Low head pico hydro off-grid networks

Panel Presentation: Energy Author: Sam Williamson Institution: University of Bristol

Low head pico hydro off

+Department of Electrical and Electronic Engineering, University of Bristol

*Department of Mechanical Engineering, University of Br

Abstract

This paper describes the initial stages of a research project that investigates the development of a pico hydro poweredoff-grid electrical network. The grid is supplied by water turbines that operate within a head range of 0.5generate up to 1kW of electrical power. Using a quantitative and qualitative selection criteria approach, a Turgo turbine ischosen for further study based on exhibiting the highest potential to satisfy the project requirements among 13 potentialturbine types available in operation. The Turgo turbine is modelled and a test rig is built to validate the system model.Future work will include the development of a plug and play controller to connect a turbine to an off

Keywords: Pico Hydro, Low Head, Turgo, Off

Introduction

There is a distinct link between poverty and access to modern energy sources. With electricity, people are able to improvetheir productivity and their income through better use of their time, which allows them tIn urban areas of developing countries, the percentage of the population with access to electricity is high, due to the lowcost of connection to the grid. In rural locations, however, access is limited due to the high codensity population centres. Therefore localised off

Figure 2 shows a study published by the World Bankgeneration methods. It should be noted that taking into account the net present value would narrow the gap betweendiesel generator and pico hydro. Nevertheless, the data clearly shows that pico hydro systems represent the most costeffective way of generating off-grid electricity.

Figure 2 – Projected operating cost in 2015 for electrical energy generators under 5kW

All renewable technologies require a particular source of energy to be available. This restricts the use of picolocations in close proximity to rivers, which reduces the potential sites significantly compared toMany pico hydro installations are 1kW or less, which is not normally able to support income generation activities. Severallow head pico hydro turbines can be installed along a river and, if connected together, then the combined powerthe units can be used to for income generation activities during the day and domestic loads in the evenings. This picohydro network would also provide redundancy in the system, allowing for failure of a generating unit or maintenance ofone or more units without interruption to the electricity supply.

Pico-hydro sites are divided up into high head and low head. High head sites are normally considered to be the most costeffective, with a small amount of water being consumed by the turbine, and so

0

Pico Hydro

Wind

PV Wind Hybrid

Solar PV

Diesel/Gasoline

Generator

Generator Type

EWB-UK National Research & Education Conference 2011

Low head pico hydro off-grid networks Sam Williamson

+

Supervisors: B.H Stark+, J.D.Booker*

Department of Electrical and Electronic Engineering, University of Bristol

*Department of Mechanical Engineering, University of Bristol

This paper describes the initial stages of a research project that investigates the development of a pico hydro poweredgrid electrical network. The grid is supplied by water turbines that operate within a head range of 0.5

generate up to 1kW of electrical power. Using a quantitative and qualitative selection criteria approach, a Turgo turbine ischosen for further study based on exhibiting the highest potential to satisfy the project requirements among 13 potential

ypes available in operation. The Turgo turbine is modelled and a test rig is built to validate the system model.Future work will include the development of a plug and play controller to connect a turbine to an off

Head, Turgo, Off-Grid Network

There is a distinct link between poverty and access to modern energy sources. With electricity, people are able to improvetheir productivity and their income through better use of their time, which allows them to raise themselves out of poverty.In urban areas of developing countries, the percentage of the population with access to electricity is high, due to the lowcost of connection to the grid. In rural locations, however, access is limited due to the high cost of extending grids to lowdensity population centres. Therefore localised off-grid electrification is an attractive alternative for provision of electricity.

shows a study published by the World Bank [1] detailing the projected life-time cost of five electrical energygeneration methods. It should be noted that taking into account the net present value would narrow the gap between

dro. Nevertheless, the data clearly shows that pico hydro systems represent the most costgrid electricity.

Projected operating cost in 2015 for electrical energy generators under 5kW [1].

