Eaton advances sustainability with massive rooftop solar installation

Location: United States 

Segment: Solar 

Challenge: Develop one of America’s largest rooftop solar photovoltaic (PV) systems for reliable power containment and onsite usage without backfeed into the local utility grid.

Solution: End-to-end electrical balance of system (BOS) equipment, including AC collection for string inverters, designed to maximize power generation, reduce installation and operational costs, and ensure most efficient possible utilization of renewable power directly to the end customer.

Results: The 6.4-megawatt (MW) direct current (DC) installation generates enough electricity to meet nearly 20 percent of the building’s power needs; the equivalent of powering 1,000 homes in the area. The project also demonstrates an impactful regional model for renewable energy generation and estimated to displace approximately 6,300 metric tons of carbon dioxide annually, which is the equivalent of taking 1,300 cars off the road.

Background 

A large hospitality and entertainment company made the strategic decision to install a large, solar photovoltaic (PV) array on the roof of one of its flagship facilities. The company is committed to the principles of environmental responsibilities and wanted to advance and demonstrate that commitment. This installation was a first in the U.S. for the company, which selected the site because of its 20-acre, sun-orientated rooftop space. 

Approximately 850,000 square feet of the 950,000 squarefoot roof area was utilized to accommodate a total quantity of 21,396 PV modules and its supporting direct current (DC) and alternating current (AC) electrical infrastructure. The resulting solar installation provides a total capacity of 6.4MW DC (5MW AC) of renewable solar power.

The resort and convention center worked with a large power company to finance, construct and operate the project. Eaton was contracted by the design build firm on the project to provide electrical distribution equipment and services.

Challenge 

The resort and convention center is one of the world’s busiest and continuous uptime and easy access had to be assured throughout installation. It would be business as usual at the resort and convention center. Even when cranes were moving transformers and switchboards to the rooftop, show staging, staff and visitors could not be inconvenienced. Beyond the complexities of installation and access to the rooftop space, the sheer size, scale and conditions of the rooftop solar plant project made the groundbreaking project a first for the area.

A key challenge with this project was to ensure that no power generated by the solar plant would be able to backfeed onto the grid, as all power generated was contractually to be utilized by the property only. There would be no power purchase agreements in place with the regional electric utility and multiple safeguards had to be in place to ensure that all power was used by the building.

The solar panels and equipment required a nimble design to take full advantage of the extensive rooftop space for renewable power generation. Additionally, the large solar project would utilize over 200 SMA DC to AC 24 kilowatt (kW) three phase string inverters - making it critically necessary to implement a safe, efficient and cost effective AC collection system. The annual AC production requirement for the system was 10,379 megawatt-hours (MWh). To facilitate this need, the project required a range of AC protection and switching solutions to aggregate power, while reducing installation costs and simplifying operation with integral devices.

Unlike most rooftop solar projects, where much of the electrical equipment supporting the PV system is installed on the ground, the project required the equipment to be installed on a roof adjacent to the PV arrays. The electrical equipment involved includes (22) 480-volt (V) panelboards, (4) 480V switchboards, three 1 megavolt amperes (MVA) transformers and one 1.5MVA transformer, a data acquisition system, utility metering and relaying, as well as 12.4 kilovolts (kV) switchgear and all 12.4kV distribution.

Solution

Eaton provided AC and DC electrical power management solutions for the 6.4 MW project to help support safe, cost-effective and reliable solar generation. Eaton’s balance of system (BOS) solutions and services are designed to maximize the renewable energy harvested, while reducing installation cost and simplifying maintenance.

The DC connector units are equipped with sixteen 15A fuses, so there is a fuse on both positive and negative legs of the strings; the solution employs Eaton’s Crouse-Hinds series DC cable. Eaton cable harnesses manufactured with automated precision termination equipment are used in the installation to improve performance.

All of the AC solar power plant electrical collection equipment  is located directly on the roof areas adjacent to the solar panels to minimize the DC and AC losses. The AC electrical output of each inverter uses Eaton Bussmann series AC disconnects and is collected and combined in Eaton fusible panelboards also located on the roof. Eaton’s fusible panelboards are designed to accommodate heat concerns and high short circuit current rating (SCCR). Eaton’s scalable and customizable circuit breaker switchboards are also used in the installation; these are housed in seismic-qualified structures with an integral surge protection device.

Eaton’s Cooper Power series medium-voltage padmount transformers with an integral fused switch are used to step the voltage to a single 12.4 kilovolt (kV) distribution line, which is connected to Eaton medium voltage switchgear at ground level and travels about one mile to the final interconnection point.

The solution included a kirk-key system, designed by Eaton’s services team. The system is located both at the designated solar plant switchgear and the main interconnection point to the facility to ensure that the main utility breaker could not be opened without the solar breaker being opened first. Also, a relay system was installed at both locations with a communication system to measure the facility load and the solar power output. The communication system allows real-time remote monitoring and control features for the utility, project owner and building staff.

Additionally, the system is designed to never back feed on the grid. If the solar power output reaches 92 percent of the load, a curtailment feature in the relay system forces an automatic reduction in power output. If there are any issues, alarms will be engaged and the project owner will have the option to remotely limit the solar power output through the relay control. Based on the load profiles and expected output of the solar arrays the project owner anticipates that no curtailment will be required in the life of the system.

When the project was ready to be interconnected into the existing service, teams from Eaton, the utility, project and facility safely and effectively made sure that there was no interruption to the power coming into the facility and supporting its daily operations.

Result

At peak production, the rooftop solar installation is expected to produce enough electricity to meet nearly 20 percent of facility’s power needs. The project is also estimated to displace approximately 6,300 metric tons of carbon dioxide annually, which is the equivalent of taking 1,300 cars off the road.

At the time it was built, the project was world’s largest solar array on a convention center and the second-largest rooftop solar PV array in existence. The building owner purchases all the energy generated by the solar installation through an exclusive power purchase agreement.

The project is leading the way for other businesses to embrace environmental best practices by demonstrating that sustainability provides a powerful business advantage. By lowering demand on the local electricity grid, the project diminishes the need to import energy from outside the local energy system and reduces energy costs for the region. The project is delivering competitively priced clean energy to the resort and convention center, helping reduce energy costs in the region. At peak production, the rooftop installation is expected to produce nearly 20 percent of the facility’s power demand.

The rooftop solar installation is also an example of private sector companies working together to develop innovative technology that is changing how communities produce and consume electrical energy. By providing renewable energy during peak demand, the project is expected to provide pricing stability and reduce energy draw from the grid during the hottest time of the day. This will minimize the need to import energy from outside the local system and reduce the cost of energy for the community.

With a robust portfolio of electrical balance of system solutions, and a team of experienced engineers, Eaton builds solar systems tailored to customer requirements and provides the skills needed to successfully complete projects.