Basic solar heating for a small system

[Kobus Jooste]

Hi All

 

As it is getting into winter here, I am playing with an idea for solar heating that I thought of a few months ago.  It may not help people in the Northern Hemisphere much now, but I'll report on the progress I'm making.  I am going to start experimenting with a small unit to heat an aquarium system I'm working on.  The 300 liter aquarium is in an outside building with no insulation, and a 300 Watt heater basically never stops working to keep the temperature up above 20 degrees Celcius.  The idea I had was using left-over pieces of 6 mm multi-wall polycarbonate sheeting used in my research system as a simple flow-through solar water heating panel.  I have designed the basic plumbing, but before I spend too much time making the actual unit, I thought I'd give the idea a go.

 

First test was filling a 25 liter blue drum up with water and leaving it in the sun.  It heated slowly, but topped out at around 26 degrees.  I then siliconed up one end of a 0.5m square polycarb sheet.  I left the white backing paper on it, but step two of the experiment will be to paint the back black.

 

Although the experiment is very crude (the thermometer is cheap and the probe touches the polycarb sides) the results are promising.  The water heats up rapidly, and reaches 36 degrees Celcius in about 30 minutes (a rise of over 16 degrees Celcius).  I'm not sure what the max of this configuration can be, but it is not far above 38 degrees Celcius.

I am hoping that with the back painted black, I will be able to hit 40 degrees Celcius in 30 minutes flat.  The water volume of the entire panel (without plumbing) will be around 1.5 liters, thus it is not a massive panel.  I have a fair amount of it at my disposal though, and if the black panel is going to give me 40 degrees fast, I'm willing to see how it goes on the 300 liter aquarium.  With 45 minute rotations and around 9 hours of direct sun, I'll have 12 rotations on the panel.  The 0.5 square meter unit will thus only heat about 18 liters of water a day, which makes me think that I will have to go for 30 minute rotations and bigger panels.  On two of these panels, I will then heat 54 liters of water a day. Still, it beats having a 300 watt heater on 24 hours a day!

[David Owens]

Good Luck with the experiment! I live in the cold northern part of the U.S in Michigan and am working through a few solar heating ideas as well as my water is always around 50 degrees Fahrenheit. Keep us posted on your success

[Cai Robertson]

You could look into a heat sink as well.  A bed of gravel under the tank could work. I am doing a concrete pond and am thinking about a solar heated radiant slab as the bottom of the pond.  It will also be in the ground 5 feet which will help regulate temperatures.

[clint miller]

Those panels seem thin.  How would you get the water to flow threw.          

[Kobus Jooste]

I am hoping that I can operate water flow through pump action - I have a couple of variations to the idea that I want to test, but basically I am assuming that I will be able to push the water through the individual channels (similar diameter as typical irrigation tubing) with pump pressure.

clint miller said:

Those panels seem thin.  How would you get the water to flow threw.          

[clint miller]

Cool. So there basically like solar panel heaters for a swimming pool. 

[Kobus Jooste]

Clint - yes, it is exactly the same principle, only you have to watch the temps the water reaches before it is pumped back into the aquarium.

[TCLynx]

I was actually able to heat water rather well with a thermosiphon set up of just black irrigation tubing on my driveway to an elevated insulated water chest.  I expect with a little ingenuity you could adapt some of these panels to a thermosiphon design with a tank that could be plumbed with the fish tank.

[Kobus Jooste]

That could be possible, but I had not thought of an insulated vessel for the fish tank.  I need a larger sump than what I have now to accomodate the water loss from flooding a grow bed, thus I may just insulate it or try to find an insulated vessel such as a polystyrene box that fish are shipped in or an old cooler box. 

 

Thanks for the extra ideas! 

TCLynx said:

I was actually able to heat water rather well with a thermosiphon set up of just black irrigation tubing on my driveway to an elevated insulated water chest.  I expect with a little ingenuity you could adapt some of these panels to a thermosiphon design with a tank that could be plumbed with the fish tank.

[TCLynx]

I tested the idea with an old cooler box.  Trick is the thermosiphon method needs a tank above the solar heating plate.

 

Another option I did was allow some of my drain water to get caught in a funnel feeding to a coil of black tubing out in the sun and gravity would push it slowly through the coil and down to the sump tank while most of the water would overflow the funnel and fall directly to the sump tank.  This idea worked great to warm the water while the sun was out but I had to make sure to close the valve to it as the sun moved off and things cooled down since it will also act as a natural radiant chiller at night.

 

The thermosiphon had the benefit of being automatic and not requiring me to open a valve in the morning and close it again in the evening.

[Kobus Jooste]

The aquarium is quite elevated, thus the thermosiphon option is potentially on.  May still look for an insulated sump as that room gets very cold at night.

TCLynx said:

I tested the idea with an old cooler box.  Trick is the thermosiphon method needs a tank above the solar heating plate.

 

Another option I did was allow some of my drain water to get caught in a funnel feeding to a coil of black tubing out in the sun and gravity would push it slowly through the coil and down to the sump tank while most of the water would overflow the funnel and fall directly to the sump tank.  This idea worked great to warm the water while the sun was out but I had to make sure to close the valve to it as the sun moved off and things cooled down since it will also act as a natural radiant chiller at night.

 

The thermosiphon had the benefit of being automatic and not requiring me to open a valve in the morning and close it again in the evening.

[Mudvet]

Hi,

 

I have included some links around DIY Solar Heaters. Check out the recent Uploads from GreenPowerScience on Youtube. They have great ideas to harvest Mosquito's. Always nice to get an extra food source and to avoid mosquito bites.

 

For if your system is in a shack or greenhouse:

http://www.youtube.com/watch?v=zHdH4t8TNwM&

 

Solar Water Heater:

http://www.youtube.com/watch?v=kXXOwfZA2Rk

 

This is one for when you are serious about heating water with the sun (just imagine the efficiency of this thing with evacuated tubes):

http://www.youtube.com/watch?v=jBNhJuizQdc

 

These is a simpler system (funny to watch too):

Part 1

Part 2

 

 

[Mitchell Lowell]

Good morning Kobus, I have been fortunate to have done much work within this field with one of the largest project being a solar domestic water heating system for a resort in the Caribbean for 26 rooms.  The challenge to solar is storage once there is no more available sun light. This was an issue in the Caribbean as well even with the beautiful weather there. There are different ways to address this need throughout the system design, and materials to do this with.  Water is a great storage medium providing you have enough volume. In new England where summer temps can reach +100, and winter temps -30; the coastal ocean surface temps very around 20 degrees.   Phase shifting materials are another medium that allows heat to escape at a  slower rate then water.  I am in the north east and am dealing with cold as part of my design issues.  I have decided to to build my own fish tanks out of fiberglass with an inner, and outer shell.  My tanks are going to be set into the earth and use the earths insulation value as part of the overall tank heat retention.  The space between the inner and outer shell will have PEX tubing running through a phase shifting material.  Warm water/glycol is run through this closed loop system to heat the medium to the desired temp.  Dry packed sand is a decent inexpensive storage medium as well.  My tanks will be in an environment that will average 55 degrees, but the tanks will be about 20 degrees higher.  Most of my structure will be underground employing ground loop environment conditioning to make space climate control efficient, inexpensive, and in time self sustainable with systems to be added.