Basic Knowledge About Solar Power Systems, Inverters, and Solar Panels

The electrical energy generated from solar panels is direct current (DC). To be usable in households, a device is needed that converts the current and handles load compensation. An inverter is an electronic device that converts direct current to alternating current, or vice versa, to match the requirements of electrical appliances. In this article, I will only go into detail about the type of inverter used to convert electricity for home use.

Depending on the type of solar power system (grid-tied, off-grid, or hybrid), different types of inverters are used: On-Grid Inverter, Off-Grid Inverter, and Hybrid Inverter.

What is the difference between an On-Grid Inverter (load-following) and a Hybrid Inverter (with batteries)?

A grid-tied solar power system uses an On-Grid inverter to synchronize with the national grid, so the grid must be present for the system to operate. In addition, during a power outage, the system will automatically shut down to ensure the safety of personnel performing maintenance/repairs on the grid. Meanwhile, a grid-tied solar system with energy storage that uses a Hybrid Inverter will operate continuously: when the grid is available, the system works like a grid-tied system; when the grid fails, the system operates like an off-grid system.

There is also another device in the system called a meter, which takes on the task of distributing DC power so as to prevent electricity from the solar system from being fed back into the grid. At the time I am writing this, EVN no longer prohibits feeding power back into the grid, but before that it was mandatory to install this device or you would be fined.

I will also have a more detailed article on which type of inverter to choose, or on popular inverter brands. Because depending on your needs, you should invest differently, as the cost of an inverter that supports hybrid functionality is much higher and its components are also more complex to repair.

Solar panels come in many sizes and capacities – when should you choose which type?

On the market there are many brands, sizes, and power ratings. The panel technologies also vary. Besides the common sizes as shown in the illustration, there are much smaller panels as well; however, I do not recommend buying panels under 300W, as it relates to the total system capacity.

For example, if you install 10 panels of 560W each and one stormy day hail breaks one panel, your whole system temporarily stops working. If at that point you remove the broken panel from the series string, the total capacity will drop a bit, but if you do not understand this and you go buy a 450W panel to replace it in the string, then the entire system will be limited to a maximum capacity of 450W. That is the simple way to understand it.

“There are many types of solar panels imported from China at very cheap prices on the market, even though they are labeled Technology in Germany, in USA, in Japan… but most of them are assembled from rejected cells (low-grade cells) with high crack rates and non-uniformity when scanned by EL testing. After being used for a period from 1 to a few years, they are prone to voltage loss and thus their lifespan quickly decreases because the internal cracks expand under heat (since the cells in a solar panel are connected in series, so if one cell fails, the whole panel is considered failed).”

So it does not mean that the bigger the panel, the better. You should choose panels based on the actual available installation area and your potential for future expansion. With smaller panels, if one fails and you need to replace the whole panel, the replacement cost is also lower.

Solar panels also come in many types with different technologies

High-end products currently, such as the brand I am using, LONGI, use mono cells and offer performance warranties of around 30 years. Most other brands also primarily use this technology; you can recognize it when the panel is black with a glossy surface. Besides that, there are many other aspects related to surface treatment, aluminum frame quality, heat dissipation, etc., which affect the durability of the panel. For these, the best approach is simply to pay attention to the seller’s warranty policy when choosing, so you do not have to worry too much about the underlying manufacturing technologies.

Storage batteries come in many types and with many different output voltages – which should you choose?

Storage batteries also come in many types. For me, daytime electricity usage is more significant, while at night, when it is cooler, I hardly ever turn on the air conditioner, so investing in a storage battery system is not yet necessary. Battery storage technology has not yet fully matured to be commercialized at a reasonable cost. At present, the best type is lithium batteries; people no longer use lead-acid batteries for storage like before.

You can also start with a "grass" solar power system to get familiar with things and keep your initial investment reasonable, including the panels. I have never tried this type of system because I feel it is somewhat "unsafe" for my household usage needs.

Conclusion

The field of solar energy requires a lot of knowledge because the market is very fragmented and prices are very diverse. From my experience, prices have now stabilized relatively well; investing in a 5–6 kWh system will cost around 35–40 million VND if you buy the components yourself and install them. It is fairly easy to install as long as you know a bit about electricity and how to use a drill.

I hope this article provides enough basic information for everyone to start learning about this topic. If you have any questions, feel free to leave a comment so we can discuss further.