Alex Mathers, P.E., CxA
As interest in energy independence and efficiency grows, so does the importance of Microgrids. Microgrids are small, local, and smart energy grids which serve a defined collection of buildings and facilities. A microgrid generally operates while connected to the grid, but it can break off and operate on its own using local energy generation or storage. Due to their critical nature and safety requirements, Commissioning and functionally testing Microgrids present a number of challenges. These challenges are addressed here based on a recent project.
Sharp HealthCare is San Diego County’s leading health care provider. Sharp is focused on delivering the highest quality patient-centered care, the latest medical technology and superior service. They have more than 2,700 affiliated physicians and 18,000 employees working within four acute-care hospitals, three specialty hospitals, three affiliated medical groups and a full spectrum of other facilities and services.
The Sharp Rees-Stealy Santee Medical Center is a new 86,000 SF facility consolidating multiple medical specialties into one destination for the residents of a lower income and underdeveloped community in east San Diego County. It offers primary and specialty care, urgent care, pharmacy, laboratory, mammography, optical shop, radiology, rehabilitation services, and diabetes and nutrition education.
As part of Sharp Healthcare’s continued dedication to sustainable practices, the new project includes a power microgrid that will allow Sharp Rees-Stealy to generate solar power and save approximately $300,000 a year in electricity charges.
A microgrid is a small, local, and smart energy grid. It generally operates while connected to the grid, but it can break off and operate on its own using local energy generation or storage. The microgrid must have smart control capability to disconnect from the Utility grid and operate autonomously. This is called Islanding.
A microgrid can be powered by distributed generators, batteries, and renewable resources. Which means it can take advantage of many different distributed generation technologies, such as wind turbines, solar panels and diesel generators. The more electrical generation that is interconnected in the microgrid, the more resiliency can be achieved. However, the intermittent nature of renewable resources makes the operation of the microgrid more difficult. Therefore, energy storage devices are necessary to smooth power generation of these intermittent sources.
Finally - A microgrid is not just a secondary or distributed energy system. That is, It is not a rooftop solar panel installation or backup generator. It is designed to supply primary reliable power 24/7/365. Depending on how it’s fueled and how its requirements are managed, a microgrid might run indefinitely.
There are five main benefits of microgrids –
A microgrid improves electric reliability (energy resilience) – in the case of the Sharp Santee building the microgrid provides back up power to select, emergency loads during a power outage.
A microgrid can lower energy costs for consumers and businesses – in the case of the Sharp Santee building the microgrid offsets the building’s energy usage via the solar photovoltaic system. It also lowers utility demand charges via the Battery Energy Storage System.
Is more efficient because generation close to demand. A microgrid is more efficient than a distributed utility because power generation is physically close to power demand. this removes transportation losses.
A microgrid strengthens the central utility grid – less energy is demanded on from the local utility as the Solar Photovoltaic system operates and less power is required as the Battery energy Storage system clips/curtails the power demanded during peak periods.
A microgrid brings economic value to society. Microgrids offer economic value, they avert loss of product and work during a power outage, they attract high quality employers to a region, and they keep jobs within the community.
The Sharp microgrid is a 400 kW DC / 300 kW AC system which includes 950 LG solar panels rated at 400 Watts each. These are wired in series of 18 connected and connected to 6 inverters with integrated disconnects.
The solar inverters are connected to an 800A panel board (DG-2) which is also connected to the TESLA 140 kW inverter and 16 pod battery pack which can store 225 kWhs of electricity. The Tesla inverter is a grid-forming inverter which means it is responsible for creating and maintaining the voltage and frequency of the microgrid and it ensures that excess power is tightly synchronized to the grid.
The 800A panel board is connected to a 1,200 A panel board (DG-1) which feeds emergency loads in the building. The 1,200 A panel board is fed by a motorized breaker panel (DG-3) which houses connections to the Grid through CB-1 and a 100 kW diesel generator through CB-2. CB-1 is connected to a 3000A Main Service Board which houses incoming utility service power and normal loads for the building. I’m diagrammatically showing two buildings, but there is just one. Also included are a number of power meters which are measure the flow and direction of power in the system.
