Energy Matters Forums

[Gordon-Loomberah]

If you want to see what a medium head Francis turbine looks like:

...

It looks like you have exceeded 100%! whatever that means... but the result is the images have vanished, so you might need to post them in here, rather than provide links.

[WaveTech]

Hi People.

I have read the earlier posts about pumped Hydro and wondering if someone can give me a comparison of actual returns compared to off-peak solar in NSW.

We have an existing 200,000 litre tank within 15 metres of our 3 phase utility cables at the street ,and 65 meters of head to a place we could install 200,000 litres more of tanks at a cost of around $ 3600 for the new tank , $ 1050 for a pump , i dont have the cost yet for the platypus minihydro turbine.

What are the numbers if we used solar panels to pump that 200,000 litres of water up over an 8 hour day and then run it back down over a 3 hour period during peak demand ?

We could run a 9 kW mini hydro back to grid from that head and flow for 3 hours.

Whats the return going to be compared to just having 12 kW grid feed solar over an 8 hour day ?

[offgridQLD]

$3,600 for a 200,000lt tank? that's got my attention!

Or is that a typo and was $13,600 ?

[Gordon-Loomberah]

Put me down for one of those tanks too!

How far away is the top reservoir site?

Pipe cost will be high if you want to flow 200000l in 3hours.

[WaveTech]

$3,600 for a 200,000lt tank? that's got my attention!

Or is that a typo and was $13,600 ?

site mixed concrete using river gravel from the property , reo bar , borrowed formwork from a relo' , engineers cert but not allowing anything for my labour .

tanks size is only 10 x 5 meters x 4 meters high (internal).

If it was a government job it would be closer to $ 2 million but thats not how we do things here


ps top reservoir is about 90 meters pipe run so have to factor those losses in 75 NB poly

[davidg]

What are the numbers if we used solar panels to pump that 200,000 litres of water up over an 8 hour day and then run it back down over a 3 hour period during peak demand ?

It will not be 8 hours. The average for NSW is approx 4 hours average and that's an average so during the winter it will be a less and during the summer it will be more. Pumping water up hill is approximately 65% efficient generally, it could be more but then you using ater pumps that are relatively high/frequent maintenance.

We could run a 9 kW mini hydro back to grid from that head and flow for 3 hours.
Whats the return going to be compared to just having 12 kW grid feed solar over an 8 hour day ?

Very unlikely to run for 3 hours more like 1.5 hours maybe 2 hours.

[Gordon-Loomberah]

Agree with David re the ~2hr run time, but I think you will need larger pipe,otherwise a large proportion of potential output will be lost to pipe friction.

[lantern]

A theory we used to work on is the net head should be 75% of the static head.
This gives you the most efficient pipe.

[WaveTech]

Thanks people.

I have 3” poly here I could have used but could increase to 4” , I try to get materials second hand at auction where possible but 4” is not something I see often.

One issue I have is part of the pipe run is up a 30 meter high basalt cliff then across sloping billy goat country to where the tank will be.
I had thought of using a core drill into the basalt face and then epoxy grout some pipe supports into the core drill holes , increasing pipe size and full weight just means more supports are required I guess but I can see the maths blowing out costs a bit .

“If it was that easy everyone would be doing it”. LOL

Anyone got “back of envelope” figures on returns based on the capabilities mentioned so far ?

Maybe the simple hard truth is that it’s just not feasible ~

[Gordon-Loomberah]

Maximum output power is produced where friction loss accounts for about 1/3 of the theoretical maximum. Maximum efficiency is where frictional losses are <1%, so the 75% mentioned by Lantern above is reasonable, if you are aiming for a compromise. You have all night to deliver your energy to the grid, so it makes no sense to waste lots of it in frictional losses. Producing 1/3 the power for 3 times as long will increase your returns, and save on cost of pipe.

Is your 75mm poly rated for at least 850kPa? It would need to be, to cater for surges when turning the flow off with 65m head, and you may need a blow-off valve for extra protection as well.

I'm not sure what the wall thickness is on your pipe, but say you have a 64mm diameter ID.
Ignoring bends (try not to have any), if you have 5litres/second flow, then there will be about 4m friction head loss.

61m head X 9.81 X 5l/s = ~3kW

Depending on your turbine efficiency, and electrical efficiency, you should be able to get up to 2kW from it.
Your 200,000l tank should operate the turbine for 11 hours.

22kWh per day X whatever your FiT is, you'll have to calculate if it is worthwhile. You'll want a much larger than 2kW PV array to pump the water up each day, particularly in marginal/cloudy weather.

If you wanted to run 30l/sec through the pipe... well I think you will find that it wont flow that much!

I think the short answer is that you would be better off exporting energy directly from a PV array during the day, rather than wasting energy running a pump, friction loss, electrical inefficiency etc, before you can export.
Your night time FiT would need to be more than double your daytime FiT to make it worthwhile.
If you wanted to do it off-grid to get you through cloudy weather, it would make more sense.