Direct Charcoal Ltd
HYDROPOWER AT
BROUGH BUSINESS CENTRE
PRE-FEASIBILITY STUDY
Oliver Paish
Jon Needle
April 2007
Project Ref: 7105
117 Hazelwood Rd, Duffield
Derbyshire DE56 4AA
Tel/Fax: 01332-842942
BROUGH
HYDROPOWER AT BROUGH
Pre-Feasibility Study
1. INTRODUCTION
The land occupied by Brough Business Park was previously a mill dating from the 18th Century. The mill
building and some of the workings, including the remains of an old turbine, are still in place, and the
owners wish to investigate the potential for generating hydro-electric power on the premises.
A site survey was completed by Oliver Paish and Jon Needle of Derwent Hydro on 1st February 2007.
The key observations and conclusions are summarised below.
2. SITE OBSERVATIONS
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Bradwell Brook passes along the western boundary of the business park, spilling over a concrete weir
3.8 metres wide and 3 metres fall. 6-inch stop-boards are placed on top of the weir to raise the
upstream level, removed in times of flood. Concrete spillways either side of the weir can take
additional flow as the level rises. The weir is shown in Figure 2.
The old turbine at the northern end of the original mill building (Figure 3) was fed by around
60 metres of open leat and 70 metres of buried concrete pipe. The leat has been completely filled in,
with a tennis court over much of it, but the concrete pipe is still in place under the car-park, running
from the end of the tennis court to the turbine, including one bend.
At the turbine location, the 1 metre concrete pipe discharged into an open concrete tank where the
flow was screened for debris. It appears that the pipe ran partially filled to a depth of around 700mm.
A hole in the base of the tank allowed the water to fall vertically down through a 3 foot steel pipe to
reach the turbine at the bottom of the wheelpit. The pipe is still in place and completely filled with
gravel. The wheelpit is 1.85m wide by 2.5m from back to front.
The turbine was a vertical-shaft open-flume early reaction turbine dating from the late 19th Century.
Only part of the machine still remains.
The flow exited the wheelpit through an arched culvert which runs 8 metres back to the river. This is
in good condition, but substantially filled with silt.
The depth of water in the wheelpit was measured at 700 mm.
In general, the inlet pipe, screening tank and turbine enclosure are still in robust condition, and
provide a good basis for a new, modern installation at this point.
The incoming 3-phase low-voltage line enters the site adjacent to the turbine, where it converts from
pole-mounted to an underground line to the switchboard on the opposite side of the car park. A new
generator may be permitted to feed directly into the pole-mounted line, but this requires consultation
with the electricity company.
3. HEAD & FLOW
3.1 Head
The gross head was measured on the day of the survey to be 4.3 metres in the old wheelpit. There will
inevitably be some losses through the trashrack, turbine inlet and tailrace and for the purposes of this
report, a design head of 4.1m will be assumed.
The head at the weir was 3.15m, allowing a net head of 2.8m to be considered at this location.
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3.2 Flow
The flow on the day of the survey was estimated at the weir to be 650 litres/sec. The client reported that
the Brook sustains a consistent flow, and that the observed flow conditions were 'typical' for the winter.
Bradwell Brook is not gauged by the Environment Agency. The HydrA hydraulic model from the
Institute of Hydrology was run for this catchment, with estimated catchment area of 13.5 km2 and
average rainfall of 1150 mm per year. The key parameters are as follows:
Qmean
Q95
Q50
Q10
Average Flow
Flow exceeded 95% of the time
Median Flow – flow exceeded 50% of the time
Flow exceeded 10% of the time
310
75
220
560
litres/sec
litres/sec
litres/sec
litres/sec
The natural flow in the brook is substantially increased by the outflow from the sewage works
downstream of Bradwell. This processes the sewage from Castleton and the surrounding area and Severn
Trent Water should be able to provide an indication of the range of flows discharged into the brook at this
point.
Some flow (the 'compensation flow') would need to be left over the weir to maintain the ecology in that
stretch, so the flow available for hydropower will be reduced by perhaps 50 litres/sec.
The maximum power output that can be fed into a three-phase connection using the industry’s G83
standard1 is 11.1kW. This would imply a design flow of 450 litres/sec on 4.1m head. In the absence of
more detailed flow data, we would proposes this figure as the provisional turbine design flow for the
scheme.
4. SCHEME OPTIONS
There are two locations where a new turbine could be placed:
1) in parallel with the weir
2) in place of the old turbine.
1. In principle, it would be possible to implement a new installation on the far side of the weir. This
would involve excavating a new intake upstream of the weir in order to direct flow into a pipe
which would run some 20 metres to a turbine located low down on the river bank downstream of
the weir.
The main disadvantages with this option are:
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This location has 30 % less head than the old turbine pit, which translates into 30% less
power and energy, plus the need for a bigger turbine.
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Implementing the civil works on this side of the river (intake, pipeline, powerhouse,
discharge sump) would not be straightforward. The existing works at this end of the weir
appear to be unstable and construction firms generally do not like working this close to a
steep-sided river bank.
Some land would be required from the owner of the field backing on to the river, both for the
temporary works and the powerhouse, plus future access for maintenance of the scheme.