The system is paralleling which means synchronous operation of multiple power sources connected on a common bus in order to provide power to common loads.
Four other main items are the non-export relay, the generator controller, the Enel X site controller and the islanding controller. The Non-Export Relay makes sure that the Tesla battery does not output to the grid. It does this by monitoring M6, M3 and M4 and makes sure power through M6 is less than M3-M4 which is available power to normal loads after taking into account solar power produced. The Generator controller starts the generator and is able to vary the frequency of the generator output and sync to the grid.
The Enel controller uses the facility utility rate structure to determine when to charge/discharge the battery. Finally, the Islanding Controller ensures microgrid emergency power remains energized during a power outage
Another note is there is no True ATS. The Motorized breaker panel DG-3 has CB1, CB2 interlocked. There is no ATS because both breakers be able to be open at the same time, but they can’t both be closed at the same time because we also can’t export generator power to the grid.
One of the main purposes of the microgrid is to save money. Obviously, there must be a payback. The way Sharp is able to reduce utility cost is to use the local utility’s (SDG&E) rate structure to its advantage. SDG&E has 8 different rates depending on time of day (aka TOU or Time of Use), day of week and amount of usage. They have rates for On-Peak, Off-Peak and Super-Off-Peak.
There is also a Baseline allowance for the monthly amount of energy you can use at the lowest tier pricing. If you use more than your allowance during your billing cycle, you’ll move up to the higher-cost tier pricing. SDG&E provides customers with an additional 30% of baseline energy before the higher rates kick in.
Functional performance testing (FPT) is the bread and butter of the commissioning process. Testing a microgrid takes special attention to safety and security. Here are main points of how we tested the microgrid:
Specialized subject matter experts – We assigned our top CxA with experience in complex electrical systems.
Coordination meetings – We held multiple commissioning coordination meetings on top of MEP coordination meetings.
Testing plan meetings – We held multiple testing plan meetings
Protocol development – We developed unique Testing protocols to match scenarios
Execution – We had to test at all different times and conditions to match scenarios
During testing we found a number of issues. Some were minor and easily fixed. One major issue found was that once utility power is restored the generator continues to run. Tesla does not want responsibility of turning off generator so once utility power is restored and the power is transferred back to the utility the generator does not receive a off signal and requires manual intervention to turn it off.
Another issue found was too much power in system when in Islanding Mode. The solar Inverter curtailing sequence when on “microgrid mode” or Island mode was originally set to power up the microgrid with all the inverter’s at once and then power down one by one over time. But there were issues at utility power loss and full solar generation. Voltage was building up on the line and exceeding parameters and tripping the battery. Tesla was then sending the generator a start signal since it was tripped. Solar is a current source and you can’t interrupt current instantaneously. To fix this issue the inverter restart sequence was delayed by 10 seconds intervals and brought on one by one so curtailing could go into effect.
GMC Cx added value through the commissioning process. Specifically, we provided the following benefits:
Energy cost savings – By dialing in the adjustable setpoints we were able to enhance the performance of the microgrid system
Fewer change orders during construction – Through design review, submittal review and working with the owner we were able to help align the results to the owners expectations
Reduced project delays – By coordinating the design and installation upfront we were able to remove potential bottlenecks
Better communication among the project team – The additional commissioning meetings allowed for more interactions and solutions to issues.
Higher system reliability – The reliability of a series system is no better than the reliability of the worst component. By finding and resolving weakest link issues during testing, the resulting system was more resilient.
Longer lifecycles for building equipment – By dialing in the adjustable setpoints there is less short cycling. Also ensuring facility operators are trained on proper maintenance and operation increases the likelihood of improved equipment lifespans.
Built on the site of a long-time vacant lot in the city of Santee, the Sharp Santee Medical Office Building is an 86,000-square-foot medical office building that consolidates multiple medical specialties into one destination for the residents of the growing region of East County. The development of the Sharp Santee Medical Office Building serves as a beacon for residents and visitors of the community. Overall, this project was a success. From the commissioning of the building equipment to the optimization of the microgrid system, safety, energy efficiency and quality was the core of our work. The Microgrid has been running for about a year and we hope to see it still producing payback long into the future.