PV panels are the main component of a solar-electric system and determine its output capacity. Photons of light strike the semiconductor cells of a solar panel exciting electrons which then flow as a stream of direct (DC) current.
PV panels are rated in watts based on the maximum power they can produce under ideal sun and temperature conditions. The more directly the sun strikes the panels and the lower the air temperature around the panels’ results in the highest production. The individual panel rated output is used to determine how many panels would be needed to meet the requirements of a specific electrical demand. Multiple panels are often wired together to achieve a desired quality of electrical output and are called strings. In another type of system, panels remain individual. All the panels in a system, whether in strings or individual, are called an array.
Rigid panels are the most common form of solar electricity generation because to date they have by far the highest level of efficiency. PV modules are very durable and long lasting with all panels installed by Edison Solar carrying a 25-year manufactures warranty. They can withstand severe weather, including extreme heat, cold, and the contact of limited size hail stones.
Mounting racks are used to affix solar panels to a secure structure so that they stay in place and maintain their desired orientation to the sun. Panels can be mounted in three ways: 1) on a rooftop, 2) in a rack on top of a steel pole set in concrete, or 3) horizontally on a ground level bank mounting system. Rooftop mounting is most common because it is above many flying objects, requires no additional space, and is usually cheaper in that it does not require the construction of a support structure. In areas with a lot of space, pole or ground-mounted arrays are often chosen.
Mounting racks may incorporate other features, such as adjustability. The sun is higher in the sky during the summer and lower in the winter and moves across the sky from east to west each day. Adjustable mounting racks enable the angle of the solar array to be changed, keeping it aimed more directly at the sun. Adjusting the tilt angle increases the systems annual energy production by a few percent. The tilts of roof mounted arrays however are rarely changed in that climbing on a roof is usually difficult and dangerous. But changing the tilt angle of pole or ground-mounted arrays can be done quickly and safely. Pole-mounted arrays also can incorporate tracking devices that allow the array to automatically follow the sun across the sky from east to west each day. Tracker arrays can increase the systems daily energy output by 25 to 40 percent in some locations but are more costly.
It is most economical in the higher latitudes of the northern hemisphere as in Ohio that solar arrays face south for a cost effective system.
In string inverter systems, the direct current generated by the solar panels travels by wires from the array to a rapid shutdown device. The disconnect is usually located near the array and serves to stop the flow of current from the array. This is primarily a safety measure but also serves to allow repair further down the system.
Micro-inverters do not require disconnect, because they stop electrical production automatically.
With string inverters, the DC current travels by wire from the DC disconnect to the inverter. With micro-inverters each panel has its own inverter which converts the direct current to AC current at the panel. The purpose of an inverter is to transform the DC electricity into alternating current or (AC) electricity. This is the type of electrical current used in most residential and commercial functions. In grid-tie-in applications (to be explained below), inverters perform the additional function of synchronizing the electricity they produce with the grid’s “utility grade” AC electricity. This allows the system to feed solar-made electricity into the utility grid.
The current coming out of the inverter(s) next travels to an AC disconnect. This disconnect is required by the electric utility companies and is always located in an accessible area usually outside. By switching the current off at the AC disconnect box the utility linemen can stop the flow from the solar array into the utility companies lines. This is essential for safety when utility linemen must execute repairs on the company lines.
From the AC disconnect the electricity travels to the breaker panel which it enters through an available breaker. From its entry point into the breaker panel it can flow to all other circuits connected in the panel supplying electricity through out the home or business. If more electricity is being generated than is being used it can also flow from the breaker panel to the utility company.
From the breaker panel, wires run back and forth through a meter, to the utility company, transporting electricity. After the utility company replaces the standard meter, the amount of electricity generated from the solar array and the amount of electricity used from the utility company are measured independently. The utility company reads the meter monthly and generates either a bill or a credit.
The solar power systems that has been explained above is the type of system referred to as grid-tie-in. Grid-tie-in means that the personal solar array generated electricity is connected to the supply from the utility company. This leaves the user with two sources of supply, the utility company and their solar electric generating system. Thus sufficient electricity is always available night or day (except in the case of a utility company nighttime power failure).
Grid-tie-in has several advantages over a standalone battery system. The utility grid has a huge free storage capacity making long-term storage possible well beyond the short-term day to day capacity of battery systems. Excess production from the solar panels is usually credited by the utility company minus the transmission charge set at the lowest price they pay for electricity. The utility company then issues a credit in dollars. This credit is deducted for the electricity subsequently purchased at full price. This means, for example, if a kilowatt hour cost 12 cents, solar production would have to send roughly 2 kilowatt hours into the grid to equal one hour in return.
Alternative energy from solar can also be stored in batteries without being tied into the utility company grid. Such systems are called “stand alone”. They have the advantage of supplying power any time even when the sun is not shining and the utility company power is down. However, they are more expensive primarily because of the cost of batteries and are limited in their capacity to supply power.
