Solar Pumping & Storing Energy in a Water Resevior

2 Posts

Oct 20, 2007 04:08 pm

I live in rural Ecuador (see the ecolodge we have built: www.blacksheepinn.com) and we currently have a submersible pump connected to two 85-watt solar panels that are lifting water up over 200 feet. We are using this water for irrigation of a garden, also for a 100 meter long water slide and a small fountain/sheep watering hole.

I have been researching the possibility of converting our entire property to solar power; we are currently connected to the grid. Instead of creating the typical battery based system, the idea struck me to build a large reservoir high up on the property and to pump water on a larger scale (with a larger pump or a series of small pumps) during the day, and then run the water back down through micro-hydro to create power. This would avoid save the expense and the hazard of a large battery bank; as there are no recycling programs in Ecuador.

If we can replace 4 refrigerators with propane, then our daily electrical use is approximately 5 KHW. My questions are how much water would I need to store? I have seen micro hydro plants but I do not understand if there is some sort of electric relay that would physically open and close a water valve when there is a specific electrical demand.

Have you ever heard of anyone using water to store energy for a small home based system?

Thanks for any advise that you can give.

All the best from the Andes,

Andres

Tom M

462 Posts

Oct 21, 2007 01:29 pm

Re: Solar Pumping & Storing Energy in a Water Resevior

Andres, I have installed several hydro systems in the Andes of Peru. From what you have explained, it seems unwise to try and take the route of which you speak. The amount of power that you would expend pumping the water up into the tank may not compensate for the power gained from a storage tank of water to operate a hydro system. Hydro needs a large steady flow of water or water at high head to operate sufficiently.
There are valves that can operate automatically if you choose to go this route.
Where is the water you are pumping located? Is there a stream or channel or is it a well? Is there any way to locate the hydro near this water source? How long would the electrical runs be? Best to use batteries to store the power from the hydro if possible since different flows will produce changing electrical currents. Diversion loads may also be needed if power output continues after demand is satisfied......

Andres Hammerman

2 Posts

Oct 22, 2007 04:36 pm

Re: Solar Pumping & Storing Energy in a Water Resevior

Thanks Tom for answering.

As I understand it batteries are about 90% efficient in storing energy and efficiency drops to about 75% when storing the energy as potential energy in the form of water.

It is completely true that typical hydro systems have a large steady flow of water. I have tested here to see if one was possible and we did not have enough flow, but we do have plenty of head. Our property stretches up 150 meters.

We have a large pond at the bottom of our property, it has no direct outlet... it seeps and evaporates in the dry windy months (June through September), and its level goes up when it rains. It never dries up. It is fed by trickles of spring water and with heavy rains. The same water would be pumped up and circulate down to satisfy power needs during the night.

Solar and wind could power the electrical demands directly during the day, and during the night hydro could kick (assuming we designed for excess energy to be produced, which would be typically stored in batteries) and we have the grid as a back up. Reservoirs could also be filled by collecting rainwater run-off.

I am simply investigating the possibility of storing the energy in the form of potential energy in a large reservoir higher up on the property; to avoid batteries. The typical solar system can be designed for 2 to 5 days of cloudy weather, or has a back-up generator, this system could design for less days and have the grid as a back up instead.

There are several separate questions:
How much water is needed to produce 4-5 KHW via hydro daily with 70 meters of head, with 140 meters of head?
Does it depend on hourly demand? I can begin to gather data by the hour of our current electrical demand.
How much energy is needed to lift that quantity of water?

Complications include: inverter for solar/wind/hydro power, DC direct pumps and controllers, controllers for hydro to open and close, controllers for grid back up... very complicated!

Thank you for any advice you can give...

Tom M

462 Posts

Oct 24, 2007 08:56 am

Re: Solar Pumping & Storing Energy in a Water Resevior

Andres, once again the amount of power it would take to pump water up over 150 meters would be better spent charging batteries for extra potential and reserve. If there was some way to feed the storage tank from the springs or rain then you may be in business. Or perhaps locate the generator below the pond and use it as the storage and supply. Only drawback is that you are now further away from your demand for electical runs. You could charge individual batteries and then haul them up to wherever they are needed.
As far as output, you should be able to find charts on sites that sell hydro systems to determine required head/flow and power output. Most generators come with 1 to 4 nozzles. More nozzles needs more flow. More nozzles, more power.
You can get power requirements for pumping water from the pump manufacture for whatever pump you choose to use. Shallow well submersible pumps are probably your best bet if you choose to go that route.
I am not sure if you can operate the hydro automatically without using batteries. There are zone valves that can operater either NO / NC, so if batteries get low, the valve can open flow.......

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