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Solar-Power-Augmented Prius Takes the Grid Out of “Plug-inâ€

Discussion in 'Prius, Hybrid, EV and Alt-Fuel News' started by thorn, Aug 16, 2005.

  1. thorn

    thorn Member

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    Solar-Power-Augmented Prius Takes the Grid Out of “Plug-inâ€
    15 August 2005

    A Canadian engineer has prototyped a Photovoltaic Prius—a 2001 Prius augmented with roof-top solar panels and an additional battery system to supplement the charge in the original equipment NiMH batteries.

    Steve Lapp’s PV Prius is still a rough prototype—a demonstration of concept—but even with the limitations of the systems, he has achieved an initial 10% fuel efficiency improvement from 4.5 l/100km (52 mpg US) to 4.0 l/100km (59 mpg US).

    From the original description of the plan:

    ...the fact that [current Toyota hybrids] can run on electricity alone, with their gasoline engines off, offers the opportunity to provide them with more electricity and therefore drive further with the gasoline engine off.

    Electricity can be provided from the electrical grid by charging an onboard battery, and depending on where that electricity comes from, it will have various emissions associated with it. [The plug-in concept.] However if it is provided from renewable energy sources, such as photovoltaic panels, then it is “greenâ€.

    This begs the question of why not put the PV panels directly on a hybrid car and generate electricity onboard while the car is parked outside, or even while driving. The general reaction of people to this idea is that there could not be enough energy striking the roof of a car to provide enough electricity to drive any meaningful distance.

    This is where the incredible efficiency of the hybrid car must be taken into account. To drive a hybrid car about 1 km, takes about the same electricity as to light a 150 watt bulb for one hour! The point is not to drive the car using only solar power, but to effectively use solar power to improve gasoline fuel efficiency.

    How much gasoline can this photovoltaic hybrid car save? Well let’s look at the energy available from the sun on the roof of the car. For June and July in Kingston Ontario, about 6 kWh of energy from the sun strikes each square meter of horizontal surface. If we install 2 square meters of photovoltaic panels on the car and we collect 10% of the energy from the sun as electricity (well within present PV efficiency), we can theoretically go about 8 km each day on just the sun’s energy. If we drive 24 km on a sunny day, that is enough to reduce our gasoline consumption by 33%. This would take the Prius from 5.0 l/100km to 3.3 l/100km.

    The PV Prius uses a 12-volt PV source with a small lead acid battery and battery voltage controller, inverted to 120 VAC, transformed to 345 VAC, then rectified with current control to nominal 300 VDC. The charge from the PV batteries flows into the Prius hybrid battery when the ignition is on.

    The 300 VDC output of the solar subsystem is attached to the switched side of the original Prius battery, so the PV battery cannot recharge the NiMH while the ignition is off. The PV system can inject a maximum of up to 2 amps continuously into the battery while the ignition is on.

    Lapp’s modelling predicts a 10%–20% fuel efficiency improvement for the 270 watts of PV (to be bumped up to 360 watts with the additional of a fourth panel), so the 10% on the first trip with little optimization was “a pleasant surpriseâ€.

    He is working with between two to six 20 Ah sealed lead acid batteries, experimenting to discover useful amount of buffer storage, given typical solar and driving conditions.

    The decision not to charge the hybrid when the car is off was a pragmatic choice, given the financial and time constraints of his project. Among other issues, there would need to be a thorough analysis to determined the optimal PV-NiMH energy flow/charge relationship.
     
  2. mikepaul

    mikepaul Senior Member

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    I wouldn't mind a funny-looking roof if it'd help the MPGs and morons would leave it alone...
     
  3. HTMLSpinnr

    HTMLSpinnr Super Moderator
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    I'd love to seen an '04 with recent form fitting PV cells to match the roof line. It's not a bad idea, but I'd like to see the PV cells feed into something w/ a bit more capacity for areas such as mine with alot of sun :)

    I bet he's one of the few that does avoid covered parking :-P
     
  4. thorn

    thorn Member

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    He does not charge it with the car off. It would be a good idea, top off the battery while you are at work.
    Of course a bigger battery would be even better.
     
  5. Marlin

    Marlin New Member

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    Re: Solar-Power-Augmented Prius Takes the Grid Out of “Plug-

    I remember reading once that it takes more energy to produce a photovoltaic cell then the cell could produce in it's lifetime.

    That statement is probably 10 years out of date, so it's likely no longer true, but I wonder what the production energy vs. generated energy relationship is now.
     
  6. clett

    clett New Member

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    10% efficient solar panels are quite old now. For example, SunPower A300 cells are more than 20% efficient. Replacing his cells with these would double his energy collection and his gas savings.

    Putting 5m2 of these on a Prius is enough to collect 5kWh per day, or about 20 miles worth less gas usage every day (averaged over the year, it would be much more in summer, much less in winter).
     
