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Independent Renewable Energy

Consulting Engineers

Case Study - Castle Drogo                                Client: The National Trust

Castle Drogo is an early 20th century castle designed by Sir Edward Lutyens. The castle, originally the country home of the Drewe family, is now in the care of the National Trust. It stand high above the River Teign on the edge of Dartmoor. In 1929 two water turbine were installed on the river to provide electricity to the castle. The turbines ceased operation in the 1970s. A 400kW wood chip boiler was installed to provide heating in the castle in 2010. 
In 2015 the property team decided to review the energy use at the castle and became determined to see the hydro turbines reinstated and working once again. There were also concerns over the reliability of the biomass boiler and the amount of wood chip fuel it was consuming. 
Redcotec were asked to carry out a viability study into the feasibility of bringing the turbines back into use combined with changes to the biomass boiler such that excess electricity from the turbines could be used to reduce the quantity of wood chip being consumed. During the study the heat and electrical demands of the castle and other buildings were modelled. The original turbine manufacturers, who are still in existence, were brought in to assess the state of the turbines and provide "power curves" for their electrical output.  Using this data, combined with river flow data we were make a software model to simultaneously simulate the electricity generation, site electrical demand and castle heat demand on an hourly basis over a typical year.  The model allowed us to conclude that a viable scheme was possible whereby excess electricity from the turbines would be fed into the site heating demand, leaving only about 25% to be exported to the national grid.
Redcotec drew up an overall scheme design which was then separated into two performance specifications and tender packs, one for the hydro and one for the biomass. We provided technical advice during the contractor selection process and were retained as client's engineer for the installation of the biomass scheme.
The turbines were reinstated, including a new water intake screen. The 800m electrical cable from the turbine house to the castle was replaced and new M&E control equipment for the turbine house, grid connection point and biomass boiler house was installed. In the biomass boiler house the original 400kW boiler, that was not eligible for the RHI, was removed and replaced with two wood chip boilers, one of 200kW and one 90kW. These allow the varying heat demand to be met more efficiently. A new 2500l hot water accumulator was added to the biomass plant room with three 15kW immersion heaters and electrical control equipment design to use all the water turbines' excess electricity on each electrical phase. 
The turbine and biomass boilers were successfully commissioned and accredited for the FIT and RHI respectively. The schemes have healthy financial returns with the turbines also saving around 14 tonnes of CO2 emissions per year. The biomass boilers will continue to save over 100 tonnes of CO2 emissions. Moreover the property team are delighted to have the original turbines in their Lutyens turbine house productive and safe once more.
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