All renewable technologies require a particular source of energy to be available. This restricts the use of picolocations in close proximity to rivers, which reduces the potential sites significantly compared toMany pico hydro installations are 1kW or less, which is not normally able to support income generation activities. Severallow head pico hydro turbines can be installed along a river and, if connected together, then the combined powerthe units can be used to for income generation activities during the day and domestic loads in the evenings. This picohydro network would also provide redundancy in the system, allowing for failure of a generating unit or maintenance of

re units without interruption to the electricity supply.

hydro sites are divided up into high head and low head. High head sites are normally considered to be the most costeffective, with a small amount of water being consumed by the turbine, and so smaller and less expensive equipment is

20 40 60

US Cent/kWh

UK National Research & Education Conference 2011 ‘Our Global Future’

4th March 2011

33

Department of Electrical and Electronic Engineering, University of Bristol

This paper describes the initial stages of a research project that investigates the development of a pico hydro powered grid electrical network. The grid is supplied by water turbines that operate within a head range of 0.5 - 3.5m, and

generate up to 1kW of electrical power. Using a quantitative and qualitative selection criteria approach, a Turgo turbine is chosen for further study based on exhibiting the highest potential to satisfy the project requirements among 13 potential

ypes available in operation. The Turgo turbine is modelled and a test rig is built to validate the system model. Future work will include the development of a plug and play controller to connect a turbine to an off-grid network.

There is a distinct link between poverty and access to modern energy sources. With electricity, people are able to improve o raise themselves out of poverty.

In urban areas of developing countries, the percentage of the population with access to electricity is high, due to the low st of extending grids to low

grid electrification is an attractive alternative for provision of electricity.

time cost of five electrical energy generation methods. It should be noted that taking into account the net present value would narrow the gap between

dro. Nevertheless, the data clearly shows that pico hydro systems represent the most cost-

All renewable technologies require a particular source of energy to be available. This restricts the use of pico-hydro to locations in close proximity to rivers, which reduces the potential sites significantly compared to solar or wind power. Many pico hydro installations are 1kW or less, which is not normally able to support income generation activities. Several low head pico hydro turbines can be installed along a river and, if connected together, then the combined power from all the units can be used to for income generation activities during the day and domestic loads in the evenings. This pico hydro network would also provide redundancy in the system, allowing for failure of a generating unit or maintenance of

hydro sites are divided up into high head and low head. High head sites are normally considered to be the most cost smaller and less expensive equipment is

80


required. High head systems require a large drop of water, and therefore suited to very hilly or mountainous regions,which are often a long distance from any populated areas. By contrast, low head sites consume a laand therefore require a larger and more expensive turbine. As the site needs just a few metres drop, suitable locationsare far more numerous, and more likely to be closer to populated regionsthis research.

Application and Specification for Low Head Pico Hydro Off

Figure 3 shows Bhanbhane village in central Nepal. The villagers currently operate five proalong a 3km length of river, each supplying between 10 and 15 households. There is no distinct load centre, with thehouseholds and businesses spread geographically across the transmission area. The current sites power only doapplications, such as lighting, radios, televisions and mobile phone charging. There is the potential for four further sitesthe locality.

Figure 3 – Potential implementation site for low head pico hydro off

Using the pico hydro off-grid network concept, both the old and new sites can utilise a single turbine design able tooperate over a range of flow rates and heads. At each location, one or more turbines are inand flow availability at the site, which can each produce a nominal power of 1kW at rated flow and head. For example, atsite 8 there is enough head to cascade 3 units vertically and enough flow to place 2 units sideconnected to form a grid with a maximum power generating capacity of 17kW. The increased power will be able tosupport income generation activities, such as grain processing, a local wood workshop and saw mill and improvedirrigation for fields. The local school can also use the power to provide computers for students and villagers.


required. High head systems require a large drop of water, and therefore suited to very hilly or mountainous regions,which are often a long distance from any populated areas. By contrast, low head sites consume a laand therefore require a larger and more expensive turbine. As the site needs just a few metres drop, suitable locationsare far more numerous, and more likely to be closer to populated regions [2]. These low head systems are the subject of