  7. flareak

    flareak Fleet Captain

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    is this good for highway driving? i mean.. im thinking of the issue of AERODYNAMICS as well as PHOTOVOLTAIC CELL BEING SPLATTERED ALL OVER INTERSTATE i-70
     
  8. mikepaul

    mikepaul Senior Member

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    Hmm. OK, so it'd need a clear, strong, aerodynamic cover to protect it and protect other drivers. Perhaps not the lightest roof attachment once solidly designed...
     
  9. Marlin

    Marlin New Member

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    He doesn't charge the hybrid battery when the car is off, but he does charge his extra lead-acid batteries when the car is off. The lead acid batteries are then used to charge the hybrid battery when the car is on.

    The article says he can send up to 2 Amps continuously to the hybrid battery, which at 300 Volts is 600 Watts. However his solar panels only produce 270 Watts. Therefore the energy collected by his solar panels (and stored in the lead acid batteries) when the car is off can be transferred to the hybrid battery when the car is on, at a rate greater than the solar panels are recharging the lead acid batteries. So the energy collected while sitting in parking lot can indeed be transfered to the hybrid battery once the car is started.
     
  10. thorn

    thorn Member

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    One could use thin cells, I think that's what they are called. Could bond them to the car, less wind resistance, much lighter weight too.

    Of course the panels probably cost $1000 so it take a long while to recover their cost.

    For energy payback see:

    http://www.homepower.com/files/pvpayback.pdf
     
  11. techman322

    techman322 New Member

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    Being able to use next-gen nano photo paint to cover the whole car, or at least most of the sunlit portions would have to produce at least a rather noticeable amount of energy. At my work I get there just as the sun is coming up and park there all day, living in the desert I sould see a great improvement in mpg.
     
  12. kirbinster

    kirbinster Member

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    Actually that is not true, you produce more power from solar cells in the dead of winter than the summer. I should know, I have a system on my house that produces about 65 kwh on a good day in February and only about 53 on a typical summer day. The reason for this is that the panels are much more efficient when they are very cold, even though there are fewer hours of sun and the sun is at a much lower angle. I did not know this till I installed the system either.
     
  13. ScottY

    ScottY New Member

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    Interesting. It'll be better if you can charge your Prius using your solar panels at home during the night, and the solar panel on roof at work. So you get a Plug-in PV Prius, or PPVP!
     
  14. kirbinster

    kirbinster Member

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    Wait a second -- what am I missing here? Don't know about where you live, but where I live we don't have sun at night to be able to use solar panels with! :)
     
  15. ScottY

    ScottY New Member

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    What?! No sun at night? Then use a flash light!
    lol, I should be more clear. I meant the solar energy you accumulate in the day to charge the car at night. Or if you live around the poles, you can disregard my explanation. :wink:
     
  16. kirbinster

    kirbinster Member

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    I was just having some fun with you. Actually the way the PV system works is that it is tied to the grid and uses what is called net metering. Just like average citizens are confused that you don't plug hybrids in, most people assume the PV systems use storage batteries. While they can, that is an expensive wasteful implementation. I grid-tied system supplies your needs during the day and any extra power is fed back through your electric meter onto the utility grid - spinning your meter backwards to credit you with the excess power you generate. At night you just pull power off the grid in the normal manner. While this system will not produce power when there is a power outage, it is far cheaper to install a backup generator in addition to the solar array rather than tying the array to a battery system.
     
  17. ScottY

    ScottY New Member

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    I certainly did not know that about a PV system. Thx for the info.
     
  18. Marlin

    Marlin New Member

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    So the power grid is your "battery". You can still charge a plug-in Prius at night using the power generated during the day by you PV cells. Your power meter runs backwards during the day, "charging" your "battery", and that energy is retrieved at night to charge a plug-in Prius.
     
  19. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    so if i read this thread correctly, with more efficient panels we are looking at a possible 50% increase in mpg's with the better panels?

    how much would you pay to get 100 mpg as opposed to 60? now most probably cant do this, but i would pay a lot for that chance. i never bought the Prius because i thought i would save money on gas. (remember i bought my car when gas was only $1.50 and going down...) so my return on investment is a moot point.

    getting the word out is more than worth it for me. i am proud to say that after 14 months, i have finally talked one person at work into a Prius and am literally inches away from talking another into it also. so hopefully, that will make 3...*SIGH* out of 800... well its a start
     
  20. clett

    clett New Member

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    Yup.

    Somebody has posted a picture of the PV-Prius over at GreenHybrid!

    http://www.greenhybrid.com/discuss/gen-1-p...boost.3191.html.

    Not quite as neat an install as this one! ;) ..but still BIG respect for Steve Lapp, who's showing the big auto companies what can be done. 8)