A completely different energy storage project Topic is solved

[tomhanman]

Hello all.

I have built a couple of home energy storage projects. Both with cheap Chinese hybrid inverters (which I find work incredibly well for the measley cost) and ex EV batteries. I have one at home in the cupboard using MG 15s6p batteries 16.6kWh and a 5kW inverter but we are not allowed solar because of planning so I just use it to avoid peak rate, special high price days here in France, and all the mini power cuts common here. The other is a 24kWh ENV-200 battery split down to 14s6p with 3kW solar and a 3.2kW hybrid inverter which powers my workshop.

I don't use BMS. The inverter regulates top and bottom charge limit just as reliably (or not) as a BMS. And I have a Bluetooth active balancer on each system that keeps the cells in check. Obviously this leaves risk of a cell over charging in the event of the balancer not being able to keeps them even. But my experience ove the last three years with these systems has been that the cells are incredibly well matched by the EV manufacturers and I see virtually zero need even for the balancer. I just check in on them once a week to be sure nothing is going wonky. I'm.sure people with take issue with that. But whilst I'm allowed to cross the road by myself I figure I can make other grown up decisions also .

Anyhow, that is not why I am here.

I was wondering if anybody has considered, or even got anywhere with the idea of using the Leaf motor stack as a gravity battery driver. What I mean is using it to pull something heavy up and down in order to convert electricity to gravitational potential energy and then use regen to convert back again? Anybody? Any comments? Friendly

I have a 'spare' 2017 Leaf fully functional albeit with a bent chassis and no doors, windows, seats, linings, etc. And I have a hill. 100m tall 180m wide. I've done some light math, and can't see any reason not to. I'll leave it there for the moment and see if this gets any interest.

I should probably just stress that whilst I have a dream, I am wholly incapable of making it into a reality!! So I would be looking for collaborators.

Thanks for your time, I look forward to whatever it brings

Tom.

[johu]

I'm a bit lazy on maths, how much energy is in there per ton? Could the Leaf in its original chassis and some extra weight winch itself up the hill and down again? Or just drive up there in some guide rails.

[tomhanman]

Hi Johannes, thanks for reading.

I don't believe you are lazy at all

But no that wouldn't do much...

So for one tonne to rise 100m;
100m X 1000kg X 9.8m/s² = 980,000J
980,000J / 3600s = 272Whr storage!!

Then we'd have to get the electricity in and out of the Leaf. So either through rails or flexible cables... Both sound nasty!

I was thinking more about Leaf stack at top of hill driving a winch with about 750t of sectional weights. That would store just over 200kWh. Then I was thinking 11 of them in parallel to store about 2MWh per day. Charging on solar peak shaving for the evening, and charging on night rate for the morning. And that is ignoring any losses, of which of course there will be plenty!

What I don't know is can the Leaf stacks be converted to provide as much power in regen as propulsion? I would be looking at using 2013-17 type. And what is the efficiency of that cycle like?

Well there's an awful lot more I don't know, but better start with the basics!

[johu]

The motor is capable I'm just not sure if the stock control board will let you do it. The Leaf1 OI board was never polished up for sale, Leaf2 is your only option there right now.

Efficiency I'd estimate as 90% per conversion, so 80% for one charge/discharge cycle plus frictional losses of the weights.

[tomhanman]

10% loss in each direction is quite significant. How much of that is in the motor and how much in the inverter?

And then what AC voltage does the motor use?

Because in reality I'd like to be running it straight from 3-phase grid electric @ 400V taking from the inverter outputs sending back into the grid as desired.

Unlikely these voltages are going to line up, but if they did I assume some efficiency could be gained?

[johnspark]

What about a ~ 10,000 litre water tank at your 100 metres height, another at ground level, 50mm or 100mm diameter pipe between the two and pump the water up, and gravity feed your generator down the hill?

[tomhanman]

I should have qualified my statement on the 10% loss by saying that actually that is very good of course. The problem is having to count it twice whilst also adding maybe another 10% for frictional losses. Then a battery where you only get out two thirds of what you put in is not looking so sexy!

Must find a route in and out of the leaf Motor just as AC could that be done and could it being us to somewhere near 95% efficiency if the motor was always run at it's peak efficiency speed. I'm sure I've seen a graph somewhere showing the progression of efficiency of the motor through rpm. But don't know where.

Anyhow, yes Johnspark, pumped hydro as you describe is quite well established and works. But rather than a 10,000l tank which would store just over 2kWh, you tend to need lakes, or even glaciers! It does make some things simpler - no chains or cables or rails. But with such vast volumes of water needed (as it's only about a fifth of the heaviest concrete blocks) you need open reservoirs top and bottom... Which means evaporation, which means you need a natural source of water to maintain levels. Which I don't have. Losses are also significant in pumped hydro just with different friction.

As an aside, it just so happens that the amount of energy required to lift 1 tonne by 1 meter can be found in a single high quality AA battery!!

[arber333]

I should have qualified my statement on the 10% loss by saying that actually that is very good of course. The problem is having to count it twice whilst also adding maybe another 10% for frictional losses. Then a battery where you only get out two thirds of what you put in is not looking so sexy!

Must find a route in and out of the leaf Motor just as AC could that be done and could it being us to somewhere near 95% efficiency if the motor was always run at it's peak efficiency speed. I'm sure I've seen a graph somewhere showing the progression of efficiency of the motor through rpm. But don't know where.

