Friday, January 11, 2013

Bottling the Sun

In the last post I mentioned that I got a solar panel and hooked up one of the old train batteries to power my lights. I finally received the last piece of the puzzle, the charge controller, and wired everything in. I am now converting the radiation from the sun into electricity and storing it for later! At night, the light looks like the light from an ordinary CFL bulb, but it it has a different feel to it knowing that it is not coming from an outside source.

The first day I just plugged the panel in on the ground to check things out. Because the main roof face of the house is 72 degrees west of true south, I would like to make a pole mount that is separate from the house to hold the panel. After the trial day I screwed it onto the roof as a temporary measure until I make the pole mount. Again, I found myself working on the exterior on a day with inclement weather. This time the whole world was glistening with ice as I was voluntarily climbing on the roof. Why does nasty weather motivate me? Even with the poor mounting angle, I am still collecting more energy than I am using on most days.

The batteries and charge controller are occupying the space that will someday be the kitchen counter.

Now for a word on the charge controller. If you aren't interested in the technical end of things feel free to skip this paragraph. A charge controller links the solar array with the batteries. In Its most simple form,  it just monitors the state of charge of the battery and cuts off the charge when the battery is full. A modern controller is a bit more complicated and since I am using non traditional batteries I needed one that I could adjust myself. I ended up buying a 15 amp SunSaver MPPT from Morningstar Corp. I picked this one mainly because it is one of the few small controllers that can be programmed. As a bonus, it loggs and stores one month of data which will be fun to observe. The MPPT in the product name stands for maximum power point tracking. Consider a 12 volt system. A solar panel meant to charge a 12 volt battery will produce around 18 volts with no load. The battery pulls the voltage down to a lower level when the two are directly connected. This will be around 12-15 volts while charging. Solar panels are more efficient when they are producing a higher voltage- closer to 17 for many manufactures. The circuitry in a MPPT controller recognizes this and lets the panel produce electricity at its maximum power point, while charging the battery at the voltage it wants. In the end, this makes for a more efficient system. Under many conditions, the user can see a 20-30% increase in efficiency.

This chart is the data downloaded from the first two weeks of use. Ignore the spike on the first day, this was due to connections being made. It is also important to note that I had friends from out of town staying in the house using the lights and it was snowing/icing almost the entire time. The two spikes on the green line show the few sunny days we had. The saddle about two thirds of the way through was during a time that the panels were covered in snow. Still producing a tiny bit of energy! Still, the battery voltage steadily climbed. The next data set will be interesting to see because we had lots of sunny weather!