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  • EEVblog #48 – Solar Power Hope

    Posted on December 4th, 2009 EEVblog 47 comments

    Can solar power hope beat out the engineering reality for Dave’s latest project?
    Was Doc Brown right?

    Solar Cell DATASHEET

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    • Daniel Meinzer

      If money is really no object, these are around the size of a credit card, and can put out some good power.

      http://www.emcore.com/solar_photovoltaics/space_solar_cells

    • Nick

      Hi Dave,
      and congrats for your marvelous blog. Regarding the solar powered calculator project, was your intention to power it exclusively from the solar cell? If you intended to have some short of battery also, then maybe the small current output of it, would not be a huge problem, since the battery would be trickle charged during the standby hours. OK, it would be a problem if your calculator was so small that it would be always covered by something, but that’s another design problem…

      • Nick

        Oooops, I just saw at the beginning of the vide post that you wanted to get rid of the battery in your design.

    • Michael Thompson

      I think a lot of us have been there in one way or another.

      Thanks for taking us along on the journey, because it was still interesting and informative.

    • Brian Hoskins

      Okay, so your idea of exclusive solar power is lost. But just because you’ve lost that battle, doesn’t mean you’ve lost the war! Sometimes design is about compromise (in fact, it almost always is) as I’m sure you’re aware. So why not make a dual power system? So, in low level lighting conditions, the power would be shared between your solar panel and a small battery. But, in high level lighting conditions, the power would be generated exclusively by the solar panel.

      There’s still mileage in the idea, I think. It probably wouldn’t be a cost effective project, but unless you’re planning to sell it… who cares? Hobbyists do it for no other reason than because we can!

      Brian

    • Brian Hoskins

      Oh, I have a suggestion for your blog too. You may or may not be interested in it .

      So far, you’ve reviewed pretty much everything. You’ve done equipment reviews, development kit reviews, Microcontroller datasheet reviews, even product reviews (such as the GPS).

      But… one thing you haven’t done so far is book reviews. Personally I’ve been in the trade for over 10 years so I already have a nice list of favourite reference books that I keep close to me. After all, nobody can remember everything can they?
      Having some good reference books to hand can be priceless, it really can. Sure there’s the internet these days, and I regularly use the internet for research myself, but for electronic theory, and even practical circuit advice, sometimes you can’t beat a decent reference book that explains things properly and has information within it that you can count upon.

      So… how about it Dave? Some book reviews for the Electronics newcomers? I already have my own favourites, but I found them the hard way – by trying them. Book reviews are subjective, of course, but I still think it’d be useful to give newcomers some suggestions.

      Brian

      • http://www.eevblog.com EEVblog

        I started out doing some book reviews in the first few blogs when the blog was a “mixed bag” of stuff. That has fallen by the wayside now that the blog has evolved into a one topic per episode thing. But maybe I can do a whole episode on some of my favorites.

        • http://www.hoevendesign.com Paul

          If you’re ever going to do book reviews, have a look at slod006b.pdf or “Opamps for everyone”. 464 pages of porn about every nitty gritty detail of opamps. Directly from TI.

    • http://electrooptical.net Phil Hobbs

      Full zenith sunlight is right around 100k lux (lumens/sq metre). Nice bright indoor lights are around 100 lux–your desk lamp probably produces 300 lux on your work surface.

      But Si solar cells peak well to the red of the eye’s response.

      Cheers

      Phil Hobbs

    • http://www.idea2ic.com/ Don Sauer

      Technology over the years can be surprising. What will solar cells and LCDs be like years from now? Actually doing what use to be “impossible” is what makes electronic fun.

    • John McVirgo

      This also explains why solar panels in general are pretty pointless installing in places in the world where the light conditions are low, such as in the UK. It takes over 100 years to recoup the cost of installation, yet have a lifetime of 30 years at best.

      You’ve changed the introduction to your blog from a snazzy music number to you soundng like a self conscious virgin blogger putting an introduction on his answerphone. You could do with changing it back or making the introduction sounding more natural like your great blogs.

      • http://www.eevblog.com EEVblog

        @ John
        Yeah, the intro sucks, I know. It was just a quick’n’dirty thing so I had something. I had to ditch the music due to too many approval hoops on YouTube. So have to come up with something myself.

        • John McVirgo

          @eevblog

          By approvals do you mean copyright?

          Use a classical music piece, such as composed by Albeniz and played on piano, or transcribed for guitar. Leyenda or Seville are good examples.

