Page 30 - Zero Net Energy Case Study Homes-Volume 1

CASE STUDY NO. 1 CORONA DEL MAR NEW HOUSES
(Right) Installation of solar PV panels on the roof of 703 Helio- trope. (Photos courtesy of John Steed Homes.)
Renewable On-Site Energy Supply
The on-site solar PV system at 703 Heliotrope consists of 78 panels made by Yingli Solar (260 watts per panel), a Chinese manufacturer, for a total of 20.3 kW (DC). There are two 10kW inverters for the system located in the garage.
Since the owner considered this house to be a “luxury home”, the system was not designed to meet their estimated energy production requirements. Rather, the intent was to fill all available roof space and have the capacity to generate as much energy as possible in anticipation of possible future additional needs such as electric vehicles. The owners also felt that they wanted to be net zero carbon in all respects, so that meant having enough clean power to offset the small amount of gas use on site, personal air travel and the embodied energy of the construction materials (including that of the solar panels themselves). The marginal cost of the extra panels was considered to be affordable.
When the panels were initially installed, the owners and their neighbors realized that the row of panels nearest the street were partially visible. Although not legally required to do so, the owners removed two panels and repositioned others so that the visual aspect of the panels was less prominent. There was a 5% reduction in the power output as a result, but there was still ample surplus production.
The owners also arranged for the panels to be cleaned every three months because of the proximity of the house to the ocean, as well as to the busy Pacific Coast Highway and the Orange County airport.
The house at 609 Marigold, on the other hand, is smaller (65% of the floor area) and was built for sale to buyers with an unknown energy use pattern. The intention was to advertise a “zero-net- energy home”, so the size of the PV system was determined by assuming average energy use totals. This was calculated to be 42 panels (Yingli Solar) generating 10.9 kW (DC)., about half the size of the system at 703 Heliotrope.
The builders also provided the support structure for additional panels that could easily be added by the new owners at a future date if their energy use were higher and they wanted the house to have on-site ZNE performance. Space was provided for 26 additional panels or at least an increase in 6.7 kW (DC). As it turned out, the buyers’ household consisted of only two people and the installed PV system provided enough energy so that the house achieved ZNE.
Energy Performance
Post-Occupancy Measurement
Energy Use—Monitoring and Measurement
Southern California Edison provides monthly net meter reports to the homeowner, that is, the total net energy provided by SCE to the house every month. If the energy production by the solar PV system exceeds the energy use for a reporting period, the total net energy provided by SCE will be negative. (The meter runs backward when production exceeds demand.) If meters are installed on a solar PV system, or the output of the system is otherwise recorded, the monthly energy use can be determined from this solar PV meter data and the SCE net meter report: a simple addition of the two numbers will provide the energy use for that period.
For 703 Heliotrope, the owners installed a monitoring system by Tigo. Using the SCE net meter reports, the energy use for the house during the one-year period from November, 2016, until October, 2017, was calculated and is shown in the charts on the opposite page.
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Zero Net Energy Case Study Homes: Volume 1