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This article was originally published in the January/February 1999 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.

 

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Home Energy Magazine Online January/February 1999


trends
in energy

Making Solar Hot Water Affordable

Walter Boatright conducts an inspection of an ICS unit in Live Oak, Florida. Water is both heated and stored in the large tubes inside the unit. The hot water flows from the unit to the back-up water heater inside the house when the client uses hot water.
Table 1. SWAP Results
  Presolar Postsolar
Average family size 4.7 4.4
Average water-heating electricity consumption (kWh per system, per year) 3,100 1,500
Water-heating costs per year (8¢/kWh) $250 $120
Savings-to-investment ratio (SIR)(at 8¢/kWh) N/A 1.0
Solar fraction (percent of hot water heated by solar) N/A 53%
Average system coefficient of performance 0.73 1.4
Average SWAP solar system installed cost N/A $1,550
Gallons used per family per day 63.8 62.5
Gallons used per person per day 13.6 14.2
Average hot-water temperature (in degrees F) 119 119
Over a period of 2.5 years, the following variables were monitored every 15 minutes at 32 instrumented sites: cold- and hot-water temperatures, collector feed and return line temperatures, flow to and energy usage of the water heater, and horizontal solar radiation. A one-time measurement of pump and controller power usage for the direct-pumped systems was also taken.
Source: Florida Solar Energy Center
The direct-pumped systems include a pump and a controller mounted on the water heater. Sensors at the collector mounted on the roof and at the bottom of the water heater tell the controller when there is enough solar energy available to heat the water. At those times, the pump turns on and forces water through the solar collector, where it is heated, and returns it to the water heater for storage.
In 1995, a group of agencies in Florida teamed up to bring low-cost solar systems to low-income households so they could save money on their utility bills. By the time the program ended in June 1998, they had shown that a solar hot water system that supplies 50% of the household's hot water needs costs less to build than a conventional solar system, and still saves residents money. Under the program, more than 800 such systems were installed in households across Florida.

The Solar Weatherization Assistance Program (SWAP) was funded by the U.S. Department of Energy (DOE) and the Florida Energy Office, and was developed and implemented by the Florida Department of Community Affairs (DCA), the Florida Solar Energy Center (FSEC), local Florida weatherization agencies, and the Florida solar industry. DCA provided grants to local weatherization assistance agencies and other nonprofit agencies to operate SWAP, and SWAP-certified solar contractors installed the systems. FSEC developed all the technical guidelines for the program and provided ongoing technical assistance, system monitoring and analysis, training, and program support to DCA and all the participating local agencies and installers. The solar systems were given to the various families as part of local weatherization programs. SWAP was widely administered in rural and urban communities by nonprofit organizations and governmental agencies in cooperation with local volunteer groups.

SWAP's goals were (1) to reduce energy consumption and energy costs for low-income households, (2) to evaluate the feasibility of incorporating solar systems into national DOE weatherization programs, (3) to reduce expenditures for the Low Income Housing Energy Assistance Program (LIHEAP), which helps pay residents electric bills, and (4) to provide a niche market for the Florida solar industry. In order to monitor how well some of these goals were met, FSEC established an extensive database to compile and store information obtained by site inspections, surveys, and utility bill analysis. In addition, computerized data was collected at more than 30 selected sites to monitor such variables as water temperature, water consumption, and power usage.

Simplicity Wins Several types of solar system were installed under SWAP. The two types that were installed most often were the integral collector storage (ICS) system and the direct-pumped system.

ICS systems combine heat collection and storage in one unit. Water is heated in the ICS tubes and flows to the backup water heater when the residents use hot water. These systems are ideal for low-income clients due to their inherent simplicity, says John Harrison, SWAP program manager. They have no moving parts and no maintenance requirements. They are essentially just extensions of the current water piping system.

When the sun is shining, the temperature of the water coming out of the ICS unit is higher than the setpoint of the electric water heater, so no electricity is required to heat the water. For example, when the thermostat of the electric water heater is set at 120°F and the water coming from the ICS unit is 135°F, the electric element will not turn on.

