5 Helpful Tips to Sizing and Selecting Solar Thermal Equipment

Today’s guest post comes from Bob Ramlow, the instructor if our Solar Thermal Boot Camp. Bob Ramlow has more than 30 years of experience with solar-energy systems and is a co-founder and Board member of the Midwest Renewable Energy Association. He’s a solar thermal consultant for the Wisconsin Focus on Energy Program. We adapted this article from his book, Solar Water Heating, a Mother Earth News Book for Wiser Living. Bob teaches HeatSpring’s Solar Thermal Installer Boot Camp.

Click here to sign up for a free product training on real time solar thermal monitoring that is 50% cheaper, and 1/3 less time to install compared with traditional BTU meter based systems. 

Enter Bob Ramlow:

Rarely do we design solar water heaters to provide 100 percent of your hot water. There are just too many cloudy days over the course of a year. Nevertheless, a typical solar water heater will provide between 50- and 75 percent of your annual load. In hot climates, or during the sunniest times of the year, you can expect to get nearly 100 percent of your hot water from solar. And even during the cloudiest periods, you may get as much as 50 percent, depending on your climate.

In cool climates, you should allow 20 square feet of collector and 20 gallons of storage capacity for each person in the household. For large families, you can reduce this by 10 percent for each person over four members in the household. In warm climates, size the system with 15 square feet of collector and 25 gallons of storage for each person in the household, with the same reductions for larger families. These sizing methods will give the best return on investment. Smaller systems will work well, but your savings will be less.


4 Steps to Basic Solar Thermal Design

I’m sure you’ve noticed that as fuel and electricity prices continue to rise, the interest in solar hot water (SHW) systems is also continuing to increase, and your customers may be asking about it. Why? It’s a simple, basic, and proven technology that has been around forever.

Click here to sign up for a free training on reducing the cost and improving the reliability of solar thermal monitoring that is 50% cheaper, and 1/3 less time to install compared with traditional BTU meter-based systems. 

If you’re interested in selling and installing solar how water systems, you’ll need to understand the basics of design so that you can perform proper site visits and understand what drives the costs of the systems.
There are four basic steps in designing a pressurized, anti-freeze based solar hot water system. The details of each step can get more involved than what I’ve written here, but these are the basics.
1) Make sure the roof has solar access and enough room for collectors. Solar access is simply exposure to the sun from 9 am to 3 pm all year round and within 25 degrees, east or west, of true south. It’s best not to have any shading at all, but solar thermal collectors are much less susceptible to shading than photovoltaic systems. If you do have some shading, you can often compensate by installing larger collectors.

 How much room do solar collectors take up? Flat plate collectors are typically larger, with an average size of four feet by eight feet.

2) Next, you need to measure hot water usage. Typically, one person uses 20 gallons of hot water per day. This is a good rule of thumb. This number could be less — if there are five people living in a home, they will probably only use 80 to 90 gallons instead of the expected 100. However, some people could use far more water daily, and some could use far less. It is key to collect this information during the site visit.