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1
G83 allows pre-approved control systems to be used to connect electrical generators into the local network without
consulting the local electricity company.
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2. Overall, we believe that restoring the water supply to the old turbine enclosure, so benefiting
from the extra head and making use of the existing infra-structure, will lead to a more
economically attractive scheme, as follows.
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The intake at the bend in the brook will need to be restored, so as to direct the flow into a new
pipeline. If the pipe is set low enough to be run full, it only needs to be 600 mm diameter.
There is space to run this pipeline along the edge of the tennis court. The main difficulty will
be in connecting this pipe to the existing 1 metre concrete pipe, which may require two 90
degree bends to pass the pipe around the back of the tennis court. However, laying this
length of pipe is likely to be less risky and less costly than the riverside works required for
Option 1.
4.1 Turbine
The only type of turbine likely to be cost-effective for this head and flow is a crossflow turbine. This is a
variable-flow machine which, in its twin-cell version, can still operate at 10% of design flow. It will run
sufficiently fast to allow a low-cost belt-drive to connect to the generator.
A crossflow turbine is self-cleaning with regard to ‘soft’ debris such as leaves, but requires a reasonably
fine screen to keep out twigs and stones of a size which might jam between the runner blades.
Low-cost crossflow turbines are available from Valley Hydro in Cornwall (see Figure 1), but on long lead
times. There are more robust and efficient machines from Ossberger and WKV in Germany, which we
would generally recommend as being worth the greater expense.
Figure 1 Valley Hydro crossflow turbine installation, plus schematic illustration
A fine-meshed screen will be required upstream of the turbine to prevent the ingress of both fish and
debris. The screen itself could be a fixed bar screen, which would need to be raked at least twice daily, or
be fitted with a more complex automatic raking system, which we would generally recommend for
ensuring the efficient output of the system.
Control System
The control system will enable fully automatic operation of the turbine. It continuously monitors the
headwater level, and will open or close the turbine valve in small adjustments, according to whether the
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upstream level is rising or falling. When there is insufficient water to generate power, the turbine will
shut down completely, and will automatically restart when the river is replenished.
5. OUTPUT & REVENUE
A turbine designed for 4.1 m net head and 450 litres/sec design flow would generate a peak electrical
output of around 11kW.
Depending on the actual availability of flow (the sewage discharge being the main unknown) , the
electricity generated over one year could be expected to be in the range 50-70,000 kWh/year.
The system would run ‘in parallel’ with the local network, i.e. any power generated by the turbine would
first be consumed in the property (reducing the electricity that would otherwise be bought in) and any
excess power would pass back through the grid through a meter, and could be sold to an electricity
company.
Depending on what proportion of the power could be consumed on site, the average value of the
electricity generated by the scheme would be in the range 9-11 p/kWh, including the value of the
Renewable Obligation Certificates 2. Hence an annual value of £5000-£7000 per year (increasing with
electricity prices).
It may be possible to strike a deal with one of the electricity companies (e.g. EDF or npower) for them to
subtract the total energy exported by the hydro-scheme from the total energy imported by the business
park. This would raise the value of the power to 12-13 p/kWh.
6. COSTS
The initial broad-brush estimates for the electro-mechanical equipment and installation costs would be as
follows:
Item
Valley Hydro Turbine and belt-drive +guard
Generator, control panel and cabling
Intake screen and automatic cleaner
Detailed design and engineering
Workshop assembly, installation and commissioning
Transport and contingency
TOTAL ex VAT @5%
Option
WKV or Ossberger turbine
£
12500
6000
6500
4500
6500
2000
£38000
+10,000
In addition, work would be required for:
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Constructing the intake works at the river.
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Procuring and burying 60m or so of 600mm drainage pipe and forming a connection with the existing
concrete pipe.
Removing the old turbine and down-pipe.
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2
Electricity generated from renewable sources can be used to obtain Renewables Obligation Certificates (ROCs)
which can then be sold to one of the electricity companies. They need the ROCs in order to prove they are meeting
the governments targets for renewable energy. ROCs have a market value in the range 3.5p – 4.5p per kWh which
will vary over time depending on how well these companies are doing in meeting their targets.
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Remedial works to the turbine enclosure, including the installation of a new floor just above
maximum downstream flood level.
Running the power cable to the network connection.
Gaining planning and licensing permissions, as appropriate.
7. NEXT STEPS
A formal license from the Environment Agency is likely to be required, plus planning permission. The
main environmental criteria to be satisfied would involve fish-protection and the amount of water to be
taken in dry conditions
The logical next steps to develop the scheme would be:
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To obtain discharge figures for the treatment works from Severn-Trent Water.
To have an informal discussion with the Environment Agency to assess their viewpoint
Commission the full scheme design to present to the EA and local planners and in order to define
accurately the civil works requirements and costs.
Obtain firm quotes for the cost of the electro-mechanical equipment.
Prepare formal applications for the EA and planners.
Derwent Hydro could offer to undertake these steps, and we would recommend a budget allowance of
£3500.
Figure 2 Main Weir
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Figure 3 Old turbine pit
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