Sun Pods

[chuco35]

I'm looking at finally taking the plunge. I live in a sunny and hot climate in South Texas (almost like Phoenix without the altitude), in a rural setting. My home is well shaded, so rooftop installation does not seem to be a good choice. I've selected a solar-field site, which is about 28' X 52' in dimension, for ground installation. However, I will have to lay about 280' of conduit from the field to the juice box at home. I'm looking at installing an 8.5KW system, tied to the grid, using 36 Sharp 235s. Questions: Any particular problems I can expect with having to lay such a long conduit from the panels to my home? Any particular tips on what kind of inverter, or other type of equipment, I should look at, to protect against the extreme ambient heat conditions of my location.

I came across a factory built turn-key system called a "Sun Pod". It is totally built - frame, platform and all - at the factory, and shipped on the back of a truck to location literally ready to be plugged in. I was quoted the above system, with an SMA SB7000 inverter, for $25,000, plus shipping of about another $750. Does anyone have any experience with this type of a system?

[Sunking]

Well if you are in TX you need to do a few things first or else you could be making a huge mistake. TX does not have NET METERING LAWS, or any state incentives. Firs tthing you need to do is call your electric company and see if they even allow a grid tied system. Many do not. If they do not forget it, not going to happen.

Next if your POCO does allow grid tied interconnection you had better find out what their policy is on excess generation. Since we have no NET METERING LAW they can pay you anything they want for excess. What that means is they will only pay you wholesale prices in most cases. For example where I live standard residential rate is $0.096/Kwh unlimited. Solar GTI you pay $0.12/Kwh (27% higher rate) for what you buy from them, and they pay you $0.06/Kwh for your excess (wholesale market price) .

So if you put in say a 8 Kw system after federal rebate you end up paying some $40,000. If you finance that for 10 years @ 6% your monthly payment is $450/month plus your electric bill on top of that which will only be slightly lower than you pay now. You could find yourself paying 400 to 500% more than you do now.

You also need to think twice about if you intend to move or not in the next 5 to 10 years. That $40K system will only add about $10,000 to your homes value. At closing it could be you writing the check to sell your home to pay off your debt.

So sit down with pencil and paper before you do anything.

[chuco35]

Thanks for The Tip.

Well if you are in TX you need to do a few things first or else you could be making a huge mistake. TX does not have NET METERING LAWS, or any state incentives. Firs tthing you need to do is call your electric company and see if they even allow a grid tied system. Many do not. If they do not forget it, not going to happen.

Next if your POCO does allow grid tied interconnection you had better find out what their policy is on excess generation. Since we have no NET METERING LAW they can pay you anything they want for excess. What that means is they will only pay you wholesale prices in most cases. For example where I live standard residential rate is $0.096/Kwh unlimited. Solar GTI you pay $0.12/Kwh (27% higher rate) for what you buy from them, and they pay you $0.06/Kwh for your excess (wholesale market price) .

So if you put in say a 8 Kw system after federal rebate you end up paying some $40,000. If you finance that for 10 years @ 6% your monthly payment is $450/month plus your electric bill on top of that which will only be slightly lower than you pay now. You could find yourself paying 400 to 500% more than you do now.

You also need to think twice about if you intend to move or not in the next 5 to 10 years. That $40K system will only add about $10,000 to your homes value. At closing it could be you writing the check to sell your home to pay off your debt.

So sit down with pencil and paper before you do anything.

I am able to get on my utility's grid, but you are right, I will be credited only on a wholesale basis for any electricity I feed back into the system.

On the financing: I would pay for the system in cash, figuring on being out of pocket about $20,000 after the federal tax credit, based on the quote I've received on the Sun Pod 8.5Kw system. Right now this money is in CDs, earning less than 1% interest. If it were a $20,000 home instead, and I were to owner finance its sale at 4% over 25 years, my mortgage receipts would amount to about $105 per month. I would expect that I can reduce my electric bills by a similar amount with an 8.5Kw system -- which is over 4 times what the CD is yielding now -- over a similar time period. CD and other interest rates may rise, of course, skewing the relative returns towards CDs, but so may electric rates, producing a higher yield on the investment.

