Solar Planning Question(s) (Yes, I'm new here)

[Sunking]

The utility doesn't pay the customer retail prices for net metering. If the customer over-produces, they get paid at wholesale prices.

Which state would you be referring too?

[Tenaya]

Again, we really appreciate all the responses.

Regarding house orientation, the street we’ll be on runs east/west. The meter will be on the outside of one of the north walls, facing the street. As currently planned, the house mostly runs north/south The exception to that is a sizeable section of roof that has one due south face and will see no shade, the ideal location for the solar panels. The north end of the garage, where the main panel will reside (indoor), is about 50’ east of the center of that face (as the wire runs). There will ample space near for the inverter near the main panel . Are there any other devices I should plan for in that location?

The advice about breaker box size is a good one. Since I’m planning a workshop that will consume additional power, I’m sure the panel will be 200A, possibly larger, and maybe double to hold all the breakers.

I also like the idea of pre-installing 1” conduit from the breaker panel location through the attic to the solar panel location. The Soladeck product sounds like a good terminator (I found their website and downloaded the manual) and it looks like it takes a standard 1” conduit fitting. I’ll show it to the electrician and roofer and see what they think (they may be comfortable with other options). What gauge and type of wire is typical for the run from the panels to the inverter?

The idea of a sub panel with “critical loads” is interesting. I'll keep that in mind when we meet with the electrical sub-contractor.

I appreciate all the input about batteries, but we have decided not to try to use solar for outage power. Given the few outages we have, and how short they usually are (whatever else Xcel may be, they’re reliable), we can’t justify the expense and maintenance (battery life/replacement mostly). We do plan a backup transfer switch for the older but low hours 4KW RV generator I got for free (I was in right place at the right time).

I'm aware of the lesser payback for grid tie due to conditions in Texas. Yes, we pay a low Kwh rate, and yes the PoCo buyback rate is low, causing a less favorable rate of return. We’re willing to invest modest $$ in preparations for now, knowing there is a risk that PV doesn't make sense and we may never use them. As suggested, we are scrutinizing the return rate very carefully.

Regarding subsidies, I don’t think Texas offers a rebate, there's only the federal one. Again, I’m not certain and wiser input is welcomed.

All that said, if we can reduce our electric costs to zero, or maybe even slightly negative (I'd love to have Xcel pay us for a change), we may well be able to justify it.

I am still eager to hear from someone who has dealt with Xcel Energy. In addition to wanting to know if there really is a limit to how large a system we can have, and what that limit is, I’ve heard that they won’t even pay us wholesale, but rather the “average hourly incremental cost of energy” (AHIC). I’m not exactly sure how AHIC is calculated, but it’s probably less than wholesale. I don’t understand how all that works, but I need to.

As I mentioned in my original post, we haven’t found a solar installer in our area yet. If anyone has a suggestion/recommendation, I’m all ears.

Thanks,

Tenaya

[foo1bar]

"The utility doesn't pay the customer retail prices for net metering. If the customer over-produces, they get paid at wholesale prices."

Which state would you be referring too?

California - the same state you were referring to in the statement that I was responding to.

Overproduction is paid at something around $.05/kwh for PG&E customers. Which I assume is wholesale prices. (Or at the least it certainly isn't customer retail prices.)

[foo1bar]

What gauge and type of wire is typical for the run from the panels to the inverter?

10-AWG seems to be used fairly often.
Really it depends on voltage & amps being handled.
A Soladeck box would be a point to transition from PV wire (used outside) to THWN wire (used inside the conduit)

I believe PV wire could be used for the whole run - but it's more expensive per foot.

Most likely I would *guess* you'd wind up with 10AWG or maybe 8AWG if it's a bigger install or want to have less loss to resistance from the wires.
But you wouldn't need to install that wire now - you would pull it through the conduit when you're actually putting up the panels, etc.
(Oh - and they'd also need to pull a ground wire as well - which might be #6. It will be #6 for my install)

If you did 1" conduit you'd have lots of room in that conduit.
Even 3/4" I think would be big enough for 2 pairs of #8 plus #6 ground.

