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OPB Business Partner
ENERGY TRUST OF OREGON
  1992- 2010 Tax-Credit Certified Solar Technician
The North American Board of Certified Energy Practitioners
SOLAR RATING AND CERTIFICATION CORPORATION

SOLAR HOT WATER
FREQUENTLY ASKED QUESTIONS

How Much Energy Can I Save?

For over 50 years, Solar hot water heating has been the most common and popular way to use solar energy. You can reduce the amount of energy you use to heat hot water by 60% by installing one of these solar systems.

How Does It Work?

The way it works is quite simple. What Solar Energy Solutions, Inc. does is install two 4' x 8' solar panels on your sunny south- or west-facing roof. Then we install an 80-gallon solar preheat tank which, as the name implies, simply preheats the water in that 80-gallon solar preheat tank using the solar panels before it goes into your existing hot water tank. So, when you turn on your hot water faucet, instead of sending freezing cold tap water into your existing hot water tank, you send preheated water from your new 80-gallon solar preheat tank. This vastly reduces or eliminates altogether how much energy your existing tank uses to reach its desired temperature.

Does It Matter What Kind Of Hot Water Heater I Currently Own?

It really doesn't. But it would be best to give a call to discuss some nuances.

Where Will The 80-Gallon Preheat Tank Be Located?

Ideally, the 80 gallon solar preheat tank is located as close to your existing hot water heater as possible. However, it can be located on the opposite side of a basement or even on a different floor if necessary. Some systems even have the solar preheat tank mounted up on the roof.

How Hot Will The Water Get?

The temperature coming out of your 80 gallon solar preheat tank varies according to the time of year and hot water usage. Homes generally save about 100% of their hot water energy needs in the summer, 60% in the spring and fall, and 40% in the winter. This is a huge energy savings considering hot water heating is the second largest energy drain a house suffers from.

So, Can I Heat My House With Solar Panels?

Sadly, households cannot be heated using solar panels west of the Cascades because that time of the year, when you need the heat most, we have our greatest cloud cover and the sun is lowest on the horizon.

What Are The Different Systems You Install?

Solar Energy Solutions, Inc. carries and installs three of the most popular system configurations for heating hot water: the glycol system, the drainback system and the thermosyphon system. All three configurations have passed the 50-year test of time. This is truly a remarkable feat when one considers all of the systems that have come and gone during this same period of time and a warning against adopting new technology that has yet to pass the test of time.

Which System Is Best?

The thing to remember about solar hot water heating is that no system configuration is perfect. All system configurations have their own little things that make them better or worse than other system configurations. We have yet to discover a system configuration that is perfect in all ways.

What Are The Differences In Terms Of Efficiency, Maintenance, And Overall Cost?

With the glycol and drainback system configurations, a heat transfer fluid is circulated from the 80 gallon solar preheat tank to the solar panels and back. The heat is transferred from the solar panels to the solar preheat tank using a pump and a differential controller. The controller has two sensors; one is located by the solar panels and the other by the coldest spot on the solar tank. If the controller senses the panels are warmer than the tank, it automatically turns on the pump. The pump circulates the heat transfer fluid, which extracts the heat from the solar panels and puts it into the 80-gallon solar preheat tank. The thermosiphon system configuration works a bit differently and is discussed after the glycol and drainback systems. What makes it great is that it does not use any pumps or controls or even electricity. That’s because it is a passive solar hot water heating system.

Below are descriptions of the three kinds of solar hot water heating systems Solar Energy Solutions, Inc. advocates, carries, and installs.

GLYCOL SOLAR HOT WATER HEATING SYSTEMS

Glycol solar hot water heating systems may currently be the most prevalent system configuration installed today. The reason for this system configuration’s prevalence is due to its lack of solar loop plumbing specificity and ease of installation. Most commonly these systems will consist of two 4 x 8 solar collectors and an 80-gallon solar preheat tank. There are some variations of this, but this is the most common setup. Glycol systems allow for the greatest amount of flexibility in the plumbing of your solar system from the solar preheat tank to your solar panels. In other words, the plumbing from the solar preheat tank can go over hill and dale, inside the house, outside the house, do loopty-loops if so required, because the fluid in the pipes can’t freeze. The heat transfer fluid is non-toxic propylene glycol and is freeze proof.

The advantages of the glycol system other than the ease of installation and flexibility in plumbing scenarios are that it puts out a greater energy yield than other systems on a yearly basis, and it doesn’t make any more noise than your refrigerator. The only down side to this system is it has a built-in maintenance schedule. Every 8-10 years the glycol needs to be switched out for new glycol and the expansion tank replaced.

GLYCOL SOLAR HOT WATER HEATING SYSTEMS

We install SunEarth brand collector panels along with Rheem 80-gallon solar preheat tanks. SunEarth calls their glycol system the "SolaRay".
You can view the SolaRay by clicking here
If you want SunEarth panel information click here
Then, if you are really technically oriented you could look at the install manual by clicking here

DRAINBACK SOLAR HOT WATER HEATING SYSTEMS

The Drainback system configuration is probably the most maintenance free of any system configuration. Most commonly these systems will consist of two 4 x 8 solar collectors and an 80-gallon solar preheat tank. There are some variations of this, but this is the most common setup.

