Photovoltaic Energy - Viable Capacitor Storage ?

Why capacitors? Deep-cycle batteries are used normally.

Quite!

Why "Quiet!" - are we not allowed to mention 'super capacitors' or something?

You need very large capacity capacitors to store the energy. Perhaps it will be ideal to make these capacitors using basic theory and from long lasting material. I think it is worth discussing as Batteries, particularly Lead Acid do not last long and also are hazard due to Lead involved.

Many of you may have good idea about making capacitors from foils and simple dielectric like polypropylene or polyester. Perhaps Mylar films with high voltage breakdown can also be tried.

Assume that you want to store 10kW energy on capacitors, then see if that is really feasible as very large capacity capacitors or supper capacitor for high voltage not going to be all that easy. Storing in ionic form is much easier so it is done now, but what you can see for future is yet to be explored and is a good engineering problem.

I have no experience with ultra-caps, but some things ringing a bell in my mind:

1. I recall that they may have higher self-discharge rates than batteries. This may be a problem if storage takes place over longer periods.
2. Ultra-caps are often used where their very high discharge/charge rates (as compared to electrolytic batteries) are of benefit.
   

You are not right here.

Ultra capacitors are used to store fast and release energy slowly and are often used for backup power to memory devices to keep data for long period. As these capacitors have low leakage current, they can almost work like good battery.

If you use ultra capacitors for AC Power Signal in Audio Amplifier then they sure with have high energy in short cycles running into kHz rates of charging and discharging. For this one needs Gold Capacitors for higher voltages and high capacity with low noise and not those low voltage several Farad level capacitors used for memory data backup.

Thanks Shyam, I stand corrected! (That is why I'm on CR4 - I need to keep up with technology's march!) Would your answer also be true in power applications (100V+, 200Ah+ systems)?

BTW, any good on-line places to do a bit of research on them? The suppliers' sites often glow on the positive, neglecting to highlight some negative or limiting issues.

Polypropylene, Polyester, MKP, SF6 capacitors perhaps may be suitable to store charge for short back up time less than 1 hour and leakage resistance need to be 1000G Ohms order. Aluminum capacitors leak very fast.

No. Maybe in the next 10 years.

http://bariumtitanate.blogspot.com/2010/04/penn-state-unveils-capacitor-thats-cost.html

We're on our way to achieving capacitor type storage units. There's already a screwdriver on the market that gets it's power from a capacitor. See it at:

http://www.popularmechanics.com/technology/gadgets/4223118

Also, a friend of mine said there was some street lights in Mexico that are powered by capacitors. The capacitors are charged during the day with solar power and the capacitors power the lights at night. Seems like an efficient system to me. However, the initial cost may be such that conventional grid power may be more economical today.

But what about tomorrow?

That is about 250 capacitors at $20 each.

Total cost ~ 62 500*$20 = $125 000.

No $125 000

it must be $5 000

250*$20 = $5 000

one farad = 250 caps, 250 Farads = 62 500 caps.

Errors in my calcs.

electros: 62 500 caps at $20 = $1 250 000.

super caps: 80 caps in series make 1/80 Fd at 400V.

6 400 caps make 1 Fd at 400 Volts.

250 Fds total cost = 6400*250*$5 = $8 000 000.

Frankly, other types of energy storage are much more efficient and cheaper than caps. If you are looking for an alternative to batteries, try using compressed air or a flywheel system. You could even use a water/gravity system.

Caps are expensive, not efficient, and electrolytic ones have a bad habit of exploding....