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My Journey Toward Clean Transportation

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Ham operator here too... If you were not getting any random RF from the unit when it was making that noise, perhaps the noise wasn't electrical. It almost sounds mechanical to me. Any transformers or inductors that might be vibrating a loose shield, or a relay that might be chattering? I don't suppose the unit has a hard drive in it. That's the closest sound I can think of (random seeks).
All good ideas, but we have not been able to pin it down to anything. The tech from SolarTechAlabama came to my house and got on phone with SolarEdge and they examined the box with the covers off and ran diagnostics for a good hour, and nothing turned up. I send the video to them also. The sound has now gone away. Maybe they downloaded something to the inverter during their diagnostics session which fixed it, and didn't inform me (that never happens, does it?).... anyway the device continues to function well, achieving a peak output of 8.5 kw on occasion.

I would like to add some more panels. Since the inverter is capable of 10 kw (and that's the "nameplate" capacity for which I pay $50 per month to APCO), I think I could add another 6 panels safely. After observing the unit for a full year (to really learn its maximum output), I may do this, if SolarTechAL is willing to do it...
 
New information: I have been concerned that my big investment in solar power was going to end up increasing my cost of power due to the large "reserve capacity fee" imposed by Alabama Power (the fee is based on the theoretical maximum output power of the inverter); someone pointed out that I could still consider it a conservation effort, which is true. However, now that I am able to compare and compute actual costs, I have learned that there is actually a (small) true savings. Here is how it works out:

My total solar production for latest period (Jul 6 - Aug 6) was 1127 kWh.
Of that. APCO reported that I pushed 324 kWh to the grid, meaning that I used 1127 - 324 = 803 kWh onsite.
That is an actual savings of 803 kWh X $0.115/kWh = $92.34, plus APCO paid $8.88 for the power I pushed to the grid ($0.027/kWh, which is less than what they are supposed to be paying, but anyway); that totals $101.22, from which you subtract the $50 reserve capacity fee, for an actual net savings of $51.22. After the federal tax credit, the system cost $21,000, which means a payback of $21,000 / 51.22 = 409 months = 34 years (assuming this is the approximate monthly savings, and assuming the system works flawlessly with no maintenance costs for that time). Not that great, but since I was thinking the payback period was infinite, is better than I thought.

I still need to talk to them about what they pay for power I push to the grid. It started at 2.5 cents per kWh, and they sent me a letter saying they were going to increase this to 4 cents per kWh starting the beginning of June. What might have happened was that they didn't get around to changing the electric meter out (oddly, they have to change out the meter to support this change in what they pay for solar power) until the latter part of July, so I didn't get the new rate except for a portion of the month.

I consider that the reserve capacity fee forces solar power generators to subsidize the rates of everyone else, because it is far more than the grid capacity actually displaced by the solar system. This fee was created to cover the situation of co-generation in large companies where they generate most of their own power, but the power company still has to maintain capacity to supply them when the company's generator goes down. This is a much different situation than residential solar - why? Because in the case of solar power, the "nameplate capacity" (on which the fee is based) is never produced except for a few minutes per day when the sun is closely aligned with the solar panels (in my case, not even then); so normal electric usage well covers the household's portion of grid maintenance. This fee is just a fig leaf to cover the fact that the power company is opposed to residential solar. (They want to do it at grid scale, which saves consumers nothing). A cautionary tale - you can't know much power an inverter and given solar panel configuration will actually produce until it is installed and operating, and by that time, the fee is already determined. In my experience, solar panels don't produce their maximum output except for rare times when the sun is perfectly perpendicular to the panel, and the outside temperature is low (panel production is significantly reduced in hot weather). I'd recommend to subtract 10% to 20% from what those online solar potential calculators tell you before estimating any potential savings.
 
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New information: I have been concerned that my big investment in solar power was going to end up increasing my cost of power due to the large "reserve capacity fee" imposed by Alabama Power (the fee is based on the theoretical maximum output power of the inverter); someone pointed out that I could still consider it a conservation effort, which is true. However, now that I am able to compare and compute actual costs, I have learned that there is actually a (small) true savings. Here is how it works out:

My total solar production for latest period (Jul 6 - Aug 6) was 1127 kWh.
Of that. APCO reported that I pushed 324 kWh to the grid, meaning that I used 1127 - 324 = 803 kWh onsite.
That is an actual savings of 803 kWh X $0.115/kWh = $92.34, plus APCO paid $8.88 for the power I pushed to the grid ($0.027/kWh, which is less than what they are supposed to be paying, but anyway); that totals $101.22, from which you subtract the $50 reserve capacity fee, for an actual net savings of $51.22. After the federal tax credit, the system cost $21,000, which means a payback of $21,000 / 51.22 = 409 months = 34 years (assuming this is the approximate monthly savings, and assuming the system works flawlessly with no maintenance costs for that time). Not that great, but since I was thinking the payback period was infinite, is better than I thought.

I still need to talk to them about what they pay for power I push to the grid. It started at 2.5 cents per kWh, and they sent me a letter saying they were going to increase this to 4 cents per kWh starting the beginning of June. What might have happened was that they didn't get around to changing the electric meter out (oddly, they have to change out the meter to support this change in what they pay for solar power) until the latter part of July, so I didn't get the new rate except for a portion of the month.

I consider that the reserve capacity fee forces solar power generators to subsidize the rates of everyone else, because it is far more than the grid capacity actually displaced by the solar system. This fee was created to cover the situation of co-generation in large companies where they generate most of their own power, but the power company still has to maintain capacity to supply them when the company's generator goes down. This is a much different situation than residential solar - why? Because in the case of solar power, the "nameplate capacity" (on which the fee is based) is never produced except for a few minutes per day when the sun is closely aligned with the solar panels (in my case, not even then); so normal electric usage well covers the household's portion of grid maintenance. This fee is just a fig leaf to cover the fact that the power company is opposed to residential solar. (They want to do it at grid scale, which saves consumers nothing). A cautionary tale - you can't know much power an inverter and given solar panel configuration will actually produce until it is installed and operating, and by that time, the fee is already determined. In my experience, solar panels don't produce their maximum output except for rare times when the sun is perfectly perpendicular to the panel, and the outside temperature is low (panel production is significantly reduced in hot weather). I'd recommend to subtract 10% to 20% from what those online solar potential calculators tell you before estimating any potential savings.
The Southern Environmental Law Center has filed a formal complaint with the Public Service Commission about the Reserve Capacity fee. The law firm Ragsdale LLC has now also become involved. Contact them if you want to help, maybe this could be made into a class action lawsuit if PSC is not responsive.