Tips and Tricks
I get a lot of customers looking for absorber that have the passion and excitement required to take on a project, but really have not conducted enough research to decide what, where, and how to do it. Hopefully some of the below information will be of value.
Traditional Energy production & Solar Panel Potential;
A typical hot water solar collector will generate about 100 BTU’s per hour per square foot of collector. Since most people have no idea what 100, a 1,000 or 100,000 BTU’s really means, let’s look at some typical heat energy sources and see what they produce. One KWh of electricity will generate approximately 3412 BTU’s. One gallon of Propane will produce about 93,000 BTU’s. One cubic foot of Natural Gas will produce about 1030 BTU’s.
So, if you know how much energy you are using of the fuel source you will supplement or replace with solar, you should be able to use these values to calculate a comparable production rate of your solar collector (what you can expect in solar heat collection) based on it’s size. This is important, because many builders have unrealistic expectations of the amount of solar energy they will get from a small panel. Remember, you will need to take your total collection area, times 100 BTU’s per hour, times the average amount of hours of sunlight. I’ve posted a few good sites that give you the average daily sun by region, with the first link being pretty detailed, and the second and third link being more basic solar maps.
What type of hot water collector should I build?
We'll concentrate on flat plate, as that is one of the easiest for the DIY builder to build and it's what I have the most experience with. I've seen a nice "trickle down" system by John C. and George P. builds a great tracking "concentrator", but I think Gary Reysa and I have found the flat plate to be the more desirable option for most first time builders.
There are two basic plumbing layouts for the inside of our collectors. Manifold and riser designs typically use a lower and upper manifolds running horizontally, with several "risers" running vertically between the manifolds. There are some builders using this same principal with vertical manifolds and horizontal risers, although this is the exception rather than the rule. The second plumbing design is Serpentine, which means the inlet starts at the bottom of the collector, running horizontally, and reverses back above the previous run on every consecutive run, until reaching the top of the collector. A good example and pictures can be found here (click);
Gary has an example as well; http://www.builditsolar.com/Experimental/PEXCollector/PEXCollector.htm
Many builders ask whether manifold and riser (M&R) or serpentine are more efficient. I believe the manifold and riser design beats the serpentine by a nose, but here's why. The M&R design extract heat faster from the collector, keeping inside air temps closer to the temp of the water. Conversely, serpentine designs, with the same water needing to travel through every inch of the plumbing in the collector, have a larger temp rise of the water (but flow less water per minute) and the potential for heat loss out the glazing is larger as the water temp increases. Having said that, serpentine is almost a must for PEX designed glazed collectors, as connections that would be reliable inside a glazed collector for PEX would be cost prohibitive. With the many tests I've done over time, I really don't think there are more than a couple percentage points of difference between the two designs.
Drain back systems can use water, but due care must be applied during the building and installation to pitch all plumbing for proper drainage after shut down. The plumbing must be slightly pitched in the collector (I typically pitch only 1/8" per foot and have never had a problem, some pitch more). See the 2/07/11 update below for more details about manifold and riser construction; specifically for drain back collectors. The plumbing coming back from the panel must be pitched downhill all the way back to the tank. A few points of concern for proper drain back operation; the pump must be below water line, preferably as low as possible on the tank and must always be in "prime". The return line must be ABOVE water line to allow air to enter the system for drain back function when the pump shuts down. To ensure no water is circulated unless solar heat is present, a variety of controls can be used, from a cheap 110 or 120 degree "snap' or "button" switch to an actual "differential controller". Links to potential vendors for those products are posted below.
Closed loop systems don’t require pitching of the plumbing, but will require antifreeze if installed in a climate that will see freezing temps. They will also need an expansion tank, unless the water storage tank is atmospheric. Pumps can be used with lower head capacity, as once the system is pressurized (or bled), the only demand on the pump is flow resistance; essentially, there is no head. One area of concern with closed loop is stagnation. If the pump is not running, assuming this is not a thermosyphon system, be it a power outage, control malfunction, or pump failure, temps inside the collector can easily exceed the boiling point of the fluid. If steam is created, clearly the collector will be damaged.
Plumbing inside the collector, basically the tubing inside the absorber, is typically either copper of PEX. PEX has limitations with a maximum heat range of around 200 degrees. I’ve seen collector temps at as high as 300 degrees in stagnated panels (even melted some PEX during experiments), but will work well if the panel is carefully constructed (no connections inside the panel, vents for summer time temps, etc). PEX also works great when heating chemically treated water like pools and hot tubs, as it is impervious to those chemicals. Copper, although expensive, is one of the best conductors for transferring heat from the absorber to the water, and is pretty bullet proof for the temps seen inside most collectors. But, copper will NOT work with chemically treated water (at least no without degradation of the copper and a nice red tint to your water).
