Supercapacitor EV discussion

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CMiller

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I'm looking into an ev conversion.

I guess a good example of my question would be the chinese buses using supercaps that have to recharge at each stop and how would these buses benefit from having a solar array an the roof of the bus. How many supercaps would you need to run a 280v input dc motor and how many solar watts would you need to charge this supercap bank to give the vehicle a range of at least 100 miles. But hopefully on a sunny day the caps would always be charging.

I'm asking because I have a 4000lb "small" boxtruck with 12ft×6ft roof space that I think I could fit 5 327w solarpanels. If I had a warp11 280v input dc motor how big of a supercap bank would I need to run the motor and then would 1600watts from solar charging make any difference in range charging that supercap bank.

And would it make any difference using a higher or lower input motor.
 
CMiller said:
12ft×6ft roof space
Click to expand...
  • that would be 72 ft**2 or 6.68 m**2
  • (best case) (1367 W / m**2) * 6.68 m**2 ~= 9.132 kW :: solar flux
  • 9.132 kW * 15% ~= 1.37 kW :: best case power
Now my very much smaller, Tesla Model 3, would travel about 5 miles on that peak, best case, power.

The power saved by using solar power on the top of a vehicle could be used to provide cabin or space cooling. This could save AC costs or possibly reduce the 12V power spike effects. But it would be 'expensive.'

Bob Wilson
 
Thanks for your reply.

I understand that its probably a unreasonable idea. Especially if I was using batteries, but the reason why I think it MIGHT be possible is because of the quick recharge capabilities of the supercaps. Even if I was only able to travel 5 miles on a charge say at 60mph. That's plenty of time to recharge the super caps like 100 times, right? That solar array would be enough to charge the supercaps, I think?

Why assume I would only get 1.37kw out of 9.132? Is it because losses due to the solar charge controller? Would I need a solar charge controller for super caps?

Please correct me if I am wrong or stupid, or both. Haaa.
 
It makes sense to me that I would need to choose my motor; design a supercap bank large enough to run the motor (assume 75mph) for X amount of time; and then have a solar array (assume a sunny day) large enough to charge that supercap bank in less than X amount of time. Is that feasible in any way?
 
Solar cells, affordable ones, are about 15% efficient which means it takes a large area to gather enough energy for practical use. One clever scheme is to have panels the size of the top, stored on top, that are pulled down and oriented towards the sun. During the brightest part of the day, you are parked under solar panels charging the batteries (or massive supercaps.)
photo-14-1024x768.jpg

Personally, I find this impractical because it destroys the aerodynamics of the vehicle. I don't have a problem with conformal solar cells with micro-inverters on the body as long as they preserve the aerodynamics.

A better solution is a towable trailer with folded, solar panels and/or reflectors. Towed, it has some drag but mostly masked by the body of the towing vehicle. It also means the trailer can be 'parked' and with a layer of LiON batteries, charged during the day. When you return that evening or even if parked next to it, you should be able to get 2-4x the solar area and that becomes a much more practical amount of solar power.

As for using supercaps instead of batteries, there is something called 'power density.' Supercaps have a use but they are impractical in this case as they can't hold as much energy as an equivalent weight (and cost) battery. But you could make one heck of a portable nail gun with supercaps for personal protection ... Buck Rogers.

Bob Wilson
 
Five 300+ watt panels equipped with MPPT would give you about 0.25 kW when illuminated with 1 kW/m^2. On a nice summer day on the east coast at mid lattitude with these tilted appropriately you might get 7 hours of 1 kW/m^2 equivalent for a total harvest of 1.75 kWh. That's not a whole lot. It would take my X about 5.8 miles.

As to what it takes to go 100 miles: that depends on a lot of things. The only real number I have is that it takes my X about 300 Wh to go a mile so for 100 miles it would use 30 kW. The 1.75 kWh from the solar panels is only 5.8% of that. That's why the buses don't have solar panels on the roof but rather charge at each stop.

To answer the question about the capacitor bank we need to convert 30 kWh to joules and that's 30*3600*1000 = 1.08e+08 J. One finds on eBay arrays of 6 500 F (total 3000F) caps rated at 2.7 volts for $235 and as the energy stored in a capacitor is C*V^2/2 each can hold 5000*2.7^2/2 = 18225 J and you would need 1.08E8/18225 = 5926 of these sets worth about $1.92 M though they'd probably give you discount if you bought that many.

Bottom line is that supercaps are good for providing lots of energy over short time periods (such as that between a couple of bus stops) and as they can be charged very much more quickly than batteries, that's a feasible thing to do. They are not in any sense a replacement for batteries for longer hauls though they could be used in BEVs to, for example, capture all the regen energy when it is being produced at a rate faster than a cold battery can accept it.
 
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