Best KWH production today on my new 20KW System!

[NYHeel]

I'm in northern NJ and tweaked my PVWatts projection to increase system losses to a little over 13%. My max PVWatts day is 70 kWh for my 10.85 kW system though I've gotten no more than 67 in early to mid April. That's probably going to be my system's peak as late and early day shading is at a minimum during April.

Even with the 13% system losses I'm down 7.5% to the PVWatts projection since my panels went active (8/1/2016-4/30/2017) and down 18.5% for the period of December through end of April. I haven't had a positive month since last November. Everything seems right with my system. I'm relatively in line with the PVWatts hourly numbers on sunny days. The issue just seems to be weather. We've had more really bad days with almost no production than PVWatts projects. A few days with 5 kWh produced really pulls down monthly production numbers.

One question about PVWatts. Should I be using Premium for Module Type? I'm using 310 watt Winaico panels.

[sensij]

One question about PVWatts. Should I be using Premium for Module Type? I'm using 310 watt Winaico panels.

Here is what the technical reference says:
PVWatts.JPG


Winaico panels have an AR coating, and are about 19% efficient. The temperature coefficient of -0.43%/deg C is closer to the standard panel than the premium panel. Both the AR coating and the temperature coefficient are used in the model, although I think the temp coefficient probably has a bigger effect on the model results. I don't think efficiency is used at all in PVWatts; it is more important in SAM. I would probably run the model with both standard and premium panels, and guess that your system would be best represented by something in between.

The variance you are observing with respect to the model is within the normal expectation. As they state in the help screen:

In general, you can expect the system's total electrical output for a given month of a particular year to vary by as much as +/-30% from the long-term typical value. Similarly, the total annual output for a particular year may vary from the long-term typical value by as much as +/-10%.

[NYHeel]

Here is what the technical reference says:
PVWatts.JPG


Winaico panels have an AR coating, and are about 19% efficient. The temperature coefficient of -0.43%/deg C is closer to the standard panel than the premium panel. Both the AR coating and the temperature coefficient are used in the model, although I think the temp coefficient probably has a bigger effect on the model results. I don't think efficiency is used at all in PVWatts; it is more important in SAM. I would probably run the model with both standard and premium panels, and guess that your system would be best represented by something in between.

The variance you are observing with respect to the model is within the normal expectation. As they state in the help screen:

Thanks for that info. I'll see if standard modules make a significant difference.

I have been off by as much as 46% as I was this past January but there was also snow involved in that. Probably would have been in the 30%-40% range if not for the snow. Hopefully the summer sees sunnier days.

[J.P.M.]

Thanks for that info. I'll see if standard modules make a significant difference.

I have been off by as much as 46% as I was this past January but there was also snow involved in that. Probably would have been in the 30%-40% range if not for the snow. Hopefully the summer sees sunnier days.

The weather will have the largest effect on variation between actual and model output with the insolation being by far the largest factor. And, of course, snow cover on panels will trump everything if not removed. This is not an exact science.