Doing It Right From The Start

Fatawan · March 2011

I am going to be building a shop next to my house, and it gives me a perfect opportunity to add some PV panels to the roof. If you had this opportunity to do things from scratch, what would you do to make for the best roof installation?
I was thinking about best roof pitch, reinforced roof trusses, etc. This will be in northern illinois zip 60119.

Seven · March 2011

Re: Doing It Right From The Start

What will your power usage be?

Fatawan · March 2011

Re: Doing It Right From The Start

Well, this is not directly for the shop itself, but will feed into the house. Shop power will come off 400A main panel in the house. We use about 17,000 kwh/year+ whatever the shop might use-conservation efforts+future electric vehicles.

Seven · March 2011

Re: Doing It Right From The Start

I guess my question should have been what kind of system are you going to build. Grid tie, hybrid, or off grid? How much power do you need to make? The panels you choose may be of different size and weight. The roof pitch angle may require different bracing if it is a strange angle. Are you planning on an adjustable mounting, or are just just going to base the angle on summer sun?

Seven · March 2011

Re: Doing It Right From The Start

http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/US/Illinois/
Look here for your expected sun.

Fatawan · March 2011

Re: Doing It Right From The Start

Leper wrote: »

I guess my question should have been what kind of system are you going to build. Grid tie, hybrid, or off grid? How much power do you need to make? The panels you choose may be of different size and weight. The roof pitch angle may require different bracing if it is a strange angle. Are you planning on an adjustable mounting, or are just just going to base the angle on summer sun?

Well, that is the input I was looking for. It will be grid tie for sure. I can pitch the roof however I desire. What is best? Should I use adjustable on a roof? If not, shoot for best angle in summer or winter? We have snow cover usually for 60-90 days in winter.

BB. · March 2011

Re: Doing It Right From The Start

Using PV Watts for a 10,000 watt array near Chicago:

"Station Identification"
"City:","Chicago"
"State:","Illinois"
"Lat (deg N):", 41.78
"Long (deg W):", 87.75
"Elev (m): ", 190
"PV System Specifications"
"DC Rating:"," 10.0 kW"
"DC to AC Derate Factor:"," 0.770"
"AC Rating:"," 7.7 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 42.0"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 8.4 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 3.04, 755, 63.42
2, 3.78, 839, 70.48
3, 4.34, 1049, 88.12
4, 5.11, 1137, 95.51
5, 5.68, 1244, 104.50
6, 5.66, 1176, 98.78
7, 5.92, 1243, 104.41
8, 5.22, 1111, 93.32
9, 4.94, 1036, 87.02
10, 4.26, 973, 81.73
11, 2.83, 645, 54.18
12, 2.27, 551, 46.28
"Year", 4.42, 11760, 987.84

A 10kW system is not small, and would give you ~11,700 kWH per year (fixed array).

Call it around $60-$80,000 installed less 30% federal tax credit (and any local kickbacks) for a GT system.

Is this what you are thinking about?

Suggestions, when you trench out to the new construction, place a couple extra empty conduits. One for the solar 240 VAC power (two hots, probably neutral, and ground, plus a second one for misc cabling--cheap to do while you have the ground open).

The above was based on an "Array Tilt:"," 42.0" degrees from horizontal.

A higher tilt may make sense to optimize for more summer production if you have Air Conditioning and/or Time of Use metering (I pay/receive around $0.12 per kWH in the winter afternoons, and around $0.27 per kWH in summer afternoons). So even though a flatter pitch roof may produce less power overall, optimizing summer may make better economic return.

Also, think about micro inverters or central inverter. And what is your AC power voltage like... Basically you have voltage "rise" of ~3% (maximum) which at 250 VAC would be 7.5 volts. Some places may get high line voltage of 255 volts or more, and add 7.5 volts (because of long wire run from garage to main panel to street transformer) may take you over ~260-264 VAC, the point at which GT inverters shutdown for safety.

If you place the solar panels and run the solar array DC voltage to the GT inverter installed near main panel/meter, you avoid the extra voltage drop of the garage to main panel run (not everyone will have this high line issue and in some cases the utility may "fix" the high line voltage for you).

What kind of roofing material would you be using? Talk with installers/roofers in the area about what they would recommend for type of roof, flashing, etc. for long 30-50 year roof life.

Another question would solar hot water be interesting for heating your shop/home? Solar Thermal can really save money even in very cold climates (assuming you have good sun):

Solar Shed and other Solar Thermal Links

-Bill

Seven · March 2011

Re: Doing It Right From The Start

Bill rocks!

