OPERATION AND DIAGRAM OF A SUNLIGHT-POWERED GENERATOR
The diagram below shows power stages and the wiring of a typical grid-connected solar powered generator
. Such a system contains two main sections: the devices that generate electric energy from sunlight and the devices that convert it into a form convenient for household use. Each of these sections in turn consists of a number of components. We'll take a closer look at these components and go over the basics of their operation. Whether you are looking to buy a solar power system or build it by yourself, this guide will explain you how it works and tell you the important things to know about it. You may also see Evans Miller's guide on the best solar generators
that explains how they work, what size you need, their benefits, and things to look out for before buying one such generator.
This is where incident light is converted into electricity. The array provides DC voltage as a function of several factors: the light's intensity, the number of the photovoltaic (PV) panels, their orientation, efficiency, and connection method
The array often consists of several paralleled strings of series-connected panels.
Note that if several strings are used, each one should contain the same amount of the panels. Such a series-parallel connection allows you to achieve desired voltage and power levels. The strings are wired to a combiner, where each of them is usually protected by an individual fuse or a circuit breaker.
Technically, it is possible to wire several circuits to the same fuse. However, if some of the cells will be partially shaded, they may be damaged by reverse electric current forced by the active panels. You can bypass the modules with reverse diodes to prevent their overheating or damage. Ask your installer about such precaution. Some panels come with built-in diodes. From the combiner one of the busses passes through the first DC disconnect
. It should be located as close as possible to the place where the cables enter the house. This switch is followed by a ground fault interrupter (GFI)
, which is intended to open the circuit when it detects a conductive path ("leakage") to earth from an ungrounded wire. Since the panels are installed outdoors and connected via long cables, the generator also needs a protection from lightning strikes. This diagram shows a single metal-oxide varistor (MOV) across the DC line. This is a minimum you should have (aside from a proper grounding rod). However, a stronger protection consisting of a combination of fast-acting MOV and high-energy spark gap surge arresters is always desirable. Once your inverter warranty expires (typically after 3 to 5 years), you are going to be on your own if lightning fries it. Request from your installer an advanced surge protection.
The solar generators intended for off-grid or for on-grid backup systems contain storage batteries
. They can be charged either from the PV array, or from utility voltage. The inverter in turn can be powered either from the stored energy or directly from the solar panels. The above diagram shows a possible arrangement of the grid tie system. In our example there are two passes for power flow provided by the diodes D1 and D2. When sunlight is not sufficient, or during power interruptions, the battery bank supplies current via D1. Otherwise, under normal conditions, when the batteries are fully charged, electric current from the panels can flow directly to the inverter via D2. Such arrangement is useful with Li Ion batteries which should not float. With lead acid batteries you don't need the diodes- the charger will provide a small “trickle-charge” or float-charge current depending on its algorithm. D2 also prevents batteries discharge at night by the solar panels. The NEC® requires another DC disconnect switch after the battery bank. Of course, if you are on grid, the storage bank is optional. Actually, most systems on the market are batteryless. They are cheaper, but they will not provide any emergency power. For a reference, average installation cost of a small solar system in 2013 was approximately $6,000 per rated kilowatt, although about half of this cost or more could be offset by various incentives and rebates.
This is an electronic device that converts DC voltage generated by solar cells into a conventional alternating current (AC). In reality, commercial models often include a charger and even a combiner all in one box. However, for clarity, in our diagram they are shown as separate modules. Different applications require different types of inverters. If you are connected to the grid, you should use a special grid-interactive
type. It synchronizes its operation with the utility voltage and uses it as a reference. This type comes in different flavors though. Many consumers do not realize that conventional grid-interactive inverters for batteryless configurations will simply shut down during a blackout even in bright sunshine. For the configurations with battery backup, you need a model designed for such an application. When it detects a power failure, instead of shutting down, it should disconnect from the grid by using a built-in transfer relay. Then it switches to internal reference and continues powering your selected circuits. This diagram
shows 120V/240V wiring typical for North American home. Two electrically “hot“ lines pass through the switches and circuit breakers. The neutral line is normally continuous and connects to a grounded buss in the electrical panel. The main distribution box is tied to the utility line. The electric branches wired to this panel will be de-energized when the grid is down. The auxiliary panel is tied to the inverter. It supplies critical circuits that you want to keep “live” during a power outage. The reason an auxiliary panel is usually used is to reduce load to the batteries: obviously the less power you draw the longer their runtime
. Of course, if your storage bank has sufficient ampere-hour capacity to feed the entire house for the desired time, you can run all branches from a single distribution panel connected to the inverter's AC OUT terminals.