Micro Hydro Pumped Storage

Long post warning!

I have perhaps an unusual property here with 200’ elevation change up a very steep hillside. At some point I will be putting a nice water storage tank up the hill to provide a buffer, so that the household water can be gravity fed without pressure tanks. A pump in the cistern at the house, set to run occasionally, would refill the uphill tank which then gravity feeds the house.

It occurs to me that a much larger version of this could be used like a large battery for off-grid solar. I did a little figuring today, and wanted to share my conclusions. Obviously all these numbers are specific to my 200’ hillside, but anyone with an elevation like this could consider a similar setup.

Pumped hydro storage systems are nothing new, they exist at utility scale all over the world, using massive lakes and hydroelectric dams. The challenge here is getting a small scale setup to be large enough to be worth the trouble, and weighing the inefficiencies against the longevity of the battery (indefinite). Plus the cost, of course.

With stored water and a high hill, we want a high-head low-flow turbine style, which means a Pelton.

• A New Zealand company is selling these DIY Pelton turbine kits for a reasonable cost, \$1400 + shipping:
• A calculator on their site helps simplify the calculations tremendously:

Also a rule of thumb I found online, which matches up fairly well with the Powerspout calculator outputs:

``````Power = 1/10 x Head x Flow
``````

This formula is based on imperial units: power in watts, head in feet, and flow in gallons per minute.

OK, let’s imagine I set up an above ground pool at the top of the hill, and another one at the bottom. a 28’ pool 54" deep holds roughly 20,000 gallons. I can get those all day long on FB Marketplace for around \$300.

Playing with the calculator, the lowest flow rate that still maintains good efficiency is around 30 GPM. I sized the system for that, with the thought of steadily charging a small buffer battery bank. It could also be throttled up and down to match the household load, but you will lose some efficiency there, especially while throttled down very low.

At a flow rate of 30GPM, the turbine should generate about 522 watts. We can run this way for 667 minutes, or about 11 hours. That gives us 5.8KWh of usable storage.

A return pump must be added to get the water back up the hill again. It’s harder to find an off-the-shelf pump to do this, but after a lot of reading pump charts and efficiency curves, it looks like a 3HP electric motor with the correct style pump should put out 80GPM at 100PSI. The pressure is needed to get up the hill, and the flow is needed to refill the tank within 4 hours, which is our average full-sun hours. This motor will take around 2500w to run, after 4 hours it will have used about 10KWh. This is the downside to this setup, you will lose around 40-50% of your input energy to efficiency losses. More on that later. This pump will cost somewhere around \$1200.

I would need around 500’ of 2" pipe to get down the hill, another \$1200. Adding another thousand for valves, wiring, and misc. pieces, we arrive at \$5400, for our 5.8 KWh storage battery. About \$1K per KWh.

Expanding the capacity of the system would be cheap, two more pools for \$600 to add another 5.8 KWh, bringing us to \$517 per KWh. Or dig a really big pond, which I may want to do anyway. Nothing else need change, the turbine can flow well over 30GPM efficiently, if you needed higher output - but I think 500w continuously is enough for our no-solar usage periods, mostly overnight.

An interesting effect of this is all the ways you can move water around. I could set up a high-flow woodgas powered pump to run for a few hours and recharge the system on a cloudy day. And of course the stored water is useful for lots of other things, like gardens and animals - we wouldn’t drink it, I’m not sure about the quality of water that’s been pumped hundreds of times.

Now to the cost vs efficiency question. I can buy off the shelf LIFePO4 BattleBorn (very nice) batteries for \$1000 per usable KWh, and have no moving parts, no maintenance, and have a 90% efficient round trip instead of 50%. They are warrantied for 10+ years.

Lead-acid is far cheaper, at about \$300 per usable KWh. But the lifespan is short and they are high-maintenance. You have to over-size the batteries by twice, because they can only discharge to 50%. However with good maintenance, you can get started on a tight budget.

So I probably won’t build this system. It was a fun exercise, but lead-acid is better price-wise and more conventional. Then upgrade to lithium as budget allows.

But here’s the one big advantage, the reason it won’t quite go away in my mind… repairability.

I could build, repair and maintain the entire water storage system myself, with low-tech components, and if maintained it will last forever. In a long term SHTF scenario, this would be the system of choice. I cannot make or repair lead-acid or lithium batteries, and they will all eventually need replaced. With solar panels being so cheap now, I could easily oversize the system to compensate for the low storage efficiency. Is that the price of longevity? Just throw more panels at it?