Anyhow, yes Johnspark, pumped hydro as you describe is quite well established and works. But rather than a 10,000l tank which would store just over 2kWh, you tend to need lakes, or even glaciers! It does make some things simpler - no chains or cables or rails. But with such vast volumes of water needed (as it's only about a fifth of the heaviest concrete blocks) you need open reservoirs top and bottom... Which means evaporation, which means you need a natural source of water to maintain levels. Which I don't have. Losses are also significant in pumped hydro just with different friction.

As an aside, it just so happens that the amount of energy required to lift 1 tonne by 1 meter can be found in a single high quality AA battery!!

I think even better design would be flywheel in the ground. Flywheel made of concrete (reinforced by wood fibers)
https://www.pv-magazine.com/2021/06/21/ ... ential-pv/

Your Nissan Leaf motor would work to accelerate this mechanism and later to pull energy out of it during night hours.
Containment of spinning parts is not a problem since it is underground.
About the only problem of this setup would be the reliability of bearings.
Also since flywheel does detect complete system motion not just its own, this system feels forces outside earth...

[johu]

Thinking about this further you'd need a quite substantial reduction gear which means more losses. Have no idea how much.
As a rule of thumb PM motors as you already stated are considered 95% efficient and IGBT inverters 97% - peak, under tight inverter control. Direct grid connection would run the motor in a suboptimal operating point.

Don't want to talk you out of this, but it seems devil is in the detail.

If you have a concrete block handy just winch it up and down, see what you get returned. Doesn't require specialized control

[arber333]

Thinking about this further you'd need a quite substantial reduction gear which means more losses. Have no idea how much.
As a rule of thumb PM motors as you already stated are considered 95% efficient and IGBT inverters 97% - peak, under tight inverter control. Direct grid connection would run the motor in a suboptimal operating point.

Don't want to talk you out of this, but it seems devil is in the detail.

If you have a concrete block handy just winch it up and down, see what you get returned. Doesn't require specialized control

I have been thinking about this for some time now. However not by itself. I would combine this with my existing battery and solar system.
Yes devil is in the details. I would need to optimize the winch system and motor for 48V output and best RPM operation.

My idea of setup involves that Hyundai HSG motor and Lebowski inverter.
Flywheel should not ever stop because spinning it up from 0 requires substantial torque and it would be better to keep feeding the minimal RPM.

[tomhanman]

Ahh the details and the devil. Yes indeed.

Every project needs caution and solutions in equal measure I guess. So rock on.

The flywheel is indeed a studied concept. But I am not going anywhere near it. Even for home store the speeds are ferocious and I think anyone considering it should be working in lab level precision to ensure those bearings last at least a little while before causing a separation of the tectonic plates.

I'm not completely put off my initial idea . Obviously more work is required. I wasn't looking for a pat on the head and a 'yes you've just solved the energy crisis' . There are just so many elements that I am not clear on in terms of the motor / controller / inverter functionality.

I had planned 3m³ cubes weighing 15t. And each motor stack needing to raise 25 of those in an hour in order to store 100kWh. The track would be about 200m long (slope of 30⁰) so this would translate to a speed of 5km/h. I assume the motor can't produce enough torque at that speed to make 100kW. But what if I simply removed a roadwheel and replaced it with a 65mm diameter sprocket? Then the Leaf would think it were travelling at 50km/h. Could it do it then? If not, then it is only a single 3:1 drive from that sprocket to the lifting gear to finish with the Leaf doing 150km/h whilst the weight is moving at 5km/h. Where in that range is required?

It is definitely the power in and out that is the sticking point. 3-phase grid voltage is 400V, but only after the local substation takes it down from 20,000V or even more. So the possibilities are endless. I don't know where the regulation of the motor power in/out occurs. Is it in AC or DC... Or halfway between the two?

If this were to be assembled, 1MW in/out of the 11 Leaf array would require a high voltage grid connection anyway (as would the rest of the solar install). So is a bidirectional voltage regulator / motor controller a conceivable thing? It sounds Cool that's for sure!

There are lots, and lots of things to resolve. And one of them may prove too much. But nonetheless I think it has potential, certainly as much as the Swiss bunch trying to build 100m high warehouses to do this exact thing. There are Americans trying to send train trucks up and down a hill in Nevada or somesuch place. The Scots trying to do it in disused mine shafts have got a lot going for them, but not everyone has one of those handy. I have a hill

[SuperV8]

Hi Johannes, thanks for reading.

I don't believe you are lazy at all

But no that wouldn't do much...

So for one tonne to rise 100m;
100m X 1000kg X 9.8m/s² = 980,000J
980,000J / 3600s = 272Whr storage!!

Then we'd have to get the electricity in and out of the Leaf. So either through rails or flexible cables... Both sound nasty!

I was thinking more about Leaf stack at top of hill driving a winch with about 750t of sectional weights. That would store just over 200kWh. Then I was thinking 11 of them in parallel to store about 2MWh per day. Charging on solar peak shaving for the evening, and charging on night rate for the morning. And that is ignoring any losses, of which of course there will be plenty!

What I don't know is can the Leaf stacks be converted to provide as much power in regen as propulsion? I would be looking at using 2013-17 type. And what is the efficiency of that cycle like?

Well there's an awful lot more I don't know, but better start with the basics!

Interesting idea.
750tonnes sounds a lot! I think I would do some calculations on the angle of your hill to work out how much force your cable will be cable of + safety factor.

[tomhanman]

750 tonnes is a lot. If you read everything you'd see that it would be in 15 tonne blocks... So not all 750 at the same time. Thankfully