Published on November 24th, 2017 | by Kyle Field0
Stone Edge Farm — A Sandbox For Microgrid Development
November 24th, 2017 by Kyle Field
It’s understandable that many visitors to Stone Edge Farm’s properties in Sonoma, California, would relish in the lush landscapes, expansive vineyards, and world-class wines produced there without even realizing that it was also one of the world-class test beds for microgrid development.
Behind the wines, farms, and fancy restaurants, Stone Edge Farm has built a complex microgrid from the ground up that not only challenges the status quo of grid-supplied electricity, but has the potential to completely disrupt how companies in California, in the United States, and around the world consume energy, produce their own, and intelligently manage and store energy.
The Makings of a Microgrid
The push into renewables started with a discussion between Stone Edge Farm owner Mac McQuown and Craig Wooster, CEO of Wooster Energy Engineering and general contractor for the microgrid project at Stone Edge Farm. They initially started discussing ways to reduce the farm’s electricity usage. The property uses electricity-hungry water pumps to pull groundwater up to the surface. Even with a focused effort that cut the farm’s water usage in half, the electricity used continued to be a pain point for the farm.
They quickly discovered that it was not a straightforward process to go off the grid with a complex network of 7 utility meters spread across the property in no logical fashion. The installation of a photovoltaic solar system on the roof of the agricultural shed in the north part of the farm put a spotlight on the complexity of the situation and catalyzed a more focused effort developing iterative solutions that eventually led to the establishment of the Stone Edge Farm microgrid on the property.
“The Stone Edge Farm MicroGrid Project is governed by what we call the Prime Directive: Any technology we deploy, and any system we install, must reduce the carbon footprint at Stone Edge Farm,” said Craig Wooster, Microgrid Project Manager at Stone Edge Farm. “Our goal with this project is to demonstrate the variety of clean energy solutions that can be used to provide power to a campus or even an area of a city.”
The Stone Edge Farm Microgrid
A microgrid is a group of electricity sources and loads — like a solar installation and water pumps — that might be connected to “the” grid but has the capability to fully disconnect from the grid and operate independently, if needed.
Stone Edge Farm built its microgrid iteratively, starting with a single rooftop solar installation and adding components as opportunities arose to further improve or streamline the system. Today, all of the on-site electricity generation comes from 630 solar photovoltaic panels installed across 8 buildings around the property. As more solar was added over time, the need for curtailment of solar production arose and the team started looking around for options.
The largest block of solar panels installed at the farm, a block of 290 panels, was installed with the Enphase Energy S280 microinverters (PDF). Because microinverters allow for visibility and control of each solar panel, Stone Edge Farm is looking to utilize them for intelligent solar curtailment — though, this is not currently possible.
Intelligent, Diversified Storage
Stone Edge Farm also partnered with several battery companies to install an array of stationary energy storage installations in a variety of different chemistries and formats, the largest of which is a Tesla Powerpack with a total capacity of 250 kW | 475 kWh.
The second largest battery installation is a set of 7 of SimpliPhi Power’s lithium-ferro-phosphate (LiFePo) units with a total capacity of 23.8 kW | 45 kWh. SimpliPhi Power’s batteries are unique in that the LiFePo chemistry is nontoxic and hyper-inert — extremely safe and completely recyclable. It has no flammable components, as the lithium is tightly bound, no possibility of thermal runaway, and requires no ventilation or cooling.
It can be overcharged, crushed, or burned, and provides greater energy density with no need for heat mitigation. These characteristics make it well suited for many applications, with stationary storage being one of the best since the LiFePo chemistry does not have as high of an energy density as the chemistries normally utilized in eMobility applications.
These installations soak up excess electricity from the solar panels and store it for a time when it’s needed onsite or on the grid:
All told, the solar system has a total production capacity of 368 kW, the on-site Capstone Microturbine has a capacity of 68 kW, and the ReliON fuel cell hive has a maximum output of 28 kW which depends on how much H2 is stored for a total maximum system output of 461 kW. The microgrid system uses a complex fiber optic network that provides real-time monitoring of each component of the microgrid that can be monitored remotely via the farm’s internet connection.
Typical microgrid systems are designed for 70–90% of maximum load but Stone Edge Farm was initially aiming to generate excess power in the hopes of exporting to Sonoma Power, so it built the on-site systems to 4 times its peak consumption. That dream was not realized and the unplanned turn of events resulted in a unique opportunity since the farm consistently has far more electricity than it needs.
Stone Edge Farm also installed a hydrogen electrolyzer, which uses the excess electricity to generate hydrogen from water. It was chosen since it allows for larger scale storage of energy at a lower capital cost than batteries. When the alternative to storing electricity as hydrogen is curtailing electrical generation, the ability to turn sunshine into portable hydrogen becomes a worthwhile discussion.
The hydrogen electrolyzer is an example of how a facility planning to generate 100% of its own peak demand will inevitably end up with excess production. This will happen more and more as the cost of installed solar panels continues to fall because it becomes cheaper to make more than it is to pay for the small fraction of electricity purchased from the grid.
To utilize hydrogen as a source of electricity generation, the farm installed a bank of Plug Power GenSure fuel cells that boast a peak electrical output of 26 kW. This is the base use case for the two hydrogen system at Stone Edge Farm as it allows for a lower cost, higher volume of electricity storage than would be possible with batteries.
Portable, renewably generated hydrogen gas also presents an opportunity to generate additional revenue on the site. Producing low carbon fuel, like hydrogen, gives the producer low carbon fuel credits for offsets. These credits can be sold or traded for additional revenue, just as the excess hydrogen can.
Stone Edge Farm is an example of the microgrid of the future, and through its partnerships with the vendors mentioned and many more that were not, is helping solve problems that will be able to be more easily reapplied in the future. For example, SimpliPhi Power has taken its learnings from the Stone Edge Farm microgrid and is working on a “microgrid in a box” product that will make it easier for customers to stand up a microgrid without having to build it themselves piece by piece.
Stay tuned as we unpack the Stone Edge Farm microgrid over the course of several articles based on my interview with Craig Wooster, Project Manager & General Contractor at Stone Edge Farm MicroGrid Project.
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