          • http://www.eevblog.com EEVblog

            @ John
            If I use *anything* (audio, video, even me singing song lyrics) in my blog I have to tick the box that says I don’t own it, and then I have to prove that I have the rights to use that material. My old music was free to use under creative commons, and specifically allowed on YouTube, but because it’s not mine I have to provide the same proof and get the same approval for every video I upload, forever, ad nauseum. That sucks.

    • http://www.testequipmentsolutions.com.au Duncan Livingston

      I’ve got an idea to boost your power output from the solar cells.
      Why not have lenses that can direct more of the available light onto you solar cells. I’ve used 5mm LEDs, heatshrink and cheap fishing line to create “fibre optic” starfields on a ceiling before. You should be able to do the reverse and bend focus extra light onto PV cell.

      Duncan

      • http://www.eevblog.com EEVblog

        @ Duncan
        Can’t do that in 3mm thickness I’m afraid.

        • Sean

          So, what you need is a very thin, rectangular 1F capacitor, hmmm…

      • http://www.simonsphotography.org.uk Simon

        no lenses: mirrors, I have pondered this myself for a very long time and without making something bigger and more involved than the extra panels themselves, at best you may ged 2 X light but need to make it very strong for wind

    • Qno

      There you have it.
      They are called Solar cells.
      Now you know why.

      Imagine how many mirrors and lenses would be needed to increase the power only 10 times.

    • Brent Bagley

      Dave,

      I believe that your idea still has legs, so
      I wouldn’t give up quite so quickly.

      Here’s a thought…

      I think you’re working too hard to make these
      devices do something that they weren’t meant to do.

      Since these cells are really intended as a
      constant source of energy (you never turn
      them off) and your calculator application
      is probably an intermittent consumer of energy,
      why not just average things out over time and
      regulate the result. I’ll bet that you’ll get
      your 200+ uA for the odd calculation then.

      Someone suggested a battery for storage, but
      a cooler idea might be based on a “supercapacitor”,
      which is way more efficient and should come in
      under 3mm in some form factors. You might need
      a couple of these, as the voltage ratings are
      typically kinda low.

      BTW, there is a whole class of strange ideas
      these days to harvest “wasted” energy, based
      on piezos, electrothermal, induction coils,
      etc. A solar cell based design begins to
      sound pretty conservative by comparison.

      Cheers.

      • http://www.eevblog.com EEVblog

        @ Brent
        I’ve already thought abut this, and it already has a supercap in it.
        But any rechargeable solution just won’t be viable I suspect. It might work for someone who deliberately leaves the device out in the light/sun to charge, but you can’t assume people are going to this. It could just as easily sit in a wallet or desk draw for months at a time without use, and in that case it’s likely going to be dead when you actually need to use it.
        And there is other stuff like the touch chip to factor in that takes more current again.
        The whole product feature set changes when it has to be flea power like this.

    • T Robb

      Hi Dave, love the blog very funny sometimes! Have you thought about a flip up lid with cells on the inside?

      Toby,

      Blue mountains, Australia.

    • Ray Jones

      I watched this video a while back, but your 90dB has been bugging me since.

      dB = 10 log10 (ratio)

      This means 90dB = 1,000,000,000:1, not 30,000:1

      Granted if you convert voltages to power, yep 30,000:1 is a power ratio of 90dB – but that uses V^2 => 20 log10 (ratio)

      Your example was lumens to lumens however…..

      • http://www.eevblog.com EEVblog

        You are correct that lumens is an intensity (and hence power), so the 10log ratio applies, so it should be 1,000,000,000:1
        For some reason I can’t fathom I decided to treat them as magnitudes and not powers.
        It realised during editing, but I didn’t want to go back and have to re-film. I probably should have added some overlay text to correct *sigh*
        I was hoping no one would notice :)

        • Ray Jones

          Never mind, I have been dealing with dB a lot lately, and it immediately made me sit up and take notice.
          See you have a new blog on dB, I’ll have to watch it :-)

    • AskJacob

      It gets boring being stuck in the calculated zone – as a good engineer sometimes it gets drilled out of you on being creative. Sometimes you have to sit on the floor lego-style and just plug bits together and see if it works.

      Good on you for trying – you win for 2 reasons:
      1 – you did learn more about current state of art (well, available to normal humans) solar cells
      2 – Now you have a spark in your head that one day may well end up in some distant project.

      I am not an engineer – but I appreciate the work. I work in project management, my hobby is electronics, and I enjoy having the freedom to “freestyle” with physical things for a change!

      Cheers
      Jacob

    • Robert Keller

      Love the podcast Dave. Keep up the great work.

      Just one question for you. What is the model number for that calculator you used in the podcast?

