I am going solar

Over production is caused by 'cooling'. Panels loose efficiency, the hotter they get. So for a short time as the sun begins to come out from behind a cloud - bam - cooled panel with bright sun. There's a name for the phenomena but I don't recall right now what that is.
Our system is rated at 7.1kW's (AC) - but during the partly cloudy day situation - that sun coming from behind clouds scenario will yield a few seconds of as much as 8.4kW's.
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NO, I was referring to a plain 2500KW overproduction..............I never stated any KH per hour production

 

Usb,
I thought about your tax credit a little more.
If your bill splits out the work done as prep for PV from the other work I think you would be safe.

 

Just curious, how's your system holding up? Is it covering your entire usage? I'm trying my best to make that happen but the winter was rough for us and we saved money, but it wasn't that impactful. I'm looking forward to the spring and summer and hopefully earning credits versus still paying for electricity...

 

I saw this one partly cloudy February day: the peak output was 6096W for the day. Since then, on very sunny days I have not ever seen that peak again. Yet.

The problem is, you did (and I assume paid for) this in 2014. You can't claim 2014 expenses towards the 30% federal credit in TY 2015.

 

As I understand, the system has to be operational before you can claim. Someone who told me this could be wrong....But we were trying to get the people to finish it before the winter kicked it and would force us to next year.

 

That's absolutely correct. System must be operationalized for the credit. For example, we contracted in October 2014, installation in Feb '15 so tax credit claim will be 2015. Even though the contract date was October, and even though we paid a $1,000 deposit in CY 2014.

 

commissioned in 2008 it is still outputting at its specified rating. It's output covers all of our home electricity usage, including an average of 6kWh per day which covers our 12k EV miles per year for the last 48 months. By recently enacted legislation (past 3years) our utility now has to pay us for our surplus kWh's ... a paltry 2.9¢/kWh. Prior to that we didn't even get a thankyou.
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What state ? Here we don't get paid by utilities, we get credited at the exact same charge though

 

Did you claim the deposit ?

IIRC, the standard rating of panels is based on 800 watt perpendicular radiation. In nature it is often higher, and funny things can happen at the edge of clouds. I think the effect is prism like, but I am not sure.

 

HMMMMM, interesting notion, does that mean 800 watts w/in a given area, such as in a square inch or square foot or centimeter or meter?
EDIT:
Aaahhhh... ok - I found this on one of a few solar energy websites;

..... which makes sense, as the latest & greatest residential panels run about a 20% efficiency. That means 80% of the heat energy is not captured - while 20% of the potential PV electricity is captured.... then maybe another 2%-4% is lost converting to AC power.
So - that'd mean a 1.5 meter square of new/"high efficiency" panels would potentially yield appx. 300 watts Peak - if it were perpendicular to the sun ... at the equator, on a 70 degree Fahrenheit day - during 12 noon summer. Of course, older/less efficient panels - coupled with a much lower azimuth here in North America would drop off that amount of watts a good amount. And ... non-summer hours lower azimuth .. Plus clouds ... Plus morning hours' lower azimuth ... plus evening hours' lower azimuth ... suddenly you realize why your "theoretical" 10kW watt DC system is lucky to yield 6kW for a few hours of each day.
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Prior post deleted ..

I was wrong -- both of the standard measurements (STC and PTC) are based off 1000 watts per m*m.

This is a good synopsis:

HARMONY FARM SOLAR presents MAILING: P.O. Box 460 Graton, CA 95444 FAX (707) 823-1734 Email: [email protected]

