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

POSTED ON  BY shrey joshi

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 ouruser 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