Is my roof compatible with solar panels and if it is what roofing system should I re roof with?

[Joe_]

A little background.
I‘m located in the Sonoran desert. Can be continually 115-16 in the summer with lows in the high 80’s Low 90’s for weeks on end.
Winter temps typically run low 30’s with highs in the high sixties. It’s also windy here. 45 mph winds aren’t that uncommon.

Not a lot of rain days, but not that uncommon to experience a couple of inches an hour when it does rain. At times a great deal more. I’ve had 4” of standing water in the yard delivered in very short order at times. On those occasions all you can do is really hope it is going to stop.

The manufactured home I live in has a roof design load of 20 lbs per square ft.
The house roof is ~33 x 76. The house was placed East/West. I/2 of the roof faces south. Ideal for a solar install.
I’d guess the roof is at a 2-1/2 or 3 in 12 pitch.
The 3 tab roof is at the end of it’s life. It is a 20 year roof that has needed annual maintenance (spot shingle replacement) since year 10.
The UV here combined with the low humidity is brutal on asphalt shingles, wood and plastics.

At the moment my plan is to replace it with architectural shingles (25 yr) and hopefully get another 20 with maintenance.

My questions are:
With only a 20lb per sq ft design load roof structure, is it a bad Idea to plan on placing the panels (36) on the roof after having the roof re-done with shingles that are ~50% heavier than the originals that came on the house. Do I need to find a different place to mount my panels?

If I intend to put put a bunch of panels up there, (36) on the south facing side, should I have a different type of roofing material installed on that side when the house is re roofed, or will the architectural shingles be fine. I ask because of the heavy rains that come yearly combined with the low pitch and multiple holes that will be made to mount the panel mounting hardware. If a different roofing system? What would that be?

Thanks,
Joe

 

[MisterSandals]

If I intend to put put a bunch of panels up there, (36) on the south facing side,

36 panels? Are you looking at 100W panels?
Not only is it a pita and expensive to mount so many little panels but they may be a bunch heavier than something like 10x 360W panels.

 

[Joe_]

I’m actually planning on 400 watt panels. Not 36 panels right now, but I hope to expand over time. I don’t want to shoot myself in the foot by using a roofing system that I will have to fight with down the road as I expand. That is if the roof is sufficiently strong to actually mount panels on?

I have a cooling load of 5 ton min for the house. 2 ton mini split that intermittently runs on occasion in the separate shop. A (1) hp deep well pump,
5/8 hp swamp cooler when humidity and temperature allows in place of the 5 ton AC. 2 fridges + 2 smallish freezers which will be the first things that will be fed by solar. I‘d like to put it together allowing for expansion of the project in the future if I need to.

 

[MisterSandals]

I have a cooling load of 5 ton min for the house. 2 ton mini split that intermittently runs on occasion in the separate shop. A (1) hp deep well pump,
5/8 hp swamp cooler when humidity and temperature allows in place of the 5 ton AC. 2 fridges + 2 smallish freezers which will be the first things that will be fed by solar. I‘d like to put it together allowing for expansion of the project in the future if I need to.

If you can quantify this amount in terms of kWh per day you should be able to plan this install as well as what you'd need in the future. Its a little work that often results in a LOT of learning.

Good to hear you are planning on using big panels, i was worried.

 

[Joe_]

If you can quantify this amount in terms of kWh per day you should be able to plan this install as well as what you'd need in the future. Its a little work that often results in a LOT of learning.

Good to hear you are planning on using big panels, i was worried.

I’m doing a energy audit right now and spending a few hours each day reading. There is a steep learning curve certainly and I am studying as much as time allows.

Solar is without a doubt the most expensive way to produce electricity I have seen.

I need a reliable backup for these refrigerators and freezers if we are not here and the power goes out for an extended period of time.
When this house is shut up with the AC off in the summer, the inside temperature is a constant 105 degrees 24/7. I’ve measured it.
That is with an daily high of 110-116 ish. Neither batteries nor electronics like that sort of heat, and the refrigerators, though they can survive it will be running much harder than they do when it is the normal 78 degrees inside, what they typically see in the summer when the power is on and AC is running.
Not actually sure how to audit that at present. I haven’t run across any fudge factors to add on to the measured power usage either.

Edit: the 105 temperature was recorded with the refrigerators off. It will be significantly hotter with a bunch of electronics and
4 refrigeration compressors blazing away. If the panels are roof mounted their shade might help some if there are enough of them. It’s definitely complicated.

 

[OffGridForGood]

Not actually sure how to audit that at present. I haven’t run across any fudge factors to add on to the measured power usage either.

First off, I feel you are on the right path, keep going.
For 120 volt items that cycle - like the refrigerators, use a Kil-o-Wat plug in device (look it up online) and it will track the total kW consumed and the hours so you can calculate energy use per 24-hour day. As you noted already, some loads are seasonal, so you need to adjust from experience. For large 240vAC items like central A/C where you can't easily plug in a kil-o-wat device, I have used monthly bills from summer (when you know this load is on) and winter (when you know this load is off) and look at the difference. With all your other loads figured out, you can also just subtract known from the total for a month to calculate the unknown load. Data on the equipment will also assist you, as will energuide data if available.

