The State of Residential Wind Turbines

So my post yesterday about solar shingles got me thinking about roof-mounted wind turbines and what it might look like for me to install one on my house.  So, I decided to do a little bit of research on the topic today.  If you are interested in the topic, you should probably check out Bergey's Wind School first before you read more below.  If you really want to get into it, don't read anything below.  Rather go to Home Power Magazine and start your research there.  There is plenty of information on the internet to decide if you should learn more - which is to say you won't be able to conclude that you should or shouldn't buy a turbine without ultimately talking to the manufacturer, or better, talking to the installation company.  The balance of system and electrical integration costs are likely to be non-trival and need to be considered - its not just the per kW cost of the turbine!

Horizontal Turbines

These are the ones you think of when somebody says windmill or wind turbine.  The blades spin around a horizontally mounted axis, like an aircraft propeller.  Standard fare that has been around for some time and is reasonably mature (I think) in its design and engineering.  Typically, these guys use permanent magnet motors and have no gearing.  Simple is better with respect to reliability.  Some are shrouded like the TAM Energy / Honeywell turbine.

Vertical Turbines

These are not really that new, but not often used in utility scale machines.  However, from what I can tell, there does seem to be a fair bit of interest in using them in roof-mounted applications.  Unfortunately (though unsurprisingly), these appear to suffer from the same issues as the horizontal turbines with respect to average wind speed.  See below in Take-Aways.

Mounting

Roof Mounted

Two different types of roofs are dealt with - flat (common for commercial buildings) and peaked (common for residential).    Both mounting systems look quite reasonable and well-engineered, but what I can't find any information about acoustic coupling with the building.  Bergey cautions against roof mounting for this reason, but I don't know really how good or bad it can be.  TAM Energy suggests (and includes in the sale of their turbines) a "roof box" that is added on top of the original roof.  Perhaps this provides some amount of decoupling between the turbine and the roof?

Pole Mounted

I think that this is most typical of all wind turbine applications.  There are two options here: guy-wired setup and a self-standing pole.  The latter is more expensive, but doesn't require as much flexibility with your space.

Take-Aways

There is probably nothing here for me.  Bergey recommends not pursuing if you have less than 1 acre and 6+ mph average wind speeds.  I have neither.  Just shy of 1 acre in the suburbia surrounding DC.  The 30 meter (above the surface) wind speed map provided by the government suggests that I have between 4 and 4.5 mph average wind speed.  Though I do pay more than 10¢ per kWh for my electricity, its not much more.  My payback period is probably quite high and would be a riskier proposition than just continuing to purchase from the utility.  A vertical turbine manufacturer, Urwind, suggests that at 4.5 mph average wind speed, their product would produce very little output. 

Low speed performance turbine will have to improve substantially, I'm guessing, before it will make sense for me to go down this route.  This is not impossible.  One of the big achievements of utility-scale wind turbines over the last decade has been to raise capacity factors from the high 20% range to the low 40's.  And that is after choosing the best wind sites, previously.  The same could potentially change here, though the pace of change is likely to be slower given the relatively small market size for residential wind turbines.

Though the above sites suggest that measuring wind speeds at your residence for a year is likely to be overkill (expensive and can be modeled well), I think it would be interesting to measure over the course of the year.  Then, I'd cross the wind-speed duration curve with the power output curve of various wind turbines to see what opportunity to offset electricity usage that I'd have.

I think that I'd be most inclined to go with the TAM Energy / Honeywell roof-mounted turbine if I was going to do anything.  They start producing power at relatively low wind speeds - 2 mph.  I have space on my roof, so I'd spring for 2 - which would cost me $30,000.  They claim that I'd be offsetting about 2000 kWh per year for each turbine.  For me that equates to roughly (10.1¢/kWh * 4,000 kWh) = $404/year savings.  That means I'd need 75 years to pay off the investment.  The design lifetime of the device is only 20 years.  This won't really work - even if the output was double the projected output for an average site.  So much for my investment in wind power, at least for now.

To make it work, I would need to see a 7 year payback.  If the performance of the turbine can't be improved, there is really just one way to make this work: reduce the cost of the two turbines by ~90% to $2,828.  Not likely to happen any time soon.  Probably sub-scale for the balance of plant portion, too.  Which means, I think that the turbines need to improve before this all goes around.

Further Research

I have by no means exhausted the research areas for this topic.  If the turbine technology improves meaningfully, I think each of the following areas would require more thought and study:

• What are local zoning laws (if any) that need to be complied with?  Is it any different than installing an antenna on your roof?
• What is reasonable to assume the acoustic signature is for a roof-mounted turbine?
• How much should it cost to install?
• What are the additional components required to integrate into one's home electrical system?
• How would Dominion (my local utility) deal with my power costs?  How much would be truly offset?

Next up: Residential solar.  Like I have noted before, I'd really like to have a solar-driven stirling engine.  Or rather, a solar/propane CHP system.