Any thoughts on my conduit question? On high ambient heat resistent inverters, or other heat resistant equipment? Is a $20,000 (after credits) 8.5Kw turn-key Sun Pod system with 36 Sharp 235s too good to be a reliable buy? (Actually the company quotes $17,352 for the system after credits, I've factored in the difference for transportation and site costs.)

[Mike90250]

.... However, I will have to lay about 280' of conduit from the field to the juice box at home. I'm looking at installing an 8.5KW system, tied to the grid, using 36 Sharp 235s. Questions: Any particular problems I can expect with having to lay such a long conduit from the panels to my home? ....

Just the normal stuff, a pull box every 360 of bends in the conduit, or at least 1 pull box in the middle, whatever local codes require. Run the panel strings at the highest your inverter can accept, to reduce the copper wire losses. Maybe aluminum wire is appropriate, with the long run, and stable J-boxes at each end. use aluminum rated gear only, and anti-ox goop. Buy the wire pre-spooled into 300' rolls for easy pull, I did 980' pull with several helpers, a tractor, and a set of pulleys.

Inverter goes close to the electrical service drop, if it's a long run to your closest transformer, you may have issues with the inverter faulting on over-voltage when it pings the grid.

Use the wire loss spreadsheet in my .sig to figure the right size, aluminum wire needs to be 2#'s heavier than the copper it replaces, if #6 copper is called for, #4 aluminum will work.
P1050435c.jpgP1050454c.jpgP1050434c.jpg

[rick1]

1/0 copper

Just the normal stuff, a pull box every 360 of bends in the conduit, or at least 1 pull box in the middle, whatever local codes require. Run the panel strings at the highest your inverter can accept, to reduce the copper wire losses. Maybe aluminum wire is appropriate, with the long run, and stable J-boxes at each end. use aluminum rated gear only, and anti-ox goop. Buy the wire pre-spooled into 300' rolls for easy pull, I did 980' pull with several helpers, a tractor, and a set of pulleys.

Inverter goes close to the electrical service drop, if it's a long run to your closest transformer, you may have issues with the inverter faulting on over-voltage when it pings the grid.

Use the wire loss spreadsheet in my .sig to figure the right size, aluminum wire needs to be 2#'s heavier than the copper it replaces, if #6 copper is called for, #4 aluminum will work.
[ATTACH=CONFIG]2147[/ATTACH][ATTACH=CONFIG]2145[/ATTACH][ATTACH=CONFIG]2146[/ATTACH]

On my 10.8 kw with distance of 300 ft. ground mount I used 2" conduit 1/0 copper and #4 GROUND. I used 400 ft. of 3/4" dia. pull rope and used lawn tractor to pull wire. Some might say the 1/0 is too big but I think it helps with voltage drop and efficiency. I beat most systems my size on PVoutput.com. http://pvoutput.org/list.jsp?id=7932&sid=6416

[Sunking]

On my 10.8 kw with distance of 300 ft. ground mount I used 2" conduit 1/0 copper and #4 GROUND. I used 400 ft. of 3/4" dia. pull rope and used lawn tractor to pull wire. Some might say the 1/0 is too big but I think it helps with voltage drop and efficiency. I beat most systems my size on PVoutput.com. http://pvoutput.org/list.jsp?id=7932&sid=6416

So what PV DC voltage are you running for this 300 feet 1-way distance at 10.8 Kw?

[Mike90250]

The tractor was only used to hold the pulleys up, to guide the cables into the condouit. We used a shop vac to suck a string, to pull a mule tape through, with a braided wire gripper, to pull the wire bundle. And then you add the hippo snot cable lube, and it's a real mess. The "pull" was done by hand, it's too easy to have a winch break something, or saw through the condouit.

[rick1]

So what PV DC voltage are you running for this 300 feet 1-way distance at 10.8 Kw?

I use Micro inverters 240v AC. 300 ft. one way or 600 ft. both as it is AC.