Case Study 1 | Case Study 2
12.5KW 120VAC Single Phase Dual Ground Mount Grid-Tied Residential PV System with both Enphase and string inverters (designed to offset 100%+ of the home’s electric usage), and a two-panel, eighty-gallon solar hot water system (designed to provide all hot water).
In addition to offsetting his family’s electric and hot water energy consumption, this client was interested in gathering first-hand field data on the performance of micro inverters compared to string inverters operating under the same conditions, and this system was the perfect opportunity to compare the two options. Enphase micro inverters are a relatively new type of inverter which has an added efficiency over string inverters. The increased energy harvest provided by micro inverters varies depending on individual installation conditions, but the working principle behind the 5%-10% production boost is that there is essentially an inverter at each module/panel—thus, if one panel is shaded by a cloud, it no longer is dragging down the output of the entire system (as is the case with a traditional string inverter installation). Another benefit of micro inverters is the ability to monitor performance at an individual level—the monitoring system can read and measure the output of every panel instead of the array as a whole. And if one panel isn’t operating at its peak, it’s easy to spot and can be quickly rectified to keep the system output maximized.
PHASE ONE: INFORMATION GATHERING, PRICING AND SECURING INCENTIVE/REBATE MONEY
Even with the unique objectives of the system, the start-to-finish process is consistent with a typical installation of a Smucker’s residential solar PV system. The client’s electric usage is analyzed using the previous year’s electric bill, a complete site survey is done to identify any challenges unique to the installation, a detailed shade analysis is done on-site, and client specifications such as budget, aesthetic details, and electrical offset amount are reviewed. With all this information in hand, decisions are made on system size and type (roof, pole, or ground mount; grid-tied or off-grid, etc.). And in terms of the solar hot water system, the household hot water needs are evaluated to determine the necessary system size. This includes the number of occupants, number of appliances using hot water, and the size and adequacy of the current hot water tank.
The client is then presented with a contract, complete with the installed system price and a financial analysis detailing return on investment and projected payback time. Once a signed contract and a deposit are secured, Smucker’s Energy completes the paperwork to secure incentive money.
PHASE TWO: DESIGN,PREPLANNING, AND PERMITTING
The PV system size was determined to be 12.5KW and the type of system was decided to be a grid-tied ground mount. In order to meet the objective of comparing micro inverter and string inverter performance, the system was designed to consist of two equally-sized ground mounted arrays. Each array consists of 28 Sharp 224W solar panels. Together, the fifty-six panels deliver 12.5KW of power. The solar panels produce DC (direct current) electricity, which needs to be converted to AC (alternating current) for use in a typical home. The DC created from the front array (Array 1) is converted to AC using one standard string inverter: the SMA Sunny Boy 6000US. And the back array (Array 2) uses Enphase micro inverters. The solar hot water system was determined to be a two-panel, eighty-gallon tank system with the solar hot water panels installed on the south-facing roof for optimal exposure to sunlight.
Once the design is complete, fully engineered drawings of the system are generated, including the site plan and one-line electrical drawings. Once the electrical drawings are complete, the permit application is submitted. At the same time, the Interconnection Utility Agreement (Part A) is submitted. The drawings are also reviewed by the Smucker’s team of technicians and electricians who will complete the installation, and an installation plan and schedule are created. For this system, four days are set aside for a crew of three to do the PV installation, and one day for the crew to do the solar hot water installation.
PHASE THREE: INSTALLATION
The first step in the PV Installation is to measure and mark the area for the ground mount as well as the for the wiring trench. Once pole holes are dug, the poles are set in concrete and left to dry for four days. Work resumes with the excavation of the wiring trench, and as soon as the trench is dug, the task of running the conduit and pulling wires from the arrays to the utility interconnection on the side of the house takes place. Back at the site of the system, the ground mount racking is assembled and the panels and inverters are attached—Array 1 receives its one string inverter (mounted behind the array), and Array 2 has the twenty-eight Enphase inverters connected to the back of each of the solar panels. A combiner box is added, which consolidates the output of each array at the point of interconnection to the utility, which in this case is at the utility meter.
A disconnect is also added that allows the power from the PV System to quickly be disconnected from the grid for servicing or emergencies. A second meter was also installed (pictured) for the purpose of measuring all the energy produced by the system as a record for Green Energy Credits (or SRECs). Lastly, the installation of the internet monitoring system takes place, which allows the owner to track in real time via the internet the PV production of the system, including the individual panel performance on Array 2 thanks to the Enphase inverters. All told, the installation is completed in just over four days.
PHASE FOUR: INSPECTION AND START UP
With the installation completed and tested, arrangements are made for inspections by the local municipality and the utility company. Following the inspections, a final interconnection approval is given by the utility. Once the utility’s final approval letter is received, the system can be turned on and can begin sending excess power to the grid. At this point, Smucker’s Energy fills out the completion paperwork required by the state grant program, enabling the reserved grant money to be forwarded to the system owner.
PHASE FIVE: REGISTERING FOR GREEN ENERGY CREDITS/RECS AND MONITORING OUTPUT
In order for the client to begin accumulating green energy credits from their PV system, it must be registered in a few ways with the correct programs. In this case, since the installation is located in Pennsylvania, it had to first be registered with the Pennsylvania Alternative Energy Portfolio Standard Program (PA-EPS). Once registered, PA-EPS provides a certification number. This number is used to register the system with GATS (Generation Attribute Tracking System). The GATS system is what tracks the solar production over time. GATS turns the meter readings into actual SRECs that are ready to sell. For each 1,000 KWH (1 MWH) the system produces, the owner will receive one green energy credit that can be sold on a market much like that of a carbon market model. These credits are accumulated regardless of whether the client uses the energy the system produces or if it is pumped back into the local utility grid. Green Energy Credits in Pennsylvania are called AECs (Alternative Energy Credits); other states refer to them as RECs or SRECs (Renewable Energy Credits and Solar Renewable Energy Credits, respectively). As a courtesy to our clients, Smucker’s Energy provides an aggregation service to handle all of your SRECs including all the paperwork; or you are free to enlist an aggregator of your choice.