Application and Specification for Low Head Pico Hydro Off-Grid Network

shows Bhanbhane village in central Nepal. The villagers currently operate five propeller turbines at four sitesalong a 3km length of river, each supplying between 10 and 15 households. There is no distinct load centre, with thehouseholds and businesses spread geographically across the transmission area. The current sites power only doapplications, such as lighting, radios, televisions and mobile phone charging. There is the potential for four further sites

Potential implementation site for low head pico hydro off-grid network in Nepal

grid network concept, both the old and new sites can utilise a single turbine design able tooperate over a range of flow rates and heads. At each location, one or more turbines are installed, depending on the headand flow availability at the site, which can each produce a nominal power of 1kW at rated flow and head. For example, atsite 8 there is enough head to cascade 3 units vertically and enough flow to place 2 units side-connected to form a grid with a maximum power generating capacity of 17kW. The increased power will be able tosupport income generation activities, such as grain processing, a local wood workshop and saw mill and improved

for fields. The local school can also use the power to provide computers for students and villagers.


4th March 2011

34

required. High head systems require a large drop of water, and therefore suited to very hilly or mountainous regions, which are often a long distance from any populated areas. By contrast, low head sites consume a larger quantity of water and therefore require a larger and more expensive turbine. As the site needs just a few metres drop, suitable locations

low head systems are the subject of

peller turbines at four sites along a 3km length of river, each supplying between 10 and 15 households. There is no distinct load centre, with the households and businesses spread geographically across the transmission area. The current sites power only domestic applications, such as lighting, radios, televisions and mobile phone charging. There is the potential for four further sites in

rk in Nepal [3].

grid network concept, both the old and new sites can utilise a single turbine design able to stalled, depending on the head

and flow availability at the site, which can each produce a nominal power of 1kW at rated flow and head. For example, at -by-side. All the turbines are

connected to form a grid with a maximum power generating capacity of 17kW. The increased power will be able to support income generation activities, such as grain processing, a local wood workshop and saw mill and improved

for fields. The local school can also use the power to provide computers for students and villagers.


The specification for the pico hydro system was derived from the original project brief through discussions with project stakeholders. The key attributes the chosen pico hydro system is to possess are as follows:

• Power: 1kW generation at 3.5m head;• Head range: 0.5 – 3.5m; • High reliability; • Modular design allowing unskilled labour to diagnose faults and replace modules as required;• Plug-and-play capability of a generator unit to form a network;• Low cost.

It is initially assumed converter between the chosen turbine and the grid interface is approximately 75% efficient, therefore the turbine will have to generate 1.3kW at 3.5m head.

Turbine Selection

Table 1 summarises the 7 main turbine types used over the different head ranges

.

Turbine Type High (>50m)

Impulse Pelton, Turgo,

Multi

Reaction

Table 1 - Widely accepted use of turbines at head ranges

This suggests that the most suitable type for the above specification woucommercially available turbines at low heads for pico hydro are propeller turbines. However, high head impulse turbines can be used at low heads [4], but there are drawbacks with the sare alternative selection criteria that are important, such as cost, ease of manufacture or maintainability, these turbines may become more appropriate for the situation. To include these criteria here,quantitative and qualitative analyses to select a turbine type

Following this methodology, a number of priority criteria (type of criteria given in brackets) were devised:

• Portability (Quantitative) – How easy is the unit to transport in an area of limited transport infrastructure? Assessed using a power density function.

• Rated Flow Efficiency (Quantitative) • Part Flow Efficiency (Qualitative) • Civil Works (Qualitative) – How much civil works need to be constructed to realise the system?• Modularity (Qualitative) – What modules can the system be divi

identification and servicing? • Maintainability and Serviceability (Qualitative)

The scores from each of the analyses were combined at each of the differenexample set of combined results at 2.5m head is shown in


The specification for the pico hydro system was derived from the original project brief through discussions with project the chosen pico hydro system is to possess are as follows:

Power: 1kW generation at 3.5m head;

Modular design allowing unskilled labour to diagnose faults and replace modules as required;f a generator unit to form a network;

It is initially assumed converter between the chosen turbine and the grid interface is approximately 75% efficient, therefore the turbine will have to generate 1.3kW at 3.5m head.

summarises the 7 main turbine types used over the different head ranges

Head

High (>50m) Medium (10-50m)

Pelton, Turgo,

Multi-jet Pelton

Crossflow, Turgo, Multi-jet Pelton

Francis

Widely accepted use of turbines at head ranges [2].

