Community Pico Hydro in Sub-Saharan Africa/ Case Study Two/Thima, Kirinyaga District, Kenya

A

Turbine HouseThis building houses the pump-as-turbine and generator equipment and ensures that the water is returneddirectly to the river. It is built above flood level but otherwise close to the riverbank. The location was chosen tomaximise the available head whilst minimising the penstock length. A draft tube was added to the outlet of thepump to obtain and extra 1metre of head. Extra floor area was added to the building since the intention is to usethe fan end of the generator shaft to drive a ‘posho’ (maize) mill. Double-ended generators such as this cansometimes be requested from the supplier or otherwise a shaft extension can be fabricated in a workshop andwelded in position.

T$

uthor: P.Maher, Micro Hydro Centre, The Nottingham Trent University, 07/0

River

View 2

4 m

etre

s

This concrete channel should extend at least 1 metre from the turbine house3 metres

View 1

Penstockpipe

Large window withgrill and woodenshutters (1m x 1m)

Thima Pico Hydro

Kirinyaga District, Kenya26th November 2000

Turbine house layout tailrace design

Turbine door opensoutwards. This makesit easier to open if the turbine house floods

0.8mTurbine is fixedby bolts set in concrete

View 2

Draft tube extends into water

0.4m

Flow control valve

100mm concrete floor

water in

Pump as turbine

Draft tube

Sloping channelwith concrete liningreturns waterto river

concrete channel 1m min.from turbine house. Slope 1cm in 20cm

0.5m

View 1Wall ofturbine house

0.8m

1m

1.4m

Generator

ShaftExtension

his scheme was installed in 10 days at a cost of2,600 (excluding distribution and house wiring).

The induction motor as generator produces

2.2kW but a shaft extension provides a 3kWdrive for mechanical loads.

2/02 4/7

Community Pico Hydro in Sub-Saharan Africa/ Case Study Two/Thima, Kirinyaga District, Kenya

Pump-as-TurbineSince the head at this site was not sufficient for a Pelton turbine, another low-cost and robust solution wasselected. Standard centrifugal pumps can be used as turbine generator units if carefully matched to the site. Inthis case a ‘mono-bloc’ type was used which is supplied with a directly-coupled induction motor. The pumpimpeller becomes the turbine runner and the motor is used as an induction generator. The difficulty lies inpredicting precisely how a particular pump will perform as a turbine at a given site. Performance predictionequations can be used to select a particular machine if the site conditions are known. The Indian manufacturerKirloskar Brothers supplied the pump used for this project since they have a sales outlet in Nairobi. To calculatethe power output from this pump when it is used as a turbine, it is necessary to look at the pump best efficiencydata which was obtained from the manufacturer. The following equations can then be used which take intoaccount the speed increase necessary when operating the pump connected directly to an induction motor whichis used as a generator.

tQ = 8.0maxηbep

p

t QNN

× tH = 2.1max

2

ηbep

p

t HNN

×

Where:Qt = Flow rate using pump as turbine (litres per second) tN = Speed of turbine (rpm)

Ht = Head using pump as turbine (metres) pN = Speed of pump (rpm)

Qbep = Flow rate at best efficiency point (litres per second) ηmax= maximum efficiency (%)

Hbep = Head at best efficiency point (metres)

Using data for a Kiloskar 515+ pump, Qt and Ht were calculated and found to approximately match the siteconditions allowing for approximately 2 metres of head loss in the penstock. Despite the prediction, the pump asturbine output was not as high as expected at the speed required for 50Hz. The diameter of the impeller wasreduced on a lathe to tune it more exactly to the site conditions. A stuffing box type seal was specified ratherthan a mechanical seal as replacement parts for the mechanical seal are more difficult to obtain. A bronzeimpeller was selected instead of cast iron because of the improved resistance to corrosion.

A draft tube increases the head by 1m whilstensuring that the turbine remains above floodlevel.

Author: P.Maher, Micro Hydro Centre, The Nottingham Trent University, 0

GeneratorThe KDS 515+ pump is fitted with a 3.7kW (5h.p.) inductwhen driven by the turbine (pump impeller). The motor volrather than 240V and the winding insulation Class F rathesize. Both of these measures help to prolong the life of tlower temperature than their rated temperature. A 3kW inand frequency regulation by diverting excess power to acurrent device (RCD) with 30mA tripping current maximisean earth fault develops, either because of a faulty appliance

Two 1.8kW cooking rings have been used as aballast load. An RCD (left) improves consumersafety by minimising the risk of dangerouselectric shocks.