"Regarding subsidies, I don’t think Texas offers a rebate, there's only the federal one."
Yes - and only until 12/31/2015.
Which depending on when you do this, that may be too late.

[fun2drive]

Federal ITC

I think you have the date off a year on the ITC.

http://www.seia.org/policy/finance-tax/solar-investment-tax-credit

I believe it is the last day of 2016 according to this web site referenced above...

[PVAndy]

How big are you thinking?
9.6kW or smaller you can do a 40A or smaller breaker end-feeding a 200A main panel (40A breaker at one end of the panel connected to the solar, 200A main disconnect at the opposite end)
If you want bigger, you have to either use a smaller main breaker (ex. 150A main breaker, would allow you to have a 90A solar breaker)

OR you install a 400A main panel.
homedepot has 400A meter/main panel for $700 vs. $150 for the 200A version.
And then I think that one is actualy that it has a pair of 200A main breakers/main shutoffs - one for the built-in 200A busbar, and one for feeding to a separate 200A subpanel. If you go that path, then you could have the subpanel be a dedicated panel just for the solar.


I'd lean toward the 400A main.
But then I'm spending *your* money, not mine.

Where's the main panel and meter going to be located?





Ideally they'd be on the north side of the house with wall space adjacent to them where you can put the inverter.
(best to have the inverter not have direct sunlight on it)
Another option might be in the garage. (ex. meter is outside the garage, main panel and inverter are on inside wall)
Maybe with a drawing of layout of the house (roof, main panel & meter location & orientation (which way's north?)) others might have better suggestions.

Last suggestion I'd have - think about how you'd run conduit from your inverter location to the panels on the roof. And make sure that you'll be able to access that space - ex. no dead-space attic that you can't get into without tearing a hole in the living room ceiling. You could run conduit ahead of time if you have confidence in what you'll do. Can do conduit up through roof into bottom of a "Soladeck" roof mount box. There might be other/better option for the roof penetration - Soladeck is one I know of that I've seen used... I've also seen conduit come up and into a LR conduit elbow or a J-box just above the roof penetration. And of course figure out how to get that conduit to the spot where your inverter is. And if your inverter isn't going to be right by your main panel, then I think you'll have conduit from the inverter to the main panel (so you'll need to figure that out too)
And if you install conduit now, I'd go with at least 3/4" conduit - maybe 1".
Installing conduit now *may* be a really good idea - especially where you want it installed inside of a wall - as you wouldn't have to open up the wall (remove siding? break up stucco? remove bricks? Or from the inside, cut open drywall and repair and patch)

Possibly you can call up a solar installer in the area and ask them if they'd be willing to go over your plans with you if you pay them an hourly amount (maybe $100 for an hour of their time?) The problem is going to be getting someone who *isn't* just a salesman - but rather someone who can look at where conduit would be run, where the inverter would go, etc. etc.

Oh - and I'd say put plenty of room in your attic so you can easily store crap up there as well as do things like run conduit. Make the attic space be an area you can stand up in (and store the christmas decorations, and store all the things you can't bear to throw out) You'll thank yourself later for doing it - and adding it now during planning stages, it'll probably cost less than a month or two of storage at a storage locker.

I wanted to correct an error in this post. First you cannot backfeed a 9600 W system into a breaker in a 200 A panel. The most you can backfeed a 200 A panel is 7600 W 120% of 200 A is 240 A 240 A- 200 A is 40 A available backfeed 9600 W / 240 V = 40 A times 1.25 is 50 A 10 A too many. Usually a 400A panel is not necessary in a residence. A fused disconnect in a side tap is much simplier and less expensive.
Of course many new 200A panels have 225 A buses in which case you can backfeed 65 A. I routinely backfeed 20 kw AC systems into 200A services.

Andy
NABCEP Certified Installation Professional
PV Design Engineer

[bcroe]

What gauge and type of wire is typical for the run from the
panels to the inverter? Tenaya

I wouldn't put any copper wire into the conduit, till there is a final design. Be a shame
to waste $ on the wrong wire. The advantage of conduit is, you can always pull the
wires later.

