Like a necklace displaying many jewels, the MicroGrid encircles Stone Edge Farm with a variety of interconnected electrical generation, storage, and consumption devices.
The distributed energy resources or DERs (solar panels, microturbine, fuel cell hives) produce power that can be consumed directly by loads (irrigation pumps, buildings) or stored by several assets (batteries, hydrogen) for later use.
The MicroGrid unites seven electrical services on five formerly separate parcels that constitute the farm. A continuous loop, the trunk line routes power through five nodes and the DER plant/H₂ park (see below).
Stone Edge Farm comprises 16 buildings on 16 acres. Currently in place are 630 photovoltaic panels on eight buildings generating 300 kilowatts (kW). We plan to add more PV panels to produce close to 0.5 megawatts (MW).
The farm actually has two grids. The Critical Grid is a backup solar-powered battery system to support essential equipment.
In emergencies, when electrical harmonics and distortions could disrupt the MicroGrid, the Critical Grid ensures continuous operation of critical devices (computer servers, Ethernet and fiber optics switches, alarm systems, emergency lighting, electrically operated gates).
Nodes are convenient switching points where two or more electrical services exist in close proximity. Switches join these circuits and enable movement of energy where and when it’s needed on the farm.
Of Stone Edge Farm’s seven electrical services, four are 240-volt/single phase (240V/1P) and three, 480-volt/three phase (480V/3P). Each node has management (communications and control) and backup power systems.
Four nodes made up our U-shaped MicroGrid until early 2017, when installation of a fifth node closed the U to form a complete ring, preventing any single point of failure from disrupting the MicroGrid.
Located in the southeastern part of the farm, this “prime” node connects three of the farm’s seven electrical services – two 480V/3P 200-amp (200A) and one 240V/1P 400A.
Emerson ASCO automatic transfer switches (ATSs) can automatically connect or separate our MicroGrid from the utility grid. If the grid goes down and the MicroGrid is producing electricity, these “gatekeeper” switches can route power onto the grid.
A natural gas-fired 65kW Capstone microturbine, basically a stationary jet engine, provides backup power within three minutes.
Exhaust heat from the microturbine can be captured for a hydronic (liquid heat and cold transfer) plant capable of heating and cooling four buildings and two swimming pools. Thus, node one is a tri-generation or combined cooling, heating, power (CCHP) plant.
On top of the microturbine, a heat exchanger raises efficiency to above 90% utilizing exhaust to heat two 500-gallon water tanks that provide radiant heating. A 10-ton Yazaki lithium bromide absorption chiller converts warm water to cold for summer cooling.
Instead of using a conventional cooling tower, which can evaporate 1,000 gallons of water per day, the heat exchanger has a closed pipe loop to circulate water through existing wells, cooling it with ground water.
Nearby, seven non-toxic 3.4W SimpliPhi Power lithium ferro phosphate batteries, connected in a 23.8kW/45kWh stack, and a 6kW, 120/240V Schneider inverter protect Critical Grid functions at the Zen spa and observatory.
Set between the shop and the Butler building on the farm’s southwestern side, this node forms one large circuit by joining two 480V/3P services.
Here, an Eaton computerized panel provides MicroGrid power management with breakers operated by the control system. If the farm goes dark, the panel automatically and instantly sheds non-critical loads for three minutes while the microturbine fires up to provide backup power.
An Energy Storage Systems (ESS) iron flow cell battery is located here. This 10kW/65kWh capacity non-toxic storage system, housed in a shipping container, has an iron and saltwater electrolyte, patented pH stabilization to ensure long life, and is paired with three 10.8kW Outback Power FXR Series inverters/chargers.
The Butler building contains Critical Grid servers, backed up by a stack of eight Sony lithium iron phosphate batteries with a combined rate and capacity of 2.4kW/9.6kWh paired with a 6kW 120/240V Schneider inverter.
The 480V/3P ESS battery has a product life of >20,000 cycles and 70% round-trip efficiency. Two 500-gallon tanks hold electrolyte fluid that is phosphorescent green when charged and rusty brown when discharged.
The battery electroplates (deposits iron) on the negative side to charge, and deplates on the positive side to discharge (returning iron into the tank). Its container is mounted on a raised concrete pad with air space so that a nearby 250-year-old oak tree’s roots can “breathe.”
Near the chicken coop at the north end of the farm is a 480V/3P junction where north meets south electrically.
Energy now flows from the solar-panel rich north to the solar-poor (mature shade trees) but power-demanding south. This is the main hub of the MicroGrid trunk line.
With real-time monitoring, we can turn motorized mechanical breakers here on and off remotely from the controller, shutting down high voltage in case of fire or natural disaster. Meanwhile, remote control is very convenient.
Maintaining the Critical Grid here are two 5kW/20kWh Redflow zinc bromide flow cell batteries with a 120/240V Magnum inverter.
This node has switching for 240V/1P 400A services to each of three houses – called Guest, Glide, and Gate – on the farm’s east side. Installing the trunk line from this node south to node one recently changed the U-shaped MicroGrid into a complete loop.
Nearby are five stacks of 16 trays inside white cabinets that contain the same Tesla lithium ion batteries that power the manufacturer’s cars. This Powerpack, with its 250kW/475kWh capacity, delivers substantial power in a short amount of time through a Dynapower inverter. When the MicroGrid operates in island mode, the Tesla battery can generate its own 60 Hertz cycles, serving in a master role.