Grid-Tied Photovoltaic System Sizing Solar Energy

The intensity (or power) of sunshine is called irradiance and is measured in watts per square meter (W/m2). The amount of solar radiant power that hits the earth’s outer atmosphere is a nearly constant 1,360 W/m2. On a clear day, approximately 70% of this radiation makes it through to the earth’s surface. The southwestern United States frequently exceeds 1,000 W/m2 at ground level. In some mountain areas, readings of over 1,200 W/m2 are common. Average values are generally lower elsewhere, but can reach instantaneous values as high as 1,500 W/m2 when puffy clouds are present to focus the sunshine. The amount of solar energy received on a given area over time is measured in kilowatt-hours per square meter (kWhr/m2) and is called insolation (one kilowatt equals 1,000 watts). Insolation (energy) differs from irradiance (power) because of the inclusion of time. Solar Module Output Power Photovoltaic (PV) modules (and systems) are called out and sized using wattage determined under Standard Test Conditions (STC). This is the manufacturer’s specified nameplate wattage and represents module output as measured under very controlled factory conditions. Specifically, STC are 1,000 W/m2 solar irradiance and 25 deg.C module temperature. STC wattage provides a good relative comparison between module and system sizes, but not a good real world output measure. PVUSA (an industry consortium) developed another set of solar module test conditions called PVUSA Test Conditions (PTC) to more closely reflect real world conditions. PTC are 1,000 W/m2 solar irradiance, 20 deg.C ambient temperature, and 1 m/s wind speed. PTC differs from STC in that its test conditions of ambient temperature and wind speed will result in a PV module temperature of about 50 deg.C, instead of the 25 deg.C for STC. Silicon photovoltaic cells produce less power at higher temperatures. Consequently, for crystalline silicon PV systems with a power degradation due to temperature of -0.5% per degree C (typical), the PV module PTC power rating is about 88% of the PV module nameplate (STC) rating. System Output Power Determining the AC power expected out of a PV system requires additional considerations. The DC wattage expected from the solar modules must be reduced further to estimate the actual AC power produced. Typical de-rating factors include: - Module Production Tolerance .95 - Dirt/Dust .93 - Module mismatch .98 - Wiring losses .97 - Inverter conversion losses .94 Combined with the 88% temperature de-rating factor discussed above, the total de-rating from the system nameplate wattage (STC) is approximately 70%. This means that in the real world, a 1,000 watt PV system would be expected to produce an average of 700 watts on a full sunny day

 

By the way Hill, PV arithmetic is so much easier in metric and knowing that standard ("rated") irradiation is 1000 watts per m*m. E.g.:

Say you have 20 square meters of panels rated at 16%:
Each square meter can collect 1000*0.16 = 160 watts, and the array is 20*160 = 3.2 kW

 

Whoops, it looks like during my prior edit - we were both typing at roughly the same time .... and kind of saying the same thing ...

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But your memory wasn't completely out to lunch, as there is another rating system that that does use 800 watts per m^2. I think it is NOTC.

 

oh YEAH!!! especially true back in the day of mechanical kWh meters where you simply had a dial that either spins counterclockwise or clockwise. Our system was commissioned in 08 but it took weeks for SCE to get their feces together. You can bet our PV was running whenever we'd need to run our biggest energy pig, the central air (it's on a 50 amp breaker - drawing 9,500 watts ) - and even if the PV was (illegally?) cranking at full capacity - we'd still be drawing over 2kW from the grid. I wonder if the bar could discipline me for that ....

Below is a bill copy that's a couple years old but it reflects pretty much our average consumption - or surplus, from month to month. Since we put more on the grid than we actually use during most months, we always get a few bucks back from Edison at the end of the year;

You can see that during productive days of early summer (no AC) we can push over 600kWh/month back onto the grid. Yet SCE hates PV folk that do this. They are working hard to stop this by legislation. Paying a paltry fee to PV owners wrecks their business model, or so they say. Never mind the fact SCE resells our surplus to the neighbors at up to & over 10X the price they paid us for it.
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If you are on a TOU plan, they've figured out a great way to do so: move "peak" time back by 2 hours, reducing the amount they have to pay solar producers (during two of the best generating hours).

Our final permit inspection is tomorrow, and SCE already has had the paperwork for weeks. Let's see how long it takes 'em, and if this forces us onto a TOU rate schedule.

 

If they are consistent and have moved the peak time back for everybody, then it was a dumb move since PV still represents only a small fraction of the consumer base.

 

What's your system size?