I’m curious what you folks think. Has anyone played with pumped storage?

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Hi CrisKY
My situation is similar but the properties use areas are reversed. We live at the top of the slope. So transferring 500 watts made up from the bottom to consumers or storage ~600 feet lineal “generating” down low a no-go. Plus my down slope year around creek has multi-times year fish survey people walking it. One just two days ago.

Think of other advantages to your high slope water storage though. Fire-fighting safety capability. Always having a multi-weeks supply of gravity fed for gardening and live stocks water. Could be made potable.
Regards
Steve unruh

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Here is 7.68kwh for 2800 with an inverter and MPPT for solar.
It came from a quick google search but the point is you can actually beat the 500/kwh with lithium and it is really in the 400/kwh range which is only slightly more then lead acid and this includes the inverter and charge controller which probably puts it right about lead acid price.

If you want to woodgas, with this system since it appears to have the rectifier for ac input on it already. It probably doesn’t have to be clean input, and you can spin a motor with whatever engine you have working. IE you can convert a tractor, and basically buy or build the old school type of pto generator. Any variance in frequency isn’t going to matter because it is being rectified to dc anyway.

As far as pumped hydro, you have the right idea. They do have evaporative losses, and pools tend to crack, leak and break over time. Plus water collects stuff like dirt, branches and attracts animals. Then if it freezes there you can have ice issues which will probably crack the pool.

I personally would go with the life batteries and call it a day.

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The same here Chris, after calculations gravity always falls face flat on the floor. Especially in our flat country. On cloudy days we sometimes need 100 kWh a day, haha, imagine how that would look like. Height of 30 feet max, and concrete instead of water. Nice exercise but a waste of time and money. One good reason for doing the pools is what Mr Steve said.

Nothing beat LFP. Just bought another 15 kWh battery and the guy rebuild mine in nice alu housing. Stil portable 10 kWh or 15 kWh of power. Ande for the lead acid guys. If you are a real Mc Gyver it seems possible to maintain/ rebuild a lot.

A little creek is perfect for hydro of course.

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“Played” would be the accurate word.

I built this as a lab experiment for a general energy course. The goal, mercifully, was visibility and simplicity, not efficiency. 75 feet of head (main interior stairwell), <55 gallon reservoir (free if you know which dumpsters to watch), Pelton wheel, with transparent cover so you can watch which way the water goes (45% efficiency, really too low head for the turbine wheel), 120 vac centrifugal pump (univesral motor, small, cheap, suitable pressure, 10-15% efficiency, yikes). Lots of fun, the students loved it, the building and grounds people tool some calming down.

As you said, getting a good, efficient pump will be the main task. Pelton wheels are efficient and straightforward. I used a DC brush motor, 250 watt scooter motor. Not great, but good enough, and the students measured output and efficiency as a motor in another lab. With MPPT technology now inexpensive, the turbine side of things should be easy. With a permanent magnet alternator and MPPT, you should have the durability. Look for really good diodes

You have the topography, and as others have mentioned, there are side benefits as well. Where we are, we have about 35 feet top to bottom, and that’s over nearly a quarter mile. I like solar, charcoal gas, and wood heat.

Still, batteries aren’t the end of the world, and life is short

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Funny how so many of us poked at the same idea. And all came to the same conclusion

My situation is similar to Steves, we are on the top and the lowest part of the land is about 180feet lower. A creek springs out at the top so first l calculated the usability of that. It gives a decent amount of water on rainy days, now its at its peak at about 50gal/min minimum and in this case a micro hydro wuld make a lot of sence. But the problem is in drought days it falls to under a gallon a minute. And this has happened 2 years in a row in winter too, we had no snow or rain…

So l then did calculations for a pumped storage and came to preety much the same conclusion as you guys. I will rather build ponds for irigation and fish. I have no problem eating fish over candle light thain eating nothing with the lightbulbs on

As for energy storage, halogen flow batteries interest me a lot. Iodine or bromine/zinc. Cheap, “easy” to make and scaleable.

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I am SO disappointed in you! You don’t feed your fish enough! They must be starving! You are supposed to trim the blubber off your fish, and render it and use it in your lamps.

As far as flow batteries, the ones I was looking at were the iron/table salt batteries. But you need the pumps that are controllable and are pretty expensive but I found out they are supposedly in drip coffeemakers But I dismantled two and didn’t find the pump… Then I looked at the cost of the membrane and it was like 200 dollars per square meter and I couldn’t find anything smaller. So that killed that idea. Im not spending 200 bucks to find out I am too stupid to get it to work. I can spend a lot less to figure that out.

