Solar heated fish tank

[David Palmer]

I'm trying to work out a solution in which I can get fish started in February so that they can be plate ready in November and December. I'm in Portland Oregon, where it's known to get bellow freezing.  Our last frost this year was in May (lots of people lost plants on this one).  Although perch or trout might survive the cold, the bacteria won't be so happy with the cold and there won't be much fish growth unless kept warm.

I'm looking for something easy to build and inexpensive as a DIY project.  A green house is probably too expensive of a solution.  An electric water heater would be an ongoing expense that runs up the electric bill too much.  I expect the fish tank and grow bed will require Styrofoam insulation.  I am partial to plastic row covers.  Although needed, I'm thinking the row cover won't be enough heating at night (or might it be too much heating in the day?).

I've seen a few youtube videos on the subject of solar water heaters for aquaponics.  These have used a simple PVC tubing in a black frame to heat water in the tubing.  A pump can be used to cycle water through the tubing when the fish tank temperature reaches a low temp setting and presumably turns it off at night.

In the comments, it was noted that the PVC pipes melted in the summer.  Another problem I see with this is that the tubing is likely to freeze and burst at night in the winter.  It also does not store heat for use at night other than what is already transferred to the fish tank. 

TCLynx posted some comments back in 2008 about the need for a heat-exchange.  The solar collector continuously heats water in a reservoir.  Then an extra set of tubing goes between the fish tank and the reservoir to heat water when needed - day or night.  Although she did some experiments, I didn't see any finished designs.

Anyone know of a completed design suitable for keeping the fish and bacteria warm in the winter?  Or am I being overly concerned about the cold?

Dave

[Converse]

Dave,

   I am in the Columbia Gorge just east of you, and you are right to be concerned about the cold. If you are on an exposed site you might try looking into those homemade soda can solar heaters.They need direct sunlight. There are plans for these on the web, and lots of u-tube videos showing how to make them...I just did some research on this for my place.( too many trees and clouds to make it successful as a dependable source for us)..For heat at night you'd have to have stored the heat in an exchanger..

   So for my place it is the PVC pipe through a thermophylic compost pile and heat the water routine...It is labor intensive, but I have the time and want-to, and not a lot of $$, so it is my best option right now.  If you have access to hot compost materials you might look into this option. I'd really like to get one of those Wise-Way Pellet Stoves that R. Stillwagon has promoted on this forum!   

- Converse

[David Palmer]

Thanks, I found the web site for the soda can heater.  However, the design is for heating air, not water.  If the water is exposed to light, I'll be expecting algae .

I did find a number of Water Heating Plans

In the mix is a section on water heating for animals, including stock tank heaters.  I'll look over some of these and see what I find.  Also, it has a compost water heater.

If anyone has experience using a solar water heater, please share.  Thanks!

[Rob Torcellini]

A few of things to ponder:  How large is your system and what temperature do you want to keep your water?  For each gallon of water, you need a system that generates 8.34 BTU's to raise it one degree (not including any mass from your stones).  If you only heat the water, and not the greenhouse space, you will have terrible condensation in your greenhouse.  Hoop houses are terrible for retaining heat so you also need to have a building that can hold some kind of heat.  Even double-wall polycarb is poor with an R-value of around 1.8...but at least it's better than a sheet of plastic.  Also keep in mind that you need to generate enough heat in a few hours of sunlight during the worst of winter to store enough heat to last the other 20 hours of the day....very hard to to with solar in a northern climate.  I'm in CT and the daily average sunlight we get in the dead of winter is less than 3 hours.  Heat isn't you only battle, but the amount of sunlight your plants get will be another.....

You may want to invest in a pellet heater like Dave suggested.  I can heat my 1100 sq ft greenhouse and burn about 80 pounds of pellets on a bad day.  ("Heating" is keeping the air around 58F and the fish are at 60).  I could never imaging spending the money to heat it up any warmer to raise something like tilapia!

[David Palmer]

Well,Portland, OR has average sunlight hours per day of 4.0

I'm thinking about 300 gallons as a trial system.
Your comments are making me think I'll have to use a Compact Linear Fresnel Reflector and saltpeter for thermal storage.  Of course, that might be a little risky for a DIY project considering the potential for high temperatures.  I'll need to figure out what is "good enough".

The target is to use this in an inner-city environment; say on top of a short building.  I expect that they won't like the pellet stove.  Of course, molten salts probably won't go over well either.

At minimum, I'd like to keep the water from freezing at night and from boiling in the day. 

Thanks for the pointer about the row cover plastic - evaporation and condensation would leak a lot of heat.  I'll have to think about that...

[David Palmer]

Found a great link for the solar radation data manual.  This notes that in Portland, I'm at 45 degrees latitude (I knew that), and with a fix-flat plate solar collector, I might expect an average of 2.6 kWh/m^2/day in February. 

Note that water has a specific heat of 4.18 J/gC and 1 liter of water weighs 1 kg.  With a little math, I can start sizing the solar collector to heat the water.