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Electric Cars and Photovoltaic Solar Cells

Discussion in 'Roadster' started by mherzfeld, May 24, 2007.

  1. mherzfeld

    mherzfeld Member

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    “Question: How many solar panels do I need to power my Tesla Roadster?

    The calculations appear to be correct actual installed physical ~ 15 x 15 foot array add setback. Parts, for example, would be modules, one source string, one inverter at ~2500 watts, one residential 2 pole 15A breaker on the load side, grounding electrode conductor, equipment grounding conductor, one DC disconnect, …

    [​IMG]
    Picture of highlighted actual installed ~ 15 x 15 foot multicrystalline photovoltaic array.​
     
  2. TEG

    TEG TMC Moderator

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    Those calculations seem somewhat optimized.
    What if you live in the northern part of the USA with less daily sunlight?
    What if your slope angle isn't ideal?
    What if you get some shade on the solar panels some of the time (due to trees, buildings, etc?)
    What if you are in an area that is cloudy, hazy or smoggy sometimes?

    Unless you live in New Mexico or Arizona, I think "your mileage may vary, actual mileage will probably be less".

    Also, your driving habits could use more power. What if you covered your 35 miles per day at 80mph?
     
  3. mherzfeld

    mherzfeld Member

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    Those calculations seem somewhat optimized.

    Yes, and appear to be fairly accurate. There are spacing of the modules to help reduce the temperature of the array and setback for ground mounted arrays. Also there would be about height of object for shadow distance away from array. In addition, if you are on an optimal rate schedule you may reduce the size of the array if the calculations are based on cost energy. For the BP3160s shown, the actual has been about 2.6 MWh/year + shading reduction as expected. There are BOS losses, USE-2 RHW-2 wire, inverter, module mismatch of IV curves, ... at a factor at about .7 in the system shown. Also there is a purdy looks thing having and the number of modules.

    What if you live in the northern part of the USA with less daily sunlight?

    Northern California is good generally and better than most for solar electric systems and Germany has quite a number of solar electric systems installed and they don't have much sun it seems.

    What if your slope angle isn't ideal?

    For ground mounted arrays, there are various angles used in the calculation based on latitude at about 34 degrees in this area. There is the leading edge height, tilt angle, horizontal and the maximum allowable array height. About 2 inch galvanized poles installed on the ground using trigonometric functions to calculate the optimal angle. In addition, there is also the azimuth which may optimize to the solar noon. You also may wish to optimize for the winter or summer months.

    Attached is a link which outlines some other factors.

    http://www.unirac.com/ula/ulaequest/ulaquest.htm

    What if you get some shade on the solar panels some of the time (due to trees, buildings, etc?)

    Calculations for shading quite straight forward and may be found at the following link. Some shading is tolerable if based on cost of energy as opposed to energy produced. The orientation of the modules of portrait or landscape with bypass diodes makes a difference and the impact of shading.

    http://www.solarpathfinder.com/formulas.html

    What if you are in an area that is cloudy, hazy or smoggy sometimes?

    The 'edge of cloud effect' actually increased the power of the array because the array is cooler than normal.

    http://forums.sma-america.com/showthreaded.php?Cat=&Board=Performance_forum&Number=193&page=0&view=collapsed&sb=5&o=&vc=1

    Unless you live in New Mexico or Arizona, I think "your mileage may vary, actual mileage will probably be less".

    As the ambient temperature increased the power decreases for monocrystalline and multicrystalline photovoltaic arrays. These climates seem to be warmer than California However, there tends to be more sun which increases the energy produced. Respectfully, more miles ?

    Also, your driving habits could use more power. What if you covered your 35 miles per day at 80mph?

    It would be interesting to view power consumption curves as speed increases.
     
  4. tonybelding

    tonybelding Active Member

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    For whatever it's worth, I've read that PV panels work best in cooler temperatures. The ideal site is cool-but-sunny. So in fact Arizona or New Mexico (at least the southern half) may not be the most ideal climates for this.
     
  5. vfx

    vfx Well-Known Member

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    First off it's great to have TEG (or whatever your name is for now) in the Tesla Motors club forum.

    Seriously, it would suck for me like it must for you if Tesla started a VFX division. Feel free to be whomever you want here -just glad to have you posting.

