ASHRAE Journal - June 2011 - 74

solar NZEB projEct
entations and combinations of different panel types to 6,000 achieve different aesthetic and geometric appearances. Micro-inverters that are factory-mounted onto solar pan5,000 els will also lower installation costs due to elimination of dc switchgear and wiring, and less installation labor. A significant hurdle for panel mounted micro-inverters 4,000 is meeting the normal panel warranty of 20 to 25 years. Central inverter warranties are typically in the five- to 3,000 10-year range. Figures 1 and 2 (Page 73) show a breakdown in 2,000 system installation cost without any tax credits or rebates. The two-axis tracking system at our lab, 1,000 installed in 2008, and the Equinox House system, installed in late 2009, show significant cost dif0 ferences. The installed cost of our lab system was 2008 2009 2010 $35,300 and the Equinox House system’s installed cost was $36,300. Two-axis tracking systems increase Figure 3: Newell Instruments Laboratory 3.2 kW solar PV system enthe solar energy collection potential by 25% in our ergy production. climate relative to a stationary array. Assuming our lab system is equivalent to a stationary 4 kW solar 1,600 PV relative to Equinox House solar PV system at 8.2 kW, the installed costs per watt for the systems 1,400 are $8.83/W and $4.43/W. The primary reason for 1,200 the substantial cost difference was a price drop in solar panels and solar system equipment in 2009. We 1,000 purchased the solar system for Equinox House as a packaged system, which included some of the array800 mounting racks, switch gear, inverters and collector panels for $28,200. For our lab system, we purchased 600 individual components. Adding the cost of the solar panels, inverter and tracker together, we have a cost 400 of $6.05/W for the lab system compared to $3.43/W PV Watts Prediction 200 for the Equinox House system package. And today, Equinox House Actual a search of similar capacity solar PV panel systems 0 will show systems with quality components (20- to 0 2 4 6 8 10 12 14 25-year panel warrantees) costing less than $3/W. Month (january = 1) Differences in installation cost will be site specific. For example, we decided to locate the Equinox House Figure 4: Comparison of PV watts model prediction with actual Equinox system on the berm in the backyard to allow visitors House solar PV system 2010 – 2011 energy collection. to see the system in detail. If we had mounted the collectors on the roof, we would have reduced the installation 30% of the 410 m2 (4,400 ft2) laboratory’s energy. The lab is cost by a few thousand dollars by eliminating the amount of all electric with ground source heat pump providing comfort support steel and site work. The site work for our lab system conditioning. We have additional plans for cost-effective buildwas more expensive than the larger array at Equinox House ing improvements that should result in approaching net-zero because it was located 61 m (200 ft) away from the building energy operation. Simulation modeling of our lab’s two-axis while the Equinox House system was only 30 m (100 ft) solar array using the National Renewable Energy Laboratory’s from the building electrical connection. Also, the system at “PV Watts” simulation program yields results within 10% of Equinox House was coordinated with other activities such that the actual energy collection during 2008 and 2009. Figure 4 the solar array concrete footers were poured with the house shows a comparison between a PV watts simulation prediction foundation, and most of the trench for the electrical conduit and the Equinox House stationary 8.2 kW array over the past was already excavated for the rainwater harvesting system year. The 2010 summer months in central Illinois were sunnier and foundation walls. than usual while the winter was more cloudy and snowy than Figure 3 shows the energy collection from our labora- average. Overall, the Equinox House system produced 12,000 tory solar PV system, which totals over 13,000 kWh since its kWh from Feb. 23, 2010, when it was activated to Feb. 23, startup in August, 2008. The system supplies approximately 2011, of this year.
74 ASHRAE Journal
Monthly Energy (kWh) kWh

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