As to your roof, you may be happy to know that covering a high percentage of the roof area with PV panels has a reasonable side benefit of reducing heat gain so lower A/C required. The 20psf roof design sounds crazy low (from a person living in 75psf snow load area) but the solar panels alone are typically 2.3 to 2.6 lbs per sqft, plus the racking. You will want to find out if your location requires anything special, permits/ review by PE etc. Better to ask and not like the answer than to build it and then have to take it down. Windy location you mention => careful review of up-lift.
I wonder if your low pitch plus windy location plus blistering sun are why the shingles took a sh@#$ kicking in your first 20-years. You may be happier with a white EPDM or TPO fully adhered roof, maybe worth investigating local options. Membrane roof systems can be easier to seal to PV mounting systems than shingles in my experience.

 

[Joe_]

First off, I feel you are on the right path, keep going.
For 120 volt items that cycle - like the refrigerators, use a Kil-o-Wat plug in device (look it up online) and it will track the total kW consumed and the hours so you can calculate energy use per 24-hour day. As you noted already, some loads are seasonal, so you need to adjust from experience. For large 240vAC items like central A/C where you can't easily plug in a kil-o-wat device, I have used monthly bills from summer (when you know this load is on) and winter (when you know this load is off) and look at the difference. With all your other loads figured out, you can also just subtract known from the total for a month to calculate the unknown load. Data on the equipment will also assist you, as will energuide data if available.

As to your roof, you may be happy to know that covering a high percentage of the roof area with PV panels has a reasonable side benefit of reducing heat gain so lower A/C required. The 20psf roof design sounds crazy low (from a person living in 75psf snow load area) but the solar panels alone are typically 2.3 to 2.6 lbs per sqft, plus the racking. You will want to find out if your location requires anything special, permits/ review by PE etc. Better to ask and not like the answer than to build it and then have to take it down. Windy location you mention => careful review of up-lift.
I wonder if your low pitch plus windy location plus blistering sun are why the shingles took a sh@#$ kicking in your first 20-years. You may be happier with a white EPDM or TPO fully adhered roof, maybe worth investigating local options. Membrane roof systems can be easier to seal to PV mounting systems than shingles in my experience.

Thanks for the info.
I really appreciate everyone who replied input. I’m rethinking most things now. Just about everything actually. Much better now than later.

I’m glad the roof is an option. Though perhaps not the best option. I’ll know more after talking with the inspector.
Uplift could be a real problem as these trusses are 2x2 wood and undoubtedly we’re not designed for load in that direction.
Yuck.
Next step looks like a review of the code book and a discussion with the local authorities.
Find out what they need to see to pass an inspection.
I’ll know more as the data on usage continues to accumulate. At the minimum it looks like a 3kva inverter plus a solar mini split.
I have some questions on that calculation also. I’ll start a fresh thread for that. When I return home I’ll have some real numbers to base my questions on.

Thanks again.
Have a great day.

 

[Nobodybusiness]

A little background.
I‘m located in the Sonoran desert. Can be continually 115-16 in the summer with lows in the high 80’s Low 90’s for weeks on end.
Winter temps typically run low 30’s with highs in the high sixties. It’s also windy here. 45 mph winds aren’t that uncommon.

Not a lot of rain days, but not that uncommon to experience a couple of inches an hour when it does rain. At times a great deal more. I’ve had 4” of standing water in the yard delivered in very short order at times. On those occasions all you can do is really hope it is going to stop.

The manufactured home I live in has a roof design load of 20 lbs per square ft.
The house roof is ~33 x 76. The house was placed East/West. I/2 of the roof faces south. Ideal for a solar install.
I’d guess the roof is at a 2-1/2 or 3 in 12 pitch.
The 3 tab roof is at the end of it’s life. It is a 20 year roof that has needed annual maintenance (spot shingle replacement) since year 10.
The UV here combined with the low humidity is brutal on asphalt shingles, wood and plastics.

At the moment my plan is to replace it with architectural shingles (25 yr) and hopefully get another 20 with maintenance.

My questions are:
With only a 20lb per sq ft design load roof structure, is it a bad Idea to plan on placing the panels (36) on the roof after having the roof re-done with shingles that are ~50% heavier than the originals that came on the house. Do I need to find a different place to mount my panels?

If I intend to put put a bunch of panels up there, (36) on the south facing side, should I have a different type of roofing material installed on that side when the house is re roofed, or will the architectural shingles be fine. I ask because of the heavy rains that come yearly combined with the low pitch and multiple holes that will be made to mount the panel mounting hardware. If a different roofing system? What would that be?

Thanks,
Joe

I’m guessing you don’t have enough land for a ground mount?
You didn’t mention it..

 

[crossy]

I’m guessing you don’t have enough land for a ground mount?
You didn’t mention it..

If you have the space, I would definitely look at ground (or car port) mounting, far easier to get at when things go wrong (they will) and a leak in the car port isn't a disaster (no Monet to get water damaged).

There's no way Madam would allow panels on her "feature" roof (and knowing what it cost neither would I), so our (currently) 10.6kWp of panels sits on the car port. Easy to clean, and no disaster when a panel goes duff.

Of course, being readily accessed nothing has gone wrong, yet!

 

[OffGridForGood]

Not sure if this was mentioned so far: roof mounted means (to be code compliant) Rapid shut down, Arc fault detection etc. Ground mount doesn't. Best to know these details while you're planning.

 

[OffGridForGood]

also windy here. 45 mph winds aren’t that uncommon

PV solar AND wind turbine?
(i know nothing about wind power, that wind speed value just caught my eye!)