A departure this month from the solar electric system, and an intro into our solar hot water system. I apologize for hoppity nature of my articles, but in keeping things current, I must write about what system the weather allows me to work on. Next month I hope to have the solar electric done and will update you then.

Solar domestic hot water (SDHW) systems became common during the 1970s when President Carter passed tax incentives making them affordable to homeowners.

The basic components of a SDHW system are a collection device (flat plate collector or evacuated tubes), controller and pump, and a storage tank. The flat plate collector is typically a 4 x 8 foot insulated panel with copper tubing inside. As sun shines through the glass, it heats the copper tubing and the liquid inside. These devices have no moving parts and have proven themselves over the years. Evacuated tubes have been around for years and are the dominant collection device in Europe. They are more complex in that a tube inside a tube in a vacuum has a small absorber inside. As sun shines on the absorber, it warms the liquid and evaporates rising to where the heat is transferred to liquid in another pipe. Advantages are they operate better in cold and cloudy environments although they can cost twice that of a flat plate collector.

The controller and pump control the flow of the liquid in the system. The controller has sensors that tell the pump to turn on and off based on the temperature of the tank and the collector. There are redundant protections built into controllers that ensure the fluid in the system won’t freeze or overheat.

The storage tank is where the heat you capture is stored. There are systems that allow you to use your conventional water heater with modification to the tank. Storage tanks manufactured for SDHW systems have heat exchangers that transfer the heat from the collectors into your domestic hot water. Plumbing codes require that your domestic water be isolated from the fluids in the system by utilizing a heat exchanger. It is common to have an electric backup built-in to the system for those times when the sun isn’t shining.

There are many configurations of these components that depend on climate and house design. I’m going to focus on the two systems that are applicable to our area, closed-loop glycol and drainback. Both of these systems work in our climate because they are designed to operate in freezing weather, any other type of system will not work properly year-round here on the Palouse.

The closed-loop glycol system is the most commonly installed because it offers the most flexibility during installation and can be retrofit into most homes. The collector and plumbing are filled with anti-freeze under pressure. The controller tells the pump to circulate the fluid when the sun is shining thereby transferring heat to your hot water tank. This simple system works well and is reliable.

The drainback system is a bit more finicky to install, but offers protections the closed-loop glycol doesn’t. This system requires that the collectors be located above the storage tank and sloped to allow the fluids to drain. There is a drainback tank in the system to allow for this draining. When the pump turns on at the controller’s direction, it moves water from the drainback tank through the collector and through the storage tank. When the pump turns off, the fluid drains from the collector back into the tank. There is never liquid in the collector during freezing weather. This is the system we have installed on our home.

Any installer will be able to help you with your system design. Locally, The Natural Abode installs systems or you can go online at www.findsolar.com to help you locate an installer.

Mike is enjoying the warmer weather and looking forward to capturing its rays this spring and summer.