Innovative Solar Water Heating System

True to our original concept, the PVRES home substitutes propane for what are normally electric resistance end-uses in conventional homes. Propane will be used for the oven/range, the clothes dryer, back-up heating for hot water and a direct-vented fireplace. This is done to better allow the PV system to match the home's load. The logic is apparent when you consider that a simple resistance element in a hot water tank (4.5 kW) demands more electrical input than our entire PV system will be able to provide. The Control home contains a standard electric resistance 52 gallon storage tank (Rheem 81V5D) in the garage rated to use 4828 kWh/year (actual consumption in Florida should be much lower because of our higher inlet water temperature). However, propane is a fairly expensive fuel (approximately $1.40/gallon or $15/MBtu in Florida), so we wanted to take measures to reduce propane use by the PVRES home. One of the most important of these is the decision to use a solar water heating system with propane back up.

The hybrid solar water heating system was installed in the PVRES home in February by Solar Source, a Clearwater, Florida firm. The system consists of a forty square foot American Energy Technology AE-40 solar collector mounted on the south side of the home's roof. The collector is rated at an energy production of 45,600 Btu/day at the low temperature (95oF) rating. Parasitic pump power is avoided through the use of a 10W PV panel with SID10 (Ivan Labs) magnetic impeller pump. Collector freeze protection is provided by a Eaton FP-35 freeze protection valve. The collector feeds the solar primary tank, a Lochinvar FTA-082-K with an 80 gallon storage capacity. The storage system is made up of two tanks, a primary solar tank and an A.O. Smith FPSE 40 gallon back-up propane tank. The propane tank is a high efficiency direct vent model with electronic ignition. It is elevated so that it thermosiphons from the primary solar tank only if the water in the solar tank is warmer than the back-up; otherwise it provides feed water to the back-up tank when hot water is drawn.

Our objective is to provide at least a 70% solar fraction with the solar water heating system at the PVRES home so that consumption propane is confined mainly to clothes drying and cooking. We will be collecting data on hot water use (gallons each 15-minutes) as well as electricity use in the control home and propane consumption in the PVRES household. We should know more from the data about this time next year.