    We are able here to cover any aspect of Tesla without worring about going "off blog topic". And we know we are being heard (at least by the CEO's wife though I imagine these prose don't make for very interesting pillow talk) :)
     
  6. CEOswife

    CEOswife Member

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    You guys would be shocked to find out what we talk about! We are both engineers, and some of our conversations are AMAZINGLY boring to the average person. As I remember, our Saturday breakfast conversation was about the theory of relativity followed quickly with a discussion about the electrical panel at our house. Can you imagine how bored our kids get? Aren't you glad you're not them? :D
     
  7. vfx

    vfx Well-Known Member

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    Hmmm,

    Mom and Dad have a Roadster and Whitestar?

    I'll send over the adoption papers.
     
  8. vfx

    vfx Well-Known Member

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    OH, and TEG,

    You are the master of the link. I am constantly amazed at the breath of the internet you share.

    If only TJ would back up his ramblings with some meaty fact-links.
    (and a liberal use of the Enter key too)  :-\
     
  9. mherzfeld

    mherzfeld Member

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    In comparison, if the PV Array Maximum Output Power is 1584 then in AZ, based only on abmient temperature would be 1440 watts a reduction of about 144 watts based on the array and inverter configuration shown. And the Estimated Inverter Maximum Output Power vs. High Temperature would be 1481 compared to 1346 watts at a reduction of about 134 watts. Not only the array, but also ampacity of the wire, for example, in accordance with NEC 310.10 and FPN No. 2 at about 17-20 degrees C or about 30 degrees F. Another method is using the Temperature Coefficient of Power or the reduction in power of the array at about 0.5% for every 1 degree C and the ambient temperature is 40 C - 25 C = 15 C or 7.5 %. or about 118 watts and appears to be linear. There is also albedo and the microclimate to consider above the amibent temperature in which the calculations are based. At about 200 watt-hours per mile, would result in less miles. The ideal site is 8) "cool-but-sunny." Thanks for catching the question!

    At about 5 hours of sun, a reduction of 2-3 miles per day or between about 730 -1095 miles a year?

    Relatively comparing the temperature between locations, can the universe be describe as a symbiotic relationship between the car and sun, earth and the sky, a relationship as simple as M = Tc. Where M is the reduction in miles, T as the total miles of the Tesla, and c constant of 0.5% for every 1 degree C. Therefore, 12,775 * 7.5% = 958 miles?
     
  10. TEG

    TEG TMC Moderator

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    I guess my general point is that it is easy to "cherry pick" numbers that sound good, but for many people they will not achieve those same results because some things are sub optimal.

    I have seen repeatedly that solar arrays are better suited towards areas with long days of sunlight and few clouds (like New Mexico), so the power degradation due to heat seems to be a minor factor in comparison.

    A nice map showing solar approx output based on location (in the USA) can be found here:
    http://upload.wikimedia.org/wikipedia/en/2/2c/Us_pv_annual_may2004.jpg
    http://en.wikipedia.org/wiki/Image:Us_pv_annual_may2004.jpg
    (As you can see being in the southwest is much preferable to being in the northeast. A solar system in Arizona is likely to be more effective than one in Michigan)

    Here is a cool site that lets you input various factors to get an output estimate:
    http://www.valentin.de/onlineberechnung/pv/pv_online.html

    Panel output gives some value in kW, that you then multiply by hours of sunlight to get kWh per day.

    You then have to subtract off all sorts of inefficiencies from that including:

    Panels not pointed in the right direction (typically southfacing is best)
    Panels not angled at an optimal angle for your location.
    (Most people mount panels on their roof, and mount them flush for aesthetic reasons. Most houses don't have a roof with ideal angles and directions for PV collection)
    Inverter efficiency (although 90-95% can be common)
    Dirty panels.
    Air quality conditions (smoke, smog, haze, clouds, etc)
    Shading from trees and such.

    I have solar panels on my house. I can tell you that they produce far less power on a cloudy day. Also, a tree in a neighbors yard a few houses away puts a small shadow on them late in the day which hurts output as well. (Most panels are connected in series, so a shadow on only one of them disrupts electron flow through many panels in a string).

    Based on looking at output for different temperature days in summer vs winter, I can tell you that I would pick a hot summer day over a cool winter day because the hours of sunlight is the really important factor.

