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Masterjoe · November 2017

So Masterjoe here again with a 4.5 KW solar system. Checking the production of the system through the latter part of October into November I notice on the best day the system produced 10.7kw that seems awfully low. According to PVwatss site I should be in the neighborhood of 16kw accounting for a modest 14% system loss this time of year in our area. With consumption at roughly say 40-50kw per day we are seriously outconsuming what the pv system is producing. I have 4 kids I chase after to keep the lights and AC off. Consequently since this is a battery backup we are not running off the battery bank at night. So from what i can gather, I have spent thousands of dollars to save maybe $20 on my energy bill. Also in the event the utility goes down and the panels don't produce even if they do I doubt I would have enough battery backup to last me 12 hours. Am I missing something here, because I really don't get it? I know the usage is bad but I expected the system would produce more than it is. I read so many stories about people with an electric bill near zero. Is this really fathomable? The way it is now we produce 200-500 watts more for 4 hours a day. The rest of the time we are pulling from the grid. From Oct 14 - Oct 31 we produced 137.2kw and Nov 1 - Nov 6 36.7kw. The inverter is running its charge cycle early in the mornings from the grid as well. I appreciate the patient explanation on a wondering mind, be gentle lol.

Photowhit · November 2017

There are much better people to answer grid tie systems...

Depending on how your system is set up, you may only be seeing the extra energy created over what you are using. So your 'extra' wattage may be hidden in your usage that wasn't drawn from the grid.

I have no idea, where you are located, but this time of year is the worse for much of the country. Between short days and slow moving fronts that make areas cloudy for days for days on end. About 3 years a go in Central Missouri, we had 13 days with just a single hour of direct sunlight!

I PVwatts uses an average solar insolation over many years. This time of year things can vary hugely! The return will be slow and steady, you are in the worse time of year for return on your investment.

mcgivor · November 2017

The hours of sunlight drop off in November, for Petersburg VA, where I think you are located, the angle of the panels, if fixed on a roof may not be at optimum angle which will further reduce production the link below will provide the best angle, direction is also part of the equation, other than location I've no information other than knowing there is reduced hours, the 4.5KW array would more than likely produce ~80% of rated figures at best or 3.6Kw, assuming 3 hours sun is about 10Kwh. Enter the information using the calculator and post the results. The stories about almost zero bills is relevant only if all data is disclosed, size of array daily consumption, cost of energy etcetera , so the return on investment will vary, depending on this, energy conservation would probably cost less to achieve more, unless the feed in tariff is very generous.
http://solarelectricityhandbook.com/solar-irradiance.html

Raj174 · November 2017

@Masterjoe
Since you are probably load shaving, (I don't think the SW will sell to the grid) and not cycling your batteries to any depth, then PV production will be limited to the amount of power the loads consume during the time of production. This should vary with the weather and battery SOC. It could be a good bit less than the PVwatts estimate. Also, I would think that your system would work like a normal off grid system if you lost the grid. By the way, I have a similar backup system, but a bit smaller array, however I cycle my batteries fairly deeply and I average about 10 kWhs per day.

Rick

mcgivor · November 2017

Raj174 said:

@Masterjoe
Since you are probably load shaving, (I don't think the SW will sell to the grid) and not cycling your batteries to any depth, then PV production will be limited to the amount of power the loads consume during the time of production. This should vary with the weather and battery SOC. It could be a good bit less than the PVwatts estimate. Also, I would think that your system would work like a normal off grid system if you lost the grid. By the way, I have a similar backup system, but a bit smaller array, however I cycle my batteries fairly deeply and I average about 10 kWhs per day.

Rick

Rick, It's an XW I'm the SW

Raj174 · November 2017

@mcgivor
Thanks for the correction, I wasn't aware that Xantrex made a 4000 watt XW series inverter. I guess lower production is due to reduced solar hours, but you would think that PVwatts would reflect that.

Estragon · November 2017

Just a thought, but as well as potentially not being at optimal angle to the low sun, it may be worth checking to see if any shade issues have cropped up. Even seemingly minor shading from a wire, small bare branch, antenna, etc can have a major effect. Might also be worth checking for bird bombs.

westbranch · November 2017

Low sun right now, it is only going to get worse from now to ~Jan1, then the sun starts to pick up, barring clouds... So if you can, optimize the Array angle for the winter. Next I would do a shading survey, every half hour... You do NOT want ANY shade across any of the panels, especially if series connected... Let us know how the array is wired and the survey results, It may be time to start the chainsaw. as others have said, if the CC is reporting the amount of power stored in the batteries, that is all you used from the previous day, in kWhr not KW.
kW is an instantaneous reading.
What was your consumption , in kWhr, before you installed your system? What has it been since? compare the same months in different years is useful as opposed to 'over the summer' etc.
hth

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