generated electricity late at night. Solar power is also part of the equation. On the bright afternoon of July 16th, 2011, the price of electricity in the middle of the day on the EEX power exchange fell to the same level as the cheap night rate. The reason for the fall in price was the high amount of PV power in the grid. German PV systems now supply up to 13GW of electricity (the equivalent of 10 nuclear power stations) to the grid during good weather conditions. Not only that, the portion of renewables in the electric power generation mix continues to increase. The catastrophe in Fukushima in particular has forced a rethink in some industrialized nations (most notably Germany). As a result, we can expect to see a massive expansion of wind, PV and solar power generation.
Currently, balancing supply and demand is a tightrope act. A new approach is needed to the problem. Some of the options are:
- Further grid expansion to enable better distribution of excess electricity
- Demand management using smart grids, for example automatically switching on user loads to compensate for oversupply
- Use of energy storage systems to manage excess or insufficient supply
Grid expansion is the cheapest option, and it is also the fastest. However, public opposition to new overland lines in the highly-developed industrialized nations continues to increase. Smart grids, where for example domestic washing machines turn on automatically in the middle of the night when excess wind-generated electricity happens to be available, are still in their infancy, and the same applies to energy storage.
To gain a clearer picture of the many different storage technologies which are available, it is useful to distinguish between grid stabilization and local electricity storage. Thermal storage systems, especially those which make use of process heat in the chemical, pulp & paper and other process industries, are becoming increasingly important.
Electricity can be converted into chemical, potential, kinetic or electromagnetic energy. Each has its advantages and disadvantages. Super caps have a low energy density, but they can supply electricity very quickly to stabilize the grid and compensate for fluctuations. Other technologies are used to store electrical energy for varying amounts of time.
Grid electric storage: from pumped water to the mega battery
Pumped-storage hydroelectricity is currently the most wide-spread form of grid electric storage. At times when cheap electricity is available, large amounts of water are pumped from a lower elevation to a reservoir at a higher elevation. During periods of peak demand the water flows downhill again, driving turbines and generators to produce electricity. The 33 pumped-storage hydroelectric stations in Germany have a peak generation capacity of 6.7GW and can store roughly 40GWh of energy. By way of comparison, maximum pumped-storage hydroelectric capacity in the US is 21.5GW.
CAES (Compressed Air Energy Storage) is based on a similar approach. Compressed air is stored in underground caverns. Gas turbines convert the energy back into electricity during periods of peak demand. Only two of these systems exist worldwide, one in Huntdorf, Germany (290MW) and the other in McIntosh, Alabama, USA (110MW). Both of these plants have been supplying power to the grid for a number of years. RWE, General Electric, Züblin and DLR have joined forces on a project to enhance the efficiency of this technology by utilizing compression heat. The Stassfurt compressed air storage plant (RWE, DLR) is scheduled to go into operation in 2013. The 90MW plant will have a storage capacity of 360megawatt hours. The gas turbine on the ADELE (adiabatic compressed air energy storage) Project in Strassfurt is designed to operate without fuel combustion. Heat generated when the air is compressed is stored and recovered when the air is decompressed. This technique increases overall efficiency from roughly 55% to as much as 70%.
The reason why relatively few grid electric storage systems are currently in use is primarily economic. Coal or gas fired plants and nuclear power stations are cheaper to operate. “Pumped-storage hydroelectricity and CAES are only commercially viable if the difference between the night and peak rates is at least 3ct/kWh,” explained Prof. Dirk Uwe Sauer from the RWTH Aachen University. Sauer pointed out that expansion of the grid is always cheaper than grid electric storage.
However in the longer term, the development and use of storage technologies will be a necessity. In contrast to conventional power generation, wind and solar power are not always available. The ratio of fluctuating power (wind and solar) to predictable power (conventional power stations) is currently around 1:5. However, the German Environment Ministry expects that the ratio will be about 1:1 by 2030. In addition, storage technologies (both for electric and thermal energy) hold the key to efficient utilization of energy in the power generation and process industries.
With this in mind, in the spring of 2011 the German Economics and Environment Ministry decided to make 200million Euros of funding available for energy storage technology research over the coming years to accelerate the pace of development. Other countries including China and the US are also providing financial support for storage technology research. $158 million has been allocated to energy storage technologies as part of the US government stimulus package. The US Energy Storage Association estimates that this funding will generate roughly $780 million of investment in storage technology. In addition to grid electric storage, the programme also includes decentralized solutions in electromobility and battery technologies.
Summary: The energy revolution is politically decided. Now is the time to provide appropriate technical solutions to compensate the fluctuations in the electricity supply from renewable sources. Solutions are required from the process industry, the chemistry, and the measurement and control technique. At ACHEMA 2012, innovative energy carriers and energy storage are a key issue. Not only in the special show exhibitors and scientists will present new solutions.
The second part of the trend report focuses on battery technology, hydrogen storage and thermal storage technologies.
(The trend reports are compiled by specialized international journalists. DECHEMA is not liable for incomplete or inaccurate information.)
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