This suggests that the most suitable type for the above specification would be a propeller turbine, and indeed most commercially available turbines at low heads for pico hydro are propeller turbines. However, high head impulse turbines

, but there are drawbacks with the size of the machine and speed of rotation. Where there are alternative selection criteria that are important, such as cost, ease of manufacture or maintainability, these turbines may become more appropriate for the situation. To include these criteria here, a selection method was devised using quantitative and qualitative analyses to select a turbine type [5].


How easy is the unit to transport in an area of limited transport infrastructure? Assessed using a power density function. Rated Flow Efficiency (Quantitative) – What is the efficiency of the system at its rated conditions?

iency (Qualitative) – How does the system efficiency change when the flow rate is less than rated?How much civil works need to be constructed to realise the system?What modules can the system be divided up into to aid transportation, fault

Maintainability and Serviceability (Qualitative) – How easy is it for unskilled labour to maintain the system?

The scores from each of the analyses were combined at each of the different heads within the range of 0.5m to 3.5m. An example set of combined results at 2.5m head is shown in Figure 4.


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The specification for the pico hydro system was derived from the original project brief through discussions with project

Modular design allowing unskilled labour to diagnose faults and replace modules as required;

It is initially assumed converter between the chosen turbine and the grid interface is approximately 75% efficient,

Low (<10m)

Crossflow

Francis, Propeller, Kaplan

ld be a propeller turbine, and indeed most commercially available turbines at low heads for pico hydro are propeller turbines. However, high head impulse turbines

ize of the machine and speed of rotation. Where there are alternative selection criteria that are important, such as cost, ease of manufacture or maintainability, these turbines

a selection method was devised using


How easy is the unit to transport in an area of limited transport infrastructure?

What is the efficiency of the system at its rated conditions? How does the system efficiency change when the flow rate is less than rated?

How much civil works need to be constructed to realise the system? ded up into to aid transportation, fault

How easy is it for unskilled labour to maintain the system?

t heads within the range of 0.5m to 3.5m. An


Figure 4 – Scores from combined quantitative and qualitative analysis at 2.

Overall, the propeller turbine with a draft tube gave the best score in a head range from 0.5m to 1.5m, and the single jet Turgo turbine was the best between 1.5m and 3.5m. The propeller turbine has been usedmany commercially available products. However, the single jet Turgo turbine has been shown to offer an alternative solution at low heads, so this turbine-based solution will be investigated further. Turgo turbines are not nothese low heads due to a low rotational speed and large size. However, when alternative criteria, such as serviceability or part flow efficiency are used then the Turgo turbine is shown to be a suitable solution.

Modelling

The initial modelling for the Turgo turbine has been carried out using velocity diagrams and the torque calculated using the change in momentum of the water jet shown in Figure 5. The torque decreases from a high stallshows a preferred rotational speed of around 300 rpm where the system generates most power.

Figure 5 – Turgo power and torque curves from initial modelling of full size turbine.

0.0

0.1

Breastshot Waterwheel

Undershot Waterwheel

Overshot Waterwheel

Crossflow

Archimedes Screw

Single Jet Pelton

Multiple Jet Pelton

Multiple Jet Turgo

Francis (no DT)

Propeller (no DT)

Francis (with DT)

Propeller (with DT)

Single Jet Turgo

Turbine Type

0

200

400

600

800

1000

1200

1400

0 100

Power (W)

Power

Torque

Turgo Schematic

JetTurgo

cup


Scores from combined quantitative and qualitative analysis at 2.5m head for a 1.3kW turbine (DT = Draft Tube).

