This page covers two closed loop solar water heating systems that use a PV powered pump to circulate the working fluid. Both systems have been in operation for quite a while and work well.
The first is Doug's own system, and the 2nd is a system that Doug helped friend Bob install.
This Photovoltaic (PV) pumped hot water system has been working well, with
no maintenance, for years on my house. I am now well past the point where
the money I invested in the solar water heater equals the money I would have
spent on electricity to heat water. Most of the year, we have more free hot
water than we can use. Consider the fact that in the next five to eight years
you are going to pay the cost of a solar water heater, whether you buy one or
not. I kept costs down by doing all of the work myself, and buying a used
collector panel, but still created a long lasting, efficient, high quality
I started by looking in the yellow pages under "Solar", and found a plumber in the nearest large city, with spare collector panels. I bought a 3`x13` aluminum collector with copper tubing and tempered glass cover for $100, guaranteed not to leak, but I tested it first, anyway. Assuming the collector needs to be freeze protected, a non-toxic antifreeze, usually propylene glycol, is pumped through the collector, to the heat exchanger tank.
Collector mounted on the roof. PV panel to drive circulator pump is visible at the upper left.
Solar water heater plumbing running through the attic.
The 12 volt DC circulator is mounted to the 2X4.
The pump used is no longer available, but pumps offered by Ivan Technologies (El Sid) or March Pumps would be good substitutes.
The simplest way to circulate
the anti-freeze is with a 12 volt pump directly wired to a small photovoltaic
panel, this eliminates the need for controls of any kind. When the sun is
heating water, the pump runs. I bought a matched set of a 10 watt 12 volt solar
electric panel, and bronze magnetic drive circulation pump from Zomeworks.
More on the PV pumped system here ...
most expensive single component was the Heat Exchanger (HE) tank. I looked at
what is available, and most are built around the ordinary glass lined steel
water heaters, which have a limited lifetime. For less money, I had a stainless
steel tank built with 50' of 3/4" soft copper tubing in the lower half as my
Heat Exchanger. It holds 85 gallons, and acts as a pre-heater for the regular
electric water heater. Non ferrous stainless will outlast me.
Storage tank with internal heat exchanger.
It's your choice-you can invest in solar now, demonstrating your support for sustainable energy, and getting free hot water after your payback period, or continue to pay ever-increasing energy bills, which indicates your support for maintaining the status quo."
Diagram of solar water heating system
Click on diagram to enlarge
Nov 20, 2008
My 17+ years of
success with solar hot water made my friend Bob want a similar system for his
new house. Through word of mouth, I heard about someone in Huntsville who had a
four panel solar system free for the removal.
It was installed in the early 80`s and heated domestic hot water, had fan coil units for space heating, and heated an in ground pool. The systems installed then used electronic controls to operate valves and pumps, commonly the controls develop problems and parts and knowledgeable service techs are hard to find.
Bob and I spent a long hard day removing the panels, two 120 gallon tanks, three heat exchangers, much copper piping, valves, pumps, etc. We planned on using the components to assemble more modern systems using a Photovoltaic (PV) 12 volt panel directly wired to a DC pump to eliminate the controls and use of external electrical inputs- meaning stand alone systems using only solar energy to heat and circulate a non-toxic antifreeze to the Heat Exchanger (HE). The HE then uses only gravity to circulate tap water through it, heating the 120 gallons in the insulated tank. This is called a closed loop, PV pumped solar hot water system.
Click on pictures to enlarge
There are two fluid loops:
In the collector loop, non-toxic antifreeze is pumped by the PV powered pump through the collectors, then underground to the house and through the inner tubes of the two heat exchangers, and then back to the collectors. The pump used in this loop is a Hartell MD-10-HEH 12 volt, brushless magnetic drive, PV direct.
An expansion tank is used to accommodate changes in the volume of the liquid in the loop with temperature changes. Valves are provided to allow Bob to just heat domestic water, or just flow the antifreeze through the PEX in the slab for space heating, or to do both at once. In the storage tank loop, the potable tank water in the heat exchanger is warmed by the collector water, and rises up the pipe that enters the top of the storage tank. Cool water from the bottom of the tank, being denser, flows by gravity
into the bottom of the heat exchanger to be warmed.
The circulation loop on the storage tank side uses only natural convection to circulate the fluid. In order for this to work well, the bottom of the tank must be elevated above the top of the heat exchangers.
Bob has tubing running through the concrete slab of his home, he can have the
heated antifreeze either just heat domestic water, or the slab for space
heating, or both. That's why he's using two panels, one panel and a smaller tank
would be sufficient for just domestic hot water for families of up to five. Each
panel is nearly 40 square feet. Bob never soldered copper pipe before, but he
did a good job of reusing as much tubing as he could.
Click on pictures to enlarge
All pictures are before Bob insulated all piping and the HE. Bob's main expenses were for the 12v PV panel and pump. I used a 10 watt panel on my similar system, Bob chose a 30, I feel this is larger and more expensive than necessary. The pump is mounted close to the PV panel, Bob and I modified an ammo box to house it. I built the rack to support the panels. This sort of reliable system can be put together for considerably less cash than buying a complete system, it just requires hard work and the willingness to learn. Free heat and hot water from the sun!
Jan 13, 2008
You can reach Doug at: dougkalmer AT gmail DOT com (replace AT with @, and DOT with a period)
|A small caution:
The heat exchangers in Bob's system are single wall heat exchangers.
This means that a leak in the heat exchanger wall can allow antifreeze
to enter the potable water stream. This makes it VERY important to
use non-toxic antifreeze in the system. Systems that use single
wall heat exchangers should have labels that explain to future owners
that non-toxic antifreeze must be used. Codes in some areas will
prohibit single wall heat exchangers even with non-toxic antifreeze.
Efficient double wall heat exchangers are available, and are not that much more costly.
Doug has contributed a number of projects to Build-It-Solar covering a wide range of solar and renewable energy areas -- see them all...
Thanks very much to Doug for providing this material!