Distributed Renewable Energy Operating Impacts and Valuation Study

Solar Characterization
Methodology
The first step was to create and calibrate a baseline model for the typical house. Peak demand
and annual energy use were calibrated to APS’s “Residential End Consumption Standards”: peak
demand of 7.8 kW, annual energy use of 18.3 MWh, and energy for water heating at 13 percent
of total annual energy, or 2,379 kWh.
The model was then created with SHW, based on the baseline model. The SHW model was
compared to expected kWh savings for the type of units being modeled, according to the SRCC
ratings for those types of systems. In addition, the SHW system was modeled such that it meets
the requirements of APS’s Renewable Energy Rebate Program. The output of the modeling is the
energy impacts in each hour of the year.
2.3.3 Modeling Results
Key Findings for Residential Solar Hot Water Characteristics
• SHW systems have two main parts: a solar collector and a storage tank. The collector uses
the sun to heat collector fluid in either a flat plate or evacuated tube collector. The most
common type of collector used is the flat-plate collector.
• SHW systems can be either active or passive; the most common are active systems.
• SHW systems are typically mounted on a south-facing roof, or adjacent to the house at
ground level.
• SHW technology is relatively simple and the materials and manufacturing involved have
been well understood for decades.
• Systems that were installed by APS customers between 2003 and 2008 cost between
$1,323 and $26,000 (in 2008 dollars), with an average cost of approximately $4,760.
• Maintenance costs for SHW systems has been estimated at approximately $20 per year,
with a detailed maintenance expense at 15 years estimated at approximately $70.
Key Findings of SHW Modeling
Modeling was conducted for the baseline house, with and without SHW. Without SHW, the
energy consumed for water heating is estimated to be 2,379 kWh per year. The same house,
retrofitted with a solar hot water system, is estimated to use 274 kWh per year for water heating,
a savings of 2,105 kWh, or 88 percent. Figure 2-12 illustrates the hourly savings along with
baseline customer usage on the winter and summer solstices (which represent the shortest and
longest days of the year, respectively). As the graph shows, the demand reduction is 10 to 20
percent of baseline usage in most hours. At hour 18 (the typical summer peak time of 6:00 PM
for hot water use) the reduction is significantly less than the non-coincident demand reduction,
which occurs at hour 21 to 22.
Distributed Renewable Energy Operating Impacts & Valuation Study R. W. Beck, Inc. 2-21