Sunday, 4 November 2012

Solar powered - Greenhouse Part 3

In my last post I talked about how much I like technology. My only problem has always been that I can't always afford the latest gadgets. But as one should always see the glass half full rather than half empty I think the lack of funds can make you very creative and inventive.

When we built our greenhouse we wanted to be able to use it all year round and at least supplement our groceries with some fresh herbs or even veggies throughout the "dark times" (aka New Brunswick Winter). I have talked about thermal mass and how we are (slowly) achieving all the goals we have set in the beginning of the year.

But with all the perfect heat absorption in the place, the hot days in the summer become a problem. The temperature in the greenhouse gets far too high during sunny days. We have measured up to 60 C inside in April (no plants inside then). Therefore a cooling or active ventilation system was called for.

I knew what I wanted the system to do (quite simply blow cooler air from outside into the greenhouse and facilitating a better airflow through the vents located on the upper part of the north wall), but how to achieve this with virtually no or very little money. The system I implemented cost me $40 although those costs are not really true as we will see later, as I recycle parts of the system during winter into a heating system. Two for the price of one so to speak.

Fans are readily available for free. I got mine from my workplace's IT section. Power supply units for computers are a typical problem for desktop computers. I myself had to replace 2 of them at home already and when you know a place that runs 150+ PCs, you know that there will be power supplies blowing any minute now. So I asked whether I could get the old burnt out power supply units before they get thrown out. Most places will not really care as they were going to throw them out anyway.

I opened the metal boxes and took out the little fans inside. Computer fans are perfect because they often run on 12 VDC which is exactly what the small solar panels bought from a local store produce. So one panel equals one fan. There are no batteries or charge controllers involved in my system. It is raw and direct. Hook up the solar panel to the fan and face the panel in the same direction as the greenhouse is oriented. When the sun is fully shining into the greenhouse it will also give 100% power to the solar cells. This is sufficient to run the fan.

The funny and coincidental thing with this system is, that when the sun comes in at an angle (i.e. the greenhouse is not getting too hot) the power produced from the solar panel is not really enough to run the fan and the system turns off. In other words this system is automated without any hi-tec computer programming or the likes. I ended up putting 3 fans in series and coupling them to 3 solar panels. I think I might add a few more next year, but there were a lot of days this summer where I was glad that the system was working perfectly. Without it I would have come home to a nasty surprise during some of the hotter days.

I mentioned earlier that I got 2 for 1 with the cooling system. Well, in the winter the solar panels run the fan for the beer can heater that is facing the east side of the greenhouse. When we built the greenhouse we could not orient it perfectly facing south due to the nature of the ground. We quickly noticed that the early morning sun does not reach into the insides and therefore it takes a while to heat the place up. I opted to build a beer can heater after seeing one at a friends place and researching it on the web.  Simply google "beer can heater" and you will get a ton of results, from simple to elaborate.

So far, I have only built a prototype. Partially because I wanted to see how I would fare building it and partially because I do not drink enough canned beer (I make my own in glass bottles. In my mind, 500 mL is better than 355 mL) and getting all the cans for a full system would take me years. The friend I mentioned that introduced me to the system used 248 cans....

As the days are getting much shorter now and we needed some light in the greenhouse and the fact that I got tired of running an extension cord from the garage to the greenhouse whenever I had to do some work requiring power tools, we decided to get power into the greenhouse directly.

In order to achieve this, I first thought about running a cable from the garage to the greenhouse and tapping into the power from the garage. Which is what I did. However, I am certain that the insurance would have had a thing or two to say about that particular solution. I also wasn't happy that I tainted this wonderful Permaculture structure with "dirty" conventional power.

So in true Permaculture fashion I set up a solar power system with a deep cycle battery and a 15 W solar panel. A 15 W system is not really all that powerful and it takes a while to recharge the battery if it goes completely empty. That shouldn't really happen, but if you forget to turn the light off the battery will drain at some stage. I myself will add a second solar panel whenever I can find a cheap one to speed up the recharge time. 
This concludes our Greenhouse series for now. However, I am sure that our further plans for our greenhouse will warrant a mention or even an extension of the series at a later stage.


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  2. Love the article, can you tell us where you purchased the supplies, IE Solar panels, fans, etc. Could you also show us a wiring diagram on who you wired up the computer fans?