As you can imagine, I read a lot of pages and press releases about renewable energy. This morning I saw three articles that introduced the Windwheel, an architectural marvel that may be built in Rotterdam, Netherlands. While everyone is fascinated by its appearance (hey - I am too), the engineer in me wondered about the feasibility of its wind energy production.
No - it’s not the Eye of Sauron!
The Windwheel promises to be a stunning piece of architecture, featuring apartments, rotating cabins, a restaurant with spectacular views, and a hotel. It will also showcase a number of sustainable design practices, such as rainwater collection, passive solar design, waste-to-biogas conversion, and photovoltaic-thermal (PVT) modules. Most notably, however, is the feature for which the structure derives half of its name: wind power.
Electrostatic Wind Conversion
The windwheel will use the innovative Electrostatic Wind Energy Converter (EWICON) that was developed from research conducted at Delft University. EWICON was the subject of a 2008 doctoral dissertation that concluded that the system was capable of producing energy, but with very low efficiencies -- 1.7% at best, in the researcher’s experiments -- far less than the efficiency of a large wind turbine. Of course, the advantage of EWICON is that there’s no moving rotor, so it doesn’t cause vibration in the building. In short, they won’t be putting a giant rotating turbine in the center of the building, so let’s not compare the EWICON to a traditional turbine.
I do, however, wonder how much energy the EWICON could actually produce, and whether it would be more practical to use another source of renewable energy in the same space. So once again I headed for the back of an envelope (this one required two envelopes) to do some arithmetic. These are very round numbers based on averages.
The outer diameter of the Windwheel is 174m. Although they didn’t specify the inner diameter, I estimate it to be around 87m. That’s a cross-sectional area of just under 6000m2. Rotterdam’s average wind speed is 6m/s, so the total available power in the wind is 794 kW. At 1.7% efficiency, the EWICON would generate roughly 13.5 kW, or about 324 kWh/day.
Solar Equivalent
6000m2 would hold a 1500 kW (DC) photovoltaic array. Taking into account the average sunlight in Rotterdam and the fact that the panels would be tilted at 90o (vertical) so they don’t shade each other, such a system could produce an average of 2500 kWh per day - almost eight times the amount that the EWICON is capable of delivering. To make the EWICON competitive with solar PV, it would need to have an efficiency of at least 13%.
On the other hand, a wall of PV panels would block the view through the center of the Windwheel. Suppose we use one fourth the number of panels, tilt them at 45o and space them out so they don’t shade each other or impede much of the view. That system would produce about 1100 kWh/day - more than triple the EWICON's production. (If you're wondering why cutting the number of panels by a factor of four doesn't cut production by the same factor, it's because the panels will generate more power when tilted at 45o than they would at 90o.)
Is It Worthwhile?
As a tourist attraction, the developers expect the building to become profitable in ten years or less. At this point the Windwheel is a concept. The planners are searching for more partners, and have not yet made the costs public. That makes it difficult to determine the return on investment or the payback period of the EWICON. One thing that raises my eyebrow: Delft University, where the EWICON was developed, now says this on its web site:
“In March 2013 TU Delft and its partners unveiled the EWICON. Scientific data has shown that the principle works on a small scale. However there is no evidence that this principle is suitable for use on a commercial scale. At present TU Delft is not actively involved in the further development of the EWICON.”
Final Grade
The building’s architecture is eye-catching, to say the least. As a model of energy efficiency, passive heating and cooling, PVT, and water conservation, the Windwheel deserves accolades. I give it an A+ in those categories. The jury is still out on its wind power capabilities, so it gets an “incomplete” on that one. Given that Delft University has suspended its research on the EWICON, that “incomplete” seems likely to turn into an F. I realize that part of the Windwheel’s purpose is to be a demonstration of sustainable energy, but I’m not sure of the value in demonstrating a technology that’s not very pragmatic.
Maybe they should add more solar and change the name to “Sunwheel.”