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Before you do it, check the liability laws in your state. An above ground pool might be considered an attractive nuisance and require a fence. A lot of them around here have a deck that goes around to make it like 8ft high so kids can’t get in. Whether trespassing or not, you would be liable in our state. You may also have to pay extra for home/property insurance, but I forgot the explanation on why the person i was talking to had to pay for insurance for his pool. It may have been because the deck to the pool connected to the back porch or because of liability or both. I don’t recall exactly.

Sean, you must excuse my poor mind. I wuld never come up with such genius

Have you got any details over the iron salt batery? Im interested… never heared of it. lots of times the membrane can be simplified a lot. Maybe not as efficiant and fancy but probably good enaugh for a diy.

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You would if your fish weren’t starving!

These guys have the patents for it. It is technically iron chloride but i was thinking they use salt to get the chloride. And now that look at their drawing I don’t see the expensive separator…

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I would say it depends on what your biggest loads are. what you are talking about I think is what to do with extra energy either from a woodgas rig or a large solar array. For solar I would look closely on air to liquid heat pumps myself. Heat or cool (or heat and cool) large quantities of water when the sun shines and keep your house cool or warm through the rest of the day cycle using stored heat or cold. Our heat pump draws 1.5kWHr per hour of run time and is slated to become the dump load for my very modest solar array in the summer.

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I think, and I’m not sure how to check, that these were sold by the solar/hydro/wind folks a few years ago. Safer chemistry, but large size and weight, and relatively low current. They may have had durability issues. They kind of dropped of the websites, with some comments about credit toward other batteries. Not positive about all this, but it would be worth checking the history before you start a project.

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Aquion tried this a decade ago. They could never get the density required to make it a viable option. They went belly up and the patents got bought. Not sure its the same tech…
Correction not the same tech. Its a flow battery. One of the holy grails for the last 20 years. maybe this is the one?

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They had a flow battery but it was a different chemistry.

These don’t have a super high density, maybe even lower then what aquion had but it is extremely cheap and safe for a diy flow battery, and I think they only sell these to commercial/industrial companies. Aquion was trying to sell to the homeowner market.

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Aquion was and still is crazy expensive. I think some company in Austria still tries to sell them.

Looked for the bromium too, but again to expensive.
And for diy, the key is the membrane I think. Promising tech but hard to compete with LFP. Here in the Netherlands was some company too trying to sell salt water batt. Probably died silently….

Hello Chris,
not far from where I used to live in Colorado, the utility has a pumped storage facility, Cabin Creek, just outside of Georgetown, Co. This was a large-scale site, at night went the coal-fired plants had excess power they were able to energize the turbine to pump water uphill for use the next day.
do you spend time on the “other power” forums, feildlines. com? lots of information there. good luck, Kent

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I was thinking Aquion was a flow battery, but they are just a salt water battery. The cost of materials is what made them so expensive. plus they only have like a 70% efficiency. But I suspect they may freeze. But if you have access to 55 gallon plastic barrels, scrap copper and scrap zinc. and maybe an old root cellar (be careful they might offgas hydrogen) It could be really cheap.

They actually have a link to a DIY how-to video on their website now.

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As someone mentioned the Aquion battery’s came here to Australia and i have had my fair chance to buy them for next to nothing in the past , maybe next time a stack of 48 volts come up i will give them a go just for the hell of it .
Dave

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Consumers Energy has a pumped storage system a couple hours from where I live. They pump water from Lake Michigan up onto a bluff. Parts of it are open to the public to observe the size of the system. I remember being there some 35 years ago.

If you had a falling/flowing stream of water that you could use a number of ram pumps in series or using wind power then you could use the stored water for peak demand needs. 200ft of elevation change requires 87psi just to get water up that elevation. Pumping and plumbing losses are additional. It seems to me that to plan on daily use of solar pumped storage has too much inherent losses to be practical.

The neat part of the elevation that is available to you is that same head pressure can significantly improve efficiency of turbines.

Mother Earth News had articles years ago on using outboard boat motors for the propellor and lower unit gear box for mountain stream hydropower.
.

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I think consumers pumped hydro is only like 70-75% efficient without counting water losses from evaporation. They have to figure that into their cost on whether there is enough spread between high/low times to justify using it. I was in it once. They were repaving the interior because it started leaking, and the guy told me I could go down to the bottom. I think the manager was one of my dad’s former students.

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