Overall, the propeller turbine with a draft tube gave the best score in a head range from 0.5m to 1.5m, and the single jet Turgo turbine was the best between 1.5m and 3.5m. The propeller turbine has been used extensively at low heads, with many commercially available products. However, the single jet Turgo turbine has been shown to offer an alternative

based solution will be investigated further. Turgo turbines are not nothese low heads due to a low rotational speed and large size. However, when alternative criteria, such as serviceability or part flow efficiency are used then the Turgo turbine is shown to be a suitable solution.

ling for the Turgo turbine has been carried out using velocity diagrams and the torque calculated using the change in momentum of the water jet [6]. This model provides the torque-speed and power

. The torque decreases from a high stall-torque to a low free running torque, whereas the power curve shows a preferred rotational speed of around 300 rpm where the system generates most power.

Turgo power and torque curves from initial modelling of full size turbine.

0.1

0.2

0.3

0.4

0.5

0.6

Score

200 300 400 500

Rotational Speed (RPM)

Max. Power: 1326 W

Speed: 304 rpm

(3.5m Head, Ø87mm

Nozzle, Ø435mm wheel)

Turgo Schematic

Direction

of rotation


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5m head for a 1.3kW turbine (DT = Draft

Overall, the propeller turbine with a draft tube gave the best score in a head range from 0.5m to 1.5m, and the single jet extensively at low heads, with

many commercially available products. However, the single jet Turgo turbine has been shown to offer an alternative based solution will be investigated further. Turgo turbines are not normally used at

these low heads due to a low rotational speed and large size. However, when alternative criteria, such as serviceability or

ling for the Turgo turbine has been carried out using velocity diagrams and the torque calculated using speed and power-speed characteristics, as

torque to a low free running torque, whereas the power curve shows a preferred rotational speed of around 300 rpm where the system generates most power.

Turgo power and torque curves from initial modelling of full size turbine.

0.6

0.7

0.8

500 600

0

10

20

30

40

50

60

70

80

90

Torque (Nm)

Max. Power: 1326 W

Speed: 304 rpm

(3.5m Head, Ø87mm

Nozzle, Ø435mm wheel)


From the literature research, it was found that the minimum ratio of jet to wheel diameter is 1:5, which keeps the volume of the unit to a minimum whilst allowing for a high maximum power speed. The maximum power shaft speed is around 300 rpm, which is lower than normally chosen for pico hydro turbines, but for a 50 Hz output a 10 pole machine could be used.

There are several losses that are currently

• Flow entering and exiting at different radii;• Splashing; • Non-ideal incidence on cup; • Jet not impinging on the cup all the time;• Jet obstructed by incoming cups.

These losses will be included in future extensions to the experimental data derived from a scaled test rig.

Experimental Test Rig

A turbine testing rig (Figure 6) was designed and built to validate the Turgo turbine moperation at low heads. It is divided into two parts:

• Flow control and pipework – Valves V1 and V2 are used to control the losses in the pipe, changing the head and flow to the turbine. The flow rate and static pressure

• Turbine – The turbine is set up as would be in a site. The angle and position of the nozzle is adjustable. The torque output is measured with a torque transducer located in between the turbine and a generator. The load on the generator controls the speed of rotation. The frequency of the generator output is measured to give the rotational speed of the turbine.

The test rig is near completion, initial tests are required to assess its operating characteristics before testing the turbin

Future Work

Once the turbine testing rig is operational the validation of the Turgo model will take place, followed by the optimisation of the turbine design for low head conditions. The grid connection unit for the generation unit will then be studied, assessing how to control several independent generating units.

To keep up to date with the research please visit http://twitter.com/saminnepal.

Acknowledgements

This research is funded by Renishaw plc, and supported by Engineers Without Borders, UK.

References

[1] ESMAP., "Technical and Economic Assessment of OffDecember 2007. ESMAP Technical Paper 121/07.