      Thanks,

      Robert

      • http://www.eevblog.com EEVblog

        It’s a Tandy EC-4032
        A rebadged Casio

        • Robert Keller

          Thanks Dave, That is awesome. I had one very similar in High School and have been looking for a replacement for some time. It was excellent for doing electronics calculations. Having a model number will help greatly.

          Best Wish’s

          Robert

    • http://devrandom.pl XANi

      Hmm im thinking solar powered meter with supercap instead of battery ? U never have to change batteries! ;]

    • http://windandsolarpower.moreoneteam.com/ solar generators

      We wanted to tell you howdy. I are already visiting the site.

    • http://open.salon.com/blog/smallsolarpanels4/2010/02/19/back_to_basics_building_your_own_home_solar_panels Brain Ricketts

      I was searching for small solar panel data and luckily found this write-up. I discovered similar sites, like http://www.propeller.com/story/2010/01/20/small-solar-panels/ that help you install your own solar panels but I need to find out where to get the solar panels.

    • Valentin Buck

      While seeing your great blog, I had the idea to load a lipo-accumulator with the energy from the solar cells. You’d just have to take a step-up converter and a lipo-loader like the MAX1811. If you’d use a 100mAh lipo, you could use your product quite a long time.
      Would that work?
      Thank you for your ingenious blogs.
      Valentin Buck

    • http://www.projectorlampinfo.com Kylie Sanchez

      Solar Energy is one of the best sources of clean and green electricity. I think that we should build more efficient solar thermal power plants and solar cells. frequently. ‘

    • Alex

      Unfortunately for some unknown reason IXYS does not allow Mouser to sell those in my country (Portugal). :(

    • http://www.ampaccessories.net  Amp Accessories

      solar cells are very good but they are not very efficient and they are costly~;”

    • Bernhard Weller

      There are some other things to keep in mind while selecting a solar cell. It’s the lights spectrum. It differs greatly between outdoor sun and indoor lamps.
      So basically there are different types of solar cells, made to gather more energy at a special spectrum.

      For example take a look at http://www.schottsolar.com, they offer indoor modules: http://www.schottsolar.com/global/products/off-grid-solutions/asi-oem-indoor/
      and outdoor modules: http://www.schottsolar.com/global/products/off-grid-solutions/asi-oem-outdoor/

      If you take a look at the specs, you’ll see that the frequency response is fairly the same, but it has some slight differences and well it seems to enhance the energy harvested under low light indoor situations. So maybe in your next design you can keep this in mind.

    • Matt Gholston

      I had the same idea about the supercap that the other gentleman above had… but i would augment that with a microusb charging port on the side of the watch to keep the caps topped off or quickly recharge the unit when the it is not going to be used in a well lit area for long periods of time, etc… I know that it is kinda cheating since you wanted 100% solar power, but no more so than a watch winder like people keep motion wound watches in.
      This solution would allow users to start off with a fully charged watch with little waiting, and let the solar cell maintain the charge most of the time.

      Also the if you actually put a usb host in the device and not just a charging port you could use the port for firmware updates etc…

    • Leo Bodnar

      It’s really that simple!

      Your lighting in the lab looks equivalent to say about 2x 100W incandescent bulbs.

      The incandescent bulb would be about 2% efficient at converting electric energy into visible light.

      So we have 4W of light energy generated by lighting to go around.

      Your solar cells looks like 1cm x 10cm in size (occupying area of 0.001 sq.m) and if they are 2m away from lights then they will get hit by only 4W * 0.001 / 50 or just 80uW of visible light energy. Where 50 is surface area of 2m radius sphere in sq.m.

      Since energy efficiency of the solar cells is 18% then 80uW of light energy becomes about 15uW of electric energy. That’s 4uA at 3V.

      Here you go. No need to even purchase samples. Rough calculation! Tadaaa!

      Cheers
      Leo

    • chuck

      So from the video, looks like the Fluke 87 only has one uA range, and it defaults to AC current.

      But the 187 that I think you’ve shown in the past, has 4 settings for current. Would AC measuring be the primary difference why you should ditch the 87 and go with the 187?

    • Dave

      Nice Video, but you mention the illumination inside and in full sun as a figure measured in lumens, to be measured by a lux meter.
      This is not strictly correct. Lux is a measure of illumination of a surface, which is what you were referring to.
      Lumens are a measure of optical power integrated over a spherical area. The lumen output of a light is a measure of the entire optical output of the light, not just the part that is incident on a particular surface.
      The lumen output of a light may be measured with an integrating sphere or estimated using a photogoniometer (a sort of scanner of light output over a range of angles).

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