Grid-tied solar

[Redneck in training]

Dave,

Just found this thread and haven't had a chance to read it all the way through. But I was wondering how much this had actually reduced your utility bills. How much of your usage did you intend on replacing. Seems like you are running as expected maybe a little better.

We don't have net metering. Our electric bill is about $200/month less. Predicted pay back is about 15 years. If the cost of power goes up or we buy electric car it might be significantly shorter. I estimate that with net metering our system would be paid off in about 8 years because of our electric bill would be zero.

Our utility is hostile to alternative sources of energy. We used to have a discount heating rate during winter and since I generate my own power they took it away.

BTW we are on our way to about match the predicted energy generated 36MWh.

So to answer your question: It depends on the deal you get from your utility and size of the system.
If you get net metering it is best to match your yearly consumption.

 

[dave1949]

Dave,

Just found this thread and haven't had a chance to read it all the way through. But I was wondering how much this had acuaully reduced your utility bills. How much of your usage did you intend on replacing. Seems like you are running as expected maybe a little better.

So far, it's doing a lot better than we thought it would. The original thought was to replace propane with sunshine, and maybe make a dent in the rest of the electric bill. The way it has worked out, it replaces the propane and ~75% of the electric bill over all.

We were buying ~315 gallons of propane yearly and I think >90% of that was for the water heater now that it's gone and I can see how little we use for cooking.

Once in a while we get an electric bill of $15-$25 dollars when our use exceeds the system output. Right now, we are carrying a 122 kWh credit into December. The way the sun has been playing hide 'n seek this month, I'm pretty sure we will use those up on the next bill.

We always pay $9.36 per month for being connected to the utility no matter how little we use. The credits are on a use them or lose them within twelve months rule in Maine. So here, you want to produce just a little less than you use over a year's time.

The system has been trouble free. We've had a couple of good, close lightening storms the past year too. I think lightening is probably the biggest threat of damage to the inverter.

It's just the wife and I and we weren't big electric power users to begin with. We are considering installing AC. If we do, I would like to add another set of panels and inverter. I have a smaller but otherwise identical install location available on the tractor garage, and our main service panel is out there too which would make it simple.

 

[farmer2009]

Thanks Dave and Ladia. One more question and it may show my knowledge of solar, but if your system is a 5 kWh system how long of a time frame before you produce that. Is it a day, week, or year or something else.

 

[dave1949]

Thanks Dave and Ladia. One more question and it may show my knowledge of solar, but if your system is a 5 kWh system how long of a time frame before you produce that. Is it a day, week, or year or something else.

A 5 kW system is one that can produce 5,000 watts at any given moment, or an instant in time is a way to think of it. If it produces that much continuously for one hour, you have 5 KWh. If it did that continuously for 4 hours, you have 20 kWh.

The system would be rated in kilowatts by multiplying the number of panels by the output of each panel. The panel rating assumes more or less ideal conditions: perpendicular light angle of incidence, 70*F ambient temp.

What the total system may produce in a month or a year is estimated/modeled in kilowatt hours because the model "knows" how many hours of daylight and of what quality you could expect on average.

 

[Redneck in training]

The production curve has a bell shape. The panels wake up when sun comes up and gradually increase production to maximum at noon (Provided that they are facing south. If they face somewhat south-east or south-west the peak will come earlier or later.) and gradually decline as the sun travels west. Attached image shows two curves at different sunny days and at different ambient temperature. The curve is instantaneous power while the area under the curve is produced energy for the day. The flat part of one of the curves is caused by inverter clamping. That hapens when panels produce more DC power than the inverter can convert to AC. The biggest enemy of solar is shading such as trees, hills, buildings and also clouds. Therefore selection of location is important. There are models available on Internet where "what if" analysis is easily done. PVWatts Calculator

 

[Barry 1]

The biggest enemy of solar is shading such as trees, hills, buildings and also clouds.

And freezing rain and snow! Half of my system is sleeping,under 3" of snow and ice.

 

[farmer2009]

Thanks guys. That helps shine some light on it. That is a nice link too.

 

[BrandonR]

The biggest enemy of solar is shading such as trees, hills, buildings and also clouds.

And freezing rain and snow! Half of my system is sleeping,under 3" of snow and ice.

Our 4kw system hasn't hit over 110 watts all week thanks to the snow that's covering it.

 

[jimmyj]

I just wanted to say "great thread" and thanks for keeping it going. Our electricity has gone up very substantially over the last few years and is predicted to go up 10% per year each of the next 5 so my wife and I are very interested in this topic. I will likely be posting more about it next year once we get into it and thank you in advance for answering some of our questions already.

Jim

 

[dave1949]

I just wanted to say "great thread" and thanks for keeping it going. Our electricity has gone up very substantially over the last few years and is predicted to go up 10% per year each of the next 5 so my wife and I are very interested in this topic. I will likely be posting more about it next year once we get into it and thank you in advance for answering some of our questions already.

Jim

Glad you are enjoying it.

What's up with your power prices? I noticed Jason (Scooby74) saying his power is high too. Do you get supplied from Hydro Quebec?