    Also, if you have just enough panels to put power into your vehicle, you may pay more for power because you switch to a different rate schedule which can cost you more for the other power you use on your household needs.

    So, one problem is you need to size a system that is "just enough" for your household needs as well as enough extra to recharge your vehicle appropriately.
    In PG&E area if you make extra power they will not pay you for it. You want to target "break even". If you don't get enough panels, oriented properly, then you can get stuck with larger bills due to change to "time of use metering" as mentioned in this article:
    http://www.latimes.com/business/la-fi-solar8may08,0,3494064.story
    http://politics.slashdot.org/article.pl?sid=07/05/09/1241243


    Don't get me wrong... I am big proponent of Solar Panels and EVs, but I think we need to be careful not to overstate the benefits then have people reject the technology thinking that there is "bait and switch" or "false advertising" going on.

    The numbers from Martin & Elon do seem "ballpark close", but some people are likely to find their driving habits use more than 200wh/mile, and many people will find that their home solar systems produce less than 263 kWh/m^2/year.

    I recently saw a Tesla presentation showing the reducing cost of Solar panels over time. It had some mark for 2007 with something like $2/w which I would think is some kind of raw cost to manufacturer, not actual cost to consumer (which is more like $6-$8/w installed). The skeptics balk when they see costs that don't line up with what they would actually pay, or energy generation/usage that they cannot achieve. Another case in point is the note about mono-crystaline solar panels. They cost a premium, and have limited availability so many systems installed these days use less efficient poly-crystaline.
     
  11. mherzfeld

    mherzfeld Member

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    Really enjoying this discussion forum !

    _________________________________________________
    Reference: calculations based with actual installed array relative to average high temperatures:

    http://america.sma.de/newstringsizing.aspx
    http://www.solarpathfinder.com/demo.html
    http://www.pvsyst.com/
    http://www.sunwize.com/info_center/insolmap.htm

    For residential, TOU is a real good thing prior to the TOU rate change and in cooler environments with the option for just residential service in the current situation.

    http://repositories.cdlib.org/ucei/csem/CSEMWP-142/
    http://forums.sma-america.com/showthreaded.php?Cat=&Board=General_forum&Number=670&Forum=All_Forums&Words=E-7&Match=Entire%20Phrase&Searchpage=0&Limit=25&Old=allposts&Main=670&Search=true#Post670

    Other resources:

    http://www.imaginit.cc/bipv.pdf [Appendix C: Design Tools]
     
  12. TEG

    TEG TMC Moderator

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    Yes, on that SMAforum link... I got my solar system just after PG&E stopped offering the E7 TOU.
    I got stuck with E6.
    Now they re-offer E7 again this year, so I feel I got shafted.

    Also, PG&E did NOT adjust my TOU meter to compensate for extended daylight savings. They sent me a memo saying to adjust my usage habits to compensate for the fact that the meter would be off by an hour. Ha... I can't adjust the time the sun shines on the panels, so again I got shafted.

    Oh well at least PG&E does offer TOU with Solar that can work out well if you have enough capacity. I hope they let me switch from E6 to E7 when my yearly contract gets done, but I am not holding my breath. (E7 is available only again to "new" subscribers)
     
  13. mherzfeld

    mherzfeld Member

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    In relative hours of sun or irradiation 'about 5 hours of sun' about 5.44 hours at about 2.629 MWh/year compared to 6.56 hours 2.935 MWh/year about in AZ about 1.12 hour of irradiance difference. 2.629 MWh/year - 2.935 MWh/year = .307 MWh/year or ~306600 watts/per year. At about 200 watt-hours per mile would result in about 1500 more miles. Then about 1.5k miles - 1k miles ~ is about 500 more miles without shading, and other things :)... ?

     
  14. TEG

    TEG TMC Moderator

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    Well, lets just hope you are right and I am wrong.

    For those (hopefully few) who can't make the projected range numbers, they shouldn't be too far off from the projections.

    ---

    By the way - another factor - is how good the panels are at collecting sunlight from off center angles.

    In a few years we may have multi-spectrum panels that are much more efficient, so the kWh/m2/year values could get even better...
    http://www.trnmag.com/Stories/2004/042104/Material_grabs_more_sun_042104.html
     
  15. Michael

    Michael Member

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    I see that this article is over 3 years old and speculated that it would take three years to see some potential results, however I was unable to find any new information on its progress. It seems like this technology would also allow for producing power even during cloudy days.
     
