The inverter is one of the most important and most complex components in an independent energy system. To choose an inverter, you don't have to understand its inner workings, but you should know some basic functions, capabilities, and limitations. This article gives you some of the information you'll need to choose the right inverter and use it wisely.
Independent electric energy systems are untethered from the electrical utility grid. They vary in size from tiny yard lights to remote homes, villages, parks, and medical and military facilities. They also include mobile, portable, and emergency backup systems. Their common bond is the storage battery, which absorbs and releases energy in the form of direct current (DC) electricity
In contrast, the utility grid supplies you with alternating current (AC) electricity. AC is the standard form of electricity for anything that "plugs in" to utility power. DC flows in a single direction. AC alternates its direction many times per second. AC is used for grid service because it is more practical for long distance transmission.
Magnum InverterAn inverter converts DC to AC, and also changes the voltage. In other words, it is a power adapter. It allows a battery-based system to run conventional appliances through conventional home wiring. There are ways to use DC directly, but for a modern lifestyle, you will need an inverter for the vast majority, if not all of your loads (loads are devices that use energy).
Incidentally, there is another type of inverter called grid-interactive. It is used to feed solar (or other renewable) energy into a grid-connected home and to feed excess energy back into the utility grid. If such a system does not use batteries for backup storage, it is not independent from the grid, and is not within the scope of this article.
Outwardly, an inverter looks like a box with one or two switches on it, but inside there is a small universe of dynamic activity. A modern home inverter must cope with a wide range of loads, from a single night light to the big surge required to start a well pump or a power tool. The battery voltage of a solar or wind system can vary as much as 35 percent (with varying state of charge and activity).
Through all of this, the inverter must regulate the quality of its output within narrow constraints, with a minimum of power loss. This is no simple task. Additionally, some inverters provide battery backup charging, and can even feed excess power into the grid.
To choose an inverter, you should first define your needs. Then you need to learn about the inverters that are available. Inverter manufacturers print everything you need to know on their specification sheets (commonly called "spec sheets"). Here is a list of the factors that you should consider.
Application Environment - BarnWhere is the inverter to be used? Inverters are available for use in buildings (including homes), for recreational vehicles, boats, and portable applications. Will it be connected to the utility grid in some way? Electrical conventions and safety standards differ for various applications, so don't improvise.
The DC input voltage must conform to that of the electrical system and battery bank. 12 volts is no longer the dominant standard for home energy systems, except for very small, simple systems. 24 and 48 volts are the common standards now. A higher voltage system carries less current, which makes system wiring cheaper and easier.
The inverter's AC output must conform to the conventional power in the region in order to run locally available appliances. The standard for AC utility service in North America is 115 and 230 volts at a frequency of 60 Hertz (cycles per second). In Europe, South America, and most other places, it's 220 volts at 50 Hertz.
An inverter should be certified by an independent testing laboratory such as UL, ETL, CSA, etc., and be stamped accordingly. This is your assurance that it will be safe, will meet the manufacturer's specifications, and will be approved in an electrical inspection. There are different design and rating standards for various application environments (buildings, vehicles, boats, etc.). These also vary from one country to another.
How much load can an inverter handle? Its power output is rated in watts (watts = amps x volts). There are three levels of power rating-a continuous rating, a limited-time rating, and a surge rating. Continuous means the amount of power the inverter can handle for an indefinite period of hours. When an inverter is rated at a certain number of watts, that number generally refers to its continuous rating.
The limited-time rating is a higher number of watts that it can handle for a defined period of time, typically 10 or 20 minutes. The inverter specifications should define these ratings in relation to ambient temperature (the temperature of the surrounding atmosphere). When the inverter gets too hot, it will shut off. This will happen more quickly in a hot atmosphere. The third level of power rating, surge capacity, is critical to its ability to start motors, and is discussed below.
Some inverters are designed to be interconnected or expanded in a modular fashion, in order to increase their capacity. The most common scheme is to "stack" two inverters. A cable connects the two inverters to synchronize them so they perform as one unit.