Project Data

End-User: Lawrenceville School

Installer: Lighton Industries

Location: Lawrenceville, New Jersey

Date of install: May 2012

Size of system in kW: 6000kW

Energy produced since installation: ~27GWh

Special Challenges Met: Environmentally Protected Farming Land

Project Brief

THE LAWRENCEVILLE SCHOOL SOLAR PROJECT

Project Developer: TurtleEnergy LLC,  Date Built: 2012

Client: Sold to KDC Solar

Project: 6MW on thirty acres of single axis trackers, 500kW MV inverters

Cost of project: $28M, Date Energized: May 2012

John Millard's Role- principal in charge/ owner/ primary end user contact.

Civil, environmental, structural, mechanical consultant – Innovative Engineering; Wall, NJ

Permits required- NJDEP; Wetlands LOI, Flood Hazard Applicability Determination. NJ Department of Transportation- Permit to create curb cut on State Road 206. Township of Lawrence Zoning Board- Variance from Environmentally Protected Agricultural Zoning to Commercial Zoning Code. PSE&G interconnection permit, NJCEP SREC permit.

Role by John Millard: 1) Found TurtleEnergy 2003, 2) Sell Company Capabilities to Client in Nov. 2009, 3) Compete with two other companies to win $28M project, 4) Build project team to execute project, 5) Engage and Coordinate Engineering Consultants for Permits, 6) Negotiate Power Purchase Agreement, 7) Provide Due Diligence Design for Lender's Engineer to evaluate and validate for $15M non-recourse financing, 7) Estimate Annual Electricity Production for 20 year Production Guaranty, 8) Evaluate Mounting Hardware solutions for review, 9) Negotiate Procurement Contracts and Project Specific Warranties with Manufacturers of Inverters, Solar Modules, Mounting Hardware and Cable Tray. 10) Lead Site Layout and Subsurface Conduit Route for Permits, 11) Primary Liaison with Client, 12) Primary Legal Negotiator for Developer 13) Expert Witness at Zoning Board of Adjustment Hearing, 14) Negotiate SREC contracts with Load Serving Entities and SREC Brokers.

Project Achieved Zoning Approval in November of 2011 as well as all NJDEP Permits and NJDOT Permits- Project was sold to investors in April of 2011 and construction commenced in October of 2011, energizing in May of 2012 (commercial operations).

Design development issue: The Lawrenceville School's 60-year-old Electrical Load Center- would this aged electrical infrastructure be able to accommodate over 1200 A of solar power or not?
One of the obligations that the Lawrenceville school faced under the solar power purchase agreement with TurtlEnergy was the need to maintain a functional electrical room with infrastructure capable of receiving a significant amount of electricity from the sun farm. If for some reason this aged infrastructure were to break down, the Lawrenceville School would be responsible for any loss of power purchase that was delivered to the point of common coupling by the sun farm. There were other risks that the Lawrenceville School faced if they were going to persist with this 60-year-old electrical room that was the campus's nerve center for electrical power. The catastrophic disruption of electrical power to the campus would affect the hundreds of boarding students and day students who attended class in side the campuses classrooms. The question was: How was the school going to be able to pay for a new million dollar electrical center for the campus? The answer was: a gift from Henry Woods, an English teacher who served the school over a long period of time who had recently passed away bequeathed tens of millions of dollars to the school, just as this critical need was identified. 
The school engaged electrical engineers to design the new electrical building that would be located in an extension to the old power plant which had served the school for 60 years. Prior to this 60 year old powerplant being constructed, it was not uncommon for students to use candles and hurricane lamps with whale oil to study at night. With the age of the Lawrenceville school being 100 years, the school was celebrating it's Centenary in 2010. The construction of the solar project was a centerpiece of this Centenary celebration. The construction of a state-of-the-art switchgear room to serve as the school's new load center was an expense that was conveniently absorbed by this enormous gift from Henry Woods. Nevertheless, the new load center became a critical path milestone in the schedule to complete the solar project. The school's electrical engineers and the electrical contractor employed to construct the load center where under pressure to provide date certainty that an electrical breaker sufficient unto the task of accommodating the 1200 Amps of power from the sun would be complete in time to perform under the power purchase agreement. The design was coordinated with the electrical engineers designing the solar energy system, the construction contract was executed with an electrical contractor and construction began late 2010. The utility agreed to provide a new service cable to the school as part of their obligations to provide utility power to the school and their construction coincided with the new load center's construction. As it would turn out, the utility also needed to upgrade the fuses on the utility poles that protected the utility infrastructure from short-circuits on the campus. These fuses were not replaced until after the solar project had tripped them several times causing a black out to the entire campus after the system was energized in May 2012. Subsequently, the fuses were upgraded and the project has been exporting power onto the grid routinely at levels that comply with the utilities 5 MW AC for the project. This electrical risk was unforeseen by the project team and was considered a force majeure event covered by force majeure language in the power purchase agreement concerning availability of utility power. Therefore neither party was to blame for the loss of revenue created during these relatively short disruptions to the supply of electricity to the campus.