And do realize that his example is a 10000 watt array when you look at the numbers. If you only have room for 2000 watts of panels, the price tag can easily still be $10K for a GT system. What is your reason for going PV?

BB. · March 2011

Re: Doing It Right From The Start

Guys who wore pocket protectors in high school never rocked.

-Bill "been there, did not do that" B.

Fatawan · March 2011

Re: Doing It Right From The Start

Bill

That is exactly what I was looking at for size. I am working on cutting our electricity consumption in the household. I will have room on the shop roof as well as in front of the shop on the ground. My plan was to use the next generation Enphase microinverters(supposed to come out late Q2). Illinois has a great rebate program that pays 30% as well. It's almost too good to pass up a deal for 60% cost credit in total. Illinois also buys REC's. ComEd also has a Residential Real Time Pricing program which I think I can "game" with solar. For example, rates are highest, of course, during summer peak air conditioning times, which would coincide with my peak solar output. I could negate those high rate times with the solar, and use other high-use devices during low rate times. I want to go PV because I value independence. It's not to make money or anything like that. I do expect it to pay back eventually. Our rates are over 11 cents/kwh now, and rate increases are expected this year. I also would like to add electric vehicles to the family eventually(use that RRTP again for cheap-er overnight charging). Whether I am fooling myself or not I am not sure, but the whole idea does give me a sense of independence.

Solar thermal for radiant heat was definitely in the plan as well Bill. Why not?

Roofing--I will use traditional 30 year asphalt shingle to match the house. I plan t to ice&water shield the entire south facing roof sheathing. I need to do more research on mounts and flashing to get that right.

My electrician is very interested in this project. He wired the original house, and will do the shop. The shop will be very close to the meter and panel in the house.

I appreciate the input. I'll no doubt be back for more

Thanks

BB. wrote: »

Using PV Watts for a 10,000 watt array near Chicago:

A 10kW system is not small, and would give you ~11,700 kWH per year (fixed array).

Call it around $60-$80,000 installed less 30% federal tax credit (and any local kickbacks) for a GT system.

Is this what you are thinking about?

Suggestions, when you trench out to the new construction, place a couple extra empty conduits. One for the solar 240 VAC power (two hots, probably neutral, and ground, plus a second one for misc cabling--cheap to do while you have the ground open).

The above was based on an "Array Tilt:"," 42.0" degrees from horizontal.

A higher tilt may make sense to optimize for more summer production if you have Air Conditioning and/or Time of Use metering (I pay/receive around $0.12 per kWH in the winter afternoons, and around $0.27 per kWH in summer afternoons). So even though a flatter pitch roof may produce less power overall, optimizing summer may make better economic return.

Also, think about micro inverters or central inverter. And what is your AC power voltage like... Basically you have voltage "rise" of ~3% (maximum) which at 250 VAC would be 7.5 volts. Some places may get high line voltage of 255 volts or more, and add 7.5 volts (because of long wire run from garage to main panel to street transformer) may take you over ~260-264 VAC, the point at which GT inverters shutdown for safety.

If you place the solar panels and run the solar array DC voltage to the GT inverter installed near main panel/meter, you avoid the extra voltage drop of the garage to main panel run (not everyone will have this high line issue and in some cases the utility may "fix" the high line voltage for you).

What kind of roofing material would you be using? Talk with installers/roofers in the area about what they would recommend for type of roof, flashing, etc. for long 30-50 year roof life.

Another question would solar hot water be interesting for heating your shop/home? Solar Thermal can really save money even in very cold climates (assuming you have good sun):

Solar Shed and other Solar Thermal Links

-Bill

jcgee88 · March 2011

Re: Doing It Right From The Start

Fatawan wrote: »

I am going to be building a shop next to my house, and it gives me a perfect opportunity to add some PV panels to the roof. If you had this opportunity to do things from scratch, what would you do to make for the best roof installation?

My $.02:

1. Position the new building so that the roof is facing due south
and its view to the sun is unobstructed by other buildings or trees.
2. Avoid any chimneys, flues, vents on the roof that can cast shadows.
3. Regarding your snow...If you go with the typical non-adjustable
flush mount, then you will want some steepness* to your roof,
to help the panels shed snow in winter. Don't butt the lowest
edge of the lowest row up against anything like a roof cove or
the like, as then any snow that sheds will bunch up there,
thus preventing further shedding. Leave enough access to
and around the array so that you can clear the panels with a
brush or roof rake (you will get the urge to sweep them when
it is perfectly sunny out but your array is generating zero
watts because it's covered in snow).
4. Plan for an interior chase so that you don't have to run an
unsightly conduit on the outside of the building to hold wiring.
5. Don't install a PV panel in any location that has persistent
shading/shadowing. If you have some unavoidable intermittent
shading or shadowing, then consider micro-inverters.
6. Optional: if you don't have to match the shingle color
to your house, you might consider getting a lighter, more
reflective shingle color.

