日食经过
At 38.5 gigawatts of capacity - nearly half of Europe's total of 89 gigawatts - Germany has more solar PV installed than any other nation. With Friday a bright sunny day, there were worries ahead of time about the consequences of the solar eclipse scheduled to occur in the morning. Engineers knew it would cause a massive, sudden drop in solar electricity input - followed by a massive increase when the eclipse came to an end later in the morning.
There had never been such a massive and rapid drop and rapid increase in solar power before in Germany. The eclipse cut off 65 to 80 percent of incoming sunlight, depending on one's vantage point.
The task faced by engineers at Germany's four big electricity network operating companies was to make sure that the resultant huge solar power production fluctuation wouldn't destabilize the grid.
The engineers carefully prepared measures well ahead of time, coordinated all across Germany, aimed at stabilizing electricity supplies by ramping fossil-fuelled power plants up and down, timed carefully to offset the solar eclipse, so as to avoid any sudden voltage fluctuations that might cause the grid to crash.
One way to deal with the challenge would have been to simply shut off solar power systems - that's how Italy dealt with Friday's solar eclipse; they disconnected 30 percent of solar capacity to reduce their network balancing problem. But that's not how Germany's network engineers approached the challenge.
A system-wide 'stress test'
Dirk Biermann, an engineer at electricity network operator 50Hertz, said the eclipse was a "stress test" for the Energiewende - the country's gradual, massive shift toward renewable energies. The network engineers wanted to show that it's possible to deal successfully with large-scale fluctuations in renewable energy input, whether from sudden increases and decreases in solar energy or in wind power.
On Friday morning, in the hours before the eclipse, solar power production rose steadily as the sun climbed higher into the sky, and the solar power input display curve on the computer screen in the regional network management center in Neuenhagen near Berlin climbed with it.
Then, shortly after 9:30 AM, the display curve bent sharply downward. From 14,000 MW before the eclipse, it dropped quickly to 7,000 MW. So far, so good - the network remained stable.
A while later, with the eclipse ending, the display curve began to reverse itself. "We're at the bottom of the valley," Biermann said. "Now photovoltaic production will rise rapidly from 7,000 MW to 20,000 MW."
Watching the displays, Biermann saw 4,400 MW of solar power added to the grid over the course of fifteen minutes. "This is going to work," he said with satisfaction. In total, an amount of power equivalent to the output of ten nuclear power plants was coming onstream as the moon's disc gradually ended its occlusion of the sun's.
Ramping up, ramping down
To balance out the incoming rush of solar power, electricity output from some of Germany's output-controllable power plants, including gas-turbine and pumped-hydro power plants, had to be throttled back in carefully timed tandem, to keep total power supplies nice and stable - just as they'd had to be ramped up earlier in the morning.
Extra reserves were available to back up the normal automatic systems for steadying the power supply - systems which have been in place for several years, since Germany already gained 26 percent of its electricity from variable renewable energy sources in 2014.
On some days, unusually strong winds can pose challenges to the grid operators, as the turbines pound variable energy into the system. But the wind was docile Friday morning. A calm day with low wind power input made the day's network balancing task easier. Germany has over 38 gigawatts of installed wind turbine capacity, but they were delivering just 500 MW on Friday morning.
By noon, it was all over - and the engineers at the country's four network operating companies were content with the morning's work. "Good preparations paid off, we were able to handle all swings in production," said Ulrike Hörchens, spokeswoman for Tennet, one of the four network companies - the one that manages the highest share of PV input.
The system had passed the stress test.
