solar on the car roof

[JoeS]

...If the solar panels added to the Cd by even 5% or so, it would probably be a net loss - You'd lose more range by increasing the drag than you would gain.

An important point, often overlooked! If you google "flexible solar panels" you'll see a whole bunch of 100W panels (one of which might fit the i-MiEV roof), but you'd have to go through voltage conversions and regulators to make them work. Yes, you can make anything work eventually to add a few Wh, but is the cost, time, and inefficiency worth it? :roll:

 

[LMT]

Cheers Don and Joes

so regen system can create voltage from 0 to 340volts and 0 to 75A?
so half regen would create voltage 170volts and 37.5A?
if so why couldnt i use a single flexible panel.

Elfeland 190W 33V Sunpower Flexible Solar Panels
Size: Approx. 1310x785x2mm
Voltage: 33V
Power: 190W
Isc: 6.8A
guessing around 2kg

to boost braking regen?
or does regen system create constant voltage of 340V and variable current upto 75A?
im an electronic engineer and not an aeronautic engineer but would 2mm really effect drag?
are there any electrical diagrams/schematics available?
thanks again for your help guys.

 

[PV1]

The regenerative braking system simply uses the drive motor as a generator to slow the car down. The voltage generated at the DC Terminals is slightly above the pack voltage, by however much is necessary to push the amps back into the pack. Voltage stays relatively stable; it's the amps that vary widely. The voltage ranges from 300 to 361 volts DC, solely based on battery charge. To tie solar in, you need to either wire enough solar cells in series to get about 350-355 volts or find a voltage converter to take 12-24 volts up to 350 volts.

However, there is one big hurdle that is expensive to work around. The car completely disconnects the drive battery when the car is turned off, meaning that any tie in points won't be connected to the battery and can't be used to charge the battery.

 

[Don]

Cheers Don and Joes

so regen system can create voltage from 0 to 340volts and 0 to 75A?
so half regen would create voltage 170volts and 37.5A?

No - The laws of electricity don't work that way. First, regen only produces the correct charge voltage at all times - 340 to 350, whatever the actual number is. Only the amps vary . . . . not the voltage. It is carefully regulated at all times or the battery wouldn't accept it. Second, 170 volts @ 37.5 amps wouldn't be half . . . . it would be one quarter, *but* you cannot charge a 340 volt battery at all with a charge voltage of only 170 volts . . . . you would get zero amps of charge

340 volts @ 75 amps is 25,500 watts - 170 volts @ 37.5 amps is only 6,375 watts

The roof is so small that anything more than 100 watts or so of solar just won't fit and as Joe mentioned, converting from a 24 volt, 100 watt panel into something that would charge the battery involves so many steps with so many inefficiencies that you hardly have anything left by the time you get there. Your 100 watt panel not correctly aimed directly at the sun might generate only 60 watts or so of power with reasonable sun

Your 24 volt panel would have to drive an inverter to step up the voltage to 350 or 360 and the inverter might be 80% to 85% efficient and that brings your 60 watts down to only 48 or 50 watts. That inverter output would be AC, so you'd need to rectify and very carefully regulate it to get exactly the DC charge voltage required . . . . . assuming you could get the car to accept it. Those losses might bring your 50 watts down to 35 or 40. Then, if you've negatively affected the airflow over the roof in any way, you could actually be losing more range by the drag created than your 30 watts could replace

The Fisker Karma came with a 'solar roof' - They used it to run a ventilation fan when the car is parked in the sun so it doesn't get so hot inside that you use a lot of air conditioning power to cool it off when you begin to drive - A much more practical goal, though I think the solar roof added almost $5K to the price of the car. Worth it?? :?:

Not if it's my $5K :shock: - I would refuse THAT option!

Don

 

[JoeS]

Hi LMT, and a belated welcome to this forum. You might update your profile to let us know whereabouts you are located.
http://myimiev.com/forum/viewtopic.php?f=13&t=3196

In the engineering world, prior to undertaking any electrical design, we first go through a systems design process, clearly identifying the requirements and studying all the tradeoffs to arrive at a cost-effective solution.

…Just got my i 2010 model and looking for solar hack to charge main pack… my current intention is to have:
solar panel 200+W > battery charger > battery > power diode > connection to regen system.
so battery chargers during day light hours and adds to regen when braking occurs in D, E or B… i understand even if i can get it to work ill only be getting a couple of km extra a day but i think thats cool.

In this case, my take is that you are wishing to undertake a design implementation, the efficacy of which is, at best, questionable, but also recognizing this fact with wide-open eyes. It sounds as though you want to make a science project out of this, without regard that it may, at best, extend your range by, say, 5km after a day of sitting out in the sun. Perhaps you wish to drive your car to work and have the solar panel add a few Wh while the car is parked (something a number of our members have actually needed to do, but eventually gave up the idea as impracticable).