The drainback system uses the same SunEarth solar panels, same 80-gallon solar preheat tank, controller, sensors, valves, and gauges as the glycol system. What makes the drainback system different is its freeze protection. The drainback system freeze protects itself by draining all of the solar heat transfer fluid (in this case distilled water) into a separate 10–15 gallon drainback tank. When there is a heat gain to be had, the small circulating pump turns on and pumps the heat transfer fluid form the drainback tank, up to the solar panels, and then back down to the heat exchanger on the solar preheat tank. When the pump is not pumping, all of the heat transfer fluid automatically “drains back” into the drainback tank.

The drainback system configuration, unlike the glycol system configuration, requires a great deal of solar loop plumbing specificity. The solar loop plumbing run on the Drainback system cannot go over hill and dale, inside the house, outside the house, do loopty-loops etc. The solar panels actually have to be mounted on the roof so as to give them a slight slope. As a matter of fact, the entire solar loop plumbing from the solar tank to the panels needs to be plumbed giving the pipe a certain degree of slope or fall. This is essential to this system configuration as this system’s freeze protection is all based upon the entire solar loop plumbing line and solar panels being completely devoid of the heat transfer fluid during freezing temperatures. It is the rigid technical specification of this slope that prevents the drainback system configuration from being installed in many homes. Often times it is impossible to get the required solar loop plumbing slope needed, thus eliminating the drainback system configuration as an option.

There are a couple of other disadvantages to the drainback system configuration. The drainback system makes more noise than the glycol system. The sound it makes is most like the sound of popcorn popping on a stove. It never happens at night, but if you are sensitive to noise you will definitely hear it in the day if you are anywhere near the drainback tank while the system is running. The other disadvantage to the drainback system configuration is that its annual energy yield is about 200 kilowatt hours less than the glycol system.

However, the drainback system configuration has no built-in maintenance schedule at all. We have seen these systems running maintenance free for 20–30 years. This is incredible and certainly makes it worth thinking about.

You can see the SunEarth drainback system by clicking here
If you want SunEarth panel information, click here
Then, if you are really technically oriented you could look at the install manual by clicking here

THERMOSIPHON SOLAR HOT WATER HEATING SYSTEMS

Thermosiphon solar hot water heating systems are “passive”. This is to say that no electricity is used to heat the water in the 80-gallon solar preheat tank. With the thermosiphon systems instead of having the preheat tank installed near your existing tank, it is mounted on the roof above the panels. To see a picture of this system click here: The way these systems work is by plumbing your cold water to the solar preheat tank on your roof, and then back down to your primary hot water heater. The solar tank on your roof is heated by the solar panels mounted right below it. The solar panels have a heat transfer fluid in them, propylene glycol. When the sun strikes the panels it heats up the glycol. The hot molecules in the glycol then rise to a heat exchanger that is actually wrapped around the outside of the 80-gallon solar preheat tank on the roof. This kind of heat rise is called thermosiphon, or stratification. All the solar heat gain going into the preheat tank is being done through natural laws. Heat rises, cold falls.

The thermosiphon solar hot water heating system is perfect for folks who can appreciate its passive nature. It is also best used in situations where there is a big demand for hot water.

One disadvantage to the thermosiphon system is that it has no brakes. What this means is if you are away in the middle of the summer you will either have to cover the system up to turn it off, or accept the fact that it will blow its temperature and pressure relief valve, thus harmlessly releasing hot water onto your roof until it has cooled off sufficiently. And speaking of cooling off… the potable plumbing which goes from your existing tank to the solar preheat tank on your roof is also susceptible to freezing during very, very, very cold stretches of weather. The pipe will not burst because we use PEX piping for this application. PEX pipe is burst-proof. But, the possibility does exist that an ice blockage in the plumbing could develop if it got cold enough. This would mean no hot water coming out of your hot water faucet. But, once again, this is really no big deal. We install a bypass valve. So, all you would have to do is flip a single valve and presto, you would be back in hot water. We super-insulate the plumbing on these systems and have not had a pipe freeze since 1996. There is one last thing to consider with the thermosiphon system. The 80-gallon tank on your roof has a wet weight of 1,000 pounds. This means some structural adjustments will have to be made. This could mean doubling up the rafters or posting down to a load-bearing wall… no big deal really.

All of this said, the thermosyphon system is probably the most common and popular of solar hot water heating system configurations in the world. This is because it is passive. The manufacturer we have chosen to represent for this system configuration is Solahart. Solahart is probably the largest distributor of solar hot water heating systems in the world.

You can visit their web site by clicking here.

We like this system because of the 10 year warranty. In the past 20 years we have installed a bunch of Solahart systems. They are probably the favorite for folks who like do-it-yourself projects.

No matter what system configuration you choose, you will get decades of maintenance free use and loads of free hot water!