How large should my tank be?
The rule of thumb is 2 gallons per square foot of collector. A single 4 x 8 collector (32 sq ft) should have around 64 gallons of water. I’ve seen deviation from that and the systems still work. Less water and the temps climb faster, but they drop faster upon demand too. More water has the “flywheel” effect, with the minimum and maximum temps not as spread out, but getting higher temps for use in some applications is not as easy to do.
I've had a lot of builders ask about the importance of the location of the inlet and outlet when building a manifold & riser style solar collector. There are some common problems that need to watched for in your DIY panels that will greatly impact your efficiency. Since most builders are building "Drain Back" systems, slope of the manifolds has to be considered too. I typically slope only about 1/2" in 4 feet, and have had no issue with drain back (I routinely see -20 F temps in the winter here in the U.P.).
Regardless whether you have a glycol system or drain back, the first issue is to make sure each individual run in your system is the same length. You need to consider TOTAL RUN, including your manifolds. For example, if you have your inlet on the bottom left side of your panel, connecting to your bottom manifold, and your outlet is on the same side, connected to the top manifold, even if the there is no pitch to the manifolds, the water traveling through the first couple of risers travels significantly less distance than the water going to the far right side of your panel. The water WILL take the path of least resistance, or the shorter runs. The right side of your collector will warm up a lot more, and will NOT be transferring the heat to your water at the rate desired. The best rule of thumb is to make sure the inlet is at the lowest point on one side of the panel, and the outlet is at the highest point at the OPPOSITE side of the collector. If, for plumbing convenience, you want all the plumbing on one side of the panel, or even immediately next to each other at the bottom, extend the plumbing from your highest point, back along the upper manifold, and return it to the left side (or down the far right side and across the bottom). Just keep in mind your pitch requirements on this extended plumbing if you are building a drain back system. Some added advantages to running this extra plumbing inside the panel is your plumbing will not be exposed to the outside temperature, will not need insulating, and you may even pick up a bit more solar heat before exiting the panel.
As far as building the actual copper tubing "grid", it's best to cut every riser to the same length. You can assemble the whole grid "square", and after all the soldering is done, install the grid in your collector box. You can "wrack it" by installing spacers to get your pitch (for drain back systems), keeping those spacers in place until most of your absorbers are in place to hold everything. The copper is pretty soft, and will adjust easily to the slight twisting to get your "pitch". No need to perform anything special to get the required slope in the tubing before the grid is all soldered together.
Tips on use of product;
* Aluminum or copper should have barrier for corrosion at the contact area (primer &/or paint).
* The Aluminum is "Mill Finish" and has some light oil on it from the manufacturing process. It should be properly cleaned with mild soap and water before applying finish.
* The easiest place to cut the absorber to length is before it's pressed; figure out your coverage area and compute the length of your individual absorbers, based on this measurement, before ordering.
* It's not recommended to overlap the absorber "lengthwise", but overlap of the flat area (sides) is fine.
* Many builders are installing a narrow (2"-3") aluminum strip under the tubing to assist in heat transfer from the absorber to the heat transfer tube. On the 90% wrap this gives no benefit. Gary Reysa, of Build It Solar, likes to install a bead of good caulk as well.
* The "Vice Grip" Clamps we've designed work very well during final installation of the absorber on the tubing. You can make your own, or we have them available for purchase as well. Tight contact between the aluminum and tubing is essential to good collector performance.
* The best information source for home built solar projects is; www.builditsolar.com . There is more information at this website for homebuilders than any other source I've found to date.
Finding your materials;
I’ve been asked by a lot of builders where we are getting a lot of our materials. Below is a bit of a contact and/or website list where we are sourcing our materials.
Aluminum Solar Absorber;
Hopefully from us, but you can use standard soffit material or aluminum flashing. I caution on the flashing, as the aluminum thickness should be around .018” thick. Most flashing is .008” to .011”, and it will not form well over your tubing. It can be used under the manifolds to protect the material under the copper grid, where you’re not using absorber.
