PV, Vanadium Redox Batteries and MPPT

[BigBreaker]

I posted a while back about an exciting battery technology reaching maturity, Vanadium Redox (VRB).  I was reseaching MPPT recently, looking for schematics, and I ran across a VRB/MPPT article addressing a really cool implementation of MPPT technology in a VRB unit.

http://www.geocities.com/CapitolHill/3589/VANADI3.HTM

VRB can charge at almost any voltage and output at any voltage due to it's multi-tap electrode stack.  This means that VRB systems do not need all the high current switching electronics like heavy duty capacitors or power MOSFETs.  All you need for MPPT is the logic and some simple switches for the multi-tap.

The link is also pretty good at explaining VRB technology.  I haven't run the numbers in a while but is $200/kWhr still competitive with lead-acid?  Note that VRB can deep cycle to 85+% discharge so that is almost all USABLE.

[willib]

I read your other post , that was the one on flow batteries.?

that  was a really interesting post..

and was thinking how easy/hard it would be to test one out.

One would need two pumps , some vandium ion solution ,but what to use for the ion exchanger??

[willib]

from that page

"

If any inadvertent mxing of the charged electrolytes occurs there is an energy loss as heat but, because the mixed electrolytes revert back to their uncharged states, they can be recharged next time through the stack. Thus, cross contamination is not detrimental to the longevity of the battery"

So i guess it dosnt matter if the two solutions get mixed a little bit , that makes things a lot easier..

[willib]

sorry about this multiposting , but this is really some great stuff

"Additionally, this battery has a feature which allows for many new options not available with lead acid technology. It is possible to simultaneously charge the battery at one voltage while discharging it at another voltage. This feature can be utilised to make a minimum cost, high efficiency, maximum power point tracker or allows to operate the battery as a DC transformer, electro-chemically transforming a current and a voltage into a different current and voltage."

[wdyasq]

T105 ~$60 discharge to 1/2 - 200AH X 6V = 1200W/2 = .6kW therefore for same rate of 'quality discarge' ~$100kW.

Someone please verify my math.  I just did a quick calcultion to come up with this.  A large difference in discharge or changine the AH rate to 220 will yield different - but not massive - numbers.

Ron

[monte350c]

It does look expensive.

I sent them email asking for FOB costs and tech info for a 5 KWH storage setup.

I'll post back if they send anything.

Ted.

[willib]

There was another paper on the discoverer of the REDOX 2 system, which said that it could be used in automobiles , a simple exchange of fluids (solutions) and you are good to go..if i can find the link again i'll post it..

[willib]

The benefits of the Generation 2 Vanadium Redox Fuel Cell system can be summarised as follows:

·        Simpler, safer, more efficient and much lower cost than gaseous Hydrogen Fuel Cells

·        Refuelling in five minutes by exchange of electrolyte at a specialised refuelling station allows 24 hour operation of buses, taxis, fork-lift trucks and other vehicles (not possible with any other type of battery system).    

·        Electrolyte fuel is recharged in the refuelling station using renewable energy or off-peak grid power and is re-used continually

·        Silent, emission free operation in electric urban vehicles

·        160 - 180 km between refuelling stops - system energy density approximately 50 Wh/kg, twice the Generation 1 VRB energy density

·        Convenient integration into conventional IC engined fleets - refuelling points may be sited alongside diesel or petrol pumps

·        Subject to local market conditions complete Redox fuel systems could be installed for fleet operators and electric fuel could be sold at below equivalent cost for gasoline or diesel

·        Fleet operator studies conducted by the UK-based company, EFuel Techologies Ltd, and based on UK economics show overall cost savings, including capital depreciation, at less than 50% that of gasoline or diesel fuel

http://www.ceic.unsw.edu.au/centers/vrb/Magnam-VFuel%20website%20info.htm

[willib]

"Production cost: of bipolar stack in volume production is projected at $100 to $150 per kW for Redox "

http://www.ceic.unsw.edu.au/centers/vrb/Magnam-VFuel%20website%20info.htm

[BigBreaker]

You have really highlighted the key advantages.

They only two difficult things from a DIY perspective are sourcing the ion exchange membrane and preparing the electrolyte.  I don't know of any low tech uses of those membranes that would provide a consumer-type source.  Getting the vanadium (sulfate) powder is pretty easy but apparently getting it into solution at a high concentration is an art.

The pumps should be pretty simple to find.  The anode/cathode stack requires graphite contacts which should be pretty easy to find.  Worst case you can open up alkaline batteries...

The control scheme is easy in concept but would require a microcontroller - especially if you want to do the MPPT stuff.  I'm an EE and find that much less daunting than 60 foot towers or carving turbine blades, but that's just me.  YMMV...

[BigBreaker]

The cost goes down with lower power requirements.  Said another way - marginal capacity (kw*hr) is cheaper than marginal power.  I think the lifecycle is MUCH longer though.  How quickly do batteries derate?  Vanadium is an element - it never degrades.

[willib]

I agree that preperation of the electroylyte , in a workable concentration is difficult.no art involved , all science ( wink )

But since they said a little mixing of positive and negetive ions , will not hurt it at all , then just about any semipermeable membrain will do fine..