randomhumanity

I came across an interesting study recently while researching the relative environmental impact of hydroponics systems. Run by defra in the UK, it compares the impact of food grown in the UK with that of food imported from abroad in order to test the idea that locally grown food is always better for the environment. The results are mixed, of course.

What got my attention was that one of the foods examined was tomatoes, grown hydroponically in heated greenhouses in the UK, or in soil in Spain. The hydroponic tomatoes come out worse in terms of greenhouse gas emissions due to the heating (and they also pump CO2 into the greenhouses to aid photosynthesis), but better in terms of water usage, runoff and land usage, so it’s not exactly clear cut. It’s also not exactly the same situation as what I’ve got going on here. How does a home-grown hydroponic tomato compare to a Spanish tomato, or even a UK tomato? Well, they provide some decent figures for each case, so it may just be possible for me to figure it out!

What I’m proposing is to grow a tomato plant in my original system, record the energy inputs and the yield, and from that calculate the CO2 emissions per tonne (ha!). I’ll figure out the monetary cost as well while I’m at it. There are some caveats of course: I will not be including heating costs like the UK greenhouses in the study, because I would be heating my house anyway, I will be using CFL bulbs where more powerful ones are recommended for tomatoes, I may not be able to determine the environmental impact of manufacturing the nutrients I use (though I have contacted the manufacturer), I will not consider the impact of manufacturing the system itself… Also, I have never grown tomatoes before, and I hear they are difficult, so the initial yield may be low. Still, I think an attempt or two will at least be educational, and hopefully quite tasty. Am I wasting my time, money, and destroying the environment by not powering all the equipment with renewable energy? Only SCIENCE* can tell me!

*may not contain any actual science

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A better reflector

My first hydroponic system worked fairly well as it was, but one aspect of it that I thought could be improved was the lighting. It was white on the sides, which is reflective enough, but something metallic and shiny would be better. Also it was wooden, badly painted, and just not all that stylish. So, I decided to take another stab at it

One of the things I had considered for the new system I’m building was aluminum reflectors for the lights. I abandoned that idea when I discovered that for that one, the sheets alone would have cost about €160, but I decided to use the idea for the smaller system because I still wanted a chance to work with metal.

I picked up a 250mmx500mm sheet of brilliant aluminum (one side is mirror-like and comes protected by blue plastic), some thin steel bars, some small hooks and some short nuts and bolts from B&Q. The aluminum was about €20, the rest brought it to no more than €30. If you’re building several or building larger fixtures you could definitely do it cheaper with wood and reflective sheeting or paint, but for a small one-off system this is quite economical.

The intention was to bend the steel bars and use them to hold the aluminum in the shape of a parabola, or at least a curved reflector that will send most of the light downwards. I started out by putting holes to match my bolts in one end of each of the steel bars, and another about 230mm down. You will probably need a drill press to do this. Be patient or you’ll wear out your drill bit before the job is done (like I did :S). I curved the bars around a centrepoint between the two holes by pulling them against a fixed object on my workbench. This isn’t very exact, but you should be able to get a curve that is approximately the depth of a bulb and a reasonably close match between the two.

I didn’t actually cut these to length until after I had fitted the aluminum

Next I drilled a bunch of holes in the aluminum. For the bracket holes I actually drilled one side and then curved the aluminum inside the bracket to find the position for the hole on the other side. This is probably unnecessary, you could just find the position of the hole before you bend the bracket. The other holes are to support the actual light fitting (I am just reusing the ones from the previous fixture) and a hook for the chain that will support it.

I reused the light fittings from the previous reflector. All I did was put a hole through the centre of a block of wood and use a cable tie to secure the light fitting to it. The block of wood gives the bulb enough clearance. If I was really clever I’d have made the curve parabolic and used the block of wood to place the bulbs at the focal point, ensuring the maximum possible amount of light headed straight downwards. But no, I just went with a rough curve and the wood I had lying around. The block was glued to the previous reflector, but for this one I used a cable tie through the same hole and the two drilled in the aluminum.

There are more suitable fixtures than this available if you’re not as impatient as I am.

Finally, I screwed some small picture hooks through some holes in the aluminum and into the wood blocks of the light fixtures. This allows the whole thing to be suspended from a length of chain, allowing for easy raising and lowering. It also gave me an opportunity to try out the macro function on my new camera!

Here’s the finished product doing its thing. I don’t have any real action shots yet because I’ve been waiting on some shelves to house this system, but I think this should give you the general idea

I might paint this sucker black to match everything else, but it also looks good as-is.

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