Direct-pumped systems, on the other hand, consist of a flat-plate collector, a pump, and a controller that determines when the pump should be on. The pump forces water through the solar collector, where it is heated and returned to the water heater in the house. Then it is stored until it is needed. Both the ICS system and the direct-pumped system include a backup electric water heater for use during inclement weather.

Both systems were used throughout Florida in the program. The ICS system was used mainly in north and central Florida. It was chosen for these areas both because of its simplicity, and because the large thermal mass of its component tubes prevents the water inside from freezing. The direct-pumped system was used mainly in south Florida, where freezing temperatures are not as common.

Smaller Is Better The program required that the systems be sized to provide at least 50% of each home's hot-water load from solar energy. They are much smaller than the conventional systems that, in Florida, usually supply 70% or more of the load. The SWAP systems use conventional 40- to 50-gallon electric water heaters with 24-32 ft2 flat-plate solar collectors (for the pumped systems) or 24-32 ft2 collectors (for the ICS systems), and have an average installed cost of just $1,555. Conventional systems, on the other hand, typically use an 80-gallon solar tank and a 40 ft2 collector, and cost from $2,500 to more than $3,000.

FSEC determined that the smaller tanks and collectors were the most cost-effective for this program because they greatly reduced the cost of the installed systems and maximized energy utilization, and because low-income residents could easily replace the smaller water heaters in the future (they are readily available from plumbers and home improvement centers). Furthermore, the SWAP solar installers had no advertising costs and were able to make bulk purchases, which also helped keep the prices low.

NEAT SIRs FSEC monitored 32 of the installed solar systems--19 ICS systems, and 13 direct pumped systems. They were monitored for one year before and one year after the systems were installed, in order to obtain pre- and postinstallation comparisons.

A primary goal of the monitoring was to determine the savings-to-investment (SIR) ratio, according to the Department of Energy Weatherization Program's National Energy Audit (NEAT) procedure. In general, measures with SIRs of 1 or greater are considered cost-effective. The SWAP monitoring revealed that the SWAP systems met DOE weatherization program requirements, with an average SIR ratio of 1, based on electric rates of 8¢ per kWh and a 20-year system life span. Of course, the SIR increases with higher electric rates, because the measures save more money.

FSEC monitoring revealed that, overall, energy heating consumption for the SWAP system users was reduced by more than half (see Table 1). The average solar fraction for the program was 53%.

Just Flip a Switch More than 800 systems were installed at no charge in low-income homes as a result of SWAP, bringing low-cost hot water to more than 3,500 people. One user says, Since my pumped solar system has an on-off switch that turns the electricity to the water heater off, during sunny days we always keep the switch off. That way, all the hot water that I use is made by the sun. It really cuts my utility bill. Had the homeowners paid the $1,500 to $2,500 cost of the systems, they would have saved enough in energy costs to get their money back in approximately eight to nine years.

FSEC conducted detailed surveys of all program participants. More than 35% of them responded, and the majority said they were quite satisfied with their solar system, had adequate amounts of hot water, and did not experience any inconvenience once the solar system was installed. The survey did reveal, however, that residents needed more education regarding the operation and maintenance of their solar systems.

FSEC also conducted detailed inspections of more than 25% of the 801 systems to make sure they were installed properly and were operating as designed. In general, the inspections revealed that there were few component failures, that most installation discrepancies were easily fixed, and that most discrepancies were related to workmanship rather than to problems with the equipment.

A Solar Success According to Harrison, FSEC feels that SWAP was quite successful. It showed that solar hot-water systems can be cost-effective in warm-climate states, and that they can offer attractive savings to low-income clients.

The inexpensive, simple, and reliable solar systems used in this program are available to anyone. Although many people express a desire to use renewable energy resources, the high initial costs of conventional solar hot-water systems make them impractical for many consumers. SWAP shows that a reasonable balance between initial cost and final solar fraction can be achieved, thereby making solar hot water more affordable.

SWAP program director John Harrison, FSEC senior research engineer Steven Long, and freelance writer Michael Major contributed to this report.

Publication of this article was supported
by the U.S. Department of Energy's
Office of State and Community Programs, Energy Efficiency, and Renewable Energy.


 

 


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