A closer look at the technology powering Nokia’s solar mobile phone

Charles Fritt, an American inventor, is credited with creating the first working solar panel way back in 1883. He coated the semiconductor material selenium with an extremely thin layer of gold, creating a panel with just 1% efficiency. Things have come a long way since then. To see just how far, let’s take a closer look at the technology behind Lokki, Nokia’s solar powered mobile prototype.

What is Lokki?

Lokki is a Lithium-ion battery charger and data logging unit that’s been especially designed to charge and track the charging of a Lithium-ion battery. It works by using either solar power or electricity. For the field test, Lokki has been integrated into a battery cover that fits onto a Nokia C1 mobile phone.

What does it do?

Lokki uses an integrated solar panel to charge a battery. It then monitors the charging process and stores the main measured parameters to an internal memory. The stored measurements can be uploaded to a PC and server for further analysis.

What data does it provide?

Lokki provides a wealth of information in an easy to understand graph format. Each of our user updates will include graphs like this one below.

Here’s what you each of the lines represents.

Battery (V) is the phone battery voltage, which is affected by the load of the phone in different modes. When the curve increases, it means there is a more solar power than the phone needs and the battery is charged. When the curve declines, the battery is using energy faster than solar panel can supply it.

Solar (mA) is the solar charging current from solar panel. If this current is larger than the current consumption of the phone, the battery gains more charge.

Temp (C) is the internal temperature of Lokki. The temperature is very much affected by the sun’s heat.

SolarCHR (mAh) is the capacity tha attery has received from the solar panel. The battery can store 1050mAh. This capacity curve starts from zero every day, so at the end of the curve, you can see how much energy has been harvested in a day.

How does it charge?

Lokki contains two Li-ion charge controllers. One of these regulates the charge from the integrated solar panel, the other regulates the current from an external source. The controllers also incorporate a maximum charge current limit, temperature limit, and overcharge and voltage protection.

The chargers are “always on”, which means they can supply current to Lokki in the absence of battery power. They are also able to charge the battery whenever there is a current source available. In addition to this, the controllers provide an analog signal, which is proportional to the charge current and used to record it into Lokki’s memory.

What type of solar panel does it use?

For the Lokki field test, we’re using a thin film silicon solar panel. In our prototypes we also wanted to study a flexible, thin shape, as we needed to hide the additional electronics of the data logger between the solar panel and the existing battery.

The most important criteria though was that the technology had to be cost competitive. Due to the fact it uses very little electronics and mechanics, the thin film panel achieves that goal. Thin film silicon solar panels also provide good voltage throughout the usable power area. What’s more, the thin panel is readily manufactured as a series connection of several cells, which optimizes both the mechanics and the electronics.

Hopefully, you now have a little clearer picture into what Lokki is, what it does and how it works. If you want more details about any of these things or anything else to do with Lokki, let us know in the comments below.

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34 Responses to A closer look at the technology powering Nokia’s solar mobile phone

  1. John says:

    What about the li-Ion charges cycle ? If the chargers are always on, doesn’t that mean that if there is a glimpse of sunlight for 5minutes and then pitch black, a whole charge cycle would be consumed , thus reducing battery life ?

    • Joel says:

      Great question, John.

      The good thing is that a partial charge will not consume a full charge cycle of specified life time. The life time of the battery is not only counted in number of cycles, but it is improved by reduced depth of the discharge and charge cycle, as well as reduced voltage. E.g. when compared to 100% cycles, it is most probable that a battery may last 10 times more cycles that are only 10% depth and performed on lower battery voltage level. However, we need to study the temperature very carefully, as after a certain level elevated temperature starts to have negative impact to the battery life.

      Hope that clears that up.

    • Andrey says:

      Good afternoon. Very much khochet’sya to know an answer for put question. Thank you.

  2. Jacob z says:

    If the solar panel invented by Fritt in 1883 was only 1% efficiency, what the efficiency of the panel on the Lokki more than 125 years later?

  3. Aki says:

    Interesting testing. Is this the first time anyone has measured the sun power like this on a mobile phone?

    • Joel says:

      Great to hear you’re finding our field testing interesting Aki. We put your question to our Technology Manager, Matti Naskali, and here’s what he had to say.
      “There’s lots of solar data for different installations and lots of it available on webpages like NASA’s page http://eosweb.larc.nasa.gov/sse/
      Personally, I have seen many good mobile solar energy filed tests, they’re best for comparing products or their performance. But if ours goes as planned I believe it will provide totally new data and figures, about a unique of selection of mobile use cases.”

