Grid-tied solar

[Redneck in training]

Yes and No. To see the fancy stuff you have to be on Internet. I can connect dirrectly to the Envoy but that is text only.

[dave1949]

The December results.

This month was below the model, for the first time. We had a lot storms move through and extended cloudy periods.

My net usage was 492.2 KWH of which the system produced 297.2 KWH. I went from having 75 kWh banked to 120 kWh in the hole. Net usage was 87 kWh higher than Dec. 2011, most of which would be due to having an electric water heater now. Also had to run an electric space heater in the bedroom for four nights toward the end of the month due to a lack of solar heating. That is not unusual around the end of the year.

A good production day now is 20-21 kWh. The sun gets up above the tree horizon around 9:30 am and goes behind the hill to our West about 3:45 pm. Now that we are beyond the Winter Solstice, production should start picking up. The 10-day forecast has a lot of sun in it, cold, but sunny.

The PVWatts model AC kWh predicted/actual:
Aug. 383/460.7
Sep. 394/480.9
Oct. 369/378.6
Nov. 283/400.3
Dec. 331/297.2
Jan. 388/TBD
Feb. 412/TBD
Mar. 509/TBD
Apr. 374/TBD
May 353/TBD
Jun. 308/TBD
Jul. 341/TBD

[Redneck in training]

We put first bank of panels on line last week of November and completed our PV system sometime in second week in December. It produced 1700 kWh so far. We have net metering but not banking so we have to settle the account every month. We get paid 3.5 cent/kWh for the excess but we can keep our heating rate during the heating season. My calculation based on last year consumption data predicted that we should be about $180 in black over one year period.

[dave1949]

The January, 2013 results.

This month was above the model. We had several really good stretches of sunny days this month.

My net usage was 482 KWH of which the system produced 440 KWH.

We had a couple of 25 Kwh AC production days, and some 0.2 Kwh days too. The sub-zero lows during the cold spell caused us to turn on the bedroom electric space heaters three or four nights, and I had the 75W bulb on in the well pressure tank room for a week.

The PVWatts model AC kWh predicted/actual:
2012
Aug. 383/460.7
Sep. 394/480.9
Oct. 369/378.6
Nov. 283/400.3
Dec. 331/297.2
2013
Jan. 388/440
Feb. 412/TBD
Mar. 509/TBD
Apr. 374/TBD
May 353/TBD
Jun. 308/TBD
Jul. 341/TBD

[Redneck in training]

We completed our system in first half of December. Total capacity is 24kW DC. PVWatts predicted (for January) 2388 kWh/ system produced 2570 kWh. Needles to say that the efficiency coefficient is not calibrated yet. I am waiting for first electric bill for full month with new net metering meter that meters separatelly energy pushed to/ received from the grid to calculate the coeffcient with better precission. I used efficiency coeffifient 0.85 based on reported efficiency of the inverters and current and voltage drop over the cable between the arrays and the power meter.

[dave1949]

We completed our system in first half of December. Total capacity is 24kW DC. PVWatts predicted (for January) 2388 kWh/ system produced 2570 kWh. Needles to say that the efficiency coefficient is not calibrated yet. I am waiting for first electric bill for full month with new net metering meter that meters separatelly energy pushed to/ received from the grid to calculate the coeffcient with better precission. I used efficiency coeffifient 0.85 based on reported efficiency of the inverters and current and voltage drop over the cable between the arrays and the power meter.

Our system is rated at 4.2 KW, our inverter is a 4 KW model. On the really clear sunny days, the panels are exceeding the inverter capacity for 2-3 hours around mid-day, which causes the inverter to go into "derate" mode. During "derate" the inverter keeps running but limits the power throughput to what it can handle.

A 5 KW inverter would cost a good bit more, so the trade-off of losing a few Kwh's this time of year is acceptable. We didn't see any derating when the sun angle was higher, and less optimal for our panel mounting angle.

Anyways, based on that observation, the panel output ratings are not over-stated. They can easily produce their rated output. We'll see how that holds up as they age.

[Redneck in training]

Our system is rated at 4.2 KW, our inverter is a 4 KW model. On the really clear sunny days, the panels are exceeding the inverter capacity for 2-3 hours around mid-day, which causes the inverter to go into "derate" mode. During "derate" the inverter keeps running but limits the power throughput to what it can handle.

A 5 KW inverter would cost a good bit more, so the trade-off of losing a few Kwh's this time of year is acceptable. We didn't see any derating when the sun angle was higher, and less optimal for our panel mounting angle.

Anyways, based on that observation, the panel output ratings are not over-stated. They can easily produce their rated output. We'll see how that holds up as they age.

Our system is large because we heat two buildings with electric heat pumps. House has geothermal and the shop has air/air but is heated (when unoccupied) to 40F. We should get January bill sometime next week. I am hoping that there will be enough information to determine actual efficiency.

[dave1949]

The February, 2013 results.

This month was below the model. Missed it by less than two sunny days. At mid-month, it was on-track to meet or exceed the model. Too many storms rolling through the second half of the month.

My net usage was 466 kWh of which the system produced 375 kWh.

The PVWatts model AC kWh predicted/actual:
2012
Aug. 383/460.7
Sep. 394/480.9
Oct. 369/378.6
Nov. 283/400.3
Dec. 331/297.2
2013
Jan. 388/440
Feb. 412/375
Mar. 509/TBD
Apr. 374/TBD
May 353/TBD
Jun. 308/TBD
Jul. 341/TBD

[Redneck in training]

Our system also didn't make the predicted production.
predicted 2.78 MWh/actual 2.3 MWh

[dmccarty]

The latest issue of Journal of Light Construction had an article about installing solar power panels. The contractor was in Mass and said that the installation cost was $4.30 per watt. The price seems to be dropping steadily.

Later,
Dan