ComSite Construction has completed many renewable energy projects in North America and internationally, including photovoltaic installations.
A particularly interesting example is a project we did for Motorola in Sri Lanka. This Rural Electrification project implemented Sri Lanka’s first biomass village electrification system. This distributed technology solution has proven to be an attractive alternative to impractical extensions of the centralized national grid and utilized PV for the system’s backbone. The system proved to be a reliable source of power for the village.
The primary purpose was for PV water which was pumped into a storage tank during daylight hours, then distributed by gravity whenever it is needed. The PV system provided pumped water for remote livestock watering tanks, and most of the village’s water supply.
PV systems are especially well suited to locations where accessing an electrical grid is either not feasible or expensive. In many such locations, PV technology is the least-cost option for meeting remote energy needs.
The selection and proper installation of appropriately-sized components directly affect system reliability, lifetime, and initial cost. In any installation, it must be kept in mind that trade-offs are necessary in system design and component selection. Information provided here will assist in making your own system decisions.
- Stand-alone systems – Utilizes PV technology only, and are not connected to a utility grid.
- Hybrid systems – PV in combination with a diesel generation or wind system
- Grid-tied systems – PV system directly connected to the utility grid
We have experience with all areas of PV installation:
- Fixed and track.
- Ground level.
- Pole and rooftop.
- FAA Obstruction lighting backup
- Control Center Design and Installation
- Electronic controllers, converters, and inverters.
- Switches and fuses.
A photovoltaic installation is not plug and play. A safe, reliable, secure installation requires expertise in several disciplines, such as:
- Building trades. Carpentry, masonry, and even landscaping changes will likely need to be made to accommodate the system.
- Civil engineering. Will the roof hold the equipment? That’s just one civil engineering question that must be answered.
- Electrical engineering. How do you properly design circuit protection, size the transfer switch, and ensure it doesn’t burn the building down?
- Mechanical engineering. Wind shear and other mechanical stresses are design considerations.
- Security. Theft of photo arrays and copper components has become an issue with these installations. We can advise on how to inherently reduce theft vis design considerations. We can also advise on security measures such as monitoring cameras.
As noted in the other tab, installing a PV system is a multi-discipline endeavor. The National Electrical Code (NEC) provides Article 690 to address the minimum electrical installation requirements. It does not detail electrical engineering considerations; it just provides the minimum standards for making the installation safe. Not all of the requirements are in this Article. The first four Chapters (there are nine, total) also apply. The main point you need to understand is that, even if you obtained Article 690, you would not have a guide to a correct electrical installation.That said, here’s an overview of Article 690.
The system will have both AC and DC conductors. You can install these in the same raceways and junction boxes, but you must keep them separate from conductors that aren’t part of the PV system.
Conductors have to be grouped as follows:Group the conductors as follows:
- PV source circuits.
- PV output and inverter circuits.
- Multiple systems.
A key requirement is that you determine the maximum PV system voltage. You can do that in two easy steps:
- Add up the rated open-circuit voltage of the series-connected PV modules.
- Correct for the lowest-expected ambient temperature, using Table 690.7 (or manufacturer-provided correction factors).
As with any system, you need to size the conductors and circuit protective devices. But for that to happen with your PV system, you need to know the maximum circuit currents of:
- PV source (what comes into the PV system from the “solar cells). To get this, multiply the module nameplate short-circuit current rating (Isc) by 125%.
- PV output(what comes out of the PV system to the inverter). To get this, add up the parallel PV source circuit currents.
- Inverter output (what comes into the distribution system from the inverter output terminals). To get this, just look on the inverter nameplate and find the “continuous output current.”
Now with these conditions met and this preliminary work done, you’re ready to determine conductor ampacities. This brings us to section 690.8 of the NEC. To give you an idea of how much more involved the electrical requirements are, this Article 690 goes all the way up to 690.85. We’ve barely gotten started! And that doesn’t include applying those first four Chapters of the NEC.