Report 1.docx

ENERGY KITE

CHAPTER-1 INTRODUCTION Several weeks ago I received an email from Massimo Ippolito, the founder of KiteGen, enquiring about advertising on Energy Matters. KiteGen are a world leader in the development of high altitude wind technology. While I was delighted at the prospect of selling some advertising space, the enquiry came with some strings attached. Massimo wanted me to write an article on high altitude wind power. I explained I knew nothing about this having not followed the technology, believing it to be a bit ‘bonkers’. Massimo confided that everyone thought that to begin with. And so I did a little research and found some information that caught my attention. For starters, there are many companies active in this arena and one of them, Makani, had recently been bought by Google for $10 million. Secondly KiteGen claimed that high altitude kites had high energy return on energy invested (ERoEI) >300. This was the real hook, because if true, this would make high altitude wind power dirt cheap and this could substantially ease, or remove altogether, issues with intermittency (see Appendix 1 on ERoEI). And finally I came across a very unkind article called Airborne Wind Energy: It’s All Platypuses Instead Of Cheetahs that was published in Clean Technica. It struck me as rather odd that a Green Tech blog should publish an article that focussed only on the potential weaknesses of high altitude wind, totally ignoring the strengths. Could there be any truth in the notion that Green Tech does not want a cheap renewable solution? This post provides an overview of high altitude wind covering basic principles, the main types of competing technologies, ERoEI and some of the basic physics.

Department of EEE,MTIET,Palamaner

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ENERGY KITE

CHAPTER-2 NEED  Provides 80% of electricity  Environmental conservation  Renewable energy source  Abundantly Available  Less Area requried

Department of EEE,MTIET,Palamaner

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ENERGY KITE

CHAPTER-3 Why go High? The primary reason for seeking wind at high altitude is that the wind tends to blow faster and more constantly the higher you go (Figure 1)(see also Figures 6 and 7). Add to that the nominal power increases with the cube of wind speed and you will understand the attraction of reaching for the sky.

Power=0.5*r*A*V^3 r=air density A = area V= wind speed The reason for lower wind speeds at surface is wind shear between the circulating atmosphere and the surface of The Earth. Surface topography and features break up the circulation. It is useful to imagine the flow of a river that will normally be much slower at the edge than in the middle where the main volume of water can flow unimpeded by boulders and branches etc.

Department of EEE,MTIET,Palamaner

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ENERGY KITE

Fig 1: Dutch average wind speed variation with altitude

1. This is the reason that ground based turbines have grown taller and taller as they reach upwards to access that better wind resource (Figure 2). But this has also been the Achilles heel of wind turbines since as they have grown taller they have grown more massive and ever larger quantities of steel and concrete (embedded energy) are required in their construction. A three MW turbine (Vestas 3112) contains 417 tonnes of metal in the tower and nacelle and 902 tonnes of concrete in the foundations. 2. This provides the second reason to reach for the sky since the designs of the high altitude devices are much lighter than turbines they promise to deliver much higher energy return (ERoEI) and lower cost electricity. Hence the opportunity is to access greater power using lighter and cheaper devices.

Department of EEE,MTIET,Palamaner

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ENERGY KITE

Fig 2: Wind Turbine Architecture is at a Plateau Ground based turbines have an operational wind speed range of approximately 3.5 to 25 m/s (these numbers will vary with turbine size and design). 3.5 m/s is the cut-in speed where the rotor is turning with sufficient force to drive the actuator (the generator) and 14 m/s the speed at which the turbine reaches its maximum power rating (Figure 5). Turbines may continue to operate beyond 14 m/s but will not produce any more power. And when it gets too windy at say 25 m/s the turbine needs to be shut down. These features define the all too familiar intermittency issue with wind. No wind – no power, too much wind – no power.

Department of EEE,MTIET,Palamaner

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ENERGY KITE

Fig 3:Wind speed versus power for a Typical turbine

Department of EEE,MTIET,Palamaner

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ENERGY KITE

CHAPTER-4 MAKANI QUDRACOPER KITE Makani is Hawaiian for wind and was founded in 2006 by Saul Griffith, Don Montague, and Corwin Hardham. Makani is interesting, partly because of their technology concept but also because long-term supporter, Google, acquired the company into Google-x in 2013 for an undisclosed sum rumoured to be $10 million. If you are a tech company committed to reducing CO2 emissions through renewable energy innovation, then high altitude wind power is at the top of most investor’s shopping list. Makani won the competition for the most avantgarde device that is a hybrid kite / glider (Figure 11). Makani have a simple but informative web site and several informative videos two of which are linked below. Make no mistake, this is a serious high tech venture aiming to capture industrial scale energy from high altitude winds. Whether or not it can be made to work is of course another question. You just have to watch the Makani kite whizzing round in giant circles to get a feel for what might go wrong

Fig 4.1:Makani Kite

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ENERGY KITE The Makani concept is a glider tethered to the ground and so when the wind blows across the aerofoil this produces lift that may keep the glider aloft indefinitely for so long as the wind blows strongly enough. At this point I need to introduce the concept of flying cross wind. To understand this you really need to watch the video linked above where you will see the Makani flying at high speed in giant circles in the sky transverse to the wind direction. Electricity is generated by the rotors linked to actuators and is transmitted to the ground via a conducting tether. It is conceptually easy to understand how flying faster will generate more power. And at this point it is worthwhile introducing a second equation that links flight speed to wind speed and aerodynamics.

Operation: For take off and landing ,the generators turns into propellers enabling the kite to hover like a helicopter flight speed = wind speed * aerodynamic efficiency The aerodynamic efficiency is the ratio of lift to drag of the aerofoil + tether rope. The drag of the Makani kite is also increased by rotors that will slow the flight speed and reduce power but it is the braking of the flight that at the same time produces power. The Makani system is comparable to the motion described by the tips of a turbine blade but has the advantage of being much lighter. And not being constrained by the height of the tower it can fly higher to access faster winds.

Some vital stats gleaned from the videos includes a 1 MW Makani will weigh about 1/10th of an equivalent turbine (10 tonnes versus 100 tonnes) and will cost about 1/2 as much. The flight speed is 100 mph (67 m/s)

Department of EEE,MTIET,Palamaner

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