I don't care to think of solar as related to, or as part of power backup to a power line.
Off grid is an entirely different animal as well.

Bruce Roe

[foo1bar]

I wanted to correct an error in this post. First you cannot backfeed a 9600 W system into a breaker in a 200 A panel. The most you can backfeed a 200 A panel is 7600 W 120% of 200 A is 240 A 240 A- 200 A is 40 A available backfeed 9600 W / 240 V = 40 A times 1.25 is 50 A 10 A too many. Usually a 400A panel is not necessary in a residence. A fused disconnect in a side tap is much simplier and less expensive.
Of course many new 200A panels have 225 A buses in which case you can backfeed 65 A. I routinely backfeed 20 kw AC systems into 200A services.

Andy
NABCEP Certified Installation Professional
PV Design Engineer

You are right about doing that incorrectly.
Thank you for pointing out that the correct amount would be 7600W max (32A feeding in on a 40A breaker using the 120% of 200A rule)

FWIW, in my city they don't allow a side-tap. So for the OP, you *may* be able to use a side-tap (tap into the power lines before the main disconnect) which avoids the whole 120% rules. But the AHJ (and/or POCO?) may disallow it.
The option I have thought of using for myself is to downgrade the 200A main breaker to something smaller (150A?) And that would give me ability to do more than 7600W. But I don't need it currently, so that's an extra unneeded expense.

[PVAndy]

You are right about doing that incorrectly.
Thank you for pointing out that the correct amount would be 7600W max (32A feeding in on a 40A breaker using the 120% of 200A rule)

FWIW, in my city they don't allow a side-tap. So for the OP, you *may* be able to use a side-tap (tap into the power lines before the main disconnect) which avoids the whole 120% rules. But the AHJ (and/or POCO?) may disallow it.
The option I have thought of using for myself is to downgrade the 200A main breaker to something smaller (150A?) And that would give me ability to do more than 7600W. But I don't need it currently, so that's an extra unneeded expense.

Too bad about line side taps. I would argue that the NEC allows them as long as you size the wire to rating of the fused AC disconnect, not the fuse size. Downsizing a main breaker works but I've found that the cost or the replacement main usually exceeds the cost of a new panel. Most new panels have 225 A busses allowing 65A backfeed into a 200 A panel which equates to 12.48 kW inverter

[bcroe]

Too bad about line side taps. I would argue that the NEC allows them as long as you size the wire to rating of the fused AC disconnect, not the fuse size. Downsizing a main breaker works but I've found that the cost or the replacement main usually exceeds the cost of a new panel. Most new panels have 225 A busses allowing 65A backfeed into a 200 A panel which equates to 12.48 kW inverter

Side taps certainly are an undisputable solution. But the rules are a belt and suspenders
design. With the POCO and RENEWABLE input breakers at opposite ends of the bus bars,
imagine a load equal to their total in the middle. The 2 sources feed the loads from each
end, but NOWHERE on the busbar are the 2 source currents ADDITIVE. If you claim that
they do cross a common central bus section, the opposite directions are SUBTRACTIVE.
So BOTH ends could approach the bus rating without any overload.

OR, if you derate the 2 feed breaker total amps to the bus rating, there is NO NEED to
put them at opposite ends of the bus. Either method avoids overload. Bruce Roe

[SunEagle]

"The utility doesn't pay the customer retail prices for net metering. If the customer over-produces, they get paid at wholesale prices."


California - the same state you were referring to in the statement that I was responding to.

Overproduction is paid at something around $.05/kwh for PG&E customers. Which I assume is wholesale prices. (Or at the least it certainly isn't customer retail prices.)

There are some Utilities that will pay you the same amount $/kWh for what you over generate as what that they charge you. That is a true Net metering contract and is existing in a number of US states.

Based on the last DOE report the average cost of electricity in the US was between $0.11 and $0.12/kWh. It has gone up and down for many years but seems to stay around those figures. CA and Hawaii are areas of very high kWh costs but most other states are lower and Texas is one of the least expensive. I am paying about $0.125/kWh in Florida and based on my records it has fluctuated up and down the past 8 years but never higher than $0.14/kWh.