A good source in the Midwest is;
This is where I purchased mine. Similar outlets are sure to exist in other parts of the country. The problem with purchasing panels large enough to work, the shipping often far exceeds the cost of the material. This is why finding a source close enough to arrange your own pick-up is important. Most lumberyards have access to (or a stock of) the “corrugated Polycarbonate”, like the product Gary uses on most of his projects. Sealing this product is a bit more work unless you can get the “wiggle strips” too. I’ve done some panels in glass and they look very nice. I used tempered glass for safety and durability reasons. The price and weight of glass is a bit of a negative though.
Some feedback from one of my customers regarding the purchase & shipping of polycarbonate;
I found a place called Ridout Plastics in San Diego, CA (www.eplastics.com) that will cut the multi-wall panels to a smaller size for a minimal fee to
save on shipping. By having the 4'x8' sheets cut into 4'x2' panels they can
ship it much cheaper. All other places I checked into would only ship the
full sheets with a $100 to $150 crating charge in addition to shipping via
freight truck for $75 to $125. That makes the total shipping in the range
of $175 to $275, that's as much or more than the panels cost. I am having
Ridout cut 3 full sheets into 12 panels and the total shipping will only be
$37.00! I will make simple wood strips to join the panels together and act
as supports/stiffeners. Please feel free to pass this information on to
make it easier for others to get the glazing they need.
Pumps, PEX Tubing & some controls;
We’ve found the best pricing and availability to be at;
http://www.pexsupply.com I’ve personally used primarily the Taco pumps, but my brother and others have found the Grundfos pump to be a better value, especially when needing more than 11’ of lift, more flow, or multiple speed options. Make sure you consider your flow and lift requirements before buying a pump. There are flow charts on the site to allow you match the pump to your requirements.
I used the Gold Line, GL-30 for a differential controller, but was unaware of John Canivan's great website and his controller. He has a variety of different controls, including a differential controller, and other electronic components useful in our solar collector systems. His link is; http://www.jc-solarhomes.com/differential_controller_kit.htm
“Snap” or “Button” switches;
Although we’ve found some at Granger, we have a local source that has been great to deal with on controls. The company, “Controls Supply Co” in Kingsford, MI stocks the switches, and has shipped them out to several builders recently. Mark Miller, the owner, has been in the business for over 30 years, and is a great resource for the unique requirements some of our systems have. Call Mark at 906-774-8831 if you have trouble finding controls or switches for your system.
Weather-stripping, screws, paint and lumber materials;
This is the great part about DIY (do it yourself) solar panels. The bulk of the materials can be purchased locally from lumberyards and hardware stores. You support your local economy with a lot of the project, and you avoid a significant expense that is almost always part of a commercial collector; the freight. A commercial collector will need to be shipped truck, and will be exposed to damage during transport. This is aside from the very obvious cost savings of a commercial panel. No, you cannot claim a 30% tax credit on your $200 - $250 panel, but then a 30% tax credit on a $1200 panel (plus a hundred or more to ship it) would still net you well over $900 in the commercial panel.
Warning!!!!! Do not purchase from Pond Solutions in Troy MI!!!!
I used 45 mil pond liner. I bought mine from Pond Solutions in Troy MI, and
my wife never mentioned anything about the credit card bill when it came
through (she knew I was working on the project and expected some bills).
Anyways, 9 months later, while doing my taxes, I discover they charged me
an extra $500 on my card (the liner was only $149). It was too late to
dispute the charge with the credit card company, Pond Solutions refused to
even talk or correspond with me about the problem, and when the local
Chamber of Commerce attempted to resolve it, they would not respond to them
either. I highly suggest you purchase from another supplier.
If you can believe it, they still send me promotional emails too.
Links to other great websites;
Making your own clamps
Any builder with basic welding skills and a welder can make these clamps. Start with 11' "Vice Grip" clamps and a couple pieces of 1/8" x 2" x 8" long strap. We drill holes in the strap for access to screw the absorber down while clamped tightly. It's easier to drill them before they are welded. When making multiple clamps, we usually drill 4 of these, in four locations, on a drill press. Once the straps are drilled and de-burred, we place them on a table tightly to each other and center the Vice Grips over the straps. We have the Vice Grips opened so they are 1/2" back from the inside edge on each clamp. This is to ensure the actual ends of the Vice Grip do not contact the aluminum when used to clamp up the absorber. Simply weld the grips to the strap and clean them up with a grinder. If you desire, the straps can be "rounded off" where they will contact the absorber. This can be done before (preferred) or after the welding process.
We offer the modified clamps to builders interested in purchasing them. We do this more as a service than anything else. Many builders don't have the equipment to make them. We've found by purchasing the grips in bulk, we are able to sell the modified clamp for a little over the price the Vice Grip sells for in most hardware stores.