As if I needed another project, I had been tossing something around lately regarding renewable energy and the web. Low Tech Magazine, which showcases what it considers old and forgotten technology, has an edition of their website available served from a Raspberry Pi run entirely off-grid. Their setup consists of a Pi powered from a solar-charged battery, and they make it a point that depending on weather, that site may not actually be available at all.
I think that this is an interesting concept, although I’ve been tossing around the idea of taking this further. Rather than try to keep a small web server running all the time completely on solar power, what about running it only when the sun is out? In other words, whenever enough sun hits a panel to produce enough power to keep a Raspberry Pi going (about 3 watts, say). With a large panel, this means it could stay up even when it’s cloudy.
I’ve been playing with off-grid solar for years in a hobbyist capacity, and first wondered about this when seeing the green ‘charging’ light on my charge controller turn on even on a clear night with a bright moon. That is, with enough panelage, can a useful amount of power be extracted even in low light? And what ways are there to utilize solar power without trying to store it?
The system, in my mind, would be relatively simple: A photovoltaic panel, one meant for charging a 12 volt battery, would feed a Raspberry Pi via a buck converter. When there’s enough sun to keep the Pi running, it runs. When there isn’t, it shuts down. The converter would help to match the panel’s output to the Pi, supplying it with a constant 5 VDC. With a large enough panel (>20 watts?), it should be able to put out the required 3 or so watts over a range of weather conditions.
I’m wondering about some other bells and whistles, like somehow predicting when night is about to fall, and gracefully shutting down the Pi. And monitoring voltage and current as well. I may take this as an opportunity to design my own buck with some of this built in, but I think an off-the-shelf converter would work as well.
Anyways, I’m not sure when I’ll get to this, but it’s just a thought. I’m not sure how useful it will be, but it could be kind of fun.