Capacitor storage

[miahallen]

Thanks Bruce...The pump is on a 15A circuit...but I don't know more than that. My clamp meter just died and I'm waiting on a new one to arrive.

I don't know how to calculate the current delivery of the cap bank...where would I find a high current 48V SEPIC converter??? Or are there AC SEPIC converters?

The batteries are Trojan L16P-HC and the system is at 48V as you speculate. The system has been up and running for about 2 1/2 years now.

[bcroe]

I'm not proposing a solution in a neat package. Rather, how to predict the performance of what ever you might
invest in; instead of being disappointed later. Finding the right SEPIC converter might be a challenge; tend to
roll my own here. A simpler way to solve the problem might be buck convert the 48V down to a well regulated
24V (or your setting) if you can operate this way. Putting the converters at the load will give maximum efficiency,
a frequent practice in industry. This approach doesn't care about the droop.

Figures for the battery should be easy to find, or make a load test (do they agree?). If your new DC clamp on has a peak
memory, it might be good enough with a stopwatch timing the main surge and assuming a near linear ramp. A storage
scope will do a much better job if you apply one. The cap droop is directly proportional to amps withdrawn, or I/C= dV/dt
Bruce

[Mike90250]

Most of the large inverters have an internal Large Cap. One of my inverters' fault codes is Capacitor Overheat. A cap inside the inverter, is much better than trying to build and fuse a cap bank outside. And then there is the inductance of the cable from the cap to the inverter, To be low enough to be useful, you need 1" tinned copper braid, Round cable, for the surge spike, has too much inductance, At regular loads, not a problem with round wire.

[Amy@altE]

Duke Energy is testing out a system combining Aquion Energy batteries, which have a known limitation of not liking high current draws, and ultra caps to help smooth out the power. news.duke-energy.com/release...he-test-in-n-c

[SunEagle]

Duke Energy is testing out a system combining Aquion Energy batteries, which have a known limitation of not liking high current draws, and ultra caps to help smooth out the power. news.duke-energy.com/release...he-test-in-n-c

I read that article a while back. There is also another POCO, not in the US, that is testing the Aquion energy batteries for a large scale storage system. I just don't remember who but I added a link in another thread where Aquion is mentioned.

Or maybe I am getting confused with a Tesla PowerWall battery system project in Europe.

[bcroe]

Can't calculate without numbers. I still don't know if there are any AC inverters involved. Bruce Roe

[jflorey2]

Duke Energy is testing out a system combining Aquion Energy batteries, which have a known limitation of not liking high current draws, and ultra caps to help smooth out the power. news.duke-energy.com/release...he-test-in-n-c

That's one of the few renewable-energy applications that ultracaps work well for - high energy density but low power density energy storage systems.

[BackwoodsEE]

I was thinking about the idea of using some Maxwell supercaps to supplement the 48V battery during a well pump start. The startup current surge would last for a fraction of a second, so I reasoned that this might be an application that would actually make some engineering sense. (Disregard for a moment the significant cost.)

Well, (no pun intended), it didn't. Not even this short-duration situation. I simulated the capacitor and battery circuits using ESR of both and modeling the capacitor bank with the equations. I could have used SPICE for the simulation, but just programmed the thing in Python using the math and some iterative integration. (That kind of stuff is what I consider fun.)

The capacitors quit contributing to the current flow partway through the well pump start-up, and due to their ESR (which scales up directly when you put them in series, as you must), their contribution was limited from the start.

Here are some specs from Digi-Key for one of the supercaps available. Note that you would need around 22 of these things in series, with all the balancing stuff that entails, to withstand the highest charge voltage on the AGMs I plan to use, adding up to a total ESR of around 15 mOhms. That's equal to the ESR of the battery bank itself, which means the caps are only pulling half the current at most.

IMG_1068.PNG

The only thing I see capacitors as being potentially useful for in a RE storage system is smoothing out the 120 Hz cyclic current draw from an inverter. Even there, the ESR has to be extremely low, probably restricting you to a bank of paralleled electrolyics rather than series double-layer supercaps.