Ultimately, the impetus created by the solar project caused for the creation of a brand-new electrical load center to be constructed for the campus. Additionally, over 1100 feet of utility service cables were replaced at the same time that the new load center was constructed. With the completion of the solar project, 90% of the electrical infrastructure that would serve the solar project with connectivity was completely new. This fact created a great deal of comfort for both the buyer of the power and the seller of the power under the Lawrenceville power purchase agreement.

Design Development Issue: The availability of sunlight to the solar panels over time.

In determining the site coverage for the solar project there were some assumptions made about the availability of sunlight over the 20 year term of the power purchase agreement. One assumption was that the construction of any tall antenna like structure such as cell towers or other structure should be memorialized as prohibited by the buyer in the power purchase agreement. There also was concerned that the growth of trees along the eastern and western boundary of the site should be managed by the buyer over the course of the term. In order to quantify the height that was tolerated by the design of the solar energy system, site sections were drawn, bagels were defined, and contingencies were described. The growth of trees especially along the western boundary of the project which bordered the golf course and the campus was of primary concern to both parties. The school, for their part – wished to allow these trees to be grown unfettered by any topping activity or other trimming that might result in an unsightly boundary to the campus as a result of the solar projects rights of light. The solar project allocated a 130 foot shading buffer to exist between the westernmost solar panels and this vegetative buffer with the campus that had trees which exceeded 50 feet in height. The eastern boundary of the solar project was also defined by a vegetative buffer, but with much less developed, unhealthy trees that had apparently been trimmed by farmers over the years who wished to preserve the availability of sunlight for the crops that crew due west of this vegetative buffer. The design of the solar project allowed a 100 foot buffer to exist between the easternmost solar panels and this vegetative buffer with the adjoining owner, a third party farming entity. The shadows caused by these vegetative buffers to the east and the west of the solar project had already created a considerable loss of power for the solar project. All solar projects face certain obstacles on the horizon that cause for shading issues in the early morning and in the late afternoon. With a single axis tracker which tilts the modules towards the east in the morning and towards the west in the afternoon there is already a built in sheeting issue that is caused by self-feeding of the solar panels upon each other. The effect of self shading at these times of the day is mitigated by an algorithm designed into the tracking mechanism's programmable logic controller called "backtracking". What this algorithm does is it trains the solar panels to remain in a horizontal orientation in the early hours of the day as well as the late hours of the day in order to avoid creating shadows upon each other. As the sun rises in altitude and the risk of self shading diminishes, the algorithm trains the solar panels to exactly tilt so that the low altitude sun rises and the shadow that would otherwise cause the self shading of one solar panel upon another is avoided while a certain tilt angle is maximized in order to increase electricity production at these times of the day. Therefore, even if there were no obstructions on the horizon of the earth, a single axis trucker creates its own obstructions and therefore is less sensitive to low obstacles on the horizon such as these 55 foot high vegetative buffers to the east and to the west. It is also worth noting that such obstacles only remain an obstacle for a very short period of time in the morning and in the evening because of the rapid ascent and descent of the sun at these altitudes. Therefore, the team optimized the site coverage with the 130 foot buffer to the west and the 100 foot buffer to the east and was comfortable with this design which was memorialized in exhibit K of the power purchase agreement.

Design development issue: Choosing to use cable tray to distribute DC electrical power and control power to the tracker motors project wide.

As was discussed briefly in the schematic design issues of the Lawrenceville solar project, the advantages of using cable tray to distribute DC electrical power and AC control power to the tractor motors and other instrumentation are briefly revisited here below:

- Cable Tray is used in many projects where its flexiblility, cost, ease of access to conductors, labor friendliness and tendency to allow other more flexible solutions to other challenges such as combiner box locations, wire transitions from mounting hardware into combiner boxes and inverters with side entry opportunities.

