After the Fukushima nuclear disaster in Japan, the German government has decided to end the use of nuclear power and Chancellor Angela Merkel announced the immediate shutdown of its seven oldest reactors at the end of May. The rest may close by 2022. Wind energy is set to play a vital role in replacing the lost generation capacity.
But just how securely can electricity supply in Germany be maintained in a system that increasingly relies on wind energy? Work is now under way to develop cost-effective, balanced and stable energy systems designed to ensure that the lights do not go out when the wind is not blowing.
With growing amounts of wind generation now on the German system, wind power must itself play a bigger role in ensuring the stability of electricity transmission and supply. Equipped with the necessary control systems and with the right market conditions, wind power could soon supply short-term backup power. Also known as balancing or reserve power, this is required when supply and demand on the transmission system fail to match, or when instability occurs, for example through the unexpected outage of a power station.
When the wind is blowing, wind turbines can provide balancing power by operating at curtailed output, ready to open up to full output if needed, or ready to reduce output if too much power is flowing on to the system.
The German federal energy regulator, Bundesnetzagentur (BNA), has changed the market rules to make it easier for wind farms and other small generators to participate in this balancing power market. With these new BNA rules coming into force on June 27, energy companies bidding to supply primary reserve power can offer capacity lots of just 1MW each, and those supplying secondary reserve can bid in lots of 5MW instead of the previous minimum levels of 5MW and 10MW respectively.
To put this into perspective, Germany's transmission network operators are currently required to have 612MW of primary reserve capacity and 2,000MW of secondary reserve capacity available at all times. Primary reserve power must be made fully available within 30 seconds of being called up, while secondary reserves must be available within five minutes.
Access to the lucrative balancing power market will remain difficult for wind generators, however, until the tendering system for supply of balancing power takes place daily. The BNA is keen to introduce a daily tendering procedure to open up the market to wind and other renewable generators but thinks moving now from the current one-month interval to a daily mechanism is too hasty. It has heeded warnings about the administrative challenge needed for the jump to a daily system and brushes off criticism that established market players might use its concerns as a delaying tactic to prevent new electricity suppliers from entering the market.
For the time being, therefore, tendering for both primary and secondary balancing power will now take place on a weekly basis, allowing transmission network operators and balancing power suppliers to adjust to the new system.
But the federal renewable energy association, Bundesverband Erneuerbare Energie, says forecasting for several days in advance is not sufficiently precise for wind generators to be able to bid into the primary and secondary reserve markets. The BNA counters that more time is needed in any case as the provision of balancing power by wind turbines is still at the research-and-development stage and will not predict when a daily bidding system for balancing power could be introduced
But what will happen in Germany when wind energy reaches its full potential? As Germany moves towards reaching its full wind power potential - onshore wind alone could grow to 198GW and generate about 390TWh/year, equivalent to 65% of current annual electricity use - major storage may be required for when wind drops to nothing for days at a time.
Possible solutions such as using hydro and pumped storage facilities to store electricity or expanding the transmission networks to allow substantial electricity imports are now being challenged by new ideas such as producing a substitute gas - a so-called windgas - in a process powered by surplus wind energy (see box, below). This synthetic gas could provide the necessary fuel to fill the generation gap. Major German nuclear player E.on is one of the first to have announced exploratory steps in this direction.
The decision to exit nuclear power could now release a brake that had been slowing innovation as Germany looks anew for an energy market that is able to accommodate a secure renewables-based electricity supply.
CASE STUDY - LICHTENAU-ASSELN BACKING WIND WITH HYDRO AND BIOMASS
In May the 36MW Lichtenau Asseln wind farm in North Rhine-Westphalia, commissioned in 1998, began selling wind power direct to local customers, teaming up with a green electricity trader to ensure security of electricity supply.
Owner-operator Asselner Windkraft (AWK) is selling the electricity generated from Asseln for around 5% less than the standard price charged by utility RWE to its household customers and pledges to hold the price for at least ten years.
When the wind is still, Leipzig-based green electricity trader Clean Energy Sourcing (CES) guarantees to supply the electricity shortfall from hydro and biomass generation. If AWK produces surplus wind energy, this is delivered back to CES so that over the year customers get all their supply from wind energy.
Having abandoned the guaranteed fixed feed-in tariff support system, as a supplier of 100% renewable electricity AWK pays neither the renewables levy nor the eco-tax that is charged on non-renewable fossil fuel-generated electricity.
WIND AND GAS WORK TOGETHER BACKUP FOR RENEWABLES FROM RENEWABLES
A new fuel, renewable gas - dubbed windgas - may be the answer to long-term bulk storage of electricity for periods when there is no wind. Major German electricity company E.on is planning to build a pilot plant in northern Germany for commissioning in 2012 or 2013.
Windgas consists of methane - the main constituent of natural gas - produced by two chemical reactions driven by wind-generated electricity. Electrolysis splits water into hydrogen and oxygen. Subsequently, the hydrogen is converted into methane in a process known as methanation.
The energy needed to do this can typically come from wind or solar, both of which are well developed in Germany. The renewable gas is then stored in the gas network and used as fuel in standard gas-fired power stations when there is no wind or at night when solar panels are not generating power.
The idea was explored in the German environment ministry's lead Study 2010 on development of renewables to 2050, released last December. The study says the 340,000 kilometres of natural gas pipeline network along with existing gas storage caverns can provide storage capacity for renewables-generated gas sufficient to generate the around 10TWh of electricity needed as backup to wind.
E.on is well placed to develop the technology since its gas subsidiary Ruhrgas owns the largest gas pipeline network in Germany. Transporting renewable gas through the existing pipeline network to where it is needed provides an alternative to building new electricity transmission lines. The gas storage caverns are mainly in northern Germany, ideally located to take up methane produced with North and Baltic Sea offshore wind power.
If surplus wind or solar-generated electricity, with a value of EUR0.01/kWh, is used to produce renewables gas, the price of the renewables gas will be comparable with that of natural gas from about 2030, according to the study. Costs are driven up due to energy losses totalling up to 36% in the gas production processes.
"Use of the already well-developed technologies electrolysis and methanation and of the existing gas infrastructure could make the system economic at an earlier date," Martin Felder, systems analyst at the Centre for Solar Energy and Hydrogen Research said at the Hanover industry trade fair in April.
The centre is involved in a renewable-gas pilot project in partnership with the Fraunhofer Institute for Wind Energy and Energy System Technology and the company SolarFuel.