Backyard Aquaponics
A place to discuss aquaponics

I'm idly wondering if it would be possible to use an array of magnifying glasses or a fresnel lens inside the greenhouse to heat a steel sump tank?

I'd like to use a solar heater to heat the ground of the greenhouse, it gets so cold here I figure I'd need to use antifreeze instead of water; so I don't want to pump my actual fish water to a solar heater outside.

Does anyone happen to know if this idea would be worth pursuing further as a form of supplemental heat?

It`ll work
You can also use a bank of mirrors or a parabolic collector to magnify the suns power and direct it all onto a small focal point. Ideally you need direct sunlight as diffused isn`t much use ..try setting light to something with a magnifying glass on a cloudy day
Sun tracking would be good to keep the array pointed at the sun throughout the day.
You might not have much room left in the gh for the plants though

I was thinking of something decidedly simple and low tech; an array of magnifying glasses mounted in a partial sphere around the sump tank on the south side, with the backside being an insulated box. Basically a simple solar water heater custom built for the sump. If the magnifying glass works under the greenhouse glass, I could try the same thing to warm the growbeds. All the plans I found were for solar water heaters meant to be mounted outside with direct sunlight, I wasn't sure how much the greenhouse glass would interfere. I'm a year or two from having a greenhouse and just entering the planning stage.

On a side note, I'd like to use plastic as little as possible in the system. That pretty much leaves me with glass or steel for growbeds. I wouldn't mind getting a large order of 25 to 50 gallon aquariums, drilling them and using them as a bunch of little growbeds in series, but I think the increase in the number of connections would mean too much extra maintenance; plus glass can crack. That leaves me with steel, I've seen some steel tanks on this site but I don't remember seeing steel growbeds. Other than weight, is there any reason why?

humanfly,,,I'm working on stainless-steel grow beds,,,no need for them to be heavy,,have a look at your kitchen sink,,strong,light-weight,durable:)

A 12 foot by 6 foot sheet could easily be bent to be a 12 foot by 4foot by 1foot deep grow bed,,,,it's the end plates that would require a bit of work.

Even easier,,with the correct support brackets ,,the sheet could just be allowed to naturally bend into ahalf-pipe shape.
Stainless prices have risen lately (along with near everything)but cheaper than most people expect.

hm. If I'm going to go to the trouble, maybe I should just build a solar heater inline with the system, to heat the water before it gets to the sump.

Chappo, have you got any photos of your steel growbeds?

humanfly,,,Still getting quotes on the manufacturing of the end-plates,,figure i can easily do the main part myself,,but the plates?? welding thin-gauge staino ,, no time in my life for that.
Cheers

Humanfly.... just whereabouts are you???

Howdy
If you use a drain down system you wont have freezeups and can locate solar collector outside the greenhouse. Use a single 80? watt 12 dc PV panel to drive a shurflow RV 12volt pump when the sun shines. When sun goes down the pump stops and an air vent opens to allow draining to an open sump. At sunup the pump will start and the air vent will open to release the air rising to the collector. The sump should be an insulated open tank with a thermostaticly controlled circulating pump that will run when FT water cools and supply heat to coils in the FT and returning to the sump. Key is insuring no traps in the piping to and from collector to foul drain down. No antifreese needed. If the water freezes in the pipe going to the collector at start up the pressure from the pupmp and rising sun will eventuall thaw it out and no harm done. Use cheap 1/2 inch drip irrigation black plastic pipe and it will expand when frozen and draw heat itself from the sun.
Shurflow model 2088 pumps will run dry without damage. They will provide 45 psi so have plenty of lift and yield 3 gpm at 15 ft head. They cost about $80 on sale. I have run one in just such a system to heat oil for making biodiesel for 3 years sunup to sundown. I do not have to worry about overheating the oil so the collector drops direct to a coil in the drum then goes back to the sump.
This system is simple and elegant....works great. I plan to heat my AP with it. By using a header from the heated sump tank pump and temp controlled solinoid valves you could heat two or more FT. An electric heater on its own stat could provide back up heat in the event of a lack of solar. The only expensive greenhouse space given up is for a sump tank, say a 55 gal drum.

Hi Rupert,

I'm in Toronto, Canada. They say it has mild winters compared to the rest of Canada and the average winter temperature is probably only a few degrees below zero Celsius, I'm pretty sure it drops to around -20 at times.

Spiritrancho, I'll definitely keep that in mind for underground heat. I don't want to circulate my actual AP system water outside, though.

You probably get quite a lot of winter sun.
A trough collector could be cheap and easy to make, http://jc-solarhomes.com/fair/parabola20.htm
Something 4m long x 500mm wide trough with 100mm focal point could do 100-200C on a good day.

How is the air vent controlled?

Hmm...yes...is there a vent valve or is the vent always open? I had always pictured latter: the pump filling the water heater from the bottom and the warm water going down from the top of the water heater with an always-open air vent sticking up to allow air in. This makes the pump do more work since there is never a siphon effect, but allows water to drain back immediately when the pump stops.