Secondary Author(s)

Curry, Jeffrey D.

Report Number




Solar Thermal; Water Heating


This paper presents the development, implementation, and results of Lakeland Electric's solar thermal billing program in Florida. The three-phase solar program was started in 1997 with funds from the Florida Energy Office (FEO) and the technical assistance of the Florida Solar Energy Center (FSEC). It was designed as a model to expand the concept of distributed energy generation, and to augment the use of solar domestic hot water (SDHW) systems. The solar thermal billing program relies on the proceeds generated from the sale of hot water energy. Twenty-nine SDHW systems, which are owned by Lakeland Electric (LE), gradually began operation during 1999. Lakeland Electric offered homeowners a direct active system comprised of a 40 ft2 (3.7m2) glazed collector and 80 gallons (302 liters) of hot water storage. The tank is assisted by a single 4500 Watt heating element during periods of heavy hot water demand or continuous cloudy weather. The solar system operates independent from the utility grid, utilizing a 5-Watt photovoltaic module and direct current pump to circulate hot water. Billing for the hot water energy relies on a thermal electric metering approach. The metering requires a net combination of the total thermal energy delivered and the auxiliary heating energy consumption. Lakeland personnel (i.e. metering division) read the kilowatt-hour meters as part of their monthly routine activities. Net solar energy consumption is then determined and incorporated into the monthly electric bill statement of participating customers.

Results from data collected during the last 16 months indicate a varying degree of revenues which is dependent on weather but mainly on customer hot water use. During the 12-month period ending in August 2001, the average consumption for the 4.2 person household reached 66.2 gallons of hot water per day (252 liters/day). Revenues generated from the sale of hot water are determined based on Lakeland's average electricity rate of $0.075 per kilowatt hour (kWh). As a result, monthly net solar energy charges per system averaged $12.50 for the year-long period ending in December 2001. Daily hot water energy consumption for the 29 homes participating in the program totaled 9.2 kilowatt-hours per day (kWh/day). Solar energy contributed at least 5.3 kWh/day or 61% of the total hot water energy used by the household. Electric energy consumption amounts to 3.4 kWh/day (39%). Incidentally, hot water energy used for the same period represents at least 15% of the total house electric bill, of which 8% is now supplied by renewable solar energy.

Date Published



Solar Thermal; Water Heating



Rights Statement

In Copyright