Total Load for Sizing the Solar PV Array
Adding all non-HVAC house loads from BEopt, the estimated car load, and the calculated HVAC loads for the house, the total annual energy consumption estimate is shown below in Table 4. These numbers provide the basis for sizing the PV array to meet net zero energy operation. Looking at the differences between the annual total energy consumption, the range is from approximately 8,000 kWh on the lowest end to 10,550 kWh on the highest end. Since the goal of this house is to provide the ability to operate on a rainwater supply for domestic water, the system will be sized to accommodate the energy needs of the ITHERST system.
Using the PV modeling capabilities of BEOpt, it is estimated that an 8.1KW (DC) array could provide approximately 10,870kWh during a typical year in Austin. Based on the DC rating of the SolarWorld panels provided (290W), an array with a 10 degree slope comprised of 28 panels yields a system capacity of 8.12kW DC.
Beyond meeting the needs for the ITHERST System, up-sizing the PV array is also necessary to ensure the house produces enough energy for the Solar Decathlon competition. Modeling for the competition week (October 8-18) in BEOpt Estimates total energy consumption of approximately 252kWh, and solar production of approximately 277kWh. The energy consumption estimate from BEOpt is somewhat higher than our own conservative estimate (approximately 230kWh) calculated independently in Excel based on contest criteria, measured appliance performance, and name-plate ratings of light fixtures and other electric loads.