Re: SolarJolla
 

Trying to remain constructive -before you glue somebody's idea to a rock an throw it in the sea - would you care to explain how swapping a camera / keyboard / battery other half for the Sollar other half is more practical than hooking up to a solar USB charger or just a wall outlet?

Apart from that I like the Sollar OH idea, only , it will gather dust when more interesting OH come around.

Re: SolarJolla
 

Just some back-of-the envelope calculations to check feasability: up-to date light intensity data can be found here (for Germany, but the Netherlands should be close to northern Germany in terms of "sunniness"). It's given in kWh/month/m2. To obtain the total energy harvesting of your module, multiply this figure by it's power rating (as they are rated for 1kW/m2 incoming radiation power)*. So for a 1Wp (Watt peak) panel that you leave outside in the sun during the whole daylight time, you can expect ~50Wh per month to be produced in October, ~180Wh in June, and maybe ~15Wh in December. A full charge is 8Wh, plus about 20% charging losses (rough estimate) you need 10Wh to charge your battery. This means in December you can charge your mobile ~1.5 times during the month, leaving it in the sun the whole day every day. And this does not cover self discharge losses and the reduced efficiency at low light intensities.

So, a solar back might be nice for outdoor trips in summer, but it definitely
does not make charging a thing of the past. And most of us do not have transparent trouser pockets, in south direction... As cool as this project is in itself, IMHO an external panel with a buffer battery and usb charger is the much more sensible alternative.


* actually, most cell types' light conversion efficiency is significantly worse at low light intensities.

Re: SolarJolla
 

This is a very strange calculation. Can you elaborate? At which step did you include the surface area?

Re: SolarJolla
 

The surface area is included in the rating of your panel. An 1Wp-panel gives 1W at 1kW/m2 sun intensity, this can be reached by a bigger panel with low efficiency or a smaller one with higher \eta. So for 1kWh/m2 of irradiation energy your panel gives 1Wh, which means for 50kWh/m2 a month it gives 50Wh.

Is this more clear?

EDIT: As said before, efficiency is in reality not independent of light density, and also the sun spectrum changes during the day which has different effects on different cell types (depends mainly on the band gap), so this is a simplification assuming constant light conversion efficiency.

Re: SolarJolla
 

Yes, this totally makes sense now.

So, during the winter you have +-2 free charges. In the summer however, with 200kWh/m2 per month, charging is no longer necessary.

This is more convienient, as in the winter most people are inside and in the summer outside. The beach does not have a lot of power sockets!

Re: SolarJolla
 

All these calculations are above my head and I feel no motivation to become an expert here...

... BUT:

My main use case for a solar panel would not be to use it instead of regular charging. Instead, I would want it to produce just enough juice that I can use the phone a little longer while outdoors. In other words: I would be perfectly happy if such a panel could make the phone "discharge at a slower rate" (if this is technically possible at all)

Is this a realistic expectation?

Re: SolarJolla
 

I would say yes, 2h in direct summer sunlight should be enough to charge 20% with such a panel (2Wh minus losses). The pitfall is that you have to direct it at least roughly to the sun's direction, and maybe that your phone does not like getting hot.

Could make sense btw. to combine it with an extra battery to make charging without the phone possible.

EDIT: And it's dirt cheap, this 1W-panel for example is just $3.50 in single quantity.

Re: SolarJolla
 

Quite pointless calculations, as no one sits full day outside holding phone in the way that it is facing always directly the sun. However, idea might seem to be interesting, but as I have used in the past Nokia 1610 with original solar battery (BBT-1L: http://www.nokiaport.de/content/de/a...pic/bbt-1l.png), I already know that we should not have very high expectations for such solution to actually significantly increase battery life of the Jolla...

Sorry to be bit pessimistic.

Re: SolarJolla
 

It would make sense to me for it to have it's own battery so that you can leave it somewhere with sun (while you use the phone) and pop it on when you run out of juice.

I would also be less afraid to leave it under direct sunlight than the whole phone.

Re: SolarJolla
 

Well, I am happy to tell you that effiency of solar cells has increased almost the same proportion that prices have decreased :)
The BBT-1L is ancient stone-age technology :D