Brad Hughes

Thanks I think I am starting to understand now.

Here is another similar idea to what has already been proposed.

Suspend an empty water tank from a tower, and hang it from the tower with a spring. During sunlight hours, use solar power to pump water up into the tank. As the weight of the tank increases, the spring will stretch significantly.

When you need that energy, you release a valve on the bottom of tank, and as the water exits the tank under pressure of the head above it, pipe that through a hydro electric generator and generate power from the exiting water. And as the weight of the tank decreases as the water exits, the spring compresses back up, pulling the tank back up the tower, driving a generator that generates power as it climbs back up.

Thanks guys

I was thinking along the lines of having a 5 meter pipe connected to the spout the same diameter as the spout, pointing straight down, and on the bottom end of the pipe a closed valve holding the water back. When that valve is opened would the spout depth then not have increased by 5 meters? Essentially giving 5 more meters of head?

I struggle with this concept lol

The most likely way I can become energy independent is by combining both PV (solar) and hydro power.

My daily power consumption is approximately 30 kWh, but if I was to buy some new energy efficient appliances which I plan on doing, I could reduce that to around 15-20 kWh a day. Most of my usage occurs after the sun has gone down.

I am currently looking for a rural property which has river frontage, where the property elevation is at least 20 meters above the river water level. So there will be a steep river bank down to the river, with a 20m fall. It shouldn't be too hard to find, in fact I've already short listed a few.

The plan will be as follows. This will be an off-grid setup with no connection to the grid at all.

- Install a 10 kw solar array on the property (approx $12,000)
- Install a small 5 kWh battery bank (approx $5,000)
- Install a 15kw solar/hydro hybrid inverter (approx $4,000)
- Install a 500,000 litre water tank (or alternatively build a 500,000 litre dam) (At least $50,000)
- Install 3 x 1.5kw electric water pumps to pump river water up into my tank/dam. Each pump can pump 24,000 litres an hour (total 72,000 litres an hour) (Approx $4500)
- Install a 2kw hydro electric generator, that will generate power when I release my tank/dam water back into the river (approx $3500)
- Plumbing and miscellaneous costs (approx $15,000)

Total: $94,000

When the sun is shining, there should be enough power from my 10kw array to easily cover my consumption. In most hours on most days, including during cloud, with such an oversized array there will be a large excess of power being generated. That excess solar power will be used to run my 3 pumps, which will pump 72,000 litres of water an hour from the river up into my tank/dam. The pumps will run continuously until there is no longer enough excess solar power being generated to power it (or the tank becomes full), at which point they will shutdown.

At night time, when there is no solar power being generated, a valve opens on the tank/dam, and starts draining the tank/dam water back down the 20m head into the river, piped through my 2kw hydro electric generator.

Using 1 inch pipe, 20m head, 500,000 litres of water, draining at approximately 9.84 litres/sec, the hydro electric generator will generate 1158 watts of power for approx 14 hours (assuming the tank/dam is completely full), in other words around 16.2 kilowatts of power, which should easily cover my night time power needs and keep my battery bank full. I could also look at some how detecting when the battery bank is full, and slow down or stopping the release of tank water until the battery bank reaches a level where it needs topping up again.

Realistically I think the total cost to deploy something like this would exceed $100,000. The big cost will be in the tank/dam. There will also be maintenance costs for the equipment.

The whole idea behind me wanting to use hydro power at night is to try and keep the battery bank always full to significantly extend its life, but when you add up the costs associated with building the hydro setup, it would probably be cheaper just to use a larger battery bank and replace it every 3-5 years, and forget the hydro power idea.

Thoughts?

I am trying to calculate how fast water will exit from a tank using this website: http://www.efunda.com/formulae/fluids/draining_tank.cfm#calc

I am using these values:

Depth of spout: 10 meters
Fluid Density: 1 kg / litre
Spout Exit Diameter: 4 cm
Discharge Coefficent: 0.98

The flow rate calculates to 17.2 litres / second

My question is this. If I connected a 5 meter pipe to the exit spout on the tank, and aimed that pipe straight down a 5 meter drop, does the "Spout Depth" in the formula above then become 15 meters, increasing the flow rate to 21.1 litres /second?

Thanks

Here is an interesting albeit old concept

A hydraulic accumulator

http://en.wikipedia.org/wiki/Hydraulic_accumulator

The section about using a raised weight is similar to what I was thinking

Hi

I am new to the forum, greetings from melbourne australia. I find this concept interesting. It's something I have thought about for a long time.

In regards to the two problems you have posed, I don't see them as problems. Let me explain why.

Yes, it will require more energy to wind the spring than will be released when it unwinds. And yes, a human is not going to be able to wind a spring that would be capable of generating any significant amount of power.

But we are not looking for perpetual motion here or free energy, just a way to store the energy we already have.

The way I see it, we have a MASSIVE excess supply of free solar energy. I read somewhere recenty that there is enough useable solar energy availabe to power the world 50 trillion times over. In fact the solar panels on the roof of my house generate three times more power than I need. The problem of course is, that the sun is not always shining. So the problem becomes how to store that solar energy for times when the sun isn't shining, so we can harness it then. Batteries have the obvious issues. I do really think the idea of using springs to store energy has potential, no pun intended.

So in regards to the first problem you presented, we can solve that with solar. It doesn't matter that it takes more energy to wind the spring than it will release, because we have a massive excess supply of energy when the sun is shining. Energy isn't the problem, we have plenty of it, storing it is the problem. So that problem is solved by solar.

The second problem you presented, in regards to a human not being able to wind a spring big enough that could store any significant amount of power, can also be solved with solar. We use solar powered electric motors to wind the springs when the sun is shining. And then at night time, we use the energy stored from releasing the spring, to power a generator which produces the power we need at night time.

When the sun comes out the next day, the solar powered motors compress the spring again, and rinse repeat.

I've been fascinated with this concept for a while. I've also experimented with the idea of using solar polar to hoist/winch up a large weight during the day, and then release that weight at night through a series of pulleys/gears that drive a generator motor. Just thought I would chip in my 20 cents