[stevehull]

edited 3/1 2:30 pm central time

Ben,

Simply superb video. Clear, good visuals added in and understandable. But as the former university professor . . . . . let me suggest a few things. My former grad students complained all the time, but now thank me!

Needs better presentation of system power. You quote a 24 panel system, each panel of 260 watts, as a 6 kW system. Yes it is, but a quick discussion of name plate, STC (lab conditions) vs. PTC (expected reality would be helpful).

Remember that the PTC is ~ 90% of STC so your panels only put out 234 watts in real life conditions. Dust, snow, etc. further reduces this.


Why Enphase? You might explain the reasons you choose this system (as have I with many installations).

I feel that Enphase simply has the most reliable, bullet proof system out there. In all the systems I have done, only one return and it came with a new replacement with postage paid return. Others claim they are cheaper, but don't include the costs for the home monitoring in their comparisons.


Grounding. This discussion is completely absent and is critical.

Typical NEC code calls for a solid copper wire (8G?) from one point to a single 8 foot ground rod. It is code, but inadequate. I FAR prefer to ground to each rail and to use #4 braided copper to two 8 foot copper clad rods about 6 feet apart. This ground wire needs to make "soft turns" with NO sharp bends. Try to get the straightest path to the ground rods (choose their location carefully) from the roof. Sadly, this does not always "look good", but you want the absolute least resistance pathway to ground.

Here is another trick. On each 240 V wire input to the circuit breaker, coil up your wire in a loop of ~ 6 inches in diameter, maybe 10-12 turns. Tie this together with tape. This is an "rf choke" and for the cost of maybe 3 feet of extra wire, you virtually block all high frequency pulses into your home system. Lightening is a high frequency pulse. The choke does nothing, zilch at 60 Hz, so there is little money (a bit of time) to do this. The combo of the two above provide a very low impedance path to ground and a high impedance lightening block into your home and grid. Lightening is your systems enemy.


Choice of panel power to microinverter power. This too is absent and I would have chosen the less expensive Enphase M215 (which pumps out 230 W) vs the more expensive M250 (which is limited to 250 watts). Your panels, with a STC rating of 260 will only put out some 90% or about 234 watts and would be a far better match for the M215. Yes, they guarantee 215 W, but the hardware revisions done over the last few years have increased the power output to 230 W. Rather than go through the expensive certification process, they stick with the "old" M215 nomenclature and power output guarantee.

I prefer to have clipping. Clipping refers to the power output of the microinverter vs the power of the panel. For example, I put in a lot of M215's with 260 W panels. On some days,
the normal parabolic peak power output, seen at solar noon, is replaced with a flat line. This is "clipping". This is far preferred to have a system the other way where the panels never get to the inverter power (your case). Enphase has a big write up on this as a system with ~10% clipping outproduces by 10-20% more power than a system perfectly matched. On a M250 a perfect match would be a 280 W panel (90% of 280 STC = 252 W PTC). With a M250, I would choose a panel of ~ 300-310 W. On the other hand, you got a good deal on your 260 W panels. Note renvu.com has 300 W panels for about the same price per W.


Right now (March 1, 2017) renvu.com has Enphase M215's at $93 each, but they sell them all the time for $80 (cost per W ~ $0.40). Just call and "dicker". Costs of microinverters are going down fast, as are panels, but less so on racking. These prices are of of March 1, 2017 and I expect Enphase system 6 microinverter cost/W at $0.30 or less by the end of this year.

Soon, the M215's will be phased out, but for right now they are the best bang for the buck combined with 260 W panels - IF you have lots of roof area. The new IE6 microinvers will be sold for for less than the M215's by year end. Then, I expect the M250's to be selling at less than the new IE6 microinverters by year end ~ $0.05 - $0.10 less. For right now, if roof area is an issue then think of the S280 inverter with 320 W panels. More expensive, but if you don't have the roof area, and you need power, then this is the solution.


Lastly, I would discuss better how to do the mid string feeds. The mid string junction is something that you will never have to service. And if you do, it is simple to raise up one of the panels (especially on your small system). If you put the mid string disconnects in the middle of the string, it is easy to bring each string through the roof and have your junction box (with circuit breakers) up there. THEN bring one heavy cable out to the exterior near your breaker box for the manual disconnect. This also looks a LOT neater on the roof as there is less "clutter". I hate roof clutter and get frustrated when I see poorly executed and installed solar systems.

I too love the Midnight Solar PV6 disconnect switch that integrates turning breakers on and off. But several power companies I have worked with INSISTED that a manual turn off box HAD to be used. I physically showed then the Midnight Solar switch and they just shook their heads NO. You just can't change stupid, but we all know that sharing that just doesn't help.

Overall your video is so superb that a lot of people will watch it and I wanted to give you an opportunity to edit just a few parts.

I hope that my critique will be understood in that light and not a criticism of your excellent construction, roofing and planning.

Best regards,


Steve