据《连线》杂志10月11日报道，意大利科学家对一种新型风力发电装置寄予厚望，它看上去就像院子中不起眼的晾衣服架子。尽管外形乏善可陈，但风筝风力发电机（简称KiteGen）的发电量却有可能同核电站相媲美。

业余爱好激发设计灵感

风筝风力发电机的工作原理很简单：风筝在风力作用下，带动固定在地面的旋转木马式的转盘，转盘在磁场中旋转而产生电能。对于每个风筝而言，转盘都会放开一对高阻电缆，控制方向和角度。风筝并非是我们在公园常见的那种类型，而是类似于风筝牵引冲浪的类型———重量轻、抵抗力超强、可升至2000米的高空。

意大利都灵附近的小公司“巨杉自动控制”（Sequoia Automation）领导实施了这一项目，据估计，风筝风力发电机每兆瓦时能产生10亿瓦的电力，而每兆瓦时的成本仅有1.5欧元。而欧洲国家每兆瓦时发电的成本平均为43欧元，显然，风筝风力发电机的成本是后者的近三十分之一。

支持者称，这种旋转木马发动机的其他组件加起来的成本也只有36万欧元，而且只需要有限的空间。据他们估计，即便直径只有320英尺（100米），风筝风力发电机也可产生5亿瓦的能量。对巨杉自动控制公司而言，幸运的是，该公司员工可将它们带回家仔细研究。这家公司的核心产业是传感器设计和工业自动化装置。R&D负责人马西莫·伊波利托受其悬挂式滑翔和风筝牵引冲浪等周末爱好的激发，开始琢磨一种特殊的风力发电装置概念，最终风筝风力发电机诞生了。

可能带来一场能源革命

在经过6年的艰苦研究和申请了7项专利后，他领导着一个20人的团队设计出可发电的巨型旋转木马（carousel）。该小组认为这一装置将在未来两年内投入使用。48岁的伊波利托说：“它被称之为一场革命，但我将此看作是新能源未来的一部分。一旦将光电发电、光热发电及风筝风力发电机有效结合在一起，我们就能尽力满足日益上升的全球电力消耗的需求。”

伊波利托认为，鉴于其覆盖区域小却可产生巨大能量的特点，风筝风力发电机将成为首选风力发电机，使其优于诸如滑翔机发电机和风车等类似项目。迄今为止，这一项目看上去极富前景。一种称为MobileGen的小型便携式风筝风力发电机（由平板载货车拉拽的一个风筝）在8月份的测试发射中就取得了进展。它能产生一定的能量，另外还有一系列改进。伊波利托表示，研究人员看到这种发电机运行时的心情简直难以言表。

尽管如此，风筝风力发电机的发展前景似乎并不能一帆风顺。有人虽对这一概念表示赞赏，但仍持一种观望态度。

具有成本低的优点

为意大利政府机构ENEA研究再生能源的卢西亚诺·佩拉奇（Luciano Pirazzi）说：“鉴于风筝风力发电机的发电量及低成本，这确实是一个令人神往的项目。不过，该项目仍存在一系列不确定因素———目前，它基本上还只是停留在绘图板上的一个概念而已。其可行性有待于进一步证明。”人们心中对这种新型发电机的巨大疑问包括，发电机的安放位置以及令人头痛的空域许可证行政审批手续等问题。根据专家现在的推测，风筝风力发电机有可能会耸立在以前曾是特里诺维切累斯核电站所处区域的上空，那里早已是禁飞区。

到2010年，意大利必须将其再生能源的比例增至总电量的22%，以满足欧盟再生能源政策目标的要求。风力发电是再生能源的一个重要组成部分，而来自国内外企业的竞争有望进一步加剧。因在风筝风力发电机项目上的出色表现，巨杉自动控制公司于今年初被授予了“2006世界再生能源奖”。

风筝风力发电机也使都灵公用事业公司AEM相信其所具有的巨大价值，这家公司最终同意承担风筝风力发电的实验样机40%的费用，并作为技术合作伙伴在合约上签了字。这是AEM公司首次进行此类项目的投资，这家公司距意大利主要进行风车发电的沿海地区较远。AEM公司工程师安德里亚·庞塔说：“当第一眼看到这个设计时，你会忍不住发笑，因为它的样子实在有些滑稽。不过，随着对它的了解逐步深入，你会发现，这个想法安全可靠，且这项技术已经存在。” （任秋凌）

Power Kites to the Rescue!