[I just deleted a detailed math analysis of what you're trying to do, as both PV1 and Don touched upon this adequately.]

Bottom line, if you wish to pursue this then either design or find yourself a dc-dc converter that takes a very variable input low voltage and outputs something on the order of 350vdc, and then figure out where to inject this into your battery pack (there are a number of different spots, depending on whether you have CHAdeMO or not). Also, you might refrain from using the term "regen" for anything other than the electric motor feeding the battery while acting as a generator.

Wish you all the best in your endeavour.

PS An extra 5km of range can be accomplished extremely easily in the i-MiEV by simply altering your driving behavior ever-so-slightly.

 

[1branchonthevine]

You're welcome!

http://www.mouser.com/Mobile/Optoelectronics/LED-Lighting/LED-Lighting-Electronics/LED-Drivers-Power-Supplies/_/N-b1asl/?P=1yxt5h6Z1yezf2kZ1yurf38Z1yhx254Z1ytgrgn

 

[JoeS]

You're welcome!
http://www.mouser.com/Mobile/Optoelectronics/LED-Lighting/LED-Lighting-Electronics/LED-Drivers-Power-Supplies/_/N-b1asl/?P=1yxt5h6Z1yezf2kZ1yurf38Z1yhx254Z1ytgrgn

Thanks for posting. Here are the specs on these two Meanwell power supplies:
http://www.mouser.com/ds/2/260/meanwell_HLG-320H-C-spec-914652.pdf
https://www.mouser.com/ds/2/260/HVGC-150-spec-238292.pdf
Here's the link to the other thread on this topic:
http://myimiev.com/forum/viewtopic.php?f=23&t=2857&p=34002#p33998
Do let us know of your progress.

 

[Don]

The first version of the Fisker Karma had a $5K optional 'solar roof' which they used to power a fan to cool the inside of the car when it's parked so the A/C didn't have to work so hard to cool the car when you start it up after sitting in the sun for several hours

A 'cool idea' . . . . but worth $5K?

The newest version of the Fisker has a solar roof that they claim can 'power the car' which is kinda, sorta true - Any solar panel will eventually charge any battery pack, the key word being 'eventually'

In this case, 'eventually' would be sitting in perfect sun for . . . . a month :lol:

http://jalopnik.com/the-claim-that-the-karma-reveros-solar-roof-will-power-1785303277

Don

 

[JoeS]

Been some time since this thread was active, but I ran across this today - should it go under this thread or the car cover thread? :roll:

https://www.greencarreports.com/new...er-claimed-to-gain-miles-of-ev-range-each-day

IMO, not practicable in the form it is being presented (e.g., those straps will wear through the paint in no time, and avoiding snagging, and then there's the solar-to-OBC interface), but a cute concept nevertheless.

 

[gimim]

Right -- there are a couple of solar cars; but they are far more efficient than the i MiEV. There is one that is driving around the world right now on it's own power, called the SolarWorld GT built at Bochum University. The panels are very high efficiency (read: very expensive) and they provide a little over 800w, it weighs very little (under 1,000 pounds I thinking of 300w solar panel?) and the car has a Cd of just 0.14. It does seat two people, but with no creature comforts, and it can drive along at 30-60mph pretty much all day when the sun is out.

I think that more typical solar panels that you or I could get might power a couple of fans to help cool the inside of the car on a sunny day. To charge the car appreciably, it would take at least 2kW of panels, or so? That is about 8 or 10 panels that are ~3' x ~5 ' each.

Just wondering if anyone has investigated solar panels from a charging the p2 perspective - especially now that battery technology is coming into play more. Obviously its going to be impossible to fully charge (or even 10% charge) the P2 without using mains and this makes it tricky to get the cost equation to work. I am tempted to go solar for various reasons but my main electric use is to charge the car so if I am still doing that primarily through the network then not sure its worth doing... Just asking in case anyone has looked into this...

 

[MickeyS70]

Hi
Yes, I have looked into this and if your main objective for installing a PV system is to charge your car for ‘free’ then consider this:

- it will take a good few years before you can offset the installation costs
- your EV needs to be parked at home when the sun shines
- if you’re working you need to install a battery backup (for $$$$)
- charging an EV is a heavy load, you need lots of PV panels and a beefy inverter ($$$$)
- there will be large energy losses converting solar DC to mains AC and back to battery DC

I admit, circumstances vary greatly from county to county but here it makes more sense to get paid to feed excess energy back into the grid during the day and change the car overnight.

 

[JoeS]

Posting this without any personal comment because it's on topic.
Certainly a bit more elegant than that shown in Post#41

https://gosun.co/pages/ev-solar-charger

 

[MickeyS70]

Posting this without any personal comment because it's on topic.
Certainly a bit more elegant than that shown in Post#41

https://gosun.co/pages/ev-solar-charger

Looks nice, but unfortunately limited to 110V AC

I also wonder will the solar yield be 'eaten up by the addition drag created?