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After a new solar roof is installed, how hard to replace an existing rooftop condenser unit?

Hello All,
My existing 1100sf roof is leaking after the contractor added a 450sf California style roof to an probably 20 year old shingle roof. These leaks (in the existing attic) are at the valley where the new roof meets the existing one. These leaks could be there before the construction without me knowing it. Today I found another leak under the existing valley (on the left of the condenser unit) so apparently there's something wrong with the existing roof. The condenser label states the manufacturer date is May 2002 so it's probably almost 20 years old. It's still working fine but I don't know when it would die. I only have AC on 6 hours on a very hot day in a typical 4 month long Los Angeles summer.
Since I need a new roof, I'm thinking to install Tesla solar roof but I don't know how long it would take from the time I'm touch with the salesman to the time the work is done. I'll ask the rep that question.
But my question is: should I replace the condensing unit, the furnace and the evap coil (everything is working) before the solar roof installation OR there's some leeway that I can install the Condenser unit later?
I don't want the AC guy walk on a solar roof to remove the condenser and drop a tool or even worse drop the condenser to the solar roof. For that reason, if I need to install a new condenser, I would put it on the ground.
If you have another idea to just fix the roof and deal with with death of the AC unit later, please also let me know.
If I do new solar roof, I think I will also rip the 450sf new roof to replace with solar roof also as this contractor sucks at roofing. The leaks at the flashing (wet under the shingle when we temporarily remove the shingle just to inspect) but he said the leaks are from the existing roof run down to the new roof.
Thanks a lot.

IMG_20210129_150942.jpg
 

jboy210

Well-Known Member
Supporting Member
Dec 2, 2016
6,559
4,467
Northern California
I would do all of the HVAC and other roof work before installing a SolarRoof or panels. With a SolarRoof you don't want to do too much after it is installed. With panels, you may have to pay to have the solar removed and reinstalled to fix any roof issues under the panels.

The Solarroof tiles are pretty solid. One of the 220+ pound Tesla installers jump up and down on the tiles to show us while they were installing. But getting to lines and roof penetrations after the install is going to be some work.

Pricewise, I would assume the Tesla roof will be more than than a shingle roof. As part of the SolarRoof install, Tesla will remove the entire current roof down to the sheeting plywood, and at an extra cost, make any necessary repairs to the sheeting. Once the roof structure is solid, they will install the underlayment and the tiles.
 
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The 1,100sf existing roof replacement is about $15K. How much approximately for a 1,500sf (existing roof + new roof addition) solar roof cost?
This is not easy to answer, as it is highly dependent on how much of the install will be PV shingles. And that depends not only on how much you might want but on all the limits of your roof, including the various ridges/hips/valleys, obstructions like vents and the condenser, and local setback rules. It appears Tesla essentially charges you one rate per kW of installed solar plus a rate per sq. ft. of installed non-solar. Naturally, the more PV capacity you put on the same sized roof, the higher the cost.

I think all the advice you have gotten so far is good - particularly getting the HVAC off the roof, as I think you will have issues with getting contractors willing to service it, and the unit itself will not only reduce the amount of PV that can be installed but may also shade what can be (kind of like having a chimney.) If moving the HVAC is an option, I would suggest placing the order with Tesla - it seems like they are now saying the $100 is a "Refundable Order Fee" (though I do not know if there are restrictions on when it is refundable) and doing so will get you in the queue for an install as well as hopefully getting you access to somebody to talk to with questions. It should also give you an initial estimate of the cost, understanding that it will likely change as the plans proceed and a more accurate picture of how large a system is possible and desired is found. When they could install is also location-dependent, and you can hopefully get some more information from Tesla.
 
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I would do all of the HVAC and other roof work before installing a SolarRoof or panels. With a SolarRoof you don't want to do too much after it is installed. With panels, you may have to pay to have the solar removed and reinstalled to fix any roof issues under the panels.

