Ultra cap in solar charging

[Joe Lee]

Hi there,

I've a small 20W 12V solar charging setup, which charges a sealed lead acid cell via a max power point controller. The cell I am using now is rated at 12V/17AH, which takes quite some time to fully charged with my setup, that's not the problem as long as it charges, but the cell started to show it's age after couple years of use, it does not hold the charge any more, so it is time to replace it.

I am considering to purcharge a fuel cell kit, but the setup is quite complicated and the cost is high, then I find the Ultra cap, which seems quite simple and plug and play, but I've no prior experience with it, and don't know where I can purchase it, can anyone show me the way, thanks !

[Dave Turpin]

Capacitors are not really a viable energy storage option.

The energy stored on a capacitor is 1/2CV^2. I could do the calculus but just take my word for it.

Even if you had 100 Farad of capacitors (which is a friggin' huge bank of capacitors), at 12 volt you would be storing only 1/2*100*144 = 7200 Joule. Convert Joule to KwH and you get:

0.002 kWh. You could store more energy on a AAA battery. Also note that this is the ideal situation where you could use 100% of the energy on the capacitor. In reality you would be lucky to use 5% before your voltage dropped too low to use in an invertor.

Rule of thumb: If something is not widely used, there is probably a good reason why.

[Rob Beckers]

Dave, Maxwell will sell you a container (yes, 20' container) full of ultracaps, with a total capacity of 372 Farad, running at 740 Volt. That stores a whopping 100 MJ.

Before you get too excited, that's just 28 kWh.
Just enough to run a smallish North American household for about a day, if you could discharge them 100% (which you cannot). So, for that you need a container load of capacitors, and a few million bucks... :(

We got a little ways to go before supercaps become a reality.

-RoB-

[Dave Turpin]

Nice. What does that cost? 2 million?

Here is some reverse math:

Your tiny battery is 17Ah at 12v? That's 204 Wh, or 0.2 kWh. With a 12v solar panel, you would need ONLY 10,200 Farad of capacitors. Again

So, that's only 27.4 ConEx boxes full of capacitors. It would cover more square footage than your house.

On the other hand, my SUMP PUMP has a 140 Ah battery backup. ;)

[Joe Lee]

Right.... I got over excited with Ultracaps, and even more excited than with Fuel Cell, I'll need a bigger house FULL OF CASH before I can go any further !

[Rob Beckers]

Nothing wrong with excitement Joe! I'm still very hopeful for the future, that true supercaps will eventually see the light (such as those EEStor is working on). It would be a breakthrough. In fact, the real problem, or the real solution if you will, is not the production of (renewable) energy, it is storage. With better storage we could have electric cars that completely replace the utility of our current gasoline cars. Intermittent energy sources could be much better utilized. And resources such as PV in the desert would be much more feasible if we could store and move that energy without expensive transmission lines.

Invent the better battery and you're not only going to be very rich, it would change the world.

-RoB-

[Joe Lee]

Well I don't expect to have my own Ultracap farm to replace the utility any time soon, I just want to replace my tiny, poor Joe's PV charged, dirty battery, with any clean energy source/storage available and affordable, such as Fuel Cell and UC, I know they are different things designed for different use, but they both work in my application. Now it seems to me that, Fuel Cell is more feasible, in spite of the complexity in the setup and maintenance. Actually I am just looking into a FC portable power device capable to produce 60W @12V, which is good enough for my application, ie. power up and recharge my notebook (via DC-DC), and various USB gadgets...etc., and the device itself does not bigger than my notebook, it seems practical. But I am still interested in UC, I think I will give it a go if I can find something come up with 30% power of same size of the common dirty battery can produce, of course the cost is the major factor as a hobbyist.

Questions remain such as, the self discharge rate, the life span, and special care in use and charging...etc., I am very new to UC although I've some background in electronics, it is completely new thing to me, I just scratched it's surface !