Yesterday evening, we arrived in Moscow after a long day’s drive from St. Petersburg in the Editourmobil. The trikes and trailers are in storage, dissasembled, in the vehicle’s garage, and the solar panels are securely mounted on its roof. We’ve stayed overnight on a parking space close to a Coca-Cola facility on the outskirts of Moscow. Our colleague, Kay Krüger, intends to visit them tomorrow for the Go to Brau tour, our sister project.
Today is a bright and hot Moscow summer day, and we’ve decided to use the occasion to find out how well our solar panels hold up in the Moscow sun after having travelled well above 2,500 km on top of the Editourmobil. The panels have no connection to the electricity grid on board yet, so to do any tests, they have to be lowered from the rooftop first. Soon, several Russian truck drivers watch in amazement as I climb through a rooftop window on top of the Editourmobil… After unfastening the belts that hold the upper panel in place, I lower it over the edge of the roof to the vehicle’s side, where Felix is waiting to receive it and rest it securely on the ground. Since this is the third or fourth time we’ve done the operation, it goes off without a hitch.
The panels are quite large and massive for a bike trailer – 1.5 x 0.8 meters – and they weigh nearly 15 kg. Their intended use clearly is for rooftops and decidedly not for bike trailers on Siberian roads with potholes, heavy vibrations and wind. We’ve constructed a kind of iron cross that goes below each panel, both to make them much more sturdy and to have a central mounting point – the cross center – on top of which they can be balanced. This pivot makes it possible to change their angle and align them towards the sun, hopefully automatically with our Lego motors, if all goes to plan.
The panel we’ve lowered from the roof is quite dirty, and unsurprisingly, our measurements show a marked improvement in power output after cleaning it up. In fact, the output temporarily exceeds Panasonic‘s specifications: We get up to 300 Watt! This is considerably more than the 235 Watt it is rated for – more than we’ve ever measured in Heidelberg – and really good news. The output is, however, highly variable, going all the way down to 125 Watt and back up in the same minute, as a small cloud temporarily dims the Moscow sun. Output is also extremely sensitive to even minimal shadowing of tiny parts of the panel – holding a single hand over it lowers output by 30% or more. It’s quite fortunate that all the roadsides in Russia that we’ve seen so far have been cleared from forests for roughly 10 meters on either side.
It’s hard to overstate how important the power output of the panels is for the whole endeavour. We need about 1200 Wh per day, or there’s really no way we can manage the distances needed. Fortunately, the sun is up for up to 20 hours a day – a few days ago, in St. Petersburg with its famous White Nights, it didn’t get dark at all! The sun is very close to the horizon for much of the time, though, and power output is neglible then. Ideally, we would have wanted panels with twice the efficiency – they exist, but cost a thousand times as much! They are chiefly used for satellites, where every gram counts. Sadly, our budget didn’t allow for them, so we’ve settled on the best available earthly panels – they will have to do!
For now, we are quite satisfied with their performance. Even after panel output has been converted to the voltages needed for the batteries, we end up with around 200 W or more. Six midday hours of that per day, and we are golden!
Right now, Felix is outside solding longer cables to some of our Lego motors – like most of SiStour, the integration of panels and trailers is a work in progress. This, by the way, is also true of this blog! When we started a week ago, it was static text – by now it has an RSS and an Atom feed that you can use to stay informed about updates automatically, zoomable pictures, and – most importantly – comments. Comments which you, dear reader, are most welcome to make some use of – any thoughts, ideas, suggestions are more than welcome! We will try to update this blog twice a week, of course subject to Siberian internet connectivity. But for now, we’ll put the panel back onto the Editourmobil’s roof and then enjoy the bright and sunny Moscow afternoon!