The Solarroof tiles are pretty solid. One of the 220+ pound Tesla installers jump up and down on the tiles to show us while they were installing. But getting to lines and roof penetrations after the install is going to be some work.

Pricewise, I would assume the Tesla roof will be more than than a shingle roof. As part of the SolarRoof install, Tesla will remove the entire current roof down to the sheeting plywood, and at an extra cost, make any necessary repairs to the sheeting. Once the roof structure is solid, they will install the underlayment and the tiles.
Mine is skip sheathing so I guess Tesla would charge more to replace with smooth sheathing.
 
This is not easy to answer, as it is highly dependent on how much of the install will be PV shingles. And that depends not only on how much you might want but on all the limits of your roof, including the various ridges/hips/valleys, obstructions like vents and the condenser, and local setback rules. It appears Tesla essentially charges you one rate per kW of installed solar plus a rate per sq. ft. of installed non-solar. Naturally, the more PV capacity you put on the same sized roof, the higher the cost.

I think all the advice you have gotten so far is good - particularly getting the HVAC off the roof, as I think you will have issues with getting contractors willing to service it, and the unit itself will not only reduce the amount of PV that can be installed but may also shade what can be (kind of like having a chimney.) If moving the HVAC is an option, I would suggest placing the order with Tesla - it seems like they are now saying the $100 is a "Refundable Order Fee" (though I do not know if there are restrictions on when it is refundable) and doing so will get you in the queue for an install as well as hopefully getting you access to somebody to talk to with questions. It should also give you an initial estimate of the cost, understanding that it will likely change as the plans proceed and a more accurate picture of how large a system is possible and desired is found. When they could install is also location-dependent, and you can hopefully get some more information from Tesla.
Speaking of shades, there's an existing tall chimney on the roof and we never use the fireplace for the entire time we bought the house. Should we eliminate the chimney? On a side note, I check Tesla plans for another city on a daily basis (I'm an electrical engineer working for a city far from where I live).
 
Yep. They will likely have to add decking which would affect the price.
Since you are "in the business" from the engineering perspective. You might be interested in this document I created on our install.
I read it the first minute I saw it yesterday because it's a very good writeup. Thanks for that. I haven't called Tesla yet for the price but will do it soon. I need an ROI because of this orange and apple comparison:
1) Orange: My local roofer just came and quoted me $10,500 (materials + labor + permit and paid once the job is completed) for replacing the existing 1,200sf roof and repair the new 30 year roof (replace 2 long flashings incorrectly installed, raise the cricket between the roofs because the current one only has 1.5% slope (minimum 2% per code). He said it takes 4 days to complete the job.
2) Apple: I think I need to pay $100 deposit to get the guy come do the estimate but from Tesla website, it's $32,000 for a 2.9kW solar roof and (1) Powerwall based on my roof square footage of 1,600sf (400sf larger than the quote above as I will have to remove 5 month old 400sf roof). The cost would be a few grands more to replace 1,100sf skip sheathing and some unforeseen costs. I would say at least $38,000 (financed so there's also interest). Not to mentioned some cases Tesla suddenly refuse to proceed or for someone on here 8 months without progress because Tesla are simply too busy.
So with the average of $85/month for electric bill (worst case as the average now is $75), it takes at least 27 years to break even (could be a little bit longer because I still have to pay $10/month to maintain the connection with the power company). The solar roof is considered very inefficient after 25 years and it's efficiency has dropped way before that. And by that time, new generation solar roofs will be introduced with greater efficiency and life expectancy. But I need to find an efficiency chart to be sure.
Either way, that Condensing unit needs to replaced with a new one on the ground and it costs me about $4,000 for materials + labor.

At this point, I think I'm going with shingle roof. What do you think? Thanks.
 
