Author Topic: Solar Freakin' Rooftops  (Read 893 times)

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Offline greypanda

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Solar Freakin' Rooftops
« on: January 31, 2019, 08:57:45 pm »
Has anyone debunked these: https://electrek.co/2017/05/10/tesla-solar-roof-tiles-price-warranty/ ?
I can't wait to spend 30K for my new roof and figure out why half of it is not working. Trees! Doh!. :-DD
 

Online wraper

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Re: Solar Freakin' Rooftops
« Reply #1 on: January 31, 2019, 09:12:32 pm »
There is nothing to debunk  :palm:. Yes it's expensive but if you need a new roof anyway, it's not a bad deal.
Quote
I can't wait to spend 30K for my new roof and figure out why half of it is not working. Trees! Doh!. :-DD
There are tiles with and without solar cells. It's exactly as if you put separate solar cells on top of the roof.
 

Online wraper

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Re: Solar Freakin' Rooftops
« Reply #2 on: January 31, 2019, 09:16:00 pm »
 

Offline rstofer

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Re: Solar Freakin' Rooftops
« Reply #3 on: January 31, 2019, 10:06:57 pm »
A few years back we had an 8 kW array of conventional panels installed on our roof.  It was sufficient to eliminate all of the utility electric bill for the year with the exception of the required $5/mo meter charge.  That's a conventional array and they can't be as large as the Tesla array.

The one question I have is whether you can walk on the tiles.  If not, the building department may require a 3' setback from the edges of the roof and this really restricts the number of tiles and the kW.

We solar users (around here) are not allowed to become net generators and if we should happen to over-generate, the utility pays only $0.04/kWh.  Well, our setup was under a Power Purchase Agreement where we agreed to buy everything the array generated at $0.15/kWh.  We would lose $0.11/kWh for every kWh we over-generated.

OTOH, we paid exactly $0 for the installation and would pay nothing for maintenance over the 20 year contract.

Too bad our new house has an aluminum roof and nobody will install over the top of it.

I see no reason to believe the Tesla info is wrong.  Solar is a really big deal in California.

And, yes, trees can be a problem.  The installers usually do a site survey to determine how many kWh they think they can deliver.  They consider orientation and blocking.  They're pretty good at it, they do it for a living.

I don't recall the exact numbers but our utility electric bill was on the order of $300/month and it was cut in half.  The only thing different for us was the amount and the payee.

Now, couple $0.15/kWh with a battery car that was getting 5 mile/ kWh and you find yourself driving for $0.03/mile.  Pretty nice!
« Last Edit: January 31, 2019, 10:11:27 pm by rstofer »
 

Offline rstofer

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Re: Solar Freakin' Rooftops
« Reply #4 on: January 31, 2019, 10:46:01 pm »
I'm not sure where Tri (video above) lives but with our Northern California utility, PG&E, the process is different.  The array generates in parallel with the utility and this causes the meter to slow down or even run backwards (selling power).  At night the meter runs forward and we're buying (no batteries).  It goes this way for the entire year, buying and selling kWh, and then comes the settle-up date.  The NET kWh for the year (still broken down in demand periods) is charged.  That month there is an electric bill that will likely be much different than just the meter charge.  It is called "net metering".

This net metering is nice because it doesn't presume you have batteries to cover the nightime hours.  It also accounts for the fact that the best generating periods are also the high $ periods in terms of cost/kWh (on-peak, part-peak, off-peak rates are different).  So, if you aren't home and your HVAC isn't running and it's "on-peak", everything you generate is being sold at the highest rate.  At night, when you can't generate, you are buying at the "off-peak" (low cost/kWh) rate.  Hint, run the HVAC at night!  Buy low, sell high!

I watched the video and there is nothing wrong with any of the claims.  Tri only had a partial month and this is pretty useless.  More appropriate is to check out year-over-year assuming comparable weather.  But any way you cut it, the payback will be longer than 10 years.  If the project is financed, the payback will increase.  There's a question in my mind as to whether I would buy into a 10 year payback.  That's why we went with the Power Purchase Agreement.  We didn't front anything but we paid for the energy at around half of the utility rate.