- Use of cable tray eliminates 95% of trenching, conduit, and equipment required to excavate trenches. In fact, at nearly $5 per foot, these eliminations from the construction budget must be subtracted from the cost of tray which typically amounts to $5 to $10 per linear foot. The cost of pulling wire may be equated to the cost of laying wire in tray, but in fact, pulling wire is much more labor intensive than tray layout. There are other savings to be had with cable tray- and that is the savings in copper that there is to recover when applying the open air thermal resistivity coefficient to PV wire sizing- both for home uns to boxes and for larger conductors returning to DC recombiners. Tray provides a valuable route to which small control power conductors in conduit can be clipped onto the side of tray in order to separately deliver AC power to devices on the inverter pad, tracker motors or security devices.

- There is of course, the opportunity to mount combiner boxes on tray and that savings over free standing vertically mounted boxes is  equal to the full value of all concrete, excavation, and strut assemblies which amount to several hundred dollars per box. (not to mention the loss of conduit, elbows, couplings and labor associated with stubbing up.

- The back mounting of combiner boxes on tray is an electrician’s idea. The transitions from tray to box requires only a minute devation of angle for a Sealitite segment to steer conductors right through the side of the box, into the fuse holders, terminal blocks and grounding lugs. Grounding is easy with tray since the tray itself is used as a grounding conductor provided that jumpers are installed at each tray splice.

- The proximity of back mounted boxes to their respective source circuits, by nature, minimizes wirelength, improves efficiency of the system design and costs less for copper. The access to the box is from the top and allows for direct skylight to illuminuate the interior of the box. With the door sealed properly with a neopreme weather strip, NEMA 3R boxes are permissible where a NEMA 4 box might otherwise be called for.

- The Cable Tray acts as a bi-directional super highway for DC conductors to travel from source circuits to combiner boxes and from combiner boxes to inverter DC recombiners. Tray also is usefull for projects where there is a non-whole number of strings in a row of modules and a jumper is neccessary to complete a string. That jumper can ride on tray (and be shorter, easier to wire and visible) to and from one row to the other row without having to go underground.

- True, above ground distribution is an inconvenience for the lawn mower, but the improved site circulation, lack of mud, lack of fall hazards, reduced number of heavy equipment vehicles and other  effects of“trenched earth” are conspicuously absent on a site where cable tray is the rule for wire management, not the exception to the rule.

- Electricians space conductors in tray in order to benefit from the open air temperature coefficient that reduces the amount of copper required to acheive the same circuit resistance calculation as a conductor in a conduit in a trench buried under utility sand, warning tape, clear fill, top soil and landscaping because of the heat that the conductor emits inside the conduit. Savings on copper alone can amount to $1,000 to $5,000 per MW DC. In this case, the electricians are segregating the inverter home runs to the one side of the tray so that they can freely fill the other side of the tray with the smaller sub-array wiring (which is not by code required to be spaced apart). They may install a separator to insure that the smaller conductors to not creep over onto the the larger conductors which require complete expsure to fresh air according to NEC.

- Cable Tray can span up to 20’ and remain cost effective for solar projects. The project above has the tray (pictured) spanning 13’ from one mounting hardware  column to another. The tray is supported by a bracket that can be procured from any number of vendors. The bracket detail shown on the detail below is suitbale for a schedule 80 steel pipe that supports a torque tube slew ring. In this case availability of a vertical support for the cable tray is provided by the mounting hardware.

- Depending on the application, whether by tracker, fixed tilt, carport, roof mount or pole mount- cable tray opportunities to gain free support off of mounting structure often seem to be available for scrutiny, resolution and execution. The best support for a cable tray is often the ballast block that comes with the mounting solution and often it is the driven pier that has been cleared by the structural engineer to act as a dual purpose solution.

- The ability of tray to collect conductors from under solar panels is perhaps overlooked as so often we see projects pulling hundreds of feet of cable through conduit and loading those conduit runs on pipe piers and requiring the additional labor to install thermal expansion joints, couplings, elbows and other fittings just to deliver a few pairs of #10 wire to a combiner box. Cable tray is a reliable, durable alternative to conduit and a superior cable management system compared to “trenched earth”.