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1. Figure out how much you pay per Kwh and how many Kwh you use in a year.
2. Work that out for 20 years.
3. Figure out how many kwh the solar system will generate. Adding PWs makes it easier, because although PWs add to the cost, they also allow you to use 100% of the electricity generated.
4. Compute the Tesla system over 20 years by dividing the Kwh Tesla system will produce by the 20 year Tesla cost. That's easy as the Tesla loan is for 20 years.
5. At this point, its apples to apples. Because a solar roof is more expensive than panels, the number in Step 2 might still be more than the number in step 4.
6. However, subtract the cost of a new roof from the cost in Step 4. That is because essentially you get a "free" new roof.
7. Item 4 (minus the cost of a new roof) should be less than Item 2.
 
1. Figure out how much you pay per Kwh and how many Kwh you use in a year.
2. Work that out for 20 years.
3. Figure out how many kwh the solar system will generate. Adding PWs makes it easier, because although PWs add to the cost, they also allow you to use 100% of the electricity generated.
4. Compute the Tesla system over 20 years by dividing the Kwh Tesla system will produce by the 20 year Tesla cost. That's easy as the Tesla loan is for 20 years.
5. At this point, its apples to apples. Because a solar roof is more expensive than panels, the number in Step 2 might still be more than the number in step 4.
6. However, subtract the cost of a new roof from the cost in Step 4. That is because essentially you get a "free" new roof.
7. Item 4 (minus the cost of a new roof) should be less than Item 2.
I can only input some kWh. Could you please enlighten me with $ amount?

1. Figure out how much you pay per Kwh and how many Kwh you use in a year.
$0.2/kWh (currently $0.15/kWh but for the sake of the calculation), 5048kWh/year.
2. Work that out for 20 years. 5048kWh/year x 20 years = 100960 kWh.
3. Figure out how many kwh the solar system will generate. Adding PWs makes it easier, because although PWs add to the cost, they also allow you to use 100% of the electricity generated. For 2.9kW system, average 5 hours per day: 14.5 kWh/day x 365 = 5292.5 kWh/year
4. Compute the Tesla system over 20 years by dividing (did you mean multiply?) the Kwh Tesla system will produce by the 20 year Tesla cost. That's easy as the Tesla loan is for 20 years. 5292.5 kWh/year x 20 years = 105850 kWh. The problems is we need to account for the system efficiency degradation at some point before that 20 year mark. In other words, the output at 20th year will not be the same compared to the 1st year. Also can you elaborate step 4 how to convert to $ amount. I don’t have their efficiency chart. I also have the impression that you're assuming any surplus energy will be sold back to the power company at the same rate they charge me.
Thanks.
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Moderator
Nov 28, 2018
14,320
18,141
Riverside Co. CA
I dont think you pay 15 cents a kWh (all in), all the time, for a home in los angeles.

No one would buy a 2.9kW sized solar install, I doubt tesla would install one that small.

Solar generates for way more than "5 hours a day". During the winter, it generates from 8am to 4pm in general, and during the summer, it would generate from like 7am to 6:30-7pm

You might want to go to Pvwatts or something to check your location for solar. Your inputs there seem VERY far off.
 
I dont think you pay 15 cents a kWh (all in), all the time, for a home in los angeles.

No one would buy a 2.9kW sized solar install, I doubt tesla would install one that small.

Solar generates for way more than "5 hours a day". During the winter, it generates from 8am to 4pm in general, and during the summer, it would generate from like 7am to 6:30-7pm

You might want to go to Pvwatts or something to check your location for solar. Your inputs there seem VERY far off.
I know 2.9kW is very small but that number I got from Tesla roof website when I input 1600sf and that's what I got. 5 hours per day is from sunrun website but I'll try to use PVwatts to see the difference. When I entered my address, there's a message: "Unable to determine the latitude and longitude for the location you typed"
At this point, I would like to see this comparison over 20 year period:
[$ (from Tesla roof kWh generation) - $ (from normal electric usage without solar) - total solar roof cost] versus $ (regular roof cost which is $10.500)
 
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