Archive for December, 2009

Wind Turbines at the Boston Museum of Science: Production Data

December 29, 2009

[NOTE:  since I wrote the post below I have received email from David Rabkin, the project leader at the MOS.  David has commented on the post (and I will continue the conversation in the comments below) but he would like it made clear that the sensors have not been calibrated and the data is not to be considered entirely reliable.  And I want to make it clear that I have no official connection or financial interest in the MOS or any of the turbine manufacturers.  In the weeks prior to my visit I attempted to contact Mr. Rabkin by phone and email to get a tour, but as I understand he has a lot on his plate, and I didn't hear back from him - and so what I write below are my personal observations and conjectures, with no inside information.  Now that we are in touch I hope to get the real scoop on what's up with the turbines.]

This morning I had a holiday-related package to deliver to my aunt Lucy, who works at the Boston Museum of Science, and being a wind turbine enthusiast I took advantage of the opportunity to check out the exhibit and turbine installation that the museum has installed. They have a cool display that shows what each turbine is doing in real time, and an interface where you can access cumulative data for each machine as well.

First, here’s a view of the installation from the north bank of the Charles river:

From left to right, the turbines are 1. Mariah’s 1.2kW Windspire, 2. Southwest Windpower’s 2.4kW Skystream, 3. Swift’s 1kW 5 blade turbine from the UK, 4. five Aerovironment 1kW “Architectural Wind” turbines, and 5. Proven’s 6kW unit.

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Two more rows clear

December 20, 2009

The usual drill – decent forecast for the weekend, AC on the wards both days: fire up the chainsaw.  Saturday Kauf, Kelsey, and I got a leisurely start (temp was in the single digits at daybreak) but put in a couple of stints before and after lunch, dropping two decent-sized crooked pine trees, a small poplar, and and a substantial red maple.  This completed the clearing for two more rows of apple trees at the foot of the orchard.  We stacked the brush for chipping, but left the logs in place, as the sky clouded up and it started to get dark.  Snow was supposed to come in overnight, but the ground was bare in the morning and hard-frozen – perfect skidding conditions.  So Dave and I fired up the Kubota with the Farmi winch, and yarked 20 or so logs out of the orchard and all the way to the field by the flagpole.  Most of what we took was saw timber; the stuff that was too big to chip but too crooked for the sawmill we dragged over by the pole barn and pushed into the big compost pile.  It eventually did start to snow, and long about 11:30 it started to get slippery, so we called it quits with about an inch of snow on the ground.  All but a couple of the saw logs are cleared out; there is still a bunch of short crooked stout stuff that will need to get loaded in the dump trailer and pitched over the bank, but the skidding is mostly done.  Unfortunately, the same ground conditions that made for ideal skidding will prevent us from pulling out the stumps before spring – can’t win ‘em all…

Wind turbines at the Museum of Science

December 6, 2009

It was a beautiful cold and breezy day in Cambridge, after the first ~1″ snowfall of the year, so I took the pups for a walk down by the river.  I remembered that the Boston Museum of Science had installed a bunch of small wind turbines on their roof, so I headed downstream to take a look.  On the north wing of the building they have installed a Windspire (a 1.2kW vertical axis giromill) and a Skystream (a 2.4 kW horizontal-axis 3 blade downwind turbine).   The central tower sports a Swift (a ~1kW 5 blade upwind machine with a hula-hoop at the OD of the rotor and two tails) and a row of ~5 small machines by Aerovironment (1kW, 5 blade machine designed for building parapets).  The south end of the building had a big Proven machine (3 blade downwind).

