The top-left panel are shaded, just little bit, What will happen ? just guess ?

Yea, lost 1/2 energy. Technically, solar panel is not working like that..


(1) 20 cells are in a string, and

(2) 3 strings in a panel (that is why there are three by-pass diode)


If half of one cell is shadowing, the cell will generate much lower current and/or voltage drop.

those string will makes much weak power such as 10-20% (power base on the diffusion light)

The other two strings will generate the power normally, so, it will generate 100%.


100% * 2 strings * 2/3 = 66.7%

10% * 1 strings * 1/3 = 33.3%


so, finally, the power generation should be around 70%, BUT, Enphase inverter has a problem in MPPT.

They track the lower peak instead higher peak in this situation. and generate 3.3% * 3 = 10% intead 70%.

by the result, just 50% of power can be havested in this situation.


This kind of problem is happening with a full sun-light condition also. when three string show full power,

but, there are some cell mis-matching. it will generate 2-3% flatten peak points near highest power point.

Enphase inverter is detecting the lowest peak one, instead highest one also. and, it can reduce the power by 2-3% also.


You can observe the discontinual highest power peak when shutting by cloude. because, when shuttering, this inver can find the highest point, but by time, keep going down, and stay at the lowest-peak power again.


Due to the tracking problem, Enphase Micro-inverter can not havest 100% enery, if they fix it.

The power yeild can be increased 1-2% for the good sun-light condition, and by 5-30% for the shading condition.







If one cell has shaded completely, Panel voltage will drop 2/3 of normal voltage, will out-of-range of Enphase Inverter, and will not working. Even string/optimizer can handle it. BUT, Enphase MI can not handle it. Don't be fooled.


Top-right panel : 1/2 of one cell has shaded, that is why it can show 50%. if the cell has shaded completely, it will show 10%.


* Good Article to Understand Shading Model






Enphase IQ7+ minimum Vmp is 27V, 

when one sub-group is shaded, the voltage become 2/3 x 33 = 22V. 

so, IQ7+ can not track the maximum point, it is why IQ7+ can not handle correctly



First, I do not know, it has been caused by an Inverter or a Panel,

but, I am suspecting that the problem is happening by The Inverter.


Because I have verified with MPPT charger with same panel, and similar condition,

and, the power generating is +1/3 and shade two cells, and +2/3 when shade one cell.


Everybody know the shadow can reduce the power from Solar Panel,


there are 3~4 strings in a panel, if shading a string, the other strings can operated normally.

What will happen there is very small shadow 1-2 cells in a 60 cells panel ?

Yes, it can reduce the production to 30~60%,


Look at the detail production yield at my house,

Sunlight is coming from Right-Top side and, Dommer at Right Hand Side is making a shadow on Panel #6,


#1, at 09:19AM, half of two cells (right-top side, two cells in horisontal, not a panel) are shade, power production is just 10% via the other panel.

#2, at 10:23AM, very thin shade on a cell of panel (around 10~20% on right-top side of cell, not panel), production is 80% via the other panel.

#3, at 10:29AM, no shades, same power gain via the other panel.


In the solar panel test with MPPT charger,  the minimum power is aroudn 60% in #1, 90% in #2

It makes me suspect There is a critical problem in Enphase IQ inverter.


Note. Enphase IQ 7+, LG350N1C-V5










Finally, I have got PTO, and my solar system start to work ~