[Tenaya]

Lot's of good information here.

Regarding subsidies, if we do it at all, it will happen in 2015, so we should be able to count on the federal tax credit.

Regarding size, I guess it will be like all purchases: The best we can afford, in this case, the largest we can afford. It will, of course, be subject to whatever maximum our PoCo, Xcel Energy, imposes. That maximum seems to be 120% of historical usage (I'm still not clear on how that's calculated). If anyone has more information about how Xcel Energy treats Texas residential solar customers, I'd love to hear about it.

I appreciate all the input about preparation. We will probably do three things during the house build:

• Assure that the roof is strong enough to sustain the panel weight and wind load.
• Go with an appropriately sized breaker box, probably 200A, and make sure space is available if an additional panel is required.
• Install conduit from the inverter location through the attic to the roof segment where the panels will be mounted. We probably won't install the Soladeck until we install the system itself. If the attic is open enough, we may even forgo the conduit for now (the actual attic structure isn't finalized yet).

The reason we're not doing more prep is that I've become somewhat pessimistic about the ROI due to the lack of a Texas state incentive, a mediocre buy back rate and the low cost of electricity here. Here are some details:

• Over the last 5 years, our current 4,100 square foot all, electric house consumed an monthly average of 5,000 kWh, 2,300 kWh minimum, 10,000 kWh maximum. Over the past five years, our electricity rate averaged just over 8¢ per kWh.
• After all the billing shenanigans and fees, we paid just under 11¢ per kWh in September 2014. This increase is partly due to a new natural gas fired plant. Future pricing is hard to forecast, but I have a great deal of trouble believing it will go down.
• I'm expecting electricity consumption at the the new house to be below what we've used in the current house due to smaller size (~2,600 square feet), natural gas for water heating and HVAC, better insulation, and newer, more efficient equipment.
• As several people noted, not all PoCos pay retail customers for power they generate. I don't think Xcel even pays as much as wholesale. They appear to have figured out a "not unethical" way to justify paying less than that. This weighs heavily on the ROI calculations.

I'm going to keep up on my research and working the numbers, but . . .

If we actually do it, this will be a grid-tie system with no batteries. We can't really justify the backup capability and I don't want the long term maintenance expense of the batteries.

I'd like to thank everyone for their thoughts and input,

Tenaya

[foo1bar]

Lot's of good information here.

Regarding subsidies, if we do it at all, it will happen in 2015, so we should be able to count on the federal tax credit.

Regarding size, I guess it will be like all purchases: The best we can afford, in this case, the largest we can afford. It will, of course, be subject to whatever maximum our PoCo, Xcel Energy, imposes. That maximum seems to be 120% of historical usage (I'm still not clear on how that's calculated). If anyone has more information about how Xcel Energy treats Texas residential solar customers, I'd love to hear about it.

I appreciate all the input about preparation. We will probably do three things during the house build:

• Assure that the roof is strong enough to sustain the panel weight and wind load.
• Go with an appropriately sized breaker box, probably 200A, and make sure space is available if an additional panel is required.
• Install conduit from the inverter location through the attic to the roof segment where the panels will be mounted. We probably won't install the Soladeck until we install the system itself. If the attic is open enough, we may even forgo the conduit for now (the actual attic structure isn't finalized yet).

The reason we're not doing more prep is that I've become somewhat pessimistic about the ROI due to the lack of a Texas state incentive, a mediocre buy back rate and the low cost of electricity here. Here are some details:

• Over the last 5 years, our current 4,100 square foot all, electric house consumed an monthly average of 5,000 kWh, 2,300 kWh minimum, 10,000 kWh maximum. Over the past five years, our electricity rate averaged just over 8¢ per kWh.
• After all the billing shenanigans and fees, we paid just under 11¢ per kWh in September 2014. This increase is partly due to a new natural gas fired plant. Future pricing is hard to forecast, but I have a great deal of trouble believing it will go down.
• I'm expecting electricity consumption at the the new house to be below what we've used in the current house due to smaller size (~2,600 square feet), natural gas for water heating and HVAC, better insulation, and newer, more efficient equipment.
• As several people noted, not all PoCos pay retail customers for power they generate. I don't think Xcel even pays as much as wholesale. They appear to have figured out a "not unethical" way to justify paying less than that. This weighs heavily on the ROI calculations.