  16. mherzfeld

    mherzfeld Member

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    “Past Progress & Future Developments ...” ?

    http://usa.sanfrancisco.ahk.de/index.php?id=430&L=15#c744

    http://usa.sanfrancisco.ahk.de/fileadmin/user_upload/Dokumente/2007-03_Solar_Day/Bolko_von_Roedern_-_Calif07.pdf

    http://www.tvworldwide.com/events/eqtv/061016/default.cfm?id=7531&type=wmhigh
    http://www.tvworldwide.com/events/eqtv/061016/ppt/Swanson.pdf
    http://www.tvworldwide.com/events/eqtv/061016/ppt/Martin%20Green.pdf

    .
    .
    .
     
  17. mherzfeld

    mherzfeld Member

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    In further analysis, the presentations are enlightening as a humble attendee at the 'presentations' to hob nob with 'guess who's coming to dinner' leading solar technology in the world - http://usa.sanfrancisco.ahk.de/fileadmin/user_upload/Dokumente/2007-03_Solar_Day/Attendees_-_March_13__2007.pdf

    The actual solar technology shown is proven, for example, of 2005 NEC 609.7 notes based on Voc of Voltage Correction Factors for 'Crystalline and Multicrystalline Silicon Modules' of the lowest ambient in the code can actually implement and design to technology. And appears to be the largest implemented type of PV technology. It's proven, reliable, designable, implementable, and supportable and + an option available today for residential PV with electric cars.

    TEG and http://www.imaginit.cc/more_about.htm may know much, much better than I. In addition, just implementing existing solar technology may do some good things in the world.
     
  18. TEG

    TEG TMC Moderator

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    Nice set of links, Martin.

    The Germany vs USA comparison document shows that a typical site in Germany will produce about 1/2 the yearly power of a site in the southern USA.

    In a way it is a shame that Germany (rather than USA) was the country who's government decided to incent PV systems so much.
    Their demand drove up the global price for panels, yet panels installed in Germany don't get such good access to sun energy.


    Also it looks like California is moving towards encouragement of PV on new houses rather than pre-existing houses...
     
  19. mherzfeld

    mherzfeld Member

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    :eek: An epiphany!?

    'Germany has quite a number of solar electric systems installed and they don't have much sun it seems,' since PV arrays produce power even during cloudy days - PV works.

    Not sure, ground mounted arrays for commercial carports or agriculture appears to be a good thing, among other areas ... rural development ...

    http://www.sma-america.com/fileadmin/documents/Training_Event_Forms/West_Coast_Solar_Summit/solar_farming_california_new_crop.pdf
    http://www.solardevelop.com/images/Oasis-Aerial-Insert-Render-.jpg

    http://search.atomz.com/search/?sp-q=car&sp-a=sp1001112e
    http://www.imaginit.cc/imaginitnow.htm
    http://www.sunenergypower.com/projects_ch.asp
    http://www.sunenergypower.com/news.asp
     
  20. TEG

    TEG TMC Moderator

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    Yep, solar is great.

    Solar Farming!
    Solar Carports!

    Perhaps the "holy grail" is when they can integrate it with all common surfaces. Solar road coatings. Solar roof shingles (which exist in some form already).

    Someday we will look back and say "just think how much roof area they wasted with non electricity producing surfaces for all those years".

    Since we are "link-happy" here are a few more:
    http://www.theoildrum.com/uploads/2305/Solar_Insolation_map.gif

    Big solar arrays:

    http://sfgate.com/c/pictures/2004/12/20/mn_solar.jpg
    http://www.defenseindustrydaily.com/images/MISC_NAB_Coronado_Solar_Parking_Lot_lg.jpg
    http://www.equationlab.com/mtp/quantumblog/solar_2Dcell_2Dintro_small.jpg
    http://www.prometheus.org/publicfiles/active/0/191_small.jpg
    http://www.solarserver.de/l8mimages/solar_carouge_web.jpg
    http://www.solarserver.de/l8mimages/hartmannges.jpg

    Roadside solar in Germany/Switzerland/Austria:

    http://www.energieverbraucher.de/ew_images/sonnenstrom/autobahn.jpg
    http://www.prometheus.org/publicfiles/active/0/196_small.jpg
     

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