Solar Hot Water Batch Collector - Update
Since the initial construction of our solar hot water heating system we've made several adjustments to improve its functionality. Our greatest challenge has been designing the collector to work in the extreme temperatures of the desert climate. While our summer sun is incredibly intense, the winter brings freezing weather for weeks at a time. The changes we've made have helped us to achieve more consistent water temperatures and unhindered supply. Even so, additional upgrades to ensure warmer water temps in the winter will be necessary when we build our future home.
CPVC vs. Copper Pipe
Over the summer we discovered that our batch collector is extremely efficient at creating hot water. It's so efficient that our CPVC tubing could not hold up to the heat. In fact we had several blow-outs which rendered our hot water heater temporarily unusable. To correct this issue we replaced all of the tubes inside of the collector box with copper pipe. CPVC tubing still runs between the outside of the collector into the side of our travel trailer. This upgrade has kept our collector functioning even on the hottest of days.
As a result of the ruptured CPVC we had a few overflows which filled the inside of the collector with water. When we upgraded to copper pipe we also put a drain hole in the bottom of the collector box. We don't anticipate any more burst pipes, but we now recognize the importance of adding a drain to our solar water heater design.
Tempering Valve for Summer
The temperatures achieved by our solar hot water heater easily exceeded scalding over the summer months. Besides rupturing the plastic tubing in the collector, on several occasions the hot water nearly burned my hand when I turned on the faucet. We were also concerned that the extreme hot water could damage the plumbing in our camper, as it is comprised completely of plastic fittings and PVC pipe.
To remedy our overly hot water, we installed a tempering valve just outside the batch collector. The valve is designed to mix cold water in with the hot water to produce liquid that is a consistent and moderate temperature. The valve can be adjusted to produce hotter or cooler temperatures with a maximum of 120 degrees Fahrenheit. Once the water is mixed it flows into our trailer for use.
The tempering valve cost us a little over $100, but it was definitely worth it. Once installed, our summertime water was the perfect temperature for dish washing and showering. If you are experimenting with a home built solar water heater and have kids around we highly recommend installing a tempering valve for safety.
More Insulation for Winter
Once winter arrived we had a whole new set of challenges to deal with. First, we found we had to turn the tempering valve to its highest setting to get adequately hot water. Next, we built a box around the valve and insulated it to protect it from freezing temps. However, we've had a particularly cold and cloudy winter and on many days we haven't had hot water.
There are several things that we believe may be contributing to our collector's decrease in performance during the winter, aside from the weather. We think that the insulation inside the collector was damaged when it overflowed with water and it is no longer retaining maximum heat. Also, by installing the tempering valve and its insulating box we blocked sunlight from warming several outside pipes. On cold days these pipes remain frozen for most of the day and prevent warm water that has formed inside the collector from coming into the trailer. We also installed our outdoor solar shower right next to the collector and it too blocks sunlight from striking the collector at certain points during the day.
Our biggest source of heat loss is still our single paned glazing. Double paned or triple paned glass is absolutely needed for optimum performance. For now all we have is single paned glass and we plan to make a heavily insulted tarp for covering our solar hot water heater at night. Though it will help us prevent nighttime heat loss, it won't solve our problems with cold water on cloudy days.
Our Future Hot Water Heating System
As we make plans for the construction of our future house and homestead we are formulating an improved set up for our homemade solar water heating system. We plan to have several batch collectors similar to the one we currently use lined up along the south side of our home. They will feed into a large indoor hot water tank that is super insulated. We believe that by storing our hot water inside our home we will be able to keep our water hotter for longer periods of time. With this system we hope to have hot or warm water for use even when its cloudy for several days.
Tankless Water Heaters
We also plan to have a back up water heating system installed in our home. On-demand tankless water heaters can be integrated with solar water heating systems and will only fire up when absolutely needed. Tankless water heaters use propane to rapidly heat water as it flows to the faucet. They are very energy efficient as they only heat water at the time of use. They are "tankless" which means that they are not designed to heat a large tank of water, but only the amount being used.
In a solar hot water heating system, a tankless water heater will only kick on when the temperature of the solar hot water has dropped below a certain point. It will function primarily as a back up system, and will supplement solar heating only when needed. In the future we hope to power our tankless water heater with methane gas that we produce on our homestead, making our hot water system entirely off-grid.
For more info on systems with on-demand tankless water heaters, click here.
Other Ideas for Homemade Solar Water Heaters
In our research we have also come across several products that we think could improve the efficiency of our current batch collector design. We would like to experiment with selective surface materials and graphite paints which could help our collector tank retain more of its heat. I've read about a selective surface that is comprised of a metal foil with a black chemical coating on one side and adhesive on the reverse. Adhering the selective surface to the outside out the collector tank will help it to absorb and retain greater amounts of solar energy. Similarly, when applied to a collector tank graphite paint improves sun absorption and conversely reduces heat loss.
We look forward to the continuation of our solar hot water experiments and will continue to post our new ideas, current concerns and successful improvements.
More About Solar Water Heaters
- Building our Batch Collector
- We built our batch collector primarily out of recycled and scrap materials. It serves as our only source of running hot water and has definitely been a worthwhile experiment in solar water heating.
- Our First Solar Hot Water Experiment
- Our first solar water heater was a flat panel collector that we designed and built for less than $200. It works great during the summer and is best suited for climates that don't experience freezing temperatures.
- Building Our Solar Shower
- After our batch water heater was complete we built an outdoor solar shower right next to the collector. We've posted a series of constrcution photos that show how we built our solar shower.