Residential net-zero solar project: SunPower 9.16 kW photovoltaic grid-tied system
Clean energy delivers financial benefits for long-term homeowners and retirees in the Land of Enchantment



The primary goal is to lower our household's carbon footprint.   Specific design goals were to offset annual household power demand by 100% using a grid-tied architecture, and provide ground placement for the solar array.   Offsetting all household energy consumption with solar power delivers significant financial benefit, especially throughout our retirement years.  


Project Timeline

A contract was signed in April, 2016 with a Sun Power Certified installer for the design and installation of a solar PV system.   Four months of delay followed to obtain needed HOA architectural review and approval, a process that resulted in two revised project proposals to account for array height, easement and sight-line restrictions.   Written approval from the HOA was obtained in August, 2016, triggering subsequent engineering, permit and application activities.   A significant amount of time was also consumed coordinating permits with the City, and gain interconnection application approval from the electric utility, PNM.   Application screening and approval by PNM took place in October.   Site preparation began in November and required three days.   Actual rack construction, panel installation and trenching required five days to complete in December.   The system passed all three inspections made by technicians from the city and PNM during the first two weeks of January, 2017.   Three days of landscaping also concluded in early January, 2017, laying down rock, gravel and planting 15 new trees to screen the array site.   A PNM electrician performed the final grid interconnection on January 13th.   Final SunPower monitoring configuration and other project closeout activities were completed on January 17th, 2017.   Although actual on-site work required less than two weeks, the entire project timeline was nine months; half of this was consumed by delays gaining HOA written approval.  


The 9.156 kW design features a single ground solar array with 28 SunPower SPR-E20-327 solar panels, each producing 327 watts of nominal DC power, 20.4% average efficiency.   The rack is ancored by 12 steel posts with concrete footings and aluminum framing.   The panels are angled at 55 degrees for optimum average annual Southern exposure.  

Two SMA Sunny Boy SB 5000TL-US-22 inverters convert DC power from the panels to AC, each generating up to 5,300 watts of nominal AC grid power with 97.4% average efficiency.   A DC disconnect is positioned beneath each inverter.   The AC disconnect is positioned on the far right.   Both inverters were manufactured in May, 2016.   175 feet of trenching was required from the array site to the PNM interconnection meter.  


Net-Zero Operation

This 9.16 kW PV system delivers net-zero household operation on an annual basis.   PNM billing data helped derive average monthly household energy use of 1,000 wKh.   7.6 kW is needed to offset 100% of the home's annual energy demand.   The system generates 1.5 kW more than currently required, providing 17% extra production for future increases in power consumption, including a probable home addition. Increasing the array size will also help offset a gradual loss of system efficiency as the panels age.   The system has been rock solid the past five months since interconnection, and monthly PNM charges amount to just $7.67 for interconnection fees/taxes.  


ROA & Retirement Finances

Monthly PNM billing averages nearly 1,000 kWh of household consumption per month at a cost of $200, with peak usage during the Summer.   There are 300 sunny days in New Mexico, so a 7.6 kWh solar array will totally offset energy use and avoid $2,400 of annual utility expense.   Operating within the PNM net-metering program means we only pay for energy consumed above whatever the solar array generates for the grid.   The system will over-produce most of the year and accumulate enough energy credit to cover the hottest Summer months.  

The total cost for the solar array and related landscaping will be $28,000 after a 30% federal tax credit.   The estimated payback period for the entire project will be 11 years.  

There is also a payback period for our 2016 Chevrolet Spark EV commuter car, including a similar federal tax credit.   Driving a solar powered vehicle avoids thousands of dollars each year in gasoline, oil changes and higher insurance cost.  

Long-term financial savings after the payback period are significant, lowering annual household expenditure during our retirement by $6,000, avoiding $2,400 utility and $3,600 gasoline expense each year, a $500 reduction in our monthly retirement operating budget.  

As costs associated with solar technology continue to fall, ever shorter payback periods and increased financial benefits result for long-term homeowners and retirees in New Mexico.