Off Grid Home › Forums › Technical Discussion › Using capacitors instead of a battery
- This topic has 17 replies, 9 voices, and was last updated 10 years, 6 months ago by retired profile of WrethaOffGrid.
November 9, 2012 at 12:00 am #63246retired profile of WrethaOffGridSpectator
What do you think about this? I know there are a lot of great tech heads here who have an understanding about this, I’m officially picking your brain. I have wondered in the past, why you couldn’t use capacitors in this manner…
Trying to embed the video, if it doesn’t work, I’ll just post the link.
Bummer, couldn’t embed it… just watch from the link
WrethaNovember 9, 2012 at 12:00 am #66869chowanParticipant
I cant watch the vid due to connection but i could probably offer
capacitors are capeable of storing energy so it would be possible
to do something on a small scale small led lights etc.
large scale (house usage)i dont think they have the energy storage
density that lead acids do.
and on a large scale capacitors would be very dangerous they have little
or no internal resistance unlike a battery so they can dump there entire
charge in an instant.
most of us have dropped something metal across the terminals of a lead acid
battery to be rewared with huge sparking and a big fright.
a similar accident on a large capacitor bank would probably literaly
vaporise a large tool and or explode.June 11, 2013 at 12:00 am #67540
I couldn’t watch the video, but I can tell you that super capacitors are a poor choice for off-grid power storage. As Chowan has said the energy density is far less than a lead acid battery. But the real problem is that unlike a battery a capacitor will have a voltage drop that is unexceptionable. A fully charged 24v battery system will have 25.46v when fully charged (Trojan T-105’s) and at 50% DOD the voltage will be 24.2v and at 90% DOD it will still have 23.02v. The capacitor will go from 25.46v (or whatever voltage you choose to store) down to 0v when fully discharged.
Capacitors store electricity, but batteries produce not store electricity. The way a battery works is that the sulfur atom in the electrolyte (sulfuric acid) bonds to the lead alloy forming lead sulfide. This releases Hydrogen and Oxygen from the electrolyte and produces (releases) two electrons. When a load is applied to the battery terminals these electrons can flow and the chemical reaction can continue. When you charge the battery, you reverse the voltage and “Push” electrons back into the lead sulfide causing the sulfur atoms to return to the electrolyte. This is why you don’t want to discharge your batteries to far as that would allow the acid to degrade the lead plates. It is also why the most accurate method of measuring the state of charge of a lead acid battery is by measuring the specific gravity of the electrolyte with a battery hydrometer.
OK, I’ve rambled enough, the short answer is that the voltage will drop below what your inverter can use. To date, there is no more efficient way to store power than a good quality deep cycle lead acid battery.
Zathris….June 11, 2013 at 12:00 am #67542
what do you think of earth batteries?June 11, 2013 at 12:00 am #67546
Earth batteries fall into that category of interesting but mostly useless knowledge. They have very low energy density, low voltage, are terribly unreliable and can not be recharged. To get anything approaching useful power the size of the plates would have to be so large as to make the project far more expensive than buying a good battery.
There are many many ways to make a battery. Pennies and vinegar, a lemon and two pieces of metal, etc. but for a reliable power source a FLA (flooded lead acid) battery is the most practical way to go. Period.June 11, 2013 at 12:00 am #67551
there are ways to increase surface area without the electrode being huge
and depending on the polar orientation earth batteries can be quiet stable and reliable
no, you cant recharge them, but they do give steady power flow
and im not talking apples and oranges, i said “earth” and i meant it…lolJune 11, 2013 at 12:00 am #67554caverdudeParticipant
I had a friend who tried earth batteries, he lit a small LED light over his door way for quite some time with it.June 11, 2013 at 12:00 am #67559
Well if you can come up with a way to make them work, I’m all ears. But to the best of my knowledge no one has come up with a way to get any practical usage out of them. Lighting a few LED’s sure, but coming up with enough power to run my frig, TV and laptop is a different story. I suppose it could be done, but you will likely spend more trying than solar panels and batteries. I understand that early telegraph companies tried to use them but found it to be unreliable as when the ground dried out they quit working. But if you get even 50 watts out of them I would love to hear about it.
