Welcome to 2022! It’s a new year so I’m going to be much more diligent about blogging updates explaining what we’re up to. The main project is a solar greenhouse or crop protection system. By that I mean, no supplemental heat from fossil fuels, and no supplemental electric lights. Such systems are common on small farms know as “hoop houses”, “high tunnels”, “floating row covers”, or simply “greenhouses”. In Canada, these systems cannot really produce significant crops in the winter as they are simply too cold and dark. Hot house tomatoes currently grown in the Canadian winter need supplemental heat and light.
I think there is a possibility of growing tomatoes all year round in a solar greenhouse, but this is contingent on two (as yet untested) hypothesises. First, I believe tomato plants can effectively capture light coming from the side as well as the top. If this is true, then a greenhouse with a tall south wall will have an area where there is enough light for tomato production all year long, at least in southern Nova Scotia where we’re located.
The second it that most of the heat loss is at night, and with movable insulation supplemental heating will not be required. When I say movable insulation, I’m not meaning a thin blanket as in Chinese solar greenhouses (r-3) or a thermal screen, I mean full wall level insulation r-20 to r-40. Oh and the greenhouse has to be practically totally air tight too, so there are minimal infiltration losses.
Then I suppose a third project is warping all this up into a economically buildable package. It’s going to take a while. But, here is the update for the first week:
I’ve been building a growth chamber for tomatoes with artificial light on the top and “south” wall. To my knowledge no one has specifically measured light from the side on tomatoes so this had to be a custom design. I had planned to use arduino capacitive soil water sensors to measure soil humidity. I want soil, not hydroponics, because the goal is to produce organic tomatoes which are more valuable, and keep the capital cost to setup this greenhouse as low as possible.
Unfortunately, these sensors did not work at all. Lots of noise, not very sensitive. I spend a week on them last year and couldn’t make it work. Anyhow, they don’t actually measure what’s important either. The important parameter is water tension (a pressure) which tells you how easily the water in the soil can be extracted by plants. This can be measured with a tensiometer which is basically a vacuum gauge on a tube full of water with a porous ceramic interface to the soil. I decided to go with a commercial version of this, tropf-blumat where the soil sensor is a ceramic cone and the pressure differential opens a valve at the top. I got 6, one for each plant in the growth chamber. Then each plant will have a water/fertilizer bucket on a high shelf.
I set this up, but it was painful. I 3d printed bulkhead fittings for the buckets to connect to the hose, and some hose adapters, but they all leaked. This is a problem with 3d printing (ASA plastic in my case) where there are a bunch of pin hole leaks. I think I’ve repaired the problems now with hot glue coating. Hot glue is one of the few things that adheres decently well to polyethylene buckets, especially if you go slow and get the hot tip to melt and mix with the polyethylene. Then I had lots of air locks in the system, the hoses need to be filled, then routed…not prerouted and filled. Thankfully I had clear tubing so the problem was obvious.
I also measured the light in a grid on the inside of both illuminated panels after finishing the lighting system. This was quite uniform after passing though a 100% diffusing greenhouse plastic so that should make modeling easier. As the tomato plants grow I plan on making a weekly 3d scan of each one and using ray tracing to determining how much light they are capturing.
Lots of other little stuff to do but growth chamber is pretty well ready and tomato transplants are started so the experiment should begin soon. I’ll be happy when it’s on it’s way, the preparing of an experiment is always the most difficult.
Til next week-
Carl
Sun Aquasystems 