Number crunching

Congrats on recouping the cost...

Our solar panels, 35 of them on our roof, are not generating any electricity. The installation was completed three weeks ago. And the transformer and wire connecting to the grid was also upgraded on the same day. It was a quite a sight to watch three bucket trucks working in tandem to remove and replace the transformer on the pole just across from our long driveway. Everything is ready, but I still have not heard from our utility to be able to energize the panel. Only if I can cat the red tape... sigh

 

Oh?
Betcha they are.....

Considering how transformers work and how many utility people get to find out that service panel interlocks often DO NOT - it's sorta understandable how there might be a little red tape.
ONE watt of electricity is equal to one joule of work performed per second.

Whoever said "it's not the voltage that kills you" never worked in a post storm recovery period.

I'm about as far away from the muscle end of the phone biz as you can get and still be in a union and I'm looking at a foreign voltage detector sitting on top of my Lexmark printer as I tap this.

Patience.

I can't wait until @bwilson4web dumps his Tesla stock and shows us HIS crunchy numbers in this thread.

 

Nope. The system is turned off with the law required Rapid Kill Switch in OFF position. I don't know exactly how the PV panel works in absence of closed circuit to let the electrons flow. The panels exposed to the sunlight maybe capturing the electrons (i.e. generating), but no flow of electricity until the switch is turned ON.

 

Actually, you're right.
The PVs are generating voltage - like water pressure in a pipe.
You're just not allowed to let it out.

That's why when I retire my plans are to re-roof the pile of bricks and get some PV panels.....either ground or roof mounted.
I live in storm country and so I might rack 'em on the ground.
My intentions are to also have as large a spit-can (LiFePO4 bank) as my budget will allow and an interlock - already mandated when attaching my genset to the house.
I can dump amps in the can and pull them back out again all I want to - as long as I'm not grid-tied - which I will be eventually because the utilities are crunching numbers of their own.
Since I have a daily access fee my CoOp keeps their lights on whether I use their electricity or mine.
The only 'red tape' I anticipate that I will be dealing with will mark the (+) polarity of the wires in the system.

The only rapid kill switch that I will have is called a trigger.
Not required by law - BUT allowed...

 

After Net-Metering Agreement application for our simple grid-tied solar system was submitted, our utility came back with a "conditional approval" of the system. The approval was contingent on the transformer and wiring upreared (from the the sidewall of our house to the transformer on the pole across from our driveway that connects to the rest of the grid) to be able to handle the amount of proposed total electricity generated by the PV panels. We were given a warning on potential long lead time for this upgrade from 6 to 12months. Yep, that meant, I may have to wait 1 year before I can turn on the solar panel system even though the system is all installed and paid for.

I was contemplating to install "off-grid" capability on our solar system with battery back up to allow it to be used in absence of grid power. And apply to the utility for the "no-export" grid-tied system. If pursued and approved, then I would have a solar system that is tied to the grid, but not exporting any juice, but can be used to generate electricity for "in house" use only very similar to off-grid system without upgrading the transformer and wires. With this system setup, when there is no sun and no battery cap left, I would just use grid supplied electricity. But if the solar panel electricity generation exceed the battery capacity and "in house" use, then excess electricity would be simply lost. All of this would have add substantial cost, but at least I could start using the solar system sooner. So, I thought.

But to everyone's surprise, the utility came out on the same day our solar company completed the panel installation. They finished the transformer and wiring upgrade while the solar company electrician worked on the service panel upgrade to 200A. I ditched the expensive battery back-up system upgrade hoping to start using the solar panel soon on the net-metering agreement I sighed with the Utility months ago. But after 3 weeks, I am still waiting the Utility to give us the final GO.

 

Each PV cell is generating current like mad, internally. But an inherent unavoidable element of the cell's structure is a forward-biased diode. Whatever current isn't pulled out by the wires, is consumed by the internal diode. This diode forward current, dropped across this diode's voltage, does heat the cell. But simply absorbing sunlight also warms the cell, for a net wash.

