Introduction: Batch Solar Water Heater
Aim: To build a solar batch water heater using some old materials and some new. The idea behind this heater is to use as many old materials as possible, keeping them out of landfills and to use new materials as efficiently as possible. For this reason the box has been designed to use exactly two sheets of plywood without any waste. This also gives the box a trapezoid shape, making it stronger and angling the sides to reflect light onto the bottom of the tank. This was a lucky accidental feature;-)
I think this is a very simple design most people are capable of making with fairly basic tools, cheaply and without advanced carpentry skills. it is a effective heater - I have seen the water on top reach 150F on a hot spring day.
I have built a few of these and am still working on improving the design. I will log in and update this as I have more pictures and info. If these are not completely clear directions, well, this is my first instructable, so it will only get better.
Step 1: Materials Needed
Double glazed patio sliding glass door, 3' wide ideal. Should measure about 36” x 79”
Old water heater tank. I have only used 40 gal gas heaters so far, but I see no reason why larger tanks and electric tanks should not work, fine.
½ inch sheet of plywood
5/8 inch sheet of plywood
2 sheets of 1 inch foam insulation with reflective foil surface
Rustoleum or equivalent flat black metal paint, 1 pint
Stain or exterior primer and paint, 1 quart of each
¾ inch steel plugs for extra tank holes, maybe.
2 cut off pieces of 2 x 8, 16” long
One tube of latex or other caulking
Box of 1 5/8” drywall screws
10 3" wood screws for tank supports
16" long 1/2" copper pipe with cap and
2" long 3/4" threaded steel pipe
JBWeld for above
Teflon pipe tape
Step 2: Locate an Old Heater and Buy Materials
First locate an old water heater, preferably one without leaks, although leaks can probably/possibly be patched with JBweld or equivalent hardening sealant. A dump, or salvage yard may have one, also check on Craigslist, call local plumbers and be creative. The patio door can be found in similar locations, double glazed is best, although single will work too.
All other materials should be at your local hardware store
Step 3: Prepare Tank
Remove all parts that protrude from the water heater casing. This includes the burner, relief valve, drain valve, etc.
Take of the top and bottom of the casing, then use a screwdriver or pry bar to open the crimp where the casing is joined together. This can also be done using a grinder fitted with a cutoff wheel, or a Sawzall and a very fine blade. If using these methods be careful not to cut too deep as the inner tank is about an inch below the casing.
Pull the casing off and remove the foam insulation below, by scraping with a putty knife if necessary.
Sand the tank down and use a wire brush until most of the rust is removed.
Paint tank with flat black metal paint. Rusty metal primer is recommended but optional.
Step 4: Building the Box
If you have an average tank, (40gal, 16” wide) the following dimensions should work, for larger or oddly shaped tanks, other dimensions need to be figured out. These dementions are the finished dimentions of the outside of the box, not the exact panel sizes. You will have to figure out the exact sizes of each panel deducting for the width of the sheets of plywood.
To build box, rip 5/8 sheet of plywood down the middle, i.e. 24”. Cut one side down to 68” long, or as long as your patio door is tall. This will be the bottom of the box.
Cut out your trapezoid shaped box ends from the other half of the 5/8" plywood. with a top dimension of 36”, bottom of 24” and height of 24”.
The sides of the box are made by ripping the 1/2" sheet of plywood down the middle, making them 24" wide and cutting them to 68" long.
Screw trapezoid sides to bottom, and long sides onto these. Use about 1 screw every foot.
Cut trim wood to fit rim of box and screw on.
Caulk under rim to seal rim to box, and along corners, keeping moisture from entering plywood here. Do not caulk around the bottom of box as this would stop a leak from exiting the box.
When caulk drys, prime and paint outside of box and rim with exterior paint, or use two coats of high quality stain.
8.Lay tank on side raised up three inches and scribe contour of tank onto 2x8 scrap. Cut along line with scroll saw, jig saw, or saber saw. Make two of these, they are the tank supports.
9.Cut first sheet of insulation to fit in bottom of box, place tank supports at good distances from ends of box, mark around tank supports on insulation. Lift insulation out of box and cut out holes for tank supports.
10.Screw tank supports to box with five or more screws in holes cut in insulation.
11.Cut long side panels of insulation to fit snugly in box. Measure and cut trapezoid end pieces to fit angled into the box.
Step 5: Making the Supports for the Tank
Take the length of 2x6 lumber and cut it into 2 16" long pieces.
Prop the tank a couple of inches off of the table, hold the piece of wood against the end of the tank as it the diagram and mark the curve of the tank on the wood. Cut it with a jigwaw, saber saw, scroll saw or any other method you can make work.
Step 6: Insulating Box and Supporting Tank
Cut one sheet of insulation so that it fits snug in the bottom of the box. Take the tank supports and lay them out on the insulation. lay the tank on top of them and move them around until the tank seems well supported, similar to the way they are in the picture. Mark and cut holes for them to fit through the insulation and attch to the plywood.
Screw them to bottom with the 3" wood screws.
Step 7: Make a Cold Water Inlet Dispursor
To prevent the incoming water from mixing with the hot water in the tank, we need to make a disperser, done in the following way:
cut a 16 inch length of the 1/2 inch copper pipe. Drill small (about 1/8 inch) holes every inch or so along the top side of it. JB weld the cap to one end of the pipe, and JBweld the other end into the 3/4 inch steel pipe. I will take a picture of this when I get a new charger for my camera. The heater will work without this part, but it will be more effective with it, especially when it is not very hot.
Step 8: Plumbing the Tank
Prop up one end of the box underneath the tank support until the tank is at about a 30 degree angle towards the South. Place the tank in the box with the bottom facing up. Rotate it until the 3/4 inch connection closest to the bottom of the tank is pointing upwards. Screw in a 3/4 inch angle pipe here.
Screw the Cold water inlet pipe into the lowest hole in the top of the tank. plug all remaining holes with things removed during the preparing of the tank, the drain cock and pressure release valve work fine.
Again, I need my camera working again before I can show you this part, and it is not easy to describe it without pictures. Forgive me.
Cut a slot in the bottom of the lower insulation end panel, and drill two holes in the plywood, probably with a hole saw so your piping can get in and out of the box.
Step 9: Using It
Place the double glazed glass panel on top, let it heat for a few hours, then enjoy your solar heater water. Ask me if you have any questions.
Some modifications which you should try are:
Thinker insulation, maybe 2" would keep it hotter in the winter.
To keep it warm at night for use in the morning glue a sheet of insulation to a think sheet of plywood and hinge it to be a closable cover for night time and other times of no sun.
A thermometer can be made to read the temperature inside the tank by drilling out a hole in a 3/4" steel plug and JBwelding in a little kitchen thermometer into the hole.
Thanks, sorry about the quality of this article, I am not really feeling it right now, and will probably re-write it later when I am inspired.
Thanks Annie Rose for who you are, I love you like I love myself. XXXoooXXoooxXOxX