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Is there any reason

Discussion in 'Hobby Electronics' started by Michael C, Sep 20, 2006.

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  1. Michael C

    Michael C Guest

    Solar power isn't used for mobile phones? My previous mobile lasted 11 days
    on 1 charge. Surely a small solar cell could collect enough light in 11 days
    to charge the battery? Then we'd have a phone that never needed charging!!
    Wouldn't work with these new phones with huge color screens though. :)

  2. A solar cell small enough to fit on a mobile almost certainly wouldn't
    generate enough charge to be useful. You could do the numbers to find
    out based on average solar insolation, surface area, efficiency etc

    But then you add in all the other practical usability factors like:
    1) Many people put them in a case of some sort
    2) Solar cell would have to be on the back of the phone to get the most
    useful surface area, and people like to keep their phone face up so
    they can see the screen. "Flip" phones with the small front LCD are a
    bit better in this respect I guess.
    3) Solar exposure would be very low. Most people would keep them
    indoors or in their back pocket or bag etc, and of course it's useless
    at night. Usable expose could be as low as few hours a days or less.
    4) Adds extra cost, so those models simply won't sell in the cuthroat
    market. Try making it look sexy too...
    5) People don't want the inconvenience of remembering to leave it in
    the sun or other light, esp considering that plugging it in for 30min
    while in the car will generate more charge than a week in the sun.
    6) A big proportion of the market (i.e. teens) use their phone 50 times
    a day on their $300/month plan, that means much higher battery usage
    than someone like me who is lucky to use it once a week.

    Dave :)
  3. Michael C

    Michael C Guest

    I don't think any of these issues are insumountable though. For example,
    heavy users would just need to charge the phone. However looking at this

    it looks like a 1" x 2.5" solar cell will be out 0.240 watts in ideal
    conditions (I presume they're quoting ideal conditions). The nokia 6310 has
    a 600mAh battery which divided over 11 days gives an average of 0.002 watts.
    So the cell is putting out 120x the power required by the phone. With
    inefficiencies, time not in light, lower output from indoor lighting and a
    smaller solar cell we might still make it.
    The 1 x 2.5" cell is $1.60, most likely a lot cheaper in bulk.
    The idea would be they wouldn't have to remember, incidental light during
    the day would be enough.

  4. Peter

    Peter Guest

    7) Heat.

  5. I calculate 8mW ((600mAh/264h)*3.6V).
    Not that it really matters, factor in the multitude of practical
    engineering issues and it looks bleak.
    Eg. you have to have multiple cells in series to get the voltage
    needed, extra charging circuitry of some sort, inefficiency in the
    charging circuitry and the battery at low charge currents, indoor
    lighting is quite a large difference etc etc
    Read below for how much time my phone spends in any form of light, let
    alone full sun.

    I think you'll find if you did a proper engineering analysis taking
    everything into account, then it just isn't practical.
    To a mass market item like this, that's a LOT of money. Every single
    cent counts in high volume consumer items like this.
    I don't know if I'm an "average" user or not, but I would be lucky if
    my phone spends a few percent of an average week in any sort of ambient
    light let alone full sun.
    I leave it in my bag at work and home, if I go out it's in my back
    pocket, when I go to the gym it's in my bumbag, when I'm out
    adventuring it's in the pack etc. In fact the only time it's really
    getting any light is when I use it or I'm charging it!
    So I would have to drastically change the usage of my phone to get any
    benefit at all from solar power.

    Dave :)
  6. Peter

    Peter Guest

    I agree with points 1), 3) and Dave except you can change peoples habits in
    regards to usage and storage with design. You could bring back the nineties
    trend of hanging your mobile from your belt/pocket/other for example plus in
    areas with unreliable power it would be great and with phones turning into
    PPC's cameras and diaries the demand for power and having a charged unit
    will be higher. Other people that could be sold on this idea apart from
    people who are caught out with a flat battery (I haven't in years) are
    people who like camping, boating, fishing, push bike riding, motorcycle
    riding, horse riding..................
    Another plus is more phones would be stolen and then in turn more sold.
    It's not a feature I would look for or consider and advantage.