I'm going to keep up on my research and working the numbers, but . . .

If we actually do it, this will be a grid-tie system with no batteries. We can't really justify the backup capability and I don't want the long term maintenance expense of the batteries.

I'd like to thank everyone for their thoughts and input,

Tenaya

One last thing that I don't think was mentioned:
Try to route all vents away from where they might cast a shadow on that roof section.
Plumbing vent as well as bathroom/kitchen exhaust fan vents.
And dryer vent (usually those are not out the roof, but some do)
And furnace and water heater vent/flue

If it's done before the roofing is done, it's a lot easier to change. (ex: extra 15' of piping angled along the roof but just under it could make it come out near the ridge line instead of in the middle of your array.)

And if it's not feasible (ex. bathroom fan vent is already a really long pipe as it is) then look at doing something that's low profile.

BTW - if it were me, I'd opt for doing the soladeck box - even if I didn't do the full run of conduit. Because I'd want that put down by the roofer when they're doing the roofing, not messing with the shingles a year later. Of course ideally you have the roofer do the feet for the array too - so that those are properly flashed under the shingles. But that's a fair amount more $ and will look odd if you don't do solar.

[Tenaya]

One last thing that I don't think was mentioned:
Try to route all vents away from where they might cast a shadow on that roof section.
Plumbing vent as well as bathroom/kitchen exhaust fan vents.
And dryer vent (usually those are not out the roof, but some do)
And furnace and water heater vent/flue

If it's done before the roofing is done, it's a lot easier to change. (ex: extra 15' of piping angled along the roof but just under it could make it come out near the ridge line instead of in the middle of your array.)

And if it's not feasible (ex. bathroom fan vent is already a really long pipe as it is) then look at doing something that's low profile.

BTW - if it were me, I'd opt for doing the soladeck box - even if I didn't do the full run of conduit. Because I'd want that put down by the roofer when they're doing the roofing, not messing with the shingles a year later. Of course ideally you have the roofer do the feet for the array too - so that those are properly flashed under the shingles. But that's a fair amount more $ and will look odd if you don't do solar.

Hmmm, I'm glad you added that; I hadn't thought about the vents and such. I'll make sure they're not in the way.

I understand what you say about the Soladeck and the roofing, but since the roof will have to be messed with to put in the feet for the array, I think we'll opt to do it all at the same time. PLUS, it will be so soon after the build that we can use the same roofing sub-contractor.

Thanks,

Tenaya

[fun2drive]

Solar System

I am planning to start building in 2 months. I am working the last details of the approval process and I have my architect on tap to design the truss for a number of solar panels around 40. I am planning to do an integrated approach as well meaning when the roof is going up making sure the roofer and the solar panel installer are in sync to understand how this is going to be handled. I have about 4-5 months before this will happen but if there is anything I learned it is that making sure that the subs work this out with the general contractor. I have the luxury of being on sight the entire time which will make a difference.
Your list sounds quite detailed which will help.
I am hoping that we can all share ideas and results of these installations so that everyone can learn.

Regarding calculation of the installation cost vs return on investment for me that is just one factor. Living in the High Velocity area of Florida I know that I will loose power during a hurricane and that will be the hottest and most humid time of the year. Having the ability to have power the next day is huge. I have back up power with both gas and diesel generators but that requires being there after a hurricane and that isn't always possible.
Assuming he array is still standing (another good reason to use the most robust mounts possible) post hurricane power to run the essential panel meaning AC, refrig, and a few lights is huge.

The electrical power I get is from a coop and is still not very cheap based on all the added costs not the pure cost per KW. The new home I am building is over 3 times my current home. I have calculated that I will most likely be able to reduce using coop power between 50% maybe more. Hard to gage the use on a structure not yet built.

Interested in what your decision is. Mine is to integrate the install with the roofing. Reduced cost per watt coming down vs federal tax credit expiration makes April-May 2015 my sweet spot for the array installation.