  4. Roth says:

    LOL I was just commenting about when we’ll see a solar powered Nokia device on a previous blog post too:

    // Roth

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  8. Gino dela Concepcion says:

    This sounds like the Nokia of yore. The one I grew up with that set the innovations others copied. I’m not a technical person but, based on your description of the thin silicone panel it seems logical that such a panel (assuming certain transparency aspects) may be sandwitched as a layer on touchscreens of today’s smartphones. How far away would such technology be?

    • Joel says:

      Thanks Gino. We’ve got some really exciting innovations on the cards, so we’re convinced the future is rosy.

      As for your question, we’ll ask our solar power guru, Technology Manager, Matti Naskali, and get back to you.

    • Joel says:

      We put your question to Matti, Gino and here’s what he had to say:

      “One aspect to consider is that we may compromise display clarity or solar panel power when we combine them. They are conflicting objectives as a solar panel needs to absorb light, and a display needs to show content clear. Our test user Amos in Africa has run out of battery few times. He’s main applications that drain the harvested energy are radio and web browsing with a small, low power display. Also it shows that the more our test users’ phones are in use, or are carried along them, the less they harvest energy. Best harvesting has been achieved when the phone just baths in the sun. Soon we will see what kind of use cases can be best covered by solar energy at the end of the project.”

      Hope that answers your question, Gino.

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  11. m.t says:

    cool>i like it

    • E says:

      This is amazing i just sketched this idea up an a piece of paper literally… and I would live too be apart off this invention seeing how i thought off it lol without any influence. How cani have the opportunity…

  12. Aman mishra says:

    Great i really imperesed for this latest feature…

  13. Jonard says:

    Great idea, great concept. You created a need for most of us mobile phone users. This will be very beneficial for some folks here in the Philippines who don’t have direct access to electricity (and to all texters and other heavy users who need a charger ASAP)

    As per new technology though, I’m sure this will be quite pricey at first but eventually the price will go down and specs of the product will be much more sophisticated.

    I’m looking forward to have this product make waves to the mobile phone market and of course having one my palms the soonest. Nice one Nokia.

    • Joel says:

      Thanks Jonard. This is still only a prototype, but we hope that the data we get from this study will really help us better understand the possibilities and challenges of using solar technology for mobile devices.

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  18. Marcel says:


    very interesting project. I’m surprised that no one else yet come up with such as solution….

    any plans of running similar project on one of your Smartphones with Symbian S^3 / Anna / Bella rather then S40 6th?

    Does the colour of the handset have any impact on charging via solar panel?

  19. r_HR says:

    This spring I used a small solar charger (two approx. 3inch panels) with a 750mAh battery capacity. I took it with me fully charged and used it to power my nokia n8. I kept it in a clear tankbag on my bike and it was sunny (in England..) for all 5 days I was on the road. Normally I can get about 2 days out of my N8 and being abroad I used it less (3g roaming). I managed to get 5 full days out of it, including some calls, texts, pictures and navigation, so probably comparable to normal usage. However, after 5 days the battery was completely flat. My question is, in the foreseeable future, will we see pocketable solar panels which will provide enough current to not need a mains-charger anymore? Because from what I see here, 130 years of innovation has only increased efficiency by 5%, and from the Nairobi graph, it seems we’re still a couple of hundred years off of achieving this..

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  22. Stephan says:

    Hi Joel,
    why do you use Thin Film cells.
    The efficency is very low for the consumption of a mobile phone.

    We are working very close with a IC company on high efficency small Solar Panels for just these applications. The efficency of the panles are about 20%.

    • Matti says:

      Hi Stephan
      Few reasons for used thin film for this test. First we wanted to keep the test devices as thin as possible, or at least to feel thin, and the rounding helped us to keep the corners at original thickness while we were able to hide 4mm thick recorder in the center. To get most relevant mobile solar data we wanted to keep the proto as portable as the original design was. We also believed our fragile handmade prototypes could be more durable with thin film panel, it was just glued on the surface of the remade back cover. Aslo after considering the data, we assumed that it would be applicable for other relevant technologies and sizes after recalculating with proper multiplier.
      Thanks for your good question.

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