  7. Sure you can, and any manufacturer is willing to try if they want. I
    won't change though just so I can get some trickle charge here and
    No good if the cell has to be on the back of the phone.
    And not much good if you are indoors all day anyway.
    Driving too and from work you'd have to stick the thing on the dash,
    that sucks when you can just plug it into your cigarette plug and
    charge it 10 times quicker.
    and with phones getting smaller and smaller where do you put the solar
    Just use a seperate solar charger - hey another accesory they can

    When I go bush I turn my phone off, peace and quiet.
    I don't think anyone would. All the market cars about is how many MP
    the camera is and how the ring tones sound.

    Dave :)
  8. Michael C

    Michael C Guest

    Oops, I forgot to multiply by voltage :)
    Surely they could design the cells to output the voltage required.
    Maybe so but they still manage to put out phones with 3.2mp cameras, 320x240
    color screens, 4gb hard drives, a second camera, a second lcd display,
    radios, sd cards, headsets, usb cables etc etc etc.
    I don't think you're an average user. I leave my phone on the table the
    entire time I'm home, I have on my desk most of the time I'm at work, I take
    it out of my pocket in the car in case it rings. I'd say it would be in some
    sort of light for 10 hours a day.

    I think the real killer though would be it's just not cool enough.

  9. Sure, but the point is that having to do so reduces the effective area
    of the cell. That is particually important for small applications like
    So where does that leave room for the solar cells? :->
    Most people I know are the same as me. Still may not be "average",
    but's that's good enough for me to know that for myself and most people
    I know, it would be a waste of time.

    Most of time you have your phone on the desk at work or home you are
    only getting very inefficient fluorescent lighting. I've got one of
    those solar powered Citizen Eco watches, and they are really cool, but
    they don't work very well in fluorescent lighting. 30 minutes in the
    full sun is much better than days in a room. In fact, if I leave it on
    the table in a room it eventually dies through lack of charge. And this
    uses a "specially designed" cell that is supposed to work in all types
    of ambient light.

    Also, if you are in the car why not simply plug it into your car
    charger that can charge it 10 times quicker?
    No, I think the real killer is that it's most likely quite difficult
    from a manufacturing and engineering point of view. It being of little
    benefit is beside the point really I guess, it never stops the
    marketing department! Solar power is very "cool", and it would I
    suspect be a good marketing gimmick, but no one has ever done it - why?
    The cheap "clamshell" construction of todays phones would probably not
    lend itself well to adding any sort of solar cell. It ain't as easy as
    looking at a data sheet and saying, hey this could work, there is a
    massive amount of engineering and packaging work involved, the devil is
    in the detail.