文章来源：http://www.dw.de/german-power-net-survives-solar-eclipse/a-18331190
时间：2015年3月20日
分析总结
回放：
3月20日上午，北半球迎来难得一见的日全食。德国是全球光伏装机容量最大的国家。在日食期间由于缺少阳光，德国将骤然失去约70%的光伏电力；而当日食结束时，阳光突然照射，大量光伏电力又将瞬时涌入电网。 一退一进，给电网带来巨大压力，但作为全球最大的太阳能发电国家，德国经受住了这次严峻的挑战。
质疑：
日食究竟会给太阳能发电带来多大影响？德国电网是如何应对此次日食危机的？此次事件对中国的太阳能发电产业有什么借鉴意义？
解答：
“这次日食是当前光伏发电可能面临的极端状况，欧洲各国的电网运营商对此非常重视，可谓严阵以待。”国家发展和改革委员会能源研究所副研究员、国家可再生能源中心主任助理赵勇强在接受《中国科学报》记者采访时说。
这次日食开始时，月球的投影在大西洋洋面出现，历经两个半小时后在北极点附近结束，全食阶段持续2分47秒，是欧洲16年以来经历的规模最大的一次日全食。
作为全球最大的太阳能发电国家，德国拥有高达39GW的光伏装机容量，超过德国总发电装机容量的20%。据ENTSO-E发布的一份《2015年日食影响评估报告》显示，当日食发生时，整个欧洲大陆减少的光伏电力有51%来自德国，而这可能给电网带来超负荷运行的风险。对德国而言，日食过程导致的太阳能下降速率和上升速率分别高达-273兆瓦/分钟和361兆瓦/分钟。
“这个变化率可以说非常快。”中国科学院电工研究所研究员王一波说，“电网的正常运行需要保持发电量和用电量之间的实时平衡。从便于电网控制和调节的角度考虑，电源输出最好能相对稳定。但光伏发电的特性决定了它的不稳定性，在日食发生的过程中，光照在短时间内先是骤降，然后又突然回升，这对电力系统快速调节能力来讲，的确是非常大的
“虽然日全食影响很大，但是其过程可预测，这就使各国有充分的时间制定技术和非技术的预案，从而使其影响可控。其中很重要的一种预案就是欧洲各国电网公司之间的协调合作。”王一波说，“德国电网并不是孤立的，事实上整个欧洲电网可以给德国电网提供强有力的支撑，当德国面临‘日食危机’时，挪威、瑞典等对太阳能发电依赖较小的周边国家就可以伸出援手。”
在整个欧洲电网的共同协调下，德国等国家的输电系统运营商通过实时调控备用机组的发电出力，维持日食过程中的电力供需平衡，成功渡过了这一难关。
欧洲电力传输系统运营商联盟秘书长Konstantin Staschus表示：“此次日食事件是在本联盟组织之下，欧洲及区域协同合作的一个成功案例。”
本次“日食危机”是对整个欧洲电力系统的一场“大考”。理论上，欧洲的输电运营商也可以采用保守的预案来逃过这场考试，比如在日食前后的一段时间里，简单地把光伏系统全部关停，只依靠常规发电机组供电。但他们没有回避危机，在全世界面前上演了现代电网应对可再生能源发电危机的生动一课。
“这次事件意义重大，是对可再生能源发电事业的极大鼓舞。”王一波评价道，“大规模发展太阳能、风能等可再生能源并网发电，一直面临着很多质疑。人们担心这些随机性、间歇性的电源，一旦高比例接入电网，是否会对电网带来难以承受的冲击。这一次，欧洲国家集体提交了一份漂亮的答卷，证明了在技术层面上，现代电网完全能够应对这样的挑战。”
据了解，当前中国的光伏发电在全国发电量中占比尚不足1%，但是光伏装机的年均增速超过了100%。从2013年到2014年，中国的光伏新增装机容量连续两年世界第一，累计装机容量位列世界第二，仅次于德国。
赵勇强认为，德国成功应对日食危机的案例，对中国发展太阳能发电也有很大的借鉴意义：“首先，电网的调度运营组织要切实负起责任，做好预测、预报、危机评估等工作；第二，系统规划电力系统和配电网，增加电力系统的灵活性；第三，充分调动市场机制，促进辅助服务和市场供需平衡。”挑战。”
文章来源：http://guangfu.bjx.com.cn/news/20150330/603427.shtml
时间：2015年3月30日
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