How much current is generated internally? Check the module's I(SC) spec (assuming a single series cell string). What is that internal diode's forward voltage drop? Divide the module's V(OC) by the number of cells in series.

I'm so glad to be served by a solar-friendly utility, in a permit-friendly state. Energize it when I'm ready, call both the code/permit and utility inspection departments promptly, they'll get out when they can. While waiting, I could leave tit energized. LNI inspection happened the next day, utility took about two weeks. Total missed production time was about 5 minutes, while the utility inspector removed my temporary meter and put in his official meter.

 

that description does not sound like anything I'd have expected

 

But it does model the V-I characteristics of the cell.

 

Ok, I think I get it.

I'm still squinting at the "diode forward current, dropped across this diode's voltage, does heat the cell. But simply absorbing sunlight also warms the cell, for a net wash" part. It's hard to see how "this warms the cell, and also that warms the cell" works out to a net wash.

Maybe it's easier to start with the executive-summary 30,000-foot view, namely that when open-circuited, no power is electrically leaving the module, so all the power of the incident sunlight (that hasn't been reflected or passed out the bottom) has been turned into heat in the module, whatever the details of how that happened.

Then the closer view of the details would say that some of the photons were captured and turned into separated charge carriers, instead of into heat ... but then those passed through the forward-biased junction and made heat anyway, and that's the "net wash" part, so the resulting heating of the module is the same as the 30,000-foot view said it would be.

 

Throw the switch!
FREE the holes!!

 

For most people, all they need to know is that to treat a solar as a high power battery, and not to touch the part where the electricity comes out of.

 

A long wait (3+ months) is over finally. Our roof top PV panel installation was completed in September... But the utility had to install new cable to meet the spec to grant the operation. It took weekly checking, but finally, it happened. The field crew came last week and replaced the cable connecting from the brand new larger transformer to our house. The process took less than 1 hour. And after that I had to wait another week for them to process the paperwork. I just got an email from our utility granting the Approval to Operate Distributed Generation System.

I have the app recording the generation now. I don't expect much electricity generation for next few months with short winter days, but will give me a good idea of what to expect in winter months. BTW, the utility already told me that it will take a few billing cycle to activate the NET meter billing to see the credit on my bill. But if I understand it correctly, even if there is no surplus to export to the grid to be counted for the billing credit, whatever generated on the roof will be first used in-house. So, it will lower my electric usage from the grid, thus saves money that way. Will have to see how that will show on our next bill.

 

So your generated electricity can flow back into the wires? Interesting. (appreciate this is home solar 101 ).

 

True of most home solar systems that are tied to the grid.

 

That's the idea of net metering. Whatever the surplus generated electricity not used on-site will flow back to the grid. The meter count the negative flow as generation and credit my electric bill at 1:1 retail price (including distribution cost) in our state. Chances are that I will not see that happening until at least spring time around here.

I really wanted off grid system, but for that to work, I need a huge battery storage that are way too expensive. And even with a huge battery storage, not enough electricity can be generated to cover the usage during short winter days. And during summer too much electricity can be generated that can not be stored in battery. I had to settle for the grid-tied system... the caveat is that solar system only works when the grid is on. Does not work during power outage even if sun is shining. And net metering is controlled by the local utility, so I have to go by what they say in terms of operational specs and approval to operate. Thus a long waiting period after the completion of the PV panels installation.

 

I am still holding onto my community solar contract for now. I figured at least untill the daylight get longer, I will buy clean solar energy at discount.

My first day of PV operation generated whooping 1.8kWh of electricity. Yeah, from a 16kW system.
It was cloudy and I did not turn it on until noon and had less than 4 hours of daylight.

It will be interesting to see how quickly (or slowly) my PV is going to pay back. On the paper, I estimated 7-10 years pay-back period at the time I signed back in May last year. But since then our electric rate has dropped and more cost for installation added. I maybe lucky if it gets paid back before I die.

 

Produced 12.9kWh yesterday, and that was starting the day mostly covered with snow. I'll see 20+kWh with sunny days. This is a 5.2kW system