    Dave :)
  10. Michael C

    Michael C Guest

    But not insumountable.
    Obviously this would have to be a low feature business phone. Before you say
    who'd buy it, try buying a nokia 6310i. They're still up around $200 when I
    can get the new nokia wizz bang phone for the same price.
    That is simply not true. Most people don't have their phone in their pocket
    all day. Everywhere I go I see mobile phones on desks and all day at work
    the damn things are ringing and no one's there to answer them. Most people
    put them out somewhere at home so they can hear them ringing.
    Funny you should mention that I've got that same watch, the WR100. I've
    never had it stop in 5+ years and it's the reason I'm posting this thread
    :) It's such a cool idea, I never have to worry about batteries, the watch
    just runs, forever.
    I don't have a car charger. I probably need one but am sick of buying
    chargers for everything. I've also got a bluetooth headset, laptop and
    digital camera that could do with car chargers. I find them a hassle having
    those cords in the car and the contact with the lighter socket is never very
    Dunno, i think if they wanted to do it they could. They could probably
    integrate the solar cell into the LCD display which would give plenty of
    room. There are patents for solar cells integrated into laptop displays. Or
    they could have some sort of clear keyboard and put it behind that. Or as
    you said have it on the front of a flip phone.
    Well, when you're away from the charger and the phone would otherwise be
    dead I could see it as a huge benefit.
    As I said if they really wanted to do it they could.
  11. It is true for most people I know.
    As for my work place, hardly anyone leaves their mobile on their desk.
    Your experience is obviously opposite to mine, so that must mean half
    the people leave it out and half leave it away? :->
    Not that it matters, fluorescent light just isn't very efficient.
    Mine is a dress watch so spends most of it's time on the table. If it
    doesn't get direct sunlight it will die after a few months. So
    fluorescent light can barely cut it for a watch, let alone a phone.
    Watches have a massively lower power requirement than a mobile phone,
    in the order of a few microwatts.
    Get a phone car charger at least, they cost a few dollars and will save
    your sanity.
    I find the most conveinet time to charge my phone is in the car.
    Of course they could, but your question was "Is there any reason solar
    power isn't used for mobile phones?"
    There are many reasons as I've gievn, plus there are many more if you
    actually do a full enginering and cost/complexity/benefit analysis,
    which no one but the phone manufacturer is capable of doing really.
    That doesn't mean someone won't eventually do it though, if it can be
    done it probably will be done. Just don't expect it to be practical
    like your solar powered watch.

    Dave :)
  12. Lord Garth

    Lord Garth Guest

    Seems that an obvious answer is to build a stationary solar charger and
    have a second battery placed there to be ready when needed.
  13. BTW, some of the new Casio watches have a 10 year battery life, no need
    for solar at all. Impressive stuff.

    My EcoDrive watch is smart too, when the battery gets low it first goes
    into a "lower power" mode that doesn't move the second hand to save
    power. Then if the battery gets even lower it stops all hand movement,
    but not before shifting the hands to a position which indicates "charge
    me", and it still keeps the time going internally. Then if it finally
    doesn't get any charge, as it's last gasp of breath it moves the hands
    to a position which indicates "time lost". If you charge it back up
    before it loses the time it moves the hands back to the correct
    position. Very cool.

    Dave :)
  14. Michael C

    Michael C Guest

    Possibly but that just means the technology wouldn't work for some people.
    The phone would have to come with a charger anyway so those people would
    just have to charge it, but at least less often.
    I'd be interested to see exactly how much power could be extracted from
    We don't really know how they've implemented it though. The face of the
    watch doesn't look like a solar cell so I suspect it is behind the face. The
    actuall cell itself might be very small and most of the light might be
    blocked by the face.
    I probably should.
    You've raised a lot of good points although I don't think any of them are
    show stoppers except possibly for the amount of power that can be taken from
    indoor light. But we don't have any real data on that, just something I got
    from a website and your estimations.

  15. Michael C

    Michael C Guest

    The idea though is to have a phone that just runs, you don't have to worry
    about batteries or chargers.

    The solar cell takes up the entire watch face, light passes right
    through the special face material.

    Dave :)
  17. Lord Garth

    Lord Garth Guest

    Perhaps a methanol fuel cell but then the airlines would be stealing our
    Shows a "cloudy day" is 3-4 times better than indoor lighting, and
    that's 20cm under a 30W fluoro!
    The difference between a full sunny day with high solar radiation and a
    typical room in which you aren't 20cm away from the fluoro tube would
    have to be at least an order of magnitude.
    Shows that due to the super efficent cell used the new ulta low power
    technology, the face can be only 20% transparent and still work well

    Dave :)
  19. Michael C

    Michael C Guest

    That's still fairly vague. Indoor light isn't always fluros and is usually a
    mix of outside light. Most offices have banks of 40w lights everywhere, not
    just 1x30w light with no other light source.
  20. swanny

    swanny Guest

    Slightly askew of the topic, but I've thought it would be a good idea to
    get rid of the cigarette lighter socket altogether and standardise on a
    more appropriate power supply adaptor with multiple connection points
    throughout the vehicle, since most people use the socket for power
    supply rather than lighting cigarettes these days.
    I'm surprised this hasn't happened already.
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