Introduction to the Kite Wind Generator Project (PDF) at Sequoia Automation via Wired: Generating Power from Kites. I have flown a "trainer" kite for kite-surfing, and it's actually amazing how much control you have over a kite with just two strings. It's also amazing how strong a kite can be! In fact when I flew I speculated about possible power applications - not just for electricity but also for ocean ships. Now, somebody has actually done the math and some of the engineering, and it looks feasible to generate real power with kites!

As you can see in the picture, the idea is to basically control the kite for a "power cycle", similar to how a four-cycle internal combustion engine works. Start with a "power stroke", where the kite pulls the cables out and thereby delivers power. Next is a "control stroke" where you control the kite into a neutral "luffing" position - the kite is only catching enough wind to hold itself in place and is not pulling on the cables. The closing step is the "return stroke", where you reel the cables in under the luffing condition - requiring little power. Then start over.

The obvious disadvantage of this power generation system is that it's not constant - two of the three strokes actually consume power rather than generating it. A logical solution to this problem is to have multiple kites... line them up like we do with wind turbines.

However, the folks over at Sequoia have done something even more radical - they have put the kites together on a "shaft", like we do with engines, solving not the just stroke averaging problem but also the issues with constantly raising and lowering the kites. Imagine if you will a gigantic carousel, but replace the fake horses with kite controllers :-). The pulling kites are on one side, while the luffing ones are on the other. The carousel spins slowly around and generates electricity via a generator, just like a wind turbine. The kites can be much larger and the cables much longer, because now you don't need to generate power from the cable movement, freeing you up to just concentrate on the control and tension needs. You can also tandem the kites - putting 2 or more kites on each set of cables.

Now scale the carousel up, so that the kites are 30 feet across and the carousel is a kilometer (!) across. They claim that size is a 250MW installation. A two kilometer diameter is 5GW! Apparently a 3MW version (on par with big wind turbines today) is 200m across - still quite large, but in the same ball park as comparable wind turbines. Of course you have to ask about the plausibility of a 1km diameter carousel - that's big! Its probably easier than scaling a wind turbine up to a similar size though - because it's along the ground. Also because it's not solid (it's just a bunch of beams, etc) it's not as bad you think, but still I imagine the size of those beams! Also, I wonder about the possibility of kites tangling up with each other - clearly a bad disaster if it happens. Also, you sacrifice some portion of the energy that you could otherwise capture because your carousel only turns in one plane - i.e. you can no longer generate energy with the vertical component of the force on the cables, which is likely to be at least half of the force...

One thing which concerns me in their proposed carousel design is that it appears upside down. They have tension wire supports *above* the beams, which seems backwards to me since the kites are going to be pulling upward. Am I on crack or shouldn't those extra cables anchor to the base of the KiteGen structure rather than to an elevated point?

The obvious challenge in all of this is the control system - you need to make a kite controller that can keep those huge kites flying their pattern even if the wind gets nasty. This is a 21st century type of problem: embedding enough intelligence in our machines to do really amazing things automatically. I've studied enough control theory and worked with enough sensors to know that this kite control problem would be pretty hard - but certainly not impossible, especially if you had fairly steady winds. I can see the first WindGen Carousel being a tourist attraction, in the sense that watching these kites move around would be fascinating. Assuming they aren't so high as to be out of sight, of course :-)

The Sequoia people appear to have done quite a bit of work - they have a blog (in Italian, course, so use babelfish. Initial presentation of kite controllability, initial presentation of carousel concept, Project Proposal - which includes some interesting details about how they are going to create the Kite Control Unit (KCU) via a three step process. Mobile Generator (Italian PDF), their single kite, back of truck prototype system for generating power. Paper: Control of tethered airfoils for a new class of wind energy generator, which gives some of the control mathematics and simulation results. That would have been a cool project to work on!

Anyway, I'd say their biggest problem at this point is getting funding. The inventors seem to have an "Italy" mind-set - I've read in several places that they have kept the team and the funding to Italian places - no doubt this is part of their problem. The other part is that such an unconventional, innovative technology just does not fly (pun intended) with the conservative energy market. And like with the tallest wind turbines, there are airspace concerns. But I think there is serious potential, especially if they are willing to be flexible about deployment options - e.g. not bothering with the carousel for the first small installations, just using a few power kites. Maybe teaming them up with a Flow Battery to average the power. I for one would love to see kite power as a major contributor to our future energy supplies - they are suitably 21st century to really sound futuristic!