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If inverters were smaller and more efficient, they could be placed on a per-panel basis ("string inverters" or "micro inverters") for significantly better perfo

If inverters were smaller and more efficient, they could be placed on a per-panel basis ("string inverters" or "micro inverters") for significantly better performance, particularly when some of the panels are shaded. See this paper: http://tec.appstate.edu/sites/tec.appstate.edu/files/micro%20vs%20central%20inverters%20shaded%20vs%20unshaded%20dave%20lee%20raichle.pdf http://tec.appstate.edu/sites/tec.appstate.edu/files/micro%2... (EDIT: The above point is valid, but I was wrong about cable sizes improving when using micro inverters!)

eck 12y ago
> Panels commonly run at 12V (or some low multiple thereof), That is absolutely not true. Generally speaking nontrivial sized photovoltaic systems are designed with panels in series such that the voltage stays just barely within the 600v rating on the wire. For example, grid tie inverter, MPPT rated 195-550v: http://pdf.wholesalesolar.com/inverter%20pdf%20folder/Schneider-Conext-NA-range.pdf http://pdf.wholesalesolar.com/inverter%20pdf%20folder/Schnei...
- sparkman55 12y ago
  You're right, panels are generally ganged together in battery to avoid the 'thick copper cable' problem. However, the individual panel assemblies do run at lower voltages (individual cells run at the band gap of the semiconductor, 1 or 2 V). It should be noted that placing the panels in series has a significant effect on panel performance when some of the panels are shaded (The entire string outputs at the rate of the shaded panel), so it would be much better to place panels in parallel when possible.
  - marcosdumay 12y ago
    I still think that the best alternative for putting the pannels in parallel is by using DC/DC converter on then, and never thinking about 60Hz AC.
  - alexeyk 12y ago
    Why not just shortcut the shaded panels dynamically, reducing the overall resistance?
Yaggo 12y ago
I guess you know that, but just to clarify, there already exist micro-inverters small enough to be installed behind the panel. (E.g. http://enphase.com/m250/ http://enphase.com/m250/)
lutorm 12y ago
We're in the process of installing PV right now, so I've been looking into this recently. The micro inverter solution is better when there's partial shading, but the micro inverters do not have higher efficiency than the string inverters. If anything, the assertion seems to be that they actually will have lower efficiency because they generally operate at higher temperature, being up on the roof. And contrary to the idea about string inverters needing thicker wires, because the AC wiring runs at 240V but the PV DC cabling typically runs at 400-600V, you need larger wires for the micro inverter solution. (But in either cases, resistive losses in the wires are pretty negligible, tenths of a percent in our case.)

eck 12y ago

> Panels commonly run at 12V (or some low multiple thereof), That is absolutely not true. Generally speaking nontrivial sized photovoltaic systems are designed with panels in series such that the voltage stays just barely within the 600v rating on the wire. For example, grid tie inverter, MPPT rated 195-550v: http://pdf.wholesalesolar.com/inverter%20pdf%20folder/Schneider-Conext-NA-range.pdf http://pdf.wholesalesolar.com/inverter%20pdf%20folder/Schnei...

sparkman55 12y ago
You're right, panels are generally ganged together in battery to avoid the 'thick copper cable' problem. However, the individual panel assemblies do run at lower voltages (individual cells run at the band gap of the semiconductor, 1 or 2 V). It should be noted that placing the panels in series has a significant effect on panel performance when some of the panels are shaded (The entire string outputs at the rate of the shaded panel), so it would be much better to place panels in parallel when possible.
- marcosdumay 12y ago
  I still think that the best alternative for putting the pannels in parallel is by using DC/DC converter on then, and never thinking about 60Hz AC.
- alexeyk 12y ago
  Why not just shortcut the shaded panels dynamically, reducing the overall resistance?

Yaggo 12y ago

I guess you know that, but just to clarify, there already exist micro-inverters small enough to be installed behind the panel. (E.g. http://enphase.com/m250/ http://enphase.com/m250/)

lutorm 12y ago

We're in the process of installing PV right now, so I've been looking into this recently. The micro inverter solution is better when there's partial shading, but the micro inverters do not have higher efficiency than the string inverters. If anything, the assertion seems to be that they actually will have lower efficiency because they generally operate at higher temperature, being up on the roof. And contrary to the idea about string inverters needing thicker wires, because the AC wiring runs at 240V but the PV DC cabling typically runs at 400-600V, you need larger wires for the micro inverter solution. (But in either cases, resistive losses in the wires are pretty negligible, tenths of a percent in our case.)