Micro-hydro interventions

Bamerchara Micro Hydro Project :

SRE under LGED has successfully demonstrated first micro-hydro power unit at Bamerchara, Chittagong. Its installed capacity was 10kW but due to inadequate water head about 4kW power was generated. SRE has also carried out a study on prospective micro-hydro sites in the Chittagong Hill Tract reasons and eight potential sites were identified with an estimated capacity of 135kW. SRE also provided technical support to promote indigenous micro-hydro power generation unit which was developed by member of local indigenous community named Mr. Aung Thui Khoyan. 

Background: Hydropower is an eco-friendly clean power generation method. The scope of hydropower generation is very limited in Bangladesh because of its plain terrains except in some hilly region in the northeast and southeast parts of the country. However there are lot of canals, tributaries of main river  Karnafuli, Shangu, Matamuhuri as well as tiny waterfalls having good potentials for setting up mini/micro hydropower unit in Chittagong Hill Tracts(CHT) region.

Micro-hydro power is a simple technology to convert hydropower primarily to mechanical power. They are generally 5-300 kW range. It is not feasible to supply electricity to the National grid from a micro-hydro power unit. Typically they provide captive power to just one rural community. In many cases micro hydro power units do not generate electricity. They are used for grinding cereals in mills and often driven directly from the turbine shaft. Classifications of hydro power based on generated power are as follows:

Pico Hydro up to 5 kW
Micro-hydro         >5<300 kW
Mini-hydro           >300kW<3MW
Small hydro         > 3MW<10MW

A hydro power scheme requires both water flow and a drop in height (referred to as a head) to produce useful power. It is a power conservation system, absorbing power in the form of head and flow, and delivering power in the form of electricity or mechanical shaft power. Indeed no power conservation system can deliver as much useful power as it absorbs. Some power is lost by the system itself in the form of friction, heating, noise etc.

Net power generation from a hydro power unit could be obtained from the following equation:
Pnet = hgross * Q *  g  * eo
Where
Pnet   = Net power generated from the unit in kW
hgross = Gross water head in meter
Q      = Discharge in m3/sec
eo     = System efficiency
g      = gravitation force in m/sec2

A typical hydro power has about 50% power loss, out of which about  5% losses in Channel, 10% loss in Penstock, 20% loss in turbine, 15% loss in Generator, 4% losses in step-up/down transformers loss and 10% Transmission losses.

‘Bamerchara’ is basically a water storage reservoir. To facilitate irrigation in dry period earthen dam with a sluice gate was constructed by the Local Government Engineering Department in 1994. Only rainwater is stored in the reservoir during the monsoon and there is no perennial source of stream. ‘Danerchara’; another storage reservoir was also connected with ‘Bamerchara’ to provide more water storage facility. At present maximum water storage area has been increased to about three sq. km. A spill way was constructed at ‘Danerchara’ in 2000 to release extra water. In 2002 a feasibility study was conducted by an International Expert to install a micro-hydro power unit at Bamerchra. However, irrigation is the main purpose of Bamerchara project therefore only supplementary power generation is possible during monsoon and irrigation period when the sluice gate is normally kept open.

Objective of the project:

• To demonstrate micro-hydro power unit
• To integrate hydropower with the irrigation infrastructure
• To explore possible replication of the model in the CHT region

Potentials of Micro Hydro power unit in Bangladesh:  To explore potential sites of micro-hydro, several studies have been conducted by Bangladesh Water Development Board (BWDB) and BPDB in 1981. List of prospective site is shown in table 1.1

Table 1.1 : Potential Small Hydro Sites identified by BPDB and BWDB

In 2004 Sustainable Rural Energy has explored some potential micro-hydro sites in CHT region which is listed in table 1.2  

Table1.2:  Micro-Hydropower sites identified by SRE study  in 2004

 Salient feature of Bamerchara micro-hydro power unit:

LGED through Sustainable Rural Energy (SRE) Project has implemented first micro-hydro power unit in Bangladesh at Bamerchara, Chittagong. Estimated capacity of the system was 10kW. Salient feature of the unit has been illustrated below: 

• Turbine type                   : Corssflow
• Penstock                      : 52m
• Design flow                    :150 litter/sec.
• Net head available          : 6m-10m
• Preferred governor          : Flow control (Manual)
• Electrical Output                          : 4-6 KW, 50Hz, 3 phase voltage, 220 V / 440 V

Considering water head of 11 meters and flow rate of 150 l/s it was estimated that maximum 10kW hydropower could be generated from ‘Bamerchara’ site. But when irrigation starts water head falls rapidly. Consequently full power generation was not possible. Furthermore about 41% potential energy was lost by the penstock, turbine, and generator and transmission line. Figure A illustrates relationship between water head and extractable hydropower from a stream.

Conclusions and Recommendations:

• Primary purpose of Bamerchara project is irrigation therefore, extractable hydropower depends on nature and amount of irrigation. Most of the farmers are used to daytime irrigation so a considerable amount of power remains unutilized during this time. However this power could be stored in a Battery bank or could be used at grain mills or cooking.
• As there is no perennial source of water at Bamerchara, the system is run out of water within a short period and then we need to wait for the next monsoon.
• Flow rate and head are the key factors in selecting micro-hydro power unit. So Picohydro and Microhydro is suitable where there is a perennial source of flow.
• This was the first demonstration Microhydro power unit in Bangladesh. This unit helps to get insight knowledge and practical experience in harnessing micro-hydro power.