Solar PV install "infrastructure" question

[Buzz Saw]

Next year I'm hoping to install some PV panels and I'm looking for information on the "infrastructure" for an install.

So what I mean is:

-What kind of room is needed in my service panel?
- Will the power from the panels be 120v or 240v
- How many amps will the solar panels produce(for wire gauge purposes)?
- Do I run power from the solar panels to my service panel or to my meter panel? Does it matter?

- Is there a way to direct power to my future Garn or to the grid?
-Is there anything else I need to know about or prepare for?

Thanks

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[peakbagger]

Please note, the national electrical code changes every couple of years so these could change

-What kind of room is needed in my service panel?
You are limited to backfeeding the panel a maximum of 20% of the Inverter rated current. If the panel is 200 AMP panel you can hook up to 40 Amps of PV inverter. The breakers have to be on the opposite end of the panel than the main breaker. A space for a two space 240 volt breaker is all you need. It is highly recommended that you install a whole house surge protector to protect the PV inverters from surges on the incoming line and from inside the house as well as any surges coming in from PV system. I recommend a Midnight Solar SPS (it has far lower clamp voltage than other surge protectors). It is mounted in a knock out on the panel and can be tied into and two adjacent breaker (remember that you can only have one set of wires hooked into the breaker lug so you need to do a splice on the incoming lead instead of terminating two wires on the breaker lugs).

- Will the power from the panels be 120v or 240v
The vast majority of current inverters are 240 volt.
- How many amps will the solar panels produce(for wire gauge purposes)?
See first comment
- Do I run power from the solar panels to my service panel or to my meter panel? Does it matter?
See first comment, for large PV systems that exceed the 20% rule, there is something called a line side tap that goes between the main panel and the meter. Generally the utility does not allow customer wiring in the meter panel, a few utilities allow a device to be installed between the meter socket and the meter to tie in PV but the majority do not.

- Is there a way to direct power to my future Garn or to the grid?
For the majority of the inverter and micro inverter suppliers, no. SMA sells some models with Secure Power Supply (SPS) this is a switched 15 Amp circuit that operates when the sun is out and the grid is down. It has to be manually switched on when the grid goes down and off when the grid goes back on. One thing to note is if you are putting in a large PV system, over 6 KW and want to go with SPS, consider buying two smaller SMA inverters and you will end up with two SPS circuits. I am not aware of any microinverters that can run when the grid is down. There is technology developed for the German market that could make its way to the US which will allow those with large battery banks like the Tesla Powerwall that will allow the house to run off the battery bank. There currently are hybrid PV inverters available with external battery banks that allow the house to run without the grid. These add a lot of cost to PV system but the federal tax credit covers it. In addition to the initial cost, the batteries need to be replaced periodically even if you don't use them. These are quite expensive. Budget every 5 to 10 years. These are not hundreds they are thousands of dollars and also takes up space.
-Is there anything else I need to know about or prepare for?
Run a spare conduit from the attic to the main panel to run the PV home run wires. If you are installing a new roof, I strongly suggest putting Grace weathershield for the entire exposure of the roof where the PV goes under the shingles. Its a good idea under any roof but with numerous mounting brackets for the PV panels going through the shingles, the underlayment seals the roof deck. I would recommend a premium shingle as you really don't ever want to redo the roof once the panels are in place. Some folks advocate installing cheap shingles under a PV system but that sure doesn't make a lot of sense as there will be sections of the roof that have to be left open.

The roof mounts that tie through the shingles to the underlying roof are the biggest potential failure point on PV system. There are flashed in systems that have 20 year guarantees, they are more labor to install and buy but superior to the drill and goop method. No matter how good the goop is its going to need regooping at some point. If you use weathershield under the shingles, drill and goop may not cause a roof leak but why risk it.

A general observation is if you are thinking of PV you may want to do it quickly as the net metering contracts that substantially improve the payback of solar are rapidly being diluted or removed by the local utilities. PV may still make sense but the optimum size of the system may get smaller. PV systems in general get designed to optimize payback which is tied in with incentives and they are changing. I except that the next round of incentives are going to be tied with battery storage and shifting loads from off peak to off peak.




Thanks

 

[Buzz Saw]

That's a lot of info to digest.