It was interesting to compare the behavior of the various turbines.  At this point I should mention that I was part of the team that designed the Skystream turbine, so I should not pretend to be entirely objective in the following discussion.  The Windspire was running continuously and cuts a dramatic figure; it’s reasonably attractive but the blades are straight and long, and they had a sort of strobing effect as they passed the central axis and flashed in the sun.  As I got closer it appeared as if a short segment of the airfoils was missing – there was an interruption in the airfoil between the bottom and the center, which does not appear in their literature.  The ring around the very top of the rotor was not spinning quite true, which made me wonder whether there had been some kind of mishap.  Between its size and the linear nature of its rotor, the Windspire is more visually imposing than the Skystream, despite sweeping less area and producing only 170kWh/month in a standard site as compared to the Skystream’s 400kWh/month (mfg specs in both cases).   The Aerovironment machines were spinning most of the time, though a good bit of the time it appeared as if they weren’t spinning fast enough to generate power, and they were yawing around more than the larger turbines – even in such an exposed site, the flow directly above a building parapet must be fairly turbulent, and the central tower behind the turbines couldn’t have helped.  One gets the feeling from the pricing (over $10/watt) and the product literature (which does not specify energy production or offer a power curve) that these are sculpture, not renewable energy equipment.  The Swift was the least impressive; it was turning some of the time but never appeared to attain sufficient speed to come out of stall and begin producing energy.  Perhaps it was turned off (or maybe burned out).  These machines are also in the sculpural category; online articles put the installed cost at $10-12k, which is about the same as a Skystream, which has 3 times the swept area.  Off by itself at the far end of the building, the big Proven ran continuously and smo0thly; of all the machines it nodded the least to artistic notions, but projected a reliable, stoutly engineered aura, with large, dense bolt patterns visible at the blade and hub attachments.  These machines are also not cheap, with a 2.5kW model running around $18,000 as best I can tell online.

All in all, my impression was that the Skystream and Proven machines were cranking solidly, the Mariah was big for its output and looked a little beat up, and the other machines were probably not delivering much (or any) energy.  Probably not coincidentally, this rank order is the same as the heights of the towers the machines were mounted on – the Skystream and Proven machines were on substantial pole towers, while the bottom of the Mariah machine was only ~10′ off the roof, and the other turbines weren’t even visually delineated from the structure.

Elsewhere in the urban wind department, I’ve noticed that there are two big machines on a parking garage over in Alston across the river from Harvard; they appear to be Bergey 10kW units, though they’ve got an aftermarket Harvard paint job.

One in 8 on food stamps; one in 4 kids

December 1, 2009

The NYT has a long article describing the rapid increase in utilization of food stamps in the US – one in four kids is currently on food stamps; one in 8 citizens overall.  This is depressing and distressing for a number of reasons.  First, in an absolute sense food is pretty cheap.  Most staples can still be had for under a dollar per pound; it takes maybe 1.5 pounds of staple food per person per day to feed a person; so two dollars per person per day or maybe $700 per person per year could do the job if necessary, and $1000 should be workable with effort.  If people are having a hard time coming up with 3 dollars a day for food, that suggests that the level of hardship in the country is pretty extreme.  It also suggests that the social contract has pretty much broken down – for reasons of age I have only dim recollections of the Cold War, but I seem to remember that the ability of our economy to feed our people was a basic bragging point that was held over the eastern bloc.

As I’ve noted here before, this sort of data triggers in crunchy types a reflexive instinct to go out and grow some food.  Unfortunately, (and also as discussed here), there are serious practical limitations that constrain the possible food-production impact of urban and even most sub-urban casual gardening.  To grow serious food you need land measured in acres, or at least solid fractions of an acre.  For instance, an acre of apple trees can produce 20,000lb of apples a year.  This is seems like a lot, but the calories in 20,000 lb of apples feeds a modest 6-7 people for a year.

The speed with which financial turmoil turns into large-scale food poverty got me thinking about a basic, fundamental problem with an affluent consumer society – in a system where the majority of the things that people buy are frivolous, luxury, or discretionary, it follows that most people will be employed doing things that nobody really needs.  And if the average person can halve their consumption without serious direct ill effect, the resulting system will be extremely vulnerable to failures of confidence.  All people have to do is cut back to the essentials they truly need, and they will automatically beggar their neighbors, and thus (by feedback) themselves. It’s ironic in a land of plenty, but it’s actually pretty easy to see how somebody whose training is in the decorative painting of fingernails could find themselves out of work and in danger of going hungry – and that seems to be basically what’s going on.  It might be reasonable advice for anybody in a frivolous field to quickly attain some kind of basic skills.


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