[2] Paish, O., "Micro-hydropower: status and prospects." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 2002, Issue 1, Vol. 216, pp 31

[3] Bing Maps, www.bing.com.

[4] Harvey, A., et al., Micro-Hydro Design Manual: A guide to small1993. 1853391034.

[5] Williamson, S. J. et al, “Low Head Pico Hydro Turbine Selection using a MultiEnergy Congress 2011, 8-13 May, Sweden (accepted for publication).

[6] Massey, B., Mechanics of Fluids. Stanley Thornes (Publishers) Ltd, 1998. 0748740430.


From the literature research, it was found that the minimum ratio of jet to wheel diameter is 1:5, which keeps the volume ilst allowing for a high maximum power speed. The maximum power shaft speed is around

300 rpm, which is lower than normally chosen for pico hydro turbines, but for a 50 Hz output a 10 pole machine could be

There are several losses that are currently not included in this model, such as:

Flow entering and exiting at different radii;

Jet not impinging on the cup all the time; Jet obstructed by incoming cups.

These losses will be included in future extensions to the basic model. The model will then be validated against experimental data derived from a scaled test rig.

) was designed and built to validate the Turgo turbine model and assess its suitability for operation at low heads. It is divided into two parts:

Valves V1 and V2 are used to control the losses in the pipe, changing the head and flow to the turbine. The flow rate and static pressure are measured.

The turbine is set up as would be in a site. The angle and position of the nozzle is adjustable. The torque output is measured with a torque transducer located in between the turbine and a generator. The load on

ls the speed of rotation. The frequency of the generator output is measured to give the

The test rig is near completion, initial tests are required to assess its operating characteristics before testing the turbin

Once the turbine testing rig is operational the validation of the Turgo model will take place, followed by the optimisation of the turbine design for low head conditions. The grid connection unit for the generation unit will then be studied,

g how to control several independent generating units.

To keep up to date with the research please visit http://saminnepal.blogspot.com or follow me on twitter at

This research is funded by Renishaw plc, and supported by Engineers Without Borders, UK.

ESMAP., "Technical and Economic Assessment of Off-grid, Mini-grid and Grid Electrification Technologies." mber 2007. ESMAP Technical Paper 121/07.

hydropower: status and prospects." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 2002, Issue 1, Vol. 216, pp 31-40.

Hydro Design Manual: A guide to small-scale water power schemes. ITDG Publishing,

Williamson, S. J. et al, “Low Head Pico Hydro Turbine Selection using a Multi-Criteria Analysis”, World R13 May, Sweden (accepted for publication).

Massey, B., Mechanics of Fluids. Stanley Thornes (Publishers) Ltd, 1998. 0748740430.


4th March 2011

37

From the literature research, it was found that the minimum ratio of jet to wheel diameter is 1:5, which keeps the volume ilst allowing for a high maximum power speed. The maximum power shaft speed is around

300 rpm, which is lower than normally chosen for pico hydro turbines, but for a 50 Hz output a 10 pole machine could be

basic model. The model will then be validated against

odel and assess its suitability for

Valves V1 and V2 are used to control the losses in the pipe, changing the head and

The turbine is set up as would be in a site. The angle and position of the nozzle is adjustable. The torque output is measured with a torque transducer located in between the turbine and a generator. The load on

ls the speed of rotation. The frequency of the generator output is measured to give the

The test rig is near completion, initial tests are required to assess its operating characteristics before testing the turbine.

Once the turbine testing rig is operational the validation of the Turgo model will take place, followed by the optimisation of the turbine design for low head conditions. The grid connection unit for the generation unit will then be studied,

or follow me on twitter at

grid and Grid Electrification Technologies."

hydropower: status and prospects." Proceedings of the Institution of Mechanical Engineers, Part

scale water power schemes. ITDG Publishing,

Criteria Analysis”, World Renewable

Massey, B., Mechanics of Fluids. Stanley Thornes (Publishers) Ltd, 1998. 0748740430.


Figure


Figure 6 – Experimental set up for turbine testing.


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Low head pico hydro off-grid networks