Hydro-power generation in Africa

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Thread Starter

Mark Klee

I work for a non-profit organization in Swaziland, Africa and we're about to re-direct a stream of water at the top of our property to bring it down as a water source for our buildings, crops, and livestock. While water is the primary reason for capturing this water source, I feel like we also have the potential to generate a significant amount of electricity (from a cost basis) due to the extremely high costs of electricity here.

The water flow rate is only approximately 1000L/min (265 gal/min) but we have a change in elevation of about 700m (2300 ft). Unfortunately, we'll have to pipe the water close to 5 miles to the bottom of the property.

Any thoughts?
 
Is that a 700m drop over 5 miles? Are you diverting the stream or are you piping the water? Could you provide more details? Theoretically the power production would be a little over 110kW (flow rate in m/s times the head (assuming that we could get all 700m) times gravity (9.81m/s), and considering the efficiency of the hydro turbine (Approx 60%) this would drop the power production to about 70kW. This a pretty good amount of power. This sounds like a cool Engineers without Boarders project. I would be interested in learning more if you are willing to provide more information. You can contact me at ncseeley \at\ gmail [dot] com.
 
It could be viable. You can learn more by Googling "Micro hydro power". One issue would be the 5 miles of pipe. Friction head loss in that distance may be large, limiting your available power.
 
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Bruce Durdle

1 kg falling through 1 m is going to give you 9 J of energy at 100 % efficiency. You have 1000 kg per minute through 700 m so have a potential of 7 MJ/minute, which is 105 kW - so definitely worth doing from an electrical point of view. In fact, with 700 m of head, you will need to lose a lot of energy somewhere along the route.

See http://www.ecoinnovation.co.nz for some possibilities. You might need several generators along the pipeline to reduce the pressure in stages.

Bruce
 
Yes, it's a 700m drop over the 5 miles of fairly rugged terrain. We have not done anything to-date but the high-level plan is to collect the water, pump it up over a 100m ridge, and then let gravity do it's thing. One limiting factor is obviously cost. I don't think it's feasible to purchase 5 miles of pipe capable of withstanding a closed system all the way down to the farm - but I'm certainly open to suggestions. Hadn't heard of engineers without borders ... but I'm open to talk to ANYONE that can help at this point. Anybody interested can contact me at [email protected].

Thanks for all the input -

Mark
 
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Mark... do you know or can you determine what the velocity of the water-flow is at the end of the 5-mile trip?

Phil Corso
 
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You might also want to contact the folks at Home Power magazine. They frequently run articles on designing and building small hydropower projects and could certainly suggest some people to contact that have experience in this area.
 
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Namatimangan08

What is pipe diameter and the material used? Available power estimation can go badly wrong if pipe diameter is too small. Small diameter means high water velocity. Pressure loss is directly proportional to the square of water velocity. We are looking for says <8m/s for good condition. If water velocity is 8m/s and the pipe is an ordinary pipe (not very good surface finished pipe) then my estimate for pressure loss will be around 10%. If the velocity is 16m/s then pressure loss is estimated to be around 40%! More pressure loss means less useful power.
 
The pipe diameter and material used has not been determined at this point - so I can't even determine the water velocity at the bottom. I'm simply trying to determine if it's even feasible at this point. As I stated initially, the water is the primary purpose for this project, without the water we can't reliably produce crops. I'm just trying to figure out (at a high level, at this point) if we need to take into consideration possible changes to accommodate power generation. It seems from the replies that the "potential" power generation is significant enough to further explore the options. Now I've got to somehow come up with a cost/benefit analysis of installing the generators.
 
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Namatimangan08

I guess you have not yet installed the system. I suggest you should consider to size up you pipe so that water velocity is less than 2m/s. At this velocity pressure loss will be very low.

The equation for power is <pre>
P_avai = WD * g * Q *(H_g-H_l)*Eff_turb*Eff_gen

Where:

P_avai= Available power (W)

WD= water density (997kg/m3)

g = gravitational acceleration (9.8m/s2)

Q = water flow rate (m3/s)

H_g =Gross head = 700m

H_l = Pipe head loss (m)

Eff_turb =turbine efficiency (Fraction)

Eff_elec = electrical efficiency (Fraction)</pre>
I would say you shall go for Pelton turbine. Turb_eff = 0.87-0.88.

Electrical efficiency = 0.9750

Obviously total expected revenue for ROI calculation shall be based on the expected capacity factor of you potential t/generator.
 
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