Inverters

Inverters are often referred to devices that convert DC into AC. Converters have a DC input and AC output. An inverter is either plugged in the socket or there is an outlet where you plug an electrical device in. Converters are for batteries and solar panels. For solar panels, there are fewer brands, but there is still a decent choice. Solar panels require a special converter because a solar panel power reaches its maximum power at a specific voltage (which varies continously), this is called MPP trackting. There are many converters on the market for 12V and 24 which you can connect to your battery, for example, on a camping site or in the car a 230 V AC supply, but they are not suitable for solar panels. These converters are often not intended to provide the network but have a connection for your electrical device to connect to.

This article is about inverters for solar panels which can be connected on the AC network (socket in the house). In English this is called a grid-tied inverter. It is not required to use these kinf of converters. You can also you a solar charger (the charger must be suitable for solar panels) to connect to a 12V or 24V battery to charge. In caravans for example it is much used. And personally I think it is a better solution. Converting 12V DC to 230V AC and then back through a transformer to 12V to make your ADSL modem work is very cumbersome and probably has heavy losses. The problem is that if you have a large number of panels on your roof then you will neeed a whole pile of  batteries. One of those submarine accus under the floor of my house that seems like a nice solution. But no joke, the grid will for this type of renewable energy function more and more like a battery and is really best suited for this. However, I would like in the future use of batteries. Especially for certain things (such as ADSL modem, doorbell and to establish LED lighting) in this way to feed. If you want to know more about this type of work look at the site of Matthijs Hajer. He has built a battery system and has much information on its website.

Inverters vary in price from around 50 Euro to over 100 Euro per 100Wp, so they are certainly not cheap and it pays to be a cheap looking. Some brands are Gridfit, Soladin and Steca. For my test project I purchaes a gridfit because it was the cheapest (but still expensive). I bought gridfit 250lv because according to spec with one of two panels (72 cells per panel) it can work. So for my pilot project I will build a "full" panel which I can connect to the grid and later I can still connect an additional panel so the inverter it is not entirely wasted. This iverter with cable is over 160 euros and that is not really cheap. I bought mine through marketplace but at a "business", thus guarantee and receipt. I also choose gridfit because there is a larger version available (2200) which comes at a reasonable price as well.

In some of the first solar systems on the market the OK4E converter was used quite frequently. These can break and were replaced by the manufacturer. Please note therefore that if you should decide to purchase it that in the past have they caused problems. I bought 3 used for a nice price to test with. The main reason that these converters break is heat. They are encapsulated in what appears to be resin. The main reason why they break down (at least that's what I've heard) is that when they are hot the resin (or whatever material it is) expands, but it has a different expansion than the components on the PCB which then break. The standard OK4E was permanently mounted to the panel. This concept was very attractive in the past. At that time the panels were screaming expensive and then you can buy a panel, plug it in the mains and ready. Because it is mounted to the panel, the OK4E has to be watertight, therefor the resin. Many problems arise when the panel was mounted on a converter box which had no cooling. It is thus important to cool the inverter.

There are also several people involved in the self designing and building of converters. Search for "grid tied inverter schematics" on google. I myself have thought about it but I find that too risky. An inverter is connected to the grid and must therefor work properly. I have enough knowledge to use schematics to order and solder the components, but not enough knowledge (or equipment) to the measure and check the result. The risk that the inverter will malfunction is too big and I do not want to take this risk.