Micro-inverter vs Wall mount central string inverter

There is a huge difference between these two systems. A Micro-inverter, works by taking the power produced by a single panel and converting that DC power to AC power for use in your home or, sending it back into the grid for a credit from CFE.  A wall mount central string inverter, takes the power produced from all panels and converts it all into AC power for use in your home or sent back into the grid for credit from CFE.

The difference may seem minor but, it is huge. From a homeowner perspective, you want to get as much power as possible from the system you have. There is no question that this will be achieved with the micro-inverter system.

Wall mount inverters, convert power in a far less efficient way than micro-inverters. Wall mount inverters take all the power from all the panels and convert it as a chunk into AC power. The problem is that, as this power is sent to the inverter, it is restricted to what is being produced by the lowest producing panel. Each panel can be reduced in the power it produces by a number of factors, including:

  • A difference in power output straight from the factory. While production standards are rigorous, each panel can have slight variations in the power it produces. With some panels this can be as much as 3%.

  • Shading. If one panel is in shade and its production is reduced by 50%, then the entire system is reduced by 50%

  • Cloud cover. As the big fluffy clouds pass overhead they will shade different panels as they pass by. Each time this happens, the entire system production is lowered, even if only one or two panels are affected.

  • Dirty panels. While panels generally get dirty as a group and production is reduced across all panels, there is also (especially at the beach) the opportunity for one panel to be dirtier than the others, from things like bird poop. Enough poop on one panel and your entire system will be reduced in production. Pelicans can poop a lot!

  • Heat. Excessive heat causes a problem known as “clipping”. Clipping is when a panel overheats and temporarily shuts down and resets and then comes back into operation. This happens very quickly but, panels heat up at different rates and each time a panel shuts down in this manner, it reduces the entire system while it resets and comes back into operation.

All these factors contribute to a lower efficiency, for your entire system. Combine two or three of these together and your system is substantially reduced in the power it produces.

The Micro-inverter system eliminates many of these issues and reduces the effects of the others on your total power production. Micro-inverters process the power from each panel on its own, not as a group. By doing this simple change in how the power is converted, there is a huge increase in the power produced. Here is how they work differently:

  • Because they convert the individual panel power the differences in panel output from the factory do not affect the entire system.

  • If one panel is in shade it is affected but the remaining panels are not.

  • It is the same for cloud cover, only the panel in shade is affected.

  • Dirty panels have their power processed individually. As an example: the bird poop, on a 10-panel wall mount system, covering 5% of one panel, will reduce the entire system performance by 5%. The same poop on a 10 panel micro-inverter system, will reduce total production by 0.5%. In fact, it would take 10 days of the poop remaining on the micro-inverter system panel to equal the power loss of the wall mount central inverter system in one day.

 

  • Excessive heat does affect the micro-inverter systems because, it is a panel effect not an inverter effect. However, the effect is localized to one panel and the production of the other panels is unaffected.

 

This is very important. Each time a panel clips with a wall mount inverter, the entire system is effectively clipped. As well, each panel does not clip at the same time. However, with the micro-inverter system, this effect is localized to one panel only. It is important to realize that the optimum temperature for the solar panels to work, is 25 degrees Celsius. The hotter the temperature, the more subject they are to clipping. Our system testing (done with 250-watt Perlight panels) has shown, up to a 10% drop in power production using a Kaco 3 kw wall mount central inverter, due solely to clipping.

It is possible to eliminate or reduce the affects noted above and still use a wall mount central string inverter, however to do so requires the addition of special equipment on each panel. These additions cost extra and in general, push the system price up beyond that of the micro-inverter system.

Our conclusion, from a power production standpoint, is that micro-inverters are the best way to ensure your system produces the most power possible for the best price.

You can download this document by clicking on the PDF file here

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