Backup Heating for the $2K Solar Space and Water Heating System

Our $2K solar space and water heating system provides solar water heating and also space heating to part of our house.  Until recently the backup heat for this part of the house was a propane forced air furnace that came with the house.  But, last winter the furnace died and the replacement cost was $6000.  So, instead of replacing the furnace, we added a backup heat system that just adds heat to the large solar heat storage tank when there is not enough sun to keep the solar tank warm.  This approach cost about $300 (pretty good saving), and has the advantage that we no longer have a noisy and potentially unsafe gas furnace hung from the floor just below our bed.

The new backup heat system is pretty simple.  Its just an electric hot water heater that sits next to the solar tank with a small pump to circulate hot water from the electric tank to the solar tank when the solar tank temperature drops below a setpoint.  The heat is distributed to the room above by the same radiant floor pex tube system as before.

The backup heat source electric hot water tank

The TopsFlo pump that circulates water between the backup tank
and the solar tank is at the bottom of the picture -- only 15 watts.

Diagram of the new backup heat system -- really simple.

I've added a new page that describes the backup system here...

And, updated a few pages for the project to reflect the new backup heat system...

There is also some discussion of other alternative backup heating systems -- I'd be interested in hearing any ideas on a better way to do it.

Gary

The Passive Solar Bird Bath is Back

We lost Jim's very nice passive solar bird bath for a while, but is back now.

The passive solar bath provides some unfrozen water in the winter for the birds to drink.  Its a nice simple design that is easy to build and has worked well for Jim.

Thanks very much to Jim for documenting this project!

The solar collector on the bottom heats the drinking dish on the top.

If you have any ideas for improvements or any questions, or have a design of your own that you would like to report on -- please use the Comments section on this page...

All the details on Jim's passive solar bird bath...

Gary

Backdraft Dampers for Solar Air Heating Collectors

Solar air heating collectors provide a nice stream of heated air during the day when the sun is shining on them, but at night, the flow often reverses and brings unwanted cold air from the collector into the room.

Backdraft dampers are added to prevent this reverse flow of cold air.  There are several types of dampers -- both DIY and commercial.

I've added a section that lists the ones I know about -- if you know of others, please let me know.

New section on backdraft dampers for solar air heating collectors...

A example DIY backdraft damper

PV Powered Pool Pump Installation

When Bruce looked at where his electricity was going, he found that about a quarter of his total electricity use was to run his pool pump. He decided to install a new pump that would be run from PV modules.

Bruce's report gives details on the design and installation of the new pump, and on how the economics is working out. The drop in PV module prices in the 6 years since the system was installed, the payback period would now be substantially shorter.

Two 170 watt PV panels in series drive the DC motor pool pump

The installation is simple consisting of only the two 170 watt PV panels (above), a controller, and the DC powered pool pump itself.  Given the efficiency of DC pumps and the minimal losses its a very efficient setup.

The new pool pump -- the controller is visible on
the wall behind the pump

An alternative to Bruce's approach would be to retain the existing AC pool pump and add a grid-tie PV system for the whole house that would power both the pool and the rest of the house loads.  This is appealing in that one system does both jobs, but the low efficiency of typical AC pool pumps appears to require a much larger PV array (perhaps a 3000 watt PV array just to drive a 1.5 hp AC pool pump 8 hours a day).  So, the dedicated PV array to drive the DC pool pump appears to be the more cost effective solution -- do you agree?

Two speed AC pool pumps run for longer periods at lower speeds also appear to offer a larger saving in electricity at a modest initial cost.

I've added a small section on powering pool pumps efficiently that includes Bruce's PV powered pump as well as some other ideas on efficient pool pumps.  If you have any other ideas or thoughts, lets hear them.

Gary