SOLAR HOT WATER
FREQUENTLY
ASKED QUESTIONS
How Much Energy Can I Save?
Solar hot water heating is 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. If you have, or wish to install an “on
demand” hot water heater, you just have to make sure it is
“solar compatible”.
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 40-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. This service call currently costs between
$400 and $600.
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. To better understand this concept click
here.
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 you 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!
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