First thoughts in no random order.
-I plan doing a pole mount system for the panels.
- Is the 20% Amp limit an NEC code or PV panel "protocol" What is the reason for this limit?
-No plans for batteries. The technology isn't good enough yet.
- I would like to somehow limit the amount of watts the Garn uses to what the panels produce in a month.
-I like the idea of surge protectors.


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[peakbagger]

I have a pole mount for one of my systems, I designed it myself so that I can manually tilt it. I really like that as it means I can tilt it up for winter so the snow sheds off. Even though its at 30 degrees, I still have to rake the snow off on occasion. It takes me about 5 minutes to change the tilt, I do move it 4 times a year. Its a 2 KW array that I installed myself. Unfortunately most inspectors require a stamped design so most folks have to buy commercial pole mounts. I have a disconnect switch at the pole with a surge protector mounted on it. One thing to remember is you need to run a #4 ground wire that ties back into the household ground in the bottom of the trench plus install ground rods at the poles ties into the same conductor. You always want to keep all the grounds at the same potential so a strike doesn't decide to run through the panel wiring to the best ground.

The 20% rule is NEC code, my understanding of the limitation is that conceivably a panel could have 200 amps coming in from the grid and an additional 40 amps coming in from solar with 240 amps of household load which means the bus bars could be exposed to 240 amps and could heat up. The NEC is always conservative. There are panels that apparently have 250 amp rated bus bars but equipped with 200 amp breakers, if you can prove that to your inspector you could possibly go up to 50 amps (250*.2 = 50). The alternative trick which I have heard people do but not sure its kosher is take a 200 amp panel and replace the main breaker with a 150 AMP breaker. That in theory frees up 50 amps plus the 20% of the 150 amps for another 30 amps of PV. I would go for the line side tap.

I am not sure of your thinking on the future Garn, I would expect you need power 24/7 for the Garn and a PV system will not supply power at night. Unless you spend the bucks on a big battery system, the vast majority of systems use the electrical grid as a "big battery", they sell surplus into the grid when the sun is out and buy it back at night. I use a minisplit for shoulder season heating so I generate lots of spare power in the summer and buy it back in late fall warm winter days and early spring. That's where you need to do research on what your utility has in place for net metering. Some smaller utilities will not even allow gird connected PV. Others pay you far less for power sent to them then what they charge you to buy back. I happened to be lucky and I get credited at the same rate I export as I import and the credit never resets. Some utilities reset the credit once a year and either take it all or pay some far lower rate for the credit. Therefore you need to design a system around the rate in effect in your area.

 

[Buzz Saw]

The idea behind the future Garn is to use the electric heating elements when the sun is shining. I will have the fan & controls hooked up to the grid. So I just want some "free heat" from the sun in the winter. In the non heating season I would feed the grid.

My local power co-op does net metering, but not on an equal scale. I would export for less than import, at least that is how I understand it. Last time I spoke to them the do NOT have off peak rates at this time.

The other reason I want to tie the Garn into the PV panels is I can consider the Garn part of the PV panel install and get the 30% tax credit on price of the Garn. That's a big chunk of money.

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[peakbagger]

Good luck on the tax dodge, that's really pushing it but as usual only your tax advisor knows for sure

Now that I understand the Garn application you probably need to go with an Outback controller. They have far more flexible capabilities than a typical grid tied inverter. The Garn becomes what is called a diversion load where if the power isn't being used by the house the extra is sent to the diversion load which in your case is the Garn. I believe the Outback has a capability to do a zero export setup and use the garn as a diversion load. I am a grid tied guy so its definitely out of my level of competence on the Outback capabilities. You could try the folks at solarpaneltalk forum. I hang out there and there are lot of very knowledgeable folks albeit a there are few "personalities" that can be rough on stupid questions, so write a detailed description with a reason why you want to do it and you should be fine.

 

[woodgeek]

The idea behind the future Garn is to use the electric heating elements when the sun is shining. I will have the fan & controls hooked up to the grid. So I just want some "free heat" from the sun in the winter. In the non heating season I would feed the grid.

You would get nearly 3X the BTUs using a mini-split HP to burn up those solar electrons than using the coil in the Garn. Even if you installed a little less PN wattage to make up the cost of the mini, you would still be far ahead of the coil.

This assumes the Garn tax discount doesn't work out.

 

[Buzz Saw]

Can a mini split be installed with a forced air system? Or does the mini split heat the water not the air?