Zathris….June 11, 2013 at 12:00 am #67561caverdudeParticipant
Lighting yard lights maybe? lolJune 20, 2013 at 12:00 am #67648MrEnergyParticipant
Many companies are working on hybrid Lithium-Polymer-Ultracapacitor battery designs looking for the best of both worlds. The benefits of such a battery are high current capability, no “memory”, fast charging, temperature stability, very long life. Prices are high right now for all LiPo types but are coming down rapidly.
There is a way to build your own supercapacitors. My initial design shows a room sized bank of 4’x8’X8′ homebuilt supercaps in order to replace 12 L-16 Trojans. Self discharge rates are unknown until they are built, but they would be very fast charge/discharge capable and would have a very long life. Somewhere on the order of 50 years. These use large sheets of 1 micron carbon with mylar separators.
TadAugust 2, 2013 at 12:00 am #67864norcalllParticipant
NO! In short, that really is the answer. If youre like me youre going to want to know why. Think of capacitors like the front two shocks on a mountain bike. They lighten the load and strain on your battery. This will extend the life of your battery if you have multiple appliances or even a single appliance that draws 3-4x the power during startup that it does when it is running. THink A/c, Heat, maybe a large freezer, some vaccums. This all really depends on the size of your system. But honestly, you are comparing apples to oranges here. Capacitors are designed with circutry meant to discharge LARGE amounts of power or a minute or two TOPS!! They function best in blasts of 10 seconds or around there. Are they potentially helpful? yes. Are they batteries? no. they are far from batteries.March 14, 2014 at 12:00 am #68111lorenzopParticipant
capacitors are interesting, but not the best choice for solar power storage due to the way they discharge and drop in voltage faster, as other posters have mentioned. what’s interesting is, as a large capacitor drains, the voltage will drop smoothly, but eventually will be low enough an inverter will power off, even though a capacitor would still have plenty of current left to deliver.
what if, you put a capacitor bank before the charge controller? you would still need a lead acid battery, but I wonder if a capacitor bank would be worth having to supplement. may also need a dump load or disconnect to prevent over charging the capacitors. the way I picture this experiment working, solar panels charge the capacitors, which feeds into an efficient MPPT charge controller, then into a smaller lead acid battery bank. the charge controller can then pull more power from the capacitors after sundown, and draw them lower than what an inverter alone could do.
taking the experiment a bit more to the crazy side, you can wire a DPDT relay to switch 2 banks of capacitors between parallel and series. put a sensor on each bank to detect when they’re both lower than 50%, then trigger the relay to switch the banks over to series which puts your MPPT charge controller back to 100% voltage. although the current will be about 25% of what you had when it was in parallel, the voltage will be boosted high enough to allow a deeper draining of the capacitors, which they’ll be more than happy to do daily.
what do you think of my idea? I’m unsure if this would help or hurt efficiency in the real world, but it is interesting and could be worth trying. any flaws I haven’t thought of?March 15, 2014 at 12:00 am #68116MrEnergyParticipant
It would work. I’ve placed 50 farad 12 volt caps in front of the battery bank before and it does add to the total capacity of the system. The issue is that no one that I know of has ever built a massive capacitor bank in order to run from continuously. In theory a 20,000 Farad bank would perform better than any battery chemistry and would have an extreme lifespan compared to even Lithium chemistry batteries. The electric revolution is already here, but the storage side of the equation is still years away. Until Graphene hybrids are available at lead acid prices we will be moving forward at a snails pace. The company I do battery research for is working on these technologies: https://www.caleb-battery.com/
But it is still an expensive battery because of the materials they use. Graphene batteries show the promise of inexpensive batteries with long life and will perform under extreme abuse (they have shown to take bullet holes and still perform at the same capacity just like Li/Po batteries do).March 18, 2014 at 12:00 am #68119
a large capacity capacitor isnt hard to make
this could be a fun experiment and may prove usefullMarch 18, 2014 at 12:00 am #6812412vmanParticipant
If you have a higher voltage in storage, you wouldn’t need a capacitor bank as big as needed for a normal operating voltage. No charge controller needed as long as the open circuit voltage of the panels connected in series doesn’t exceed the designed capacitor bank voltage.. (A blocking diode would be needed)
In this case, the maximum storage voltage would be 90 volts and the unit would provide 12 volts @ 10 amps until the capacitor bank drained down to 50 volts.. (A 40 volt variance)
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