Concentration of CO2 in the Atmosphere

Working Together: Fortress Battery and Green Mountain Solar

In Hinesburg, VT, 24 LG panels enjoy clear-blue summer skies to power the home and charge the Fortress back-up-energy-storage system. Photos courtesy of Green Mountain Solar.

George Harvey

Fortress Power

Regular readers of Green Energy Times might have read “Battery Storage Choices Grow with Fortress Power,” an article that was published in January of this year (). That article should serve as an introduction to the relatively new battery company, which is based in Pennsylvania. A local solar company, Green Mountain Solar (GMS) has installed Fortress Power’s (FP) lithium ferrite phosphate (LiFePO) batteries in two homes that wished to add backup-battery storage to their solar systems.

FP is a company that really prides itself in the support it gives its customers. The products are designed to be user-friendly. Their systems are very long-lived, designed for 6,000 cycles to 80% depth of discharge (DOD). You might compare that with some lead-acid systems that are sometimes only good for approximately 500 cycles down to a 50% DOD.

Recently, FP has added another battery to its lineup ranging from 5.2 kilowatt-hours (kWh) to 18.5 kWh. The company has introduced a new model, the eFlex 5.4 kWh. Their batteries are suitable for simple battery backup, off-grid installations with solar power, and in combination with solar power for grid-tied solar systems, thereby reducing higher time-of-use charges during high-demand times, demand-charge curtailment.

The two Fortress Power batteries, the two white boxes at the lower right, can keep almost the entire home running in case of an outage.

Green Mountain Solar

Green Mountain Solar (GMS) is based in Williston, Vermont. Paul Lesure is the general manager. The company has been installing solar systems since 2017, with a diverse set of projects including roof, ground-mounted, and tracker systems, both for residential and commercial properties. They shared their experience for two solar installations in Vermont that included batteries from FP.

Julia Westbrook, GMS’ marketing coordinator, told us, “GMS has seen a significant rise in interest in grid-tied battery storage systems, and for good reason. Customers are enjoying the security of knowing that there will always be power, even in the worst weather. This extends far beyond just the lights staying on. It means that if you have electric heat, a bad ice storm won’t turn your home into an igloo. It means that you never have to worry about a fridge full of food spoiling after a summer thunder storm. And, at a time when people are relying on digital solutions for working and connecting, the internet will never drop out unexpectedly.”


The first of our example projects was installed in June 2019, in Hinesburg, Vermont. This is actually a somewhat complicated system, because the homeowner uses quite a lot of power most of the time and needed 50 solar panels to cover that need. The battery system is not designed to accept all that power, however, because usage would be very much reduced during times of outage. As a result, the solar system has bifurcated power delivery, with only 24 panels supplying power to the batteries.

The solar-plus-battery system includes 24 LG Neon2 335 W panels, each with an Enphase IQ 7+ Micro-inverter. The system also has a SolArk 8k hybrid inverter and a Fortress Power LiFePO 10-kWh battery. This system can power the home’s lights, outlets, water pumps, pellet stove, home entertainment center, and the electric induction stove top when used sparingly. It was designed for 12 to 24-hours of operation, even in the winter, providing a high level of resilience. It accomplishes this without the fuel and maintenance needs of a generator, and without the environmental impact of the fumes a generator would give off, or the maintenance that they require.


The second and more recent example is a system installed in January 2020, in Middlesex, Vermont. Project Manager Robert Dunn said, “This system was one of our first ‘Whole Home Minus’ installs, meaning that all but a few very high-draw appliances would be backed up in the event of a grid outage.” It is designed to provide at least two to three days of electric power, even if the sun does not shine during that time. With that much storage, it can supply power indefinitely, if reasonable conservation efforts are applied. As it happens, the owner of the home chose to keep the installed generator as a secondary backup.

The Middlesex system includes 27 LG Neon R 365 W panels with Enphase IQ 7+ microinverters. It has a SolArk 12k hybrid inverter, a newer design than the one that was installed in Hinesburg. It is built with a Fortress Power 10-kWh LiFePO battery.

Westerbrook provided a few observations about these two systems. “The biggest thing we learned was the SolArk 8k is a great inverter, and the 12k builds on that to be one of the most flexible, self-reliant pieces of renewable technology we’ve gotten our hands on. For the right person who wants a system that can be altered at the factory to withstand an electromagnetic pulse (EMP) burst*, [this can be done] with lithium iron phosphate batteries, such as the Fortress Power battery, and it is suitable for full off-grid use.”

Fortress Power’s website is

Green Mountain Solar’s website is

* For those who wonder why an EMP burst is important for a home or factory in Vermont, we might suggest looking up the Carrington Event, a coronal solar discharge that caused havoc for the budding telegraph system in this country in 1859 ().

Leave a Reply

You can use these HTML tags

<a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>