I shopped around and bought most things from different online sellers, panels and inverter are new in box, but were discounted due to being what I call (last years models), The panels were 315w and they make slightly larger wattage one now, the inverter was made in Nov 2015 and the newer one is a little different, both from Ebay sellers. Iron Ridge racking was from Webosolar. I bought things as I found good deals on them, over the winter and stored everything until spring.
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And people say solar is expensive....
- Thread starter MRPLUGIN
- Start date
I shopped around and bought most things from different online sellers, panels and inverter are new in box, but were discounted due to being what I call (last years models), The panels were 315w and they make slightly larger wattage one now, the inverter was made in Nov 2015 and the newer one is a little different, both from Ebay sellers. Iron Ridge racking was from Webosolar. I bought things as I found good deals on them, over the winter and stored everything until spring.
nwdiver
Well-Known Member
Not nearly as much of a shade threat as the pipe in the OPs photo but I thought this was an interesting demonstration of how effective bypass diodes are and how optimizers are generally not worth the extra expense... (One of these 15 panels has an optimizer... no way to tell which one)
There are two vents that cast a shadow on the array in the early morning and late evening for a few weeks in the summer when the sun rises and sets to the north of the array. This shadow can be seen on the output of the panels but the decreased output of the panels has no effect on unshaded panels thanks to the bypass diodes. Each string is on an independent MPPT (String of 7 top & String of 8 bottom). If the strings were in parallel the shaded panels WOULD lower the output of the entire array due to forcing other panels off their MPP.
There are two vents that cast a shadow on the array in the early morning and late evening for a few weeks in the summer when the sun rises and sets to the north of the array. This shadow can be seen on the output of the panels but the decreased output of the panels has no effect on unshaded panels thanks to the bypass diodes. Each string is on an independent MPPT (String of 7 top & String of 8 bottom). If the strings were in parallel the shaded panels WOULD lower the output of the entire array due to forcing other panels off their MPP.
nwdiver
Well-Known Member
The photo and output weren't taken at the same time. Since the pipes are north of the array the shade is gone shortly after the output snapshot I posted. I might do an experiment at some point around noon and intentionally shade one panel to really show the effect.
I learned about bypass diodes the hard way. My first array was built using laminates which didn't have bypass diodes since they were unfinished modules and the J-boxes were never installed. As the sun set one cell became shaded and >1kW from the other panels was dumped into the cell.... the cell temperature quickly rose. I didn't measure it but it was hot enough that I couldn't leave my hand on it for more than a few seconds (probably >150F) and this was in late evening not peak sun. Without bypass diodes ANY shade would be a HUGE fire risk.
If each string is on a separate tracker there's really no benefit to having an optimizer. Any shaded section will at most cutout 1/3 of the panel. The bypass diodes divide the module length-wise so shading a panel from top to bottom actually reduces output less than shading from left to right...
SageBrush
REJECT Fascism
Am I wrong in thinking that two strings of equal length would be half the shading effect of a single string (presuming shade on one panel) ?
nwdiver
Well-Known Member
Yes. If part of one panel is shaded then the parallel string with no shade would be forced to lower its voltage to match the shaded string causing a drop in output, the output of the entire array is reduced. The ideal arrangement is for each string to be independent which is how the new SMA inverters are designed.
For example; If the array I posted was 2 strings of 8 panels in parallel then the output voltage of the bottom string would drop by ~20v reducing the output of the array another ~60w or so even though there is no shade on the bottom row.
An array in which each string is on an independent tracker is just as shade tolerant as an array with optimizers or micros.
SageBrush
REJECT Fascism
nwdiver
Well-Known Member
For the above example yes. If you have 2 strings of 8 and 2 panels in 1 string become partially shaded as they did in the output snapshot I posted the output of the shaded string drops by ~20v. If the strings are in parallel the voltage of the unshaded string would need to drop to match which would result in a nearly proportional drop in power. Current would increase slightly and mitigate the loss but the output of the unshaded string would still be effected. This is why independent trackers are so beneficial. Shade on one string won't effect other strings and bypass diodes simply shunt current around shaded areas so unshaded sections of a string are also unaffected.
My old-school inverter experiences this everyday in the summer. There's a tree to the north of my house that will shade the back row of panels in the summer. Once those panels are shaded the output of the ENTIRE array drops by >50v so shading 3 panels reduces the output of the other 39 that still have relatively full sun. If each string was on its own tracker then shading 3 panels would only affect 3 panels.
I think the confusion arrises from the idea that parallel strings are better because the second string provides another path for current flow... but that alternative path already exists in 1 string via bypass diodes...
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Meter has been installed for about four days. Sun has been good and I am averaging 45kw per day, not bad considering the system is shaded by a tree on the south west corner by about 6:30. Only time will tell, but I am happy for now.
Looking great! Down in Utah County and installed my own system as well. Solar Edge, Silfab, and SnapNRack facing almost directly West. Saved myself $10k doing the labor on my own. 7.2kw system, but have some shading in the afternoons, so the fact that I get 42kWh per day so far this month is great if your system is facing south and has much less shading.
Well meter was installed on 6/1 mid day, Have not seen any bills as of yet, but the system as of yesterday 6/30 , had produced 1.33mwh , I sent 951kwh to the grid and had to use 550kwh from the grid. I guess I need to work on a battery set up and do better at charging the cars during the productions hours. Even though I am producing clean energy for other people to use near me, I would like to use more of it myself.
Chris
Chris
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nwdiver
Well-Known Member
Jesus... do you have commercial power? Most residential drops cap out at ~15kW to export...
nwdiver
Well-Known Member
Could it be that writing kW instead of kWh is causing some confusion?
nwdiver
Well-Known Member
Ah... that makes sense... 951kWh is about right... sometimes I think we need kWp and kWh... just stop using kW entirely...
The downside would be that phonetically 'power' and 'hour' sound similar
Utah residents using Rocky Mountain Power are capped at 25 kW systems. There is no limit to how much power you can export, but on your March bill if you have exported more than you used they just take it and reset you back to 0. No payments, no credits, etc.
nwdiver
Well-Known Member
Depends on the service drop. ~200A is typically limited to 15kW. Need 400A for 25kW.
