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译:Connecting the green dots

来源: 时间:2011-7-15 10:04:00 点击:

In renewable-energy circles, there is a real excitement about Germany’s latest plans to move away from nuclear and towards renewable energy. The state of California has similarly raised its renewable-energy goals for electricity to 33% by 2020, while China has repeatedly outstripped its wind-energy targets and is on track to install 90 gigawatts by 2015.

However, large-scale renewable power, particularly electricity generated from the sun and wind, relies heavily on the electricity grid. The electricity grid is the way power is moved from generators to customers. While coal can be shipped to a city and burned in a nearby power station, renewable energy has to be generated wherever there is a lot of sun or wind. In China and the United States in particular, this can be a long way from the large cities. As a result, renewable energy often has to travel a long distance on the grid to reach consumers.

The grid is frequently weak in the rural areas that have good renewable energy resources, so absorbing all the available power can be difficult or even impossible. Across the United States, rural areas experiencing a boom in wind farms face an overloaded grid that doesn’t reach large cities on either coast. The 2010 China Wind Power Outlook, jointly released by the Global Wind Energy Council, the Chinese Renewable Energy Industries Association and Greenpeace China tells of similar challenges facing the rapid expansion of the wind power bases in China.

Power generated from the sun and wind is also intermittent: there is no power when the sun doesn’t shine and the wind doesn’t blow. There are a few ways that grid operators – the technicians responsible for keeping electricity moving through the grid – cope with intermittent power. They can draw renewable energy from a wide area, in the hope that the wind is blowing or the sun is shining somewhere. They can manage the customer demand by arranging to disconnect large users for a few hours. Finally, they can arrange for backup power generation by a controllable power source like hydropower or natural gas turbines. Grid operators can use a blend of all three of these strategies – but the first option particularly requires lots of strong, tightly integrated grid capacity between regions.

China is currently investing heavily to create this sort of tightly integrated, strong grid that can move renewable energy from the west and north to the large cities on the coast. However, building lots of new power lines is only the beginning of what is necessary to really scale up the proportion of renewable energy used by a country. There are many supporting policies, procedures and technologies needed to allow the grid operator to make the most of intermittent renewable power.

For example, it is important to have very precise weather forecasts, particularly 24 hours ahead. High-quality weather forecasts allow the grid operator to plan on receiving at least a minimum amount of renewable power to meet the expected customer needs. Then the operator does not need to schedule as much coal or other power to be generated, reducing pollution and saving fuel.

Renewable power can be more expensive to produce than options like coal and natural gas. This is partly because fossil fuels are often subsidised, directly or indirectly, and partly because renewable-energy technologies are not yet as mature as fossil-fuel technologies. The grid operator’s standard procedure is to use the cheapest power first. So the government must mandate that the grid operator purchase the renewable power even when it is not the cheapest option. This can be done in a variety of ways, including through a renewable-portfolio standard or something called a priority-dispatch requirement, but the goal of all of the tools is to change how the grid operator chooses which generators to use each hour.

One of the grid operator’s key responsibilities is to keep the grid stable by perfectly balancing the electricity generated with the electricity demanded at all times. A stable grid requires several supporting services, called “ancillary services” in the industry. These include services like backup generation that can come online within seconds or minutes in case a power station fails unexpectedly.

Backup generation is, of course, also one strategy to manage intermittent renewable power. However, in regions – like many in China – that are heavily dependant on coal for power, there may not be good backup generation options that can come online very quickly. For coal to act as backup generation, the power plant must be constantly burning fuel to keep the boiler hot, while it waits to be needed. Thus, backing up renewable energy with coal means there is little to no pollution benefit from using the renewable energy: the coal plant is running anyway. To really see the benefits of renewable energy, it is important for the grid operator to also have cleaner options for the “ancillary services”.

In Germany, the latest wind turbines include technology that allows them to provide some other ancillary services, such as reactive power. This is a great step towards integrating renewable power in the grid, but it does not necessarily solve the specific challenge of backup generation. To take full advantage of renewable power, the grid operator and decision makers need carefully to consider the full technical and procedural options for ancillary services.

A special report on the potential of renewable energy by the Intergovernmental Panel on Climate Change, published in May, confirmed that there is enough wind, water, sun and biomass to meet our energy needs with today’s technology. However, there are many barriers to utilising that resource effectively. Building and strengthening the grid is one piece of the puzzle, but just as important are the policies, procedures and technologies used to manage the grid today. These need to adapt and grow to seamlessly integrate renewable power. Grid operators in particular will be key to maximising the greenhouse-gas reductions that we might see from using renewable energy for electricity. They have a critical role to play in the work to safeguard the climate.


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  电网运营商的一个关键责任就是通过发电和用电的全天候良好平衡,保持电网的稳定。一个稳定的电网需要多个支持性服务,即业界所说的“辅助服务”,包括备用发电等。备用发电必须要在电厂突发故障时在几分钟甚至几秒钟之内进行补位。备用发电当然也是应对间歇性可再生能源的方法之一。但是,很多对煤电高度依赖的(比如中国内的)地区,可能没有能够很快并网的备用发电方式。因为要把煤电作为备用发电方式,电厂必须不断烧煤才能保持锅炉的热度,以备不时之需。这样一来,用煤电作为可再生能源的备用发电方式就意味着可再生能源的环境效益被抵消殆尽,因为燃煤电厂还是在运行的。为了真正实现可再生能源的效益,电网运营商必须找到更清洁的 “辅助服务”方式。
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