Sustainable Energy Sources Nine Centuries Apart

Day 4: Winchester to Dartington

by Kelsey Johnson

Leaving Winchester, we stopped at the Southampton Geothermal Combined Heat and Power (CHP) Project, the Eling Tidal Mill and in the small town of Axminster as we traveled southwest to Dartington.  From these site visits we learned about renewable energy production methods and as well as history. 

Southampton City Geothermal & CHP Scheme

Similar to the geothermal power plants in Iceland, the Southampton CHP Project utilizes the Earth’s internal heat to heat and distribute fresh water.  Instead of supplying hot water to the whole country, Southampton distributes 80˚C water through a 20 km pipeline network.  Unlike Iceland, the geothermally heated water obtained from the 1.7 km deep hole is not sufficiently hot: it is 76˚C which is comparable to the normal geothermal gradient.  Freshwater heated from the geothermal brine requires an additional 4˚C heat input before distribution. Southampton CHP Plant also generates chilled water for air conditioning systems and distributes it through 5.5 km of pipeline.  Few buildings in the United Kingdom use air conditioning, so Southampton is able to charges three times the price for this commodity as heated water. 

The plant runs two gas-powered CHP engines that each produce 400 kW electricity.  During the high demand for heat during the winter months, the plant uses an additional engine: and 18-cylinder gas or diesel-powered modified standard marine liner engine that produces 5.7 MW heat and 5.7 MW electricity to sell to the national grid. 

In order to remain economically feasible, the plant needs to sell heat in addition to electricity.  Dependence on the plant deters some potential costumers: buildings that use Southampton’s heat often do not install their own boilers.  This makes them vulnerable to failures of the plant.  Fortunately for the plant, the city council requires building planners who choose not to utilize Southampton’s CHP to provide and explain reasons why it is economically infeasible for them to do so.  It is governmental support of this nature that keeps Southampton CHP in business.  As one of the four workers of the plant remarked, “What we need is more government intervention.” 

Eling Tidal Mill

This historically and currently active mill provided students with lessons in history, archeology, ecology and renewable energy.  Both river and tidal mills fill pond reservoirs that release water to turn a water wheel and thereby the millstones which grind wheat grains into flour.  River mills use ponds filled by river input, while tidal ponds fill from the opposite, downstream, side.  As the tide begins to recede, it pulls valve-like doors shut and thereby encloses a pond upstream. This captures water at a high tide elevation and creates potential for it to fall and turn the water wheel.  Historical documentation dates the Eling tidal mill as at least 900 years old, although mills have been refurbished and replaced on this site throughout history.  The mill was left to rot between 1946 and 1975 when it was bought eventually by the local council and restored. 

Per tide, the mill operates for five hours, yielding a total of 10 operating hours per day.  Tide cycles repeat every 12.5 hours, so mill operation slowly rotates around the clock.  Tidal mills are advantageous over river mills because they can operate year-round rather than seasonally.  Furthermore, tides are higher in the winter allowing greater production.  Water wheels rotate at a maximum speed of 15 RPM, whereas the millstone needs to rotate between 60 and 120 RPM to be effective.  Until the 19^th century when cast metal replaced them, a series of wooden gears transformed the rotational energy of the wheel to greater speeds required by the stone. 

The location of a mill and the class of the consumers historically dictated the type of rock of which millstones were constructed.  As a result, peasantry generally ate a diet solely of bread whose flour was ground from the cheapest millstone, sometimes even rock as weak as limestone!  Rock flour accompanied their wholemeal flour and served to abrade their teeth.  Fun facts: 1) most peasantry lost their teeth by the age of 30 and 2) archeologists can often determine an individual’s class by the degeneration and wearing down of their teeth. 

Travel to the Wytch Farm Oilfield, the only onshore oilfield in the UK, was aborted due to lack of time.

Axminster

This small town grew around a carpet factory which is no longer in operation.  Unfortunately for this study, the residences used by workers are neither still standing nor clustered together.  From talking to a local bookstore owner, we discovered that a better town in which to see residential communities of early industry exists in the nearby town of Colyton.

Kelsey Johnson is a Senior in Geosciences

CAUSE 2003 Home               Previous Dispatch         Dispatch Home        Next Dispatch

Last updated: Wednesday December 03, 2003