Early in 2017, installation of the trunk line from node four to node one created this fifth node, making a continuous loop around the entire property to prevent a single point of failure from disrupting the MicroGrid.
Previously, our U-shaped MicroGrid resembled Christmas tree lights connected in series, where a single bulb’s failure can disrupt the whole string. But in a completed loop, our trunk line’s bi-directional conduit simply re-routes energy in the opposite direction.
On a spur at the farm’s northwest corner, the distributed energy resource (DER) power plant can be electrically isolated for special study purposes.
A utility-grade connection here is the point of common coupling (PCC) with the utility grid where electricity can be exported. The MicroGrid employs the same DC Systems software used by the utility, so that one “language” is spoken across the PCC.
An Emerson ASCO Microgrid Actuation Circuit automatic transfer switch was developed to enable us to operate islanded while still open to the utility grid. When changing from on-grid to off-grid, we can bypass solar arrays so that they don’t shut down. The complex new 277V/480V/3P 400A “and/or” switch is, appropriately, called the “MAC switch.”
Located here are spaces for California Independent Service Operator (CA ISO) and Pacific Gas & Electric (PG&E) service meters and a Schweitzer relay, an extremely fast safety device that protects people working on the grid.
This area contains the ag shed with 123 photovoltaic panel arrays that generate 32kW. The hydrogen park includes a sodium ion battery, alkaline electrolyzer, hydrogen storage and fueling station, and fuel cell hives.
The Aquion Energy sodium ion battery consists of two strings of seven 48V M-Line battery modules connected in series and combined by the Ideal Power inverter into one 672V string. The 28kW/380kWh capacity battery’s electrolyte is essentially seawater. Installed in a 40-ft. shipping container, this truly sustainable, non-toxic device is not flammable, explosive, or corrosive, and was designed for daily deep cycling ideal for solar installations.
The Millennium Reign Energy electrolyzer is a controlled load that utilizes surplus solar-generated electricity to split water (including gray water) molecules into two non-greenhouse gases -- hydrogen, which is stored for later use, and oxygen. Enough hydrogen can be made and stored here to operate our fuel cells for up to 12 days.
Hydrogen run through the PlugPower ReliOn fuel cell hives reverses the electrolysis process to make water and generate electricity when needed. The three hive cabinets each contain a stack of four 2.33 kW units (total 28 kW). If a unit fails, it is easily replaced.
Our farm’s base load at night without irrigation running is 15kW, with an upper range recorded as high as 165kW. We calculate our maximum possible load at 400kW. Our system follows the base load at night; if something turns on, the hive turns on more fuel cells. Batteries buffer the cells.
Hydrogen also powers fuel cell-equipped vehicles, like the Toyota Mirai cars on the farm. In both fuel cell applications, the byproduct is pure water and zero carbon emissions.
The electrolyzer/fueling station package, called AutoARK, can produce, purify, compress, store, and dispense 12 kg of hydrogen in 24 hours, enough to fuel one car or two forklifts.
Part of the California Energy Commission (CEC) distribution resource plan (DRP) is the entry of residential and corporate resources into the energy market. Our MicroGrid’s intense resources meet the standards of that plan.
The only way to export energy onto the grid while running in parallel is if the CA ISO changes policy (specifically, Rule 21) which addresses safety concerns. CEC and California Public Utilities Commission (CPUC) changes are required. We are ready now.
Our Aquion battery, also known as an aqueous hybrid ion (AHI) battery, consists of abundant, eco-friendly materials like saltwater, cotton, carbon, and manganese oxide.
This is Aquion’s first commercial deployment with the Ideal Power 30kW multi-port power conversion system, which enables direct current (DC) level connection of solar PV and energy storage in a compact, highly efficient package.
In 24 hours, the Millennium Reign electrolyzer can produce 12 kg of 99.999% pure hydrogen compressed to 6,000 psi. The fueling and storage station contains 24 1-kg cylinders of hydrogen gas at 6,000 psi.
MicroGrid management -- systems monitoring, communication of information, and control -- enables all of our different resources to work together.
In island mode, for example, we require a master source of 60-hertz (Hz) power plus enough production to meet a load at any instant. We must monitor loads, voltage, and frequency, and be able to charge or discharge in a fraction of a second.
“Head room” is necessary, enough capacity plus or minus to handle the biggest load, or the loss of the biggest load, instantaneously.
Our utility grid-level, real-time distributed control system software is provided by DC Systems, developer of smart grid software solutions for utilities, power generators, and large energy users. They write SCADA (supervisory control and data acquisition) software for PG&E and 150 other utilities.
Our MicroGrid has three levels of control. DC Systems operates on both sides of the PCC, interacting with assets to keep the MicroGrid stable. The first level provides real time communications with the utility grid and CA ISO.
A second or middle level control runs on Emerson Ovation software "inside the wall," providing oversight and operation of the switch gear, pump systems, and generation devices, with parallel functions like fiber optics and wi-fi operating solely within Stone Edge Farm.
Our local level control is a failsafe instrument that keeps nodes running. The Heila IQ optimizer was designed on property by one of our interns, Jorge Elizondo. The optimizer translates disparate communications from numerous technological devices into a common software language. Local control is designed to work if the other two tiers are lost or compromised.