[SunEagle]

I was thinking about the idea of using some Maxwell supercaps to supplement the 48V battery during a well pump start. The startup current surge would last for a fraction of a second, so I reasoned that this might be an application that would actually make some engineering sense. (Disregard for a moment the significant cost.)

Well, (no pun intended), it didn't. Not even this short-duration situation. I simulated the capacitor and battery circuits using ESR of both and modeling the capacitor bank with the equations. I could have used SPICE for the simulation, but just programmed the thing in Python using the math and some iterative integration. (That kind of stuff is what I consider fun.)

The capacitors quit contributing to the current flow partway through the well pump start-up, and due to their ESR (which scales up directly when you put them in series, as you must), their contribution was limited from the start.

Here are some specs from Digi-Key for one of the supercaps available. Note that you would need around 22 of these things in series, with all the balancing stuff that entails, to withstand the highest charge voltage on the AGMs I plan to use, adding up to a total ESR of around 15 mOhms. That's equal to the ESR of the battery bank itself, which means the caps are only pulling half the current at most.

IMG_1068.PNG

The only thing I see capacitors as being potentially useful for in a RE storage system is smoothing out the 120 Hz cyclic current draw from an inverter. Even there, the ESR has to be extremely low, probably restricting you to a bank of paralleled electrolyics rather than series double-layer supercaps.

Thanks for providing up to date info concerning capacitors and how they really don't work as an energy storage device as some people are led to believe.

[max2k]

I was thinking about the idea of using some Maxwell supercaps to supplement the 48V battery during a well pump start. ...

you can't simply connect caps to battery in parallel due to different discharge curves. To get any noticeable energy out of the cap it has to be significantly discharged in voltage while batteries tend to keep their voltages within narrow range for the most of their capacity. That's not to say some electronics wouldn't help where they'd be charged much higher and then discharged from there using some current source type of component.

Back to your original problem- is it really necessary for your well pump to have such high starting current or it just consequence of the motor used? I mean some motor controller might help to smooth out start up process. OTOH if it needs that current to overcome some friction and not just inertia the motor controller would be useless.

[peakbagger]

Our firm talked to this company with respect to a CHP project. https://flexgen.com/platform They have operating installs in oil and gas. Standard generators can only put out a given surge load so the drillers have to oversize the gensets and idle them the rest of the time which is not great for a diesel. The Ultracapacitor basically injects power during the surge and also can absorb the step load when the load drops. Net result is the driller can get away with smaller gensets and lower fuel usage plus the equipment is happier as there isn't a major sag when the load hits.

[max2k]

Our firm talked to this company with respect to a CHP project. https://flexgen.com/platform They have operating installs in oil and gas. Standard generators can only put out a given surge load so the drillers have to oversize the gensets and idle them the rest of the time which is not great for a diesel. The Ultracapacitor basically injects power during the surge and also can absorb the step load when the load drops. Net result is the driller can get away with smaller gensets and lower fuel usage plus the equipment is happier as there isn't a major sag when the load hits.

I'm sure they're not just connecting bare caps in parallel to the generators .

[BackwoodsEE]

you can't simply connect caps to battery in parallel due to different discharge curves. To get any noticeable energy out of the cap it has to be significantly discharged in voltage while batteries tend to keep their voltages within narrow range for the most of their capacity. That's not to say some electronics wouldn't help where they'd be charged much higher and then discharged from there using some current source type of component.

You could put a bidirectional buck/boost converter between the caps and the battery to push the voltage up when the caps discharge below the 48V battery, and then drop the 48V down to recharge the discharged cap. The problem is with the tremendous currents involved. You need a massive inductor that doesn't saturate until beyond 100A, and capacitors and switching and flyback semiconductors that can carry 200A or more (for a 2:1 boost). Add in I^2*R losses from resistance of connectors, magnet wire, silicon, and PCB traces, and you start to realize that this isn't much of a solution, either.

[bcroe]

At last the cap Myth is dispelled.... Bruce Roe

[Mike90250]

Yep. Caps will give you "some" boost, but their voltage falls off rapidly. if you have a 48V battery, the cap is charged to 48V and at 47.9V it stops contributing power, even though it's still 95% full.