7/02/02 5/7

ion motor. This produces 2.2kW of electrical powertage was specified from the manufacture to be 260Vr than Class B which is standard on machines of thishe windings by ensure that they operate at a muchduction generator controller (IGC) provides voltage

ballast load (two 1.8kW cooking rings). A residuals consumer safety by disconnecting the generator if or due to someone accidentally touching a live wire.

Community Pico Hydro in Sub-Saharan Africa/ Case Study Two/Thima, Kirinyaga District, Kenya

A

Distribution System Planning Using GPS DataThe locations of the houses shown on the plan were recorded with a relatively inexpensive GPS unit (GlobalPositioning System). This uses satellite technology to triangulate a precise position by ‘tuning in’ to 3 or moresatellites (accuracy of +/-15m). The position is then referenced and stored. Downloading these points to a CAD(Computer Aided Design) program allows a map of the site to be generated. Using the CAD system, the routesfor the distribution cables was worked out and drawn in to ensure that all the consumers were connected. Aspreadsheet program was used tp determine the minimum cable diameters which could be used whilst stillensuring that all consumers would receive a connection with an acceptable voltage, no matter if their house liesat the end of the cable furthest from the generator. This helped to keep the connection costs for the consumersas low as possible.

9houses

River conference

50F

47F

Spur A

48F49F

6F

5

Church

Aba

4

5F

1

2F

3F

4F

1F

3

2

3

56

7

4

Ab

5HBhouses

RCRS

7

58F 57F 46F

4

vets house

12houses

13houses

Aab6

8

11houses

striped house

stripe3

Poultry Farm

115houses

8

Aa

Aaa

2

3

5 10houses

1045F

43F41F

42F 44F

59F 60F

9

11

55F56F

52F53F

54FAac

12

Bc 11F 13F14F

8F

9 9F Church27

16F

22F

31F

28F29F

7F

23F

Be

Bd10

11

30F

4

6 8

18F2houses

21F24F

5

25F

18F

20F

17F

12F

15F

27F

Bb

26F

500m radius

32F

38F7houses

Church

33F

10

34F35F

Powerhouse

1

9

Intake

36F37F

40F

Spur B

Ba

2

3

51F13

AadTransformer

1Kmradius

Consumer houses were surveyed using a GPS unit. Using this data a map was drawn and thenetwork planned out. Houses which are not connected have not been shown.

Grid extension to achurch

Grid extensionto a tea factorywhich followsthe road

uthor: P.Mahe

r, Micro Hydro Centre, The Nottingham Trent University, 07/02/02 6/7

Community Pico Hydro in Sub-Saharan Africa/ Case Study Two/Thima, Kirinyaga District, Kenya

Author: P.Maher, Micro Hydro Centre, The Nottingham Trent University, 07/02/02 7/7

Project CostsA cost breakdown for the scheme components is given in the table below.

Scheme Components Cost (US$)1. Civil works (turbine house) 2502. PVC penstock 6003. Turbine, Generator, Controller and Protection 1,7504. Distribution system, house wiring and energy saving bulbs (110 houses / 200 bulbs) 3,3655. Labour costs (electrical wiring:200 shillings per house, other labour provided at no cost) 400

Total $6,365

The total scheme cost averages $58 per house. This makes pico hydro very cost-effective when compared to alead acid battery which, when bought new, not only costs more but requires regular charging, provides DCpower only and has a useful life of 2 years or less. Nevertheless, batteries are still used extensively in manyparts of Africa. A solar home system, providing a similar amount of power as the pico hydro, suffers the samedrawbacks as battery only systems and costs at least 5 times more per house. Clearly pico hydro is limited toareas where suitable hydro potential exists, but given that the flows required are small, an extremely largenumber of people stand to benefit from this very affordable technology in many parts of Kenya and more broadlyin Sub Saharan Africa.

AcknowledgementsThe Micro Hydro Centre at Nottingham Trent University would like to thank all the project partners who haveworked hard to make this scheme a success. They are Stephen Gitonga and Patrick Balla from the EnergyProgram at ITDG Kenya; James Muriithi and Theuri Daniel Kahiga from the Renewable Energy Department atthe Kenyan Ministry of Energy and the committee and community members of Thima Micro Hydro Group 2000.The Micro Hydro Centre also gratefully acknowledge the funding provided by the European Commission formaking this program of demonstration and training possible.

Both demonstration sites are located quite close to each other and convienient for vehicle access.Travelling time is approximately 2.5hrs from Nairobi (Topographical Map: Sheet 121/4 Embu North)

Location ofThima PicoHydro Project

Location ofKathamba PicoHydro Project