A grid tie inverter is an especial system designed to convert DC current into AC current. The current conversion makes it possible to benefit from tons of different renewable energy applications such as solar panels on a solar power system. Since most renewable energy systems, especially solar powered systems, generates DC current power the current conversion is necessary because the majority of the appliances found on our homes are designed to work with AC current only. Besides that, different current types won’t play well in a same utility grid.
But while the task a grid tie inverter performs mistakenly makes you think that it is a simple system, it is not. In fact, not any inverter is designed for every application, it must be choose selectively based on a number of factors, with some of those changing between countries and the jurisdiction therein.
What to Consider When Selecting a Grid Tie Inverter
The first thing you need to assess before you purchase any ac inverter is your specific application requirements. You must take care to choose a system that will handle the workload of your conversion needs, otherwise you may come into serious problems and you can even damage your new purchased inverter. Here are some points you should look into before choosing your ac inverter.
Rated Output Power
This value is measured in either watts or kilowatts and it is closely related to the output voltage so you may have different values for each configuration. It relates to the conversion efficiency as well, as the effective output power you will get is the difference between the input power and the conversion loss (that is dissipated as heat).
The value of the output voltage of a specific grid tie inverter is what will define to which utility grid it can be connected. In United States, most residential utility grids are rated 240 VAC, but that varies between countries. In Japan, for instance, you would need an ac inverter with output voltage rated at 110 VAC. Although the utility grid rates will vary from countries, the residential utility grids will only range between 110 and 240 VAC. Higher output voltages may only be used in industrial environment.
This is a figure that represents the highest efficiency a specific inverter can achieve. The majority of ac inverters present in the current market have peak efficiencies of over 95%. The higher the peak efficiency the better as the energy lost on the current conversion process is converted in heat. The rated output power can be calculated by dividing the rated input power by efficiency.
CEC Weighted Efficiency
This is a more realistic figure on what may be the overall efficiency levels for a determined ac inverter in a real world application. The guys at California Energy Commission, the organization behind the GoSolar website, are in charge of testing and publishing the CEC Weighted Efficiency on their website. This is a great way to ensure you will get a good inverter which stands within good efficiency levels.
IPxx and NEMA ratings
IPxx (Ingress Protection) and NEMA ratings are used similarly to classify and rate the level of protection a specific grid tie inverter has against foreign objects (first digit – IPXX / NEMA XX) and water (second digit – IPXX / NEMA XX).
Transformerless Grid Tied Inverters
The transformerless inverters are quite popular in UK, mostly because they are more efficient, lighter and cheaper than those with high or low frequency transformers. They were not so popular in US before 2005 since people were aware about the dangers in the dc to ac conversion made that way. However, today’s transformerless grid tie inverters are manufactured upon different new guidelines to guarantee no problems in the current conversion and now they are slowly gaining a little more popularity.
The MPPT (maximum power point tracker) included in grid tie inverters present on the market enables the ac inverters to extract a limited maximum amount of power from the source, that’s what turned this system so reliable. But since the MPPT specifications will vary from solar panels to wind turbines, custom inverters are built to work inside each application so make sure you will select a grid tie converter that will fit within your requirements.
If you’re unsure about what system to choose, go with an inverter with built-in transformer. They have great efficiency, are much more reliable and will do the job flawlessly.