Grid-tied solar

aczlan · Mar 17, 2013

dave1949 said:
It should also be possible to make the inverters believe grid power is present by using a pair of automotive-type 120v, 60 hz inverters powered by a 12v battery. The DC cables on the battery could be diode protected, at least the battery wouldn't get fried if things aren't working well.

You would have to have a pair of inverters that could parallel or it would not work well.

Aaron Z

Redneck in training · Mar 17, 2013

The best think is to use inverter that can automatically switch between grid tie or stand alone. It will fail (shut down) only if the demand exceeds available power. Google hybrid solar inverter. In example Off-Grid Inverters. SMA Australia Pty Ltd

dave1949 · Mar 17, 2013

aczlan said:
You would have to have a pair of inverters that could parallel or it would not work well.

Aaron Z

Yeah, two independently running 60 Hz, 120v inverters are going to cause problems with 220v circuits.

I was thinking a generator is not really necessary. It can't take that much power for the voltage sensing lines on a couple strings of microinverters. If one of the AC devices being powered by the solar pv is a 12v battery trickle charger, it might be possible to home brew something that works without a generator running.

Or, buy one of those hybrid inverters that Ladia linked and don't burn down the house. :laughing:

dave1949 · Mar 31, 2013

The March, 2013 results.

Below the model again this month. Like last month, it was down by about 2 sunny days. This month I saw the highest daily output (30.0 AC kWh) since installation. The better days were producing 25-28 AC kWh. The first week of the month was very weak, 49 kWh in seven days.

My net usage was 489 kWh of which the system produced 462 kWh. To date, I have taken 268 AC kWh more from the grid than supplied to the grid. For a perfect result for my grid-tied arrangements here in Maine, that number would be zero by the end of this July.

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. 509/462
Apr. 374/TBD
May 353/TBD
Jun. 308/TBD
Jul. 341/TBD

TheGoose · Mar 31, 2013

Great info Dave. At these rates how long do you think the system will payback?

dave1949 · Mar 31, 2013

TheGoose said:
Great info Dave. At these rates how long do you think the system will payback?

I think the original payback estimate of 17-18 years back in post #3 is holding up. Cumulatively, I am 225 AC kWh's ahead of the model prediction, so I am not too worried about meeting that. When the system is new, and there is no history, the question that really matters is will the system produce what the model says it will, since that is the basis for the payback period. With some history now, I am gaining confidence that the model is in the ballpark.

As near as I can tell from our mostly useless percentage gauges on the propane tanks (I have two 120 gal tanks), I probably under-estimated the amount of propane that was being used for domestic hot water. If so, that would reduce the payback period some.

Redneck in training · Apr 1, 2013

dave1949 said:
The March, 2013 results.

Below the model again this month. Like last month, it was down by about 2 sunny days. This month I saw the highest daily output (30.0 AC kWh) since installation. The better days were producing 25-28 AC kWh. The first week of the month was very weak, 49 kWh in seven days.

My net usage was 489 kWh of which the system produced 462 kWh. To date, I have taken 268 AC kWh more from the grid than supplied to the grid. For a perfect result for my grid-tied arrangements here in Maine, that number would be zero by the end of this July.

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. 509/462
Apr. 374/TBD
May 353/TBD
Jun. 308/TBD
Jul. 341/TBD

My system also didn't reach predicted production.
predicted/actual
3420/3160 kWh

Redneck in training · Apr 4, 2013

Here is a different perspective of viewing PV system performance.

https://enlighten.enphaseenergy.com/pv/public_systems/h2eX136588 That is my system.

https://enlighten.enphaseenergy.com/public_systems Other public access systems. Click on "e" on the map.
When system view is displayed. Click on "Get a fresh perspective on solar monitoring. Click here to preview" on top of the screen.

dave1949 · Apr 12, 2013

April is off to a good start. 193 AC kWh for the month as of this morning. That is 51% of the model prediction in 12 days. I will count today in, April 12th, since it is going to be a loser with the storm passing through.

Redneck in training · Apr 12, 2013

I just read few days back that US solar market increased 76% last year.

Travelover · Apr 12, 2013

Redneck in training said:
I just read few days back that US solar market increased 76% last year.

I was shopping for a solar panel for my RV and was shocked at how much the price has dropped on panels - some now less than a $1 a watt. I guess it is the Chinese flooding the market.

Redneck in training · Apr 12, 2013

I think all of them are for less than $1/W. I think the solar revolution just started. Panels with efficiency over 20% just hit the market. Higher efficiency means even lower cost/W and less space for installation.
The biggest issue is that sun doesn't shine at night so storage or transformation of energy to another media (H2) is the next hurdle to overcome.

dave1949 · Apr 12, 2013

Redneck in training said:
I think all of them are for less than $1/W. I think the solar revolution just started. Panels with efficiency over 20% just hit the market. Higher efficiency means even lower cost/W and less space for installation.
The biggest issue is that sun doesn't shine at night so storage or transformation of energy to another media (H2) is the next hurdle to overcome.

There is a lot of research currently in improved lithium batteries. If a battery capable of powering a typical residence overnight could be about the size of a refrigerator, sit quietly in a corner somewhere, and not cost a fortune, that would be pretty attractive.

Hydrogen would be good for commercial-scale systems, but maybe too complex for residential use? It could feed a hydrogen fuel cell and produce electricity I suppose if the cost of fuel cells became reasonable.

Redneck in training · Apr 13, 2013

There are other more or less mechanical ways to store energy. In example by pumping water to high elevation and let it run down trough a turbine powering a generator. There are quite few of those in operation in the USA (Blue Mesa, CO comes to mind), pumping compressed air underground and use it as combustion air for a gas turbine without a compressor etc. One of those is under construction in Iowa. Heating or chilling larger amount of liquid and then use it at night for heating or cooling etc.

yelbike · Apr 13, 2013

Redneck in training said:
There are other more or less mechanical ways to store energy. In example by pumping water to high elevation and let it run down trough a turbine powering a generator. There are quite few of those in operation in the USA (Blue Mesa, CO comes to mind), pumping compressed air underground and use it as combustion air for a gas turbine without a compressor etc. One of those is under construction in Iowa. Heating or chilling larger amount of liquid and then use it at night for heating or cooling etc.

Although your right, the examples you present have been around for many years, they still remain very inefficient. A lithium ion battery is much more efficient and would be a very interesting method of storing the days sunshine for use off peak.

Redneck in training · Apr 14, 2013

It is not always about efficiency it is about storing large amount of energy instead of wasting it or shutting down the source. Water pumping systems can absorb powers in range up to hundreds MW and can be started in minutes. I don't know the efficiency but it is better than battery charging for sure. It is around for long time so it is proven. That is the beauty of it.
Batteries are OK for home use or local smaller scale power storage.

dave1949 · Apr 24, 2013

Today the system hit the model prediction for April, yahoo. Whatever it generates for the remaining six days of this month will help make up for Feb. and Mar.

I am glad to see the output is within reason of the model prediction.