Ten Mile Farm: Joe Schwartz, SolarPro

Established in 2015, Ten Mile Farm is a side project of SolarPro publisher Joe Schwartz. The off-grid farm sits at an elevation of 4,600 feet. It borders the 86,744-acre Cascade-Siskiyou National Monument, which spans the intersection of the Cascade and Siskiyou mountain ranges in southwestern Oregon and northwestern California. Like many off-grid homesteads, Schwartz’s PV system has evolved as energy requirements and solar technology have changed over the 15 years he has been developing the 50-acre property.

Schwartz designed and installed the core system in 2005. It included two pole mounts, each with six 175 W Sharp PV modules, two OutBack Power VFX3648 inverter/chargers and two OutBack MX60 charge controllers. All of the original system equipment has performed reliably and is still in use. The original bank of eight 6 V Discover AGM batteries (18.7 kWh total rated capacity at C20) operated for 11 years. The farm’s increased electrical load, including water pumping for irrigation, led to system upgrades. In 2016, Schwartz added 1.3 kW of SunPower modules to the roof of the site’s power room. In 2017, he contracted True South Solar to install a 3.45 kW SunPower array, regulated by a 600 Vdc Morningstar controller, on an agricultural building located 320 feet from the system’s power room. He also worked with his friends at Haase Energy Systems to install a 14 kW Kohler LPG backup generator.

In the fall of 2017, Schwartz upgraded the site’s energy storage to a lithium-ion system designed by Blue Planet Energy. The Blue Ion 2.0 battery consists of eight lithium iron phosphate (LiFePO4) modules manufactured by Murata (formerly Sony). Each module is made up of 224 individual 3.45 V, 9.375 Wh cells. Under its ETL listing to UL 9540, the Blue Ion 2.0 battery management unit is approved for continuous operation at charge and discharge currents up to 160 A continuous, 200 A for 30 minutes, and 220 A for 5 minutes. This makes it a good fit for systems with array capacities and inverter/charger systems of about 8 kW. Integrators can parallel multiple Blue Ion 2.0 units for capacities of up to 450 kW.

Many lithium-ion energy storage systems allow for a depth of discharge (DOD) of < 99% without any meaningful impact on cycle life. For example, the Blue Ion 2.0 system has a warranty for 8,000 cycles or 15 years at 100% DOD. The ability to fully utilize battery capacity can have significant impacts on off-grid system design, including the required storage capacity, as well as on variables such as array-to-storage capacity ratios, and backup generator capacity and projected annual run-times.

The longevity of lead acid batteries directly relates to several variables, including how deeply a bank discharges and how regularly it receives a full saturation charge at regulation voltage. In contrast, a lithium-ion battery does not require or benefit from recharging to 100% capacity, and its cycle life actually increases at lower charge voltages. This leads to interesting shifts in off-grid system operation. Heavy loading in the morning before the sun is on the array, for instance, is not a concern. In addition, routinely operating the system at a partial state of charge does not negatively affect battery longevity, which informs strategies to bridge periods of low solar insolation and charging in off-grid applications.

“During my 20-plus years working in the solar industry, there have been continual advancements in equipment for off-grid residential applications, including robust sine wave inverters, high-voltage MPPT dc charge controllers, industrial high-capacity lead-acid batteries and web-based system control and monitoring. As manufacturing scales and prices decline, lithium-ion battery systems have the potential to fundamentally impact the way off-grid systems are designed and operated.”

—Joe Schwartz, SolarPro


DESIGN: Joe Schwartz, publisher, SolarPro, solarprofessional.com

INSTALLATION: Joe Schwartz, SolarPro; True South Solar, truesouthsolar.net; Haase Energy Systems, 530.527.8989

DATE COMMISSIONED: Original system installed in 2005, upgraded in 2015 and 2017

LOCATION: Ashland, OR, 42°N

SOLAR RESOURCE: 4.9 kWh/m2/day

ASHRAE DESIGN TEMPS: 97°F 2% average high, 17.6°F extreme minimum


ANNUAL AC PRODUCTION: 8,200 kWh (potential)

Equipment Specifications

MODULES: 12 Sharp NT-R5E1U, 175 W STC, ±10%, 4.95 Imp, 35.4 Vmp, 5.55 Isc, 44.4 Voc; four SunPower E20-327, 327 W STC, +5/-0 W, 5.98 Imp, 54.7 Vmp, 6.46 Isc, 64.9 Voc; 10 SunPower X21-345-COM, 345 W STC, +5/-3%, 6.02 Imp, 57.3 Vmp, 6.39 Isc, 68.2 Voc

INVERTERS: 120/240 Vac off-grid service; two OutBack Power VFX3648, 7.2 kWac–rated continuous output; OutBack Power X240 balancing autotransformer; OutBack Power PS2DC system integration panel

CHARGE CONTROLLERS: Morningstar Tristar 600V, 60 A, 600 Vdc maximum input; two OutBack Power MX60, 60 A, 150 Vdc maximum input

ENERGY STORAGE: Blue Planet Energy Blue Ion 2.0 B12-16-18U, LiFePO4 lithium-ion chemistry, 16 kWh usable storage capacity (< 99% depth of discharge), 9 kW rated continuous power, 48 Vdc nominal, 8,000-cycle or 15-year warranty at 70% of rated capacity

GENERATOR: Kohler 14RESA, 14 kWac rated, 120/240 Vac output, LPG fuel

ARRAY 1: Two pole mounts; six Sharp NT-R5E1U modules per mount configured in two 3-module source circuits (525 W, 4.95 Imp, 106.2 Vmp, 5.55 Isc, 133.2 Voc); 1,050 W per mount, 2,100 W total

ARRAY 2: Roof mount, four SunPower E20-327 modules configured in two 2-module source circuits (654 W, 5.98 Imp, 109.4 Vmp, 6.46 Isc, 129.8 Voc), 1,308 W total

ARRAY 3: Roof mount, 10 SunPower X21-345-COM modules configured in two 5-module source circuits (1,725 W, 6.02 Imp, 286.5 Vmp, 6.39 Isc, 341 Voc), 3,450 W total

SYSTEM MONITORING: Blue Planet Energy, eGauge and OutBack Power web-based monitoring

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