microhydro forebay design

The design and example of the micro hydropower reservoir/forebay

Some hydro power stations with small flow but requirement of high amount electricity can adopt a reservoir for water shortage.

• Example(1): a mountain community/village with small water sources, minimum water flow is 2 kilograms per second during a year, head is 50 meters. There are 18 families in this village, design electricity for every family is 150watts (60 watts for the television, 90watts for 4-5 light lamps), consider to build a 3kw micro hydroelectric generator station. What is the solution for the forebay?
• Solution: For 3kw pico hydro generator, 50 meters head, client should choose a pico turgo turbine generator; designed water flow should be 10 kilograms per second (10litters/second). Because of the existing water flow is too small (2 litter/s), building a reservoir can solve this problem. Calculate the daily water flow per hour (3600 x 2 = 7.2 cubic meters, 24 hours = 172.8 cubic meters.). About 180 cubic meter water can be used to generate power. Power generation will consume 36 cubic meters water (10 litters x 3600 seconds) per hour. Power 5 hours a day, low-flow water period can guarantee the villagers lighting electricity, flood season can get more power for other electricity usage.

Digging 180 cubic meters of water pool as the reservoir can power 5 hours per day. Good soil condition can be connected with the tube directly; bad soil condition of the pool can be used with the plastic laying processing or concrete processing.

• Example (2) a hydro power station with drops 30 meters, dry season with 8.4 litter/second flow (30 cubic meters flow per hour), wet season with flow 41 litter/second (150 cubic meters per hour).

We can calculate the output of two flow conditions below:

Dry season output: 30 m ×0.0084(8.4 l/s) × 9.81×unit efficiency about 65% = 1606 watts

Wet season output: 30 m ×0.041(41 l/s) × 9.81×unit efficiency about 65% = 7843 watts

Requiring power is not less than 3000 watts; designed flow is 16 litters per second. (30 m × 16 litter/seconds × 6 = 3060 watts)

• Solution:For dry season, we need extra 8 kilograms per second water flow for the system, so we can get 8.4 litter+ 8 litters=16.4 litters water flow to meet the designed water flow condition, 3600 seconds * 8 = 28800 liters per hour (about 30 cubic meters) electricity 5 hours × 30 = 150 cubic meters.

This is consideration design for dry season, which is considered to build a 120-150 cubic reservoir, installed 6kw-8kw micro turgo turbine generator. Client can get 3kw-4kw during dry season, and get 6kw-8kw in wet season. It is advisable to make an 8kw micro turgo turbine with two nozzles.