Solar Heating with Plastic
Plastic Drums are great for storing solar heated water, BUT they do get soft at elevated temperatures. Above 170 F these round drums begin to lose their shape but if they were cubical or rectangular they would need support to maintain their shape. HOWEVER if enough tanks are used it is unnecessary to store solar heated water above 130F
Heat storage does not have to be an expensive proposition. Glass lined steel tanks might be top of the line BUT a thousand gallons worth of steel tanks containers could get expensive. AND don't forger once you drag them down into your basement you'll still have to insulate them. How would it be if you could insulate plastic tanks with dry sand. Dry sand is actually an excellent insulating material that could also be used to support plastic tanks. Round up 20 recycled 55 gallon plastic drums and place these tanks inside a sand filled container and you'll have more than 4 tons worth of multi tank solar hot water storage capacity, This means that a 10 degree F rise in water temperature will store 80,000 BTU's worth of heat.
40 sq meters worth of MTD collectors could easily harvest more than 80,000 BTUs with one hour of direct sunlight. Anyhow we're not talking about collecting heat right now we're talking about storing it in a multi tank heat storage system like this:
I always feel good when all the pieces of the puzzle fit together. In this case the multi tank method of storing heat is not only practical and efficient, it's also inexpensive and easy to install. Here is some data collected from my multi tank MTD heat storage system:
This data has been recorded from a six tank 120 gallon system in my backyard. Unfortunately I only get a maximum of 2 hours worth of direct sunlight per day so my data collection is limited HOWEVER the temperature readings from tank 2 and tank 6 clearly demonstrate the advantage of a multi tank system. Tank 2 is the second tank to receive heat from the collectors and tank 6 is the last tank through which the water is circulated before it's returned to the collector. Maximum heat transfer efficiency is achieved through stratifying the temperature differential. In other words it makes more sense to return the coldest possible water to the collectors for heat transfer. Temperature differential is directly proportional to heat transfer rate... As collector temperature approaches heat storage temperature the heat transfer rate slows down. This is why multi tank heat storage is so important. One large tank also has the ability to stratify heat through the water density differential. This is why it's better to let hot water enter the top of a hot water tank and exit from the bottom,, Multiple tanks intensify the heat stratification process.
Supporting multiple square tanks can be done with a simple support structure like this:
This is the insulated Tuff R, plywood, 2x4 support structure away from the wall. I'll leave the support system against the wall up to your imagination. This is all the support required by the inexpensive K Mart 20 gallon storage tanks. 120 gallons worth of heat storage may not be enough to heat a house but it's definitely enough to conduct thermal experiments uncontaminated by any other heat sources.
In June the MTD solar shed looked like this when I lugged it over to the Long Island Solar Fest:
In October I raised the pitch of the roof to optimize a winter heat harvest.
Now it looks something like this. Crude but effective.
This is my little sun corner, It's not much because a lot of the sun is blocked by the surrounding trees:
BUT I'm working on it. It's been overcast and rainy through out most of November and it won't get better in December, but I'm looking forward to the test results from January, February and March. If the tanks make it through the winter without freezing I will consider this experiment a success.
Stop in from time to time to see how the plastic tanks hold up. Will the Tuff R insulation with an R factor of 3.3 be enough? Better seal those cracks up before it gets too cold. Will Santa stop by for some hot coco in December? Stop in from time to time to find out.
MTD Solar Heating