cordavillemillpondmicrohydrosite

Cordaville Power & Light MicroHydro site

Hopkinton, MA

This 3 acre mill pond was built to store power for the Cordaville Cotton and Woolen Mill in the village of Cordaville, a part of Southboro, Massachusetts. The mill pond straddles the border of Hopkinton and Southboro and is formed by an impoundment on the Sudbury River. The mill no longer exists but remnants of the mill foundations, sluice gates, tail race are still there. The former mill site is now a Massachusetts Bay Transportation Authority commuter rail parking lot. The dam is made of a combination of earth, fieldstone and cut granite and was built in 1825. In 1929, the mill was 4 stories tall and had an 85 kilowatt generator driven by a 15 inch vertical turbine manufactured by the James Leffel Co. Cordaville Auction catalog fom 1929.pdf.

The dam creates 9.4 feet of head (vertical drop). When the mill was in operation, the tail race was several hundred feet downstream which added an additional 4 feet of head.

According to the US Geological Survey, there are between 2 and 150 cubic feet per second flowing depending on the time of year. This converts to from between 56 liters/second to 4,200L/S. This was measured downstream about 2 miles. Here is the data: USGS Sudbury River data. The chart is a logarithmic scale. We have measured the flow ourselves by timing a small floating stick with a stopwatch and taking a cross section of the river. We measured the river at 18 feet wide and 3 feet deep in the center. A small floating stick took 25 seconds to go 50 feet. This was the first week of December and conservatively figuring the river cross section to be about 1/2 of the rectangle, that comes out to 27 CFS or 12,000 Gallons/Minute.

Here is the flow in December 06:

Unfortunately, the MBTA owns the spillway and gate house so we can't use this portion. Our property starts at the edge of the spillway (bottom of picture). Normally under Riparian law, we would have rights to the center of the river but this segment of the river was granted mill rights in 1798 by the Governor of Massachusetts and those rights ended up as the rail station.

Here is the flow in April 07:

Another view in April 07. Notice the pond is overtopping the dam.

Here is the view from our house. As you can see we are well above the dam and river so flooding is never a problem.

Here is a Google Earth picture with some markers on it (double click on any of the images to load them full size). We own the entire southern perimeter of the pond and river on the Hopkinton (right) side. This extends from the keystone bridge (not shown) to about 250 feet upstream from where the river enters the pond.

Here is a map of our property - lots 1G and 1F

landmap.pdf

According to the MA Office of Dam Safety, you don't actually have to own a dam to apply to generate electricity from it - go figure. The safety office considers this dam to be "non-jurisdictional". This means that because it holds back less than 18 acre feet of water and the head is less than 10 feet, they don't have to inspect it because the chance of catastrophic failure or damage if it did fail is very low. There are records of the dam last being inspected in 1975. The dam is # MA02872. Use this tool MA GIS dam viewer to view the dam after entering the dam number. MBTA map showing border.pdf.

After many dollars spent on wetlands biologists, surveyors, filing fees, registered mailings and conservation commission meetings, we finally managed to get approval for the installation of the LH1000 turbine as well as permission to construct a garage which will also house the balance of the system. We were also given permission to cut trees down that have grown on the dam.

There are grants available from the MA Technology Collaborative MTC web site link. MTC oversees the Renewable Energy Trust funded by the renewable energy tax everybody pays with their electric bill. The grants can be as much as as much as $4.00/watt but they require a grid tie. Until we can work out a joint agreement with the MBTA, we cannot get permission from F.E.R.C. to tie into the grid (the FERC low impact hydro approval process requires control of the entire perimeter of site).

MA laws cap net metering at 30kW if 3 phase and 15Kw for single phase generation. Even if the river flow could support all 59kW during peak flow there is no financial incentive to capture it - NStar gets it for free.

The approved plan is to siphon feed the turbine using a pipe over the dam.

RIPARIAN PROPRIETORS - Those who own the land bounding upon a water course, are so called.
Such riparian proprietor owns that portion of the bed of the river (not navigable) which is adjoining his land usque ad filum aquce; or, in other words, to the thread or central line of the stream. The proprietor of land adjoining a navigable river has an exclusive right to the soil, between high and low water marks, for the purpose of erecting wharves or buildings thereon.

TURBINES

The LH-1000 turbine from Energy Systems and Design LH1000IN.pdf is enough to almost fully power our house (about 850 watts at 950 GPM). It is possible to install an array of LH-1000's and enable and disable them depending on water flow. The LH-1000 currently costs $2,900 including the permanent magnet alternator and rectifiers. It requires another $5,000 in related equipment like batteries, cable, inverter, diversion controller and a dump load. This system integrates well with solar panels and is easily grid tied using a UL1741 approved inverter system like the Outback or Xantrex.

The Nautilus turbine nautilus spec.pdf is another low head turbine but cost per KW is much higher - about 3Kw for $10,600 plus the cost of the PMA or backdriven 3 phase motor . The company that makes it has a dead web site and the company that sells (ABS Alaska) it doesn't return my emails so there are several strikes against this one.

A Banki or cross flow turbine is one that I could actually build myself Home Built Banki but is only marginally appropriate for such a low head site. Imagine a squirrel cage blower where the water flows in at the top, passing through the blades, then falling through the center of the wheel and then striking the blades again on the bottom as it exits. This turbine is generally great for low head sites but a drawback is that you essentially have to subtract the wheel diameter from the head. With only 2.4 meters of head, that is a significant hit in efficiency. The Ossberger company in Germany makes a packaged cross flow turbine Ossberger link that would be a good fit. Their design includes a draft tube which increases efficiency in low head applications like ours.

A Kaplan turbine is ideal for our site. Kaplan turbines are "propeller" style - what most people envision a turbine to look like and are typically used in large hydro sites that have enormous flows but less head. I found one made in China that seems to be a made for a site like ours - large flow and small head on a smaller scale to fit our site. The cost is about 13K for 9Kw for a vertically mounted unit or 10K for a horizontal and includes the control electronics. It is a great deal but I have not yet seen it. These were designed and built for a rural electrification program funded by the Chinese government and thousands have been installed. Hopefully, it is built to last and is easy to service.

Below are pictures of the horizontal version. Water flows in the horizontal pipe, passes through the turbine, turns 90 degrees and exits in the vertical direction. The turbine drives the shaft through some bearings and the the red coupling which directly turns the generator.

Toshiba turbines start at 80K!