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[peakbagger]

You would get nearly 3X the BTUs using a mini-split HP to burn up those solar electrons than using the coil in the Garn. Even if you installed a little less PN wattage to make up the cost of the mini, you would still be far ahead of the coil.

This assumes the Garn tax discount doesn't work out.

I thought of that idea also but didn't want to ruin what is a tenuous tax writeoff for a Garn.

A mini split heats or cools air, they normally are used as space heater with a wall mounted unit that circulates room air but if you get into commercial equipment I believe there are fan coil units used in VAVs that would work in ducts. The nice thing with minisplits is if you want or need cooling its great way to use up excess generation when you most likely have the greatest generation. Using a Garn for a diversion load in general not a great fit for PV. In theory unless there is a year round need for hot water, its far better to run the excess PV to a hot Water heater. The water will get and stay hotter compared to heating the entire volume of the Garn.

 

[begreen]

Can a mini split be installed with a forced air system? Or does the mini split heat the water not the air?

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Most mini-splits are air to air. Commonly the split systems have the compressor outside and a head unit mounted to the wall, but they do make some "head" units for the ceiling and some companies make air handlers for ducted forced air.

 

[Buzz Saw]

If I did a mini split it would need to be in the ductwork. We are doing a a complete gut remodel & addition at the moment. My wife don't like the look of the head units to begin with, let alone in a "brand new" house.

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[Buzz Saw]

More insite:
- I'm going with PV's also because I can make great power due to my no obstacle south property line.
- Looking to get a $0.00 electric bill
- Lessen dependence on foreign oil/fossil fuels.
-I'm doing the electric system with the Garn as an emergency backup if I'm not around in the winter to make fire. Due to bad weather or vacation. This shouldn't really need to be utilized for a few years at the soonest.
-I like to tinker and make cool stuff/ learn new stuff.

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[Seasoned Oak]

Most mini-splits are air to air. Commonly the split systems have the compressor outside and a head unit mounted to the wall, but they do make some "head" units for the ceiling and some companies make air handlers for ducted forced air.

I was wondering if that the reason the SEER ratings of whole house heat pumps tops out at around 15 and the head unit type go into the low 30s ,is it ductwork loss? Can it make that much of a difference?

 

[begreen]

Duct loss can be up to 30%, especially if they are run in a hot attic.
Some modern rotary inverter units are getting better. The Daikin SkyAir has up to SEER 20, and HSPF 12. Bryant has a pretty efficient unit too.
http://www.bryant.com/bryant/en/us/products/heat-pumps/288bnv/

 

[peakbagger]

Mitsubishi has a head unit that looks like picture frame and also ceiling mounted units that are quite discreet.

 

[iamlucky13]

I was wondering if that the reason the SEER ratings of whole house heat pumps tops out at around 15 and the head unit type go into the low 30s ,is it ductwork loss? Can it make that much of a difference?

I don't think duct losses are included in SEER ratings.

I think it mostly comes down to newer designs that are more refined to improve heat transfer where you want it, avoid it where you don't, reduce circulating losses, improve compressor geometries, and probably most importantly, use variable speed compressors (usually marketed as "inverter" driven) to keep systems running at the most efficient level for the conditions. Something I just learned about today, because your question got me curious and digging around, is that some newer units also use an adjustable expansion valve instead of a fixed one, so the expansion side of the cycle can be performed more efficiently across the full range of operating conditions.

Ductless systems probably also have some small advantage in better matching compressor design to air handlers. Ducted systems are usually designed to work with a variety of different air handlers, which themselves could be supplying a wide range of air flow rates depending on the home size and heating demand.

I think this is mainly happening in ductless systems because that's where a lot of the demand growth currently is, so that's where the development money is going.

That said, if you look around enough, there are a few ducted systems available now achieving over 20 SEER by using some of the same advances as in ductless systems:
http://www.carrier.com/residential/en/us/products/heat-pumps/25vna0/

 

[Seasoned Oak]

Ductless minisplits are good matches for wood stoves. They are the most efficient when the wood stoves are the least (IMO)which is the shoulder season.
Can be a PIA starting the wood stove when your just a couple degrees down from comfortable.

 

[begreen]

A good ducted heatpump system can be a nice match too, especially here with our long shoulder seasons. It's much more efficient and cleaner than burning wood during mild temps.

 

[Buzz Saw]

Read my mind. Since I'm going to have everything else in place I was going to look into adding a heat pump.

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