DoItYourselfSolar

A project by Nateful







A home built solar hot water collection system.

This do it yourself solar collector was built at a fraction of the cost of an equivalent commercially installed system. Any adept do-it-yourselfer could build this system. Most of the materials are available locally at the big box hardware stores, and your mom and pop hardware stores. I got the idea for this at Gary Reysa's builditsolar.com website, probably the best DIY Solar website on the net. It is based on Gary's $1000 solar hot water heater, which he documents in great detail at his site. This is a drain-back system, which means when the pump turns off, all water will drain out of the collector and pipes, thus providing freeze and overheat protection. Since there is no risk of freezing, normal water can be used as the heat transfer fluid. This style of system has a successful track record in the do-it-yourself solar community. I had a good time building it and am now enjoying free hot water from the sun!


Some features:



For details on construction of the collector panel, click here


For details on the construction of the thermal storage vessel, click here.

 


 For details on the heat exchanger and plumbing, click here
  
         

For details on the controller visit differduino.nateful.com





Some thoughts on cost and performance

Cost and materials
I spent a total of about $2000 doing this project. Some of that is tools that I purchased, and misc extra materials. Some is materials, including the extra glazing and aluminum fins, for my eventual second panel.
About $1600 could be attributed to the actual materials in this project. I wasn't really shooting for the $1000, and knew before hand that I would go well over. Several factors increased my cost.

I chose to purchase the pre-stamped fins from aluminum-solar-absorbers.com. Tom offers a great product at a very fair price for builders who would like to purchase custom length, pre-stamped aluminum absorber. rather than making their own. His website also has some examples of "$1000" style systems, and some different modifications, some of which I used.

The panel is glazed with twin-wall polycarbonate greenhouse glazing. This was not easy to find. The closest I could find was 3.5 hours away in Boise from a local greenhouse builder, Steve Herring.
He just happened to have a couple extra 4x8 sheets left over from a recent job. His website is www.greenhousesetc.com  He said he often pools orders together with other builders to save on freight, so anyone in the Northwest may consider contacting him.

I puchased a large share of the building materials and misc items from locally owned smaller retailers. I used high quality lumber, including pressure treated 2x6's for the self supporting panel, exterior grade plywood for both the tank and collector, and a boat load of polyiso insulation to insulate the heck out of my tank. 

Performance
So far, this system has been working well. My panel is performing in the range you'd expect for a flat panel of it's size.

Peak output so far is around 5600 btu per hour (1245 lbs of water X 4.5 degree F rise in tank). The pump uses a rather high 80watts, or about 275 btu, for a net gain of 5327 btu.  
That calculates to a sytem efficency of around 55%. In theory, the amount of heat from the sun is about 320 btu per sq ft per hour, or around 9600 btu per hour for a 30 sq foot collector.

If you follow conventional sizing reccomendations, t
he tank is over sized compared to collector area. Convention says your gallons of storage to collector area should be ~2:1. I'm around 5:1. Since the tank is not pressurized, I could drain it down and get hotter water, but I'm happy with it the way it is so far. A larger volume of water will harvest more energy because the water stays cooler. It also spreads the use of the collected thermal energy over a larger time. This is nice from a convenience standpoint because you can always count on having sufficient hot water, even on cloudy days. Like any electric water heater, ours takes long to recover, especially with our low inlet temperatures. With my growing family, we were constantly shuffling what time to shower, when to do laundry, when to run the dishwasher etc. Since installing this system, we rarely run out of hot water, even after several showers, dishes, etc.

Payback period
Payback of this system at Oregons .07 per KWH mainly hydro power? Maybe 10 or more years. Having water for your honey to wash her face before bed, after all the kids are showered and the dishes are done, Priceless!

UPDATE: December 2011
The system continues to run without issue, other than me frying my ethernet shield while borrowing it to test another project. Word of caution, microchips don't like to me shorted out, best to bread-board while sober. Data-logging is now back on line. Heat collection is low right now due to partial shading from neiborhood trees and a low sun, plus the short days. I'm only getting about 4 hours of collection on a full sunny day. Not great, but still something. Even 70 degree water entering my electric water heater is better than sub 50 degree water.

UPDATE: Feb 2011
The pump was not quite far enough below the water level to stay adequately primed during start-up, which caused slow starts. I remedied this by using 1" pex for the pump primer loop. Since making this change, the start-ups have been very smooth and quick.

I continue to see condensation inside the space in my dual wall glazing. This will be remedied this spring, when I build my second panel. I will be mounting both panels to my detached garage, and orient them both vertically, so then the glazing will be in the recommended orientation.

Adding the second panel and relocating the panels to the garage should nearly double my collection. The garage location is a better southern view, with less tree obstruction, especially in the low sun of winter. I will be building the second panel pretty much the same, except I will use 2" of insulation instead of 1" in the back. This will cause less heat loss out the back, and also improve start time due to the smaller inside volume. I will likewise modify the existing panel.