Solar Thermal Water Heating

Courtesy of Global Point Energy
6/7/2013

The energy of the sun is endless. It is also free. So why don't we use this plentiful and free energy more? Using the sun to heat your water can help make you much less dependent on fossil fuels, which come with wildly fluctuating costs. Unlike fossil fuels, solar thermal is also clean and safe. If these are all good reasons for you to seriously consider installing solar thermal systems on your farm right away, why haven't you?

Many will say there are just too many things to consider when making changes like this on the farm: 
  • What type of system should I use? 
  • Do they actually work that well? 
  • Can I really save money using them?
  • How long do they last?
  • Is there a lot of upkeep with them?
There are probably other things that come to mind, but this list is a pretty good one. Let's look at each of these questions. Before we get started, there is one question that needs to be answered: "How much water needs to be heated?" The answer to this question will help determine how many solar thermal panels will be needed.

The second question you will need answered is "What type of system will I need?" Will I need flat panels, or a single or double-evacuated tube system? It all really depends on the individual needs of each farm. In certain geographies, such as western and upstate New York, the evacuated tube systems work the best.

Evacuated tube collectors, as used by Global Point Energy, employ two concentric glass tubes fused together at the ends to ensure a strong seal, with a vacuum-based thermal barrier around the "heat pipe." Other designs use a single tube. In both cases, the thermal barrier inhibits the loss of absorbed solar heat back to the atmosphere. As noted before, this design is more effective in cooler geographic climes, particularly when comparing it to traditional flat plate solar panels, since there are no vacuum barriers in flat panel designs.

The system configuration favored by Global Point Energy, and many other contractors, is classified as "closed-loop." In contrast to "open-loop" configurations, where potable water is routed through the collectors directly, a closed-loop system uses an intermediate heat transfer loop using a glycol/water solution. Heat is picked up in the collectors, and the warm glycol is pumped to a heat exchanger where the heat is transferred to potable water. The glycol solution is returned to the collectors and the cycle is repeated.

A typical system that is installed by Global Point Energy has:
  • 30-tube collector panels (as many as needed for volume of water to be heated)
  • Two pumps (glycol circulation and potable water)
  • Two tanks (potable water preheat and glycol expansion
  • Two heat exchangers (double glycol/water and dump heat)
  • Controller--solid state device manages all control functions of system
How well does this type of system work? Let's look at a real example. 

A dairy farm, functioning in a Great Lakes-area climate, has 120 head and does two milkings per day. This farm uses 670 gallons of hot water per day to sanitize milk tanks. After installing 12 closed-loop collectors on a sloped metal roof, they have been able to save over $3,700 per year in electricity costs for this one function. These savings are realized because of the design effectiveness of this type of system.

You might say, "This is all well and good, but just how much heat does a typical solar evacuated tube system produce in a single day?"

One 30-tube panel, which uses 85 to 90 percent of the sun's energy it absorbs, will produce 31,100 Btu per day. This level of output will raise the temperature of 50 gallons of water 70 degrees. So if your water is at 45 degrees, this one panel will raise the temperature to 115 degrees.

How often do you have to perform maintenance on this type of system? The type of system Global Point Energy recommends needs minimal maintenance. Typically, you would have to check the glycol annually and be sure the air vents are functioning properly. Something could always happen of course, but generally very little is required.

Lastly, and perhaps the best news, is that these types of systems last over 20 years. You won't need to worry about having to change parts or components often. As you can see, it's all fairly straightforward. A solar water heating system, in the hands of a good solar thermal contractor, is easy to install and maintain. It can also save you significant energy expenses and will last up to two decades.

Call Global Point Energy or your local solar hot water company to get started.

Global Point Energy
5815 County Road 41
Farmington, NY 14425
585-398-2000, ext. 30
solar@globalpointusa.com