P9 - Practical design principlessinotechcc.co.za/Courses/workshop/P9_-_Practical_des… · ·...

Copyright On Site Generation Ltd. May 2010Not to be copied without specific prior permission 1

Practical Design Principles

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• Practical Design – what if & handy hints

• High Head

• Low Head – existing mill site

• Low Head – existing weir

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The thing that makes hydropower difficult, and therefore interesting, is the need to make all of the aspects fit together while minimising cost and maximising output.


Practical Design

High Head - Multiple abstraction options

Speddoch H

Intake A

Turbine & powerhouse B

House

Turbine & powerhouse A

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Intake B

Intake C

Low-pressure pipe

Penstock (high-pressure)

powerhouse A

Practical Design Principles:

The design principles behind the development of a run-of-river hydropower scheme require us to balance multiple factors including;hydropower scheme require us to balance multiple factors, including;

maximise the head of water available – key for power

maximising the catchment area – to maximise the flow of water

available to generate power

minimising the length of the overall scheme – to keep costs down

getting the penstock onto easily traversed terrain as early as possible

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getting the penstock onto easily traversed terrain as early as possible

– to keep costs down

finding a suitable point of consumption or export for the electricity

identifying practical access for engineering construction

And some of these are in conflict


Practical Design

Practical Designg

• Placing a intake

Practical Designg

• Placing a intake


Practical Designg

• Placing a weir

Practical Designg

• Routing the penstock and placing the powerhouse


Practical Designg

• Resulting scheme

Head: 335m –200m = 135m

Catchment Area of 1.25km2

• Practical Design

High Head – Abstraction IssuesHigh Head Abstraction Issues

• Bench into the side of the gorge and run nearly at horizontal until escaping onto easier ground

• Use a natural pool instead of a weir if possible – issue is potentially having to cut a channel through bedrock

• Use an existing weir is there is a redundant one – for example a

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• Use an existing weir is there is a redundant one – for example a drinking water abstraction point

• Water will back up behind the weir – be careful how far back it goes and whether it overspills onto the land if the banks are low – may need to build retaining walls – ‘wing walls’


Practical Design

High Head – Abstraction Issues

• Make your own ‘wash-over’ screen – a version of a Coanda Screen – a sheet of steel with just the right size and number of holes drilled or punched in it• see http://www.dulas.org.uk/coanda/content/default.asp for design principles and examples

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• If access is poor (gorge) consider prefabricating the weir and dropping it into place with a crane

Practical Design

High Head – Penstock Issues

• Penstock above 100mm diameter comes in 6m and 12m lengths. If less than 100mm then it may be provided on 100m roles; therefore much easier to work with. HDPE is the most common material –good up to a pressure of 10bar or 100m of head

• In locating the Powerhouse consider the balance of penstock length versus transmission connection length

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• If the high level section of penstock is ‘flat-ish’ then low pressure pipe can be used until the drop reaches about 10 metre (1bar)

• Keep penstock as straight as possible – in 3 dimensions – to avoid the need for thrust blocks and to minimise frictional losses


Practical Design

High Head – Penstock Issues

• Crossing rivers & strems – consider going under rather than building a ‘bridge’ which would be exposed to flood and falling trees etc

• If using a channel, design it to mitigate for animals and make provision for sedimentation isolation and removal

• When penstock is not dropping constantly then there can be airlocks at high spots and sediment accumulations at low spots – vents and

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g p psediment removal valves need to be inserted which are maintenance risks

• A minimum gradient of about 1:150 over ‘flat’ terrain is recommended

Practical Design

High Head – Powerhouse Issues

• Powerhouse foundation has to be concrete to cope with the forces in the penstock and through the turbine

• Powerhouse – consider the installation and removal of the turbine and generator for maintenance:

• If really small then make the roof removable – that is, able to be lifted off

• If a bit bigger then add a roof joist and double doors

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• Powerhouse materials:• Breezeblock• Timber• GRP• Stone

Cost vs sympathetic appearance


Practical Design

Low Head – existing mill site:

• Use as much of the existing infrastructure as possible – good for Planning Dept and minimising cost

• If the wheel or the gearing still exists they can be used – just add a ! (N l i )

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generator! (Not always an option)

• Replacement wheels can be made to order.

Low Head – Existing Mill

• Weir exists• Lade exists • Mill-house exists

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Low Head – Existing Mill

• Remains of waterwheel• Tail-race exiting the mill-house

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Option are:a) Replacement waterwheel inside the buildingb) Put a new turbine under the mill-housec) Construct an Archimedes screw down the side of the mill-house

Low Head – existing weir

• For an Archimedes screw build off to the side of the weir if there is space – this will simplify the design since there would be no impact on the weir

• If you have to put it on to the weir keep it on the same side as the fish-pass – to minimise fish confusion, apparently!

• If the weir does not have a fish-pass there may make be

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• If the weir does not have a fish-pass there may make be provision of one a condition of the licence.

• Ensure all sensitivities of river users (especially anglers) are considered. Engage early!


Practical DesignPrinciples for Low Head – Existing WeirWeir

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Low Head – Existing Weir

Direction of river

flow

Inlet channel

10m

Wall

Existing sluice

Turbine House

• Location of Archimedes screw• Access for construction of base• Condition of the weir• Flow management• Electrical interconnection

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Originalwater power channel

Archimedes screw

Head = 3.5mPower = 43kW


Practical Design

Any Head

• Tailrace – slow the velocity of the water by widening the tailrace as it approaches the river. Fish will swim up the faster flow, so we need to make sure the river itself is fastest.

• Review turbine options to optimise efficiency (therefore

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• Review turbine options to optimise efficiency (therefore energy generation), desired lifetime, wear and cost.

Practical Design

Electrical

• Comply with interconnection, safety and protection requirements

• Off-grid – use electricity to power a storage radiator, hot-water tank or batteries

• Voltage drops along the length of transmission cable. 300 metres at Low Voltage is usually the limit – but can be

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stretched by using thicker conductors (cost increasing)

• Transmission power line can be overhead or buried – cost not too much different – issue more to do with depth of soil and presence of trees


Practical Design

Legislative & Regulatory

• Comply with all environmental and planning regulations

(Covered in later session)

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Extra Slides

Photos of construction do’s and don’ts!

Images provided by the Scottish Environment Protection Agency

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Size coffer dams appropriately.

Don’t impede downstream fish passage by putting lots of rocks in place to support an impoundment.

Where required put in place plunge pools and ensure the v-notch meets regulations. Ensure there is a ‘nappe’ ( b l )(see below)


Ensure pipe routes are deep enough to prevent being exposed, especially through watercourses.

Don’t allow clean water to cross a dirty access track.

Keep clean and dirty water separate.


Ensure pipe routes and access tracks have ac s a esufficient side drains, cross drains, cut-off drains, silt pits and use appropriate material where required e.g. type 1 aggregate.

Randomly placing a few straw bales does not catch silt from a discharge.


Prevent the foundations of your structurestructure from being inundated by water.

Put in place siltMitigationmeasureson both sides of a temporary bridgeIf necessary.

Upstream of the bridge.

Also, don’tPrevent fishpassage by

tti i lputting in placeboulders across a watercourse as Downstreamsupport for the bridge.

Downstream

of the bridge.


Fords –maintain entry and exit points.

Ensure silt mitigation measures are in place.

Design appropriately and then maintain silt mitigation measures.

Going… Going….. Gone!


Don’t build a pipe route through an area prone to landslides.

Try not to get silt in the river.

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