*I have two strings. One string is at 10 degrees and it doesn't
shed snow at all. The other is at 20 degrees, and it will shed
about 30% of a snowfall.

--

Of course, before you do any of the above, I'd recommend
that you implement all the reasonable conservation measures
that you can. Get a Kill-a-Watt meter and an IR thermometer
to find where you are leaking energy.

John

SolarLurker · March 2011

Re: Doing It Right From The Start

I live in pa and just did a similar thing to what you proposed.

We built a 34 by 50 barn with a 20kw system. The barn trusses are skewed to give more roof on the south side. The south pitch is 31 degrees, we do not have time of use so 31 degree gives us highest yearly production.

We used storage rafters for the building to form a upstairs, doing so added very little to the cost, about 3000 extra. This gave us a room of 14 by 50 with 8ft ceilings. I figure you cannot built a second structure that cheap. We ran conduit underground for solar thermal down the road.

The building was engineered for a an additional 10 pounds sf snow load. System designer said 5 to 8 would be OK.

I really would not doing anything over on the PV.

I would do a few things over on the building.

I wish I when with 14ft high walls. we used 12 foot. However, 14 would have been ideal for car lifts. Also, with a 14 wall we could have use 12.5 garage doors that way if we ever should the house would appeal to rv people and truckers.

Fatawan · March 2011

Re: Doing It Right From The Start

SolarLurker--have any pics of your shop you could post?

I just called ComEd--you can't use both net metering AND the real time pricing at the same time. DOH!

jcgee--thanks for the tips. In regards to the lighter colored shingles, aren't there panels that will benefit from reflected light on the backside?

niel · March 2011

Re: Doing It Right From The Start

you should consider the angle of the roof not just for snow removal, but to optimally aim the pvs toward the sun. half the battle is facing south. they need tilted up and where you are in the world says at what angles the sun likes to hit your piece of the world. now this angle for fixed arrays can also be different depending on if going for optimal harvest on a straight gt system or one that needs more of the winter sun with possibly batteries involved. a good reference point to start is with your latitude as that would be the angle off of the flat horizontal for the pvs as well to start. now if you want the angle lower you should have the roof angled as such to match making it easier to have rails mounted at the same height above the roof. of course you can get an adjustable mount to change the angles from there too if you would like.

i'll stop here so as not to confuse with too much info on this matter. other advices are good too, but i wanted to elaborate a bit on this 1.

dgsloan · March 2011

Re: Doing It Right From The Start

Last fall I put up a platform with 1kw of panels just outside my shop. It was on a raised platform allowing me to work outdoors in nice weather. It was a bit of an experiment as I did not want to have the shop blow away when I raised the angle of the panels to 65 degrees to catch the winter sun. The platform is made with standard 24 inch spread 2x4 to measure the stress. The guy wires are used to anchor in extreme wind conditions. Interesting part is that the platform self cleaned itself all winter even though we got record snowfall this winter. Even below the platform where I have had normally over the past 25 years a three to five foot drift the snow is only max six inches. The panels did not even move in a 100 km/hr wind (60mph) at -10 f. This time of year I am producing 900 watts at noon and 6.4 kw a day on a sunny day. Don't expect this output in January = 500 watts at noon 1.5 kw a day (sunny). Bottom line is I average 30 kw a day usage on my house and up to this point have saved ten percent of that from previous years (according to our electrical company) With your usage a 2 kw system sounds about right. https://community.enphaseenergy.com/thread/1244?tstart=0

BB. · March 2011

Re: Doing It Right From The Start

Great idea--Walkway or some safe access that will not damage your roof if you walk on it.

Also, if you plan on cleaning your panels, bring up a hose connection (freeze proof) would be handy too.

-Bill

SolarLurker · March 2011

Re: Doing It Right From The Start

Here is some pictures of our barn system. The Front door will only be used in warmer months for moving mowers. We still have to finish the concrete. I will wait until spring to pour. Our plan is to lay pex piping in the floor for a solar thermal system that will be ground mounted 75 ft. behind the bar.

Doing It Right From The Start

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