We paid nothing and got our electric bill cut in half, what's not to like!

I like that roof system.  Unfortunately, our roof will last for centuries so we won't be in the market for a new roof any time soon.

As to the factory claims, watch out as they shift percentages and dollars.  Every installation will be custom.




« Last Edit: January 31, 2019, 10:48:08 pm by rstofer »
 

Offline station240

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Re: Solar Freakin' Rooftops
« Reply #5 on: February 01, 2019, 01:02:49 am »
If you look at from the point of view of an upmarket tile roof, which happens to be solar as well, then the pricing makes sense.
Most people have no idea how expensive a tile roof is, as it came with the house. They get a rude shock when the find out what it costs to replace all the tiles.
However, many US homes have ashfelt shingles stapled to plywood, which are obviously cheap and don't last.

I'm not a fan of pricing something as $x where $x = $cost-$savings.
Just openly price it as:
 $cost
-$powersavings
=$comparisonprice

If you need to buy a new tile roof anyway, or replace a crappy one with something good, then these solar tiles probably make sense.
More so if you have an odd roof shape that wouldn't fit normal solar panels anyway.

Big things I don't like about Tesla's solar tiles:
a) Still limited availability after all this time.
b) Not available for purchase as loose tiles.
c) Still limited technical information.

I'd buy a few boxes of these to put on my shed roof, it's an odd dimension to fit any standard size solar panels.
However Tesla only do US houses, and would never do a shed anyway, nor can I buy some for DIY.
 

Offline Red Squirrel

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Re: Solar Freakin' Rooftops
« Reply #6 on: February 01, 2019, 03:03:04 am »
I feel these are a SUPER niche product, like if normal panels are simply not an option (ex: HOA).

Imagine the wiring nightmare it is to connect these things?  They never talk about that part.   When you're doing a roofing job the #1 priority is to get the roof safe from rain.  It's a race against the clock.  I feel these would probably take much longer to install than standard shingles.    Not really a fan of the idea.  Tesla is not the first to come up with it either.   Companies try to "wow" people with different ways of doing solar, but traditional panels are still the best way to go.  IMO I think ground mount is better than roof top, but in most residential settings there's just not enough room for ground mount so roof is the best compromise.
 

Offline rstofer

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Re: Solar Freakin' Rooftops
« Reply #7 on: February 01, 2019, 05:41:34 pm »
I feel these are a SUPER niche product, like if normal panels are simply not an option (ex: HOA).
One thing California got right:  HOAs can not restrict the installation of solar panels.
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IMO I think ground mount is better than roof top, but in most residential settings there's just not enough room for ground mount so roof is the best compromise.
Ground mount also takes away from the dog's place to play.  It is also lower to the ground and more likely to be shaded.  There is a house a block away with a ground mount system of 24 panels or, probably, 6 kW.  The array is situated in the middle of what looks like a 1/3 acre site with no trees near by.  It is also inclined and one of the neighbors said the panels tilt.  The owner was an early adopter.  We have a lot of trees as do our neighbors.

 

Online Kleinstein

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Re: Solar Freakin' Rooftops
« Reply #8 on: February 01, 2019, 06:00:40 pm »
With all the small cells, wiring could be kind of lots of work and quite a few connectors to potentially go bad. The $35 K price tag for the solar part is also not cheap. With less cells active things would likely get more expensive.
 

Offline station240

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Re: Solar Freakin' Rooftops
« Reply #9 on: February 02, 2019, 12:23:45 am »
I found one video explaining how the Tesla Solar roof fits together.
It's a firefighting instructional video, so you get free destruction as well.  :-DD
http://youtu.be/zunHya-0EQY

Quote
Wiring for the tiles is hidden below the tiles themselves. Each solar tile represents 3 shingles – a single tile appears to be 3 shingles on the roof and one to four of these tiles can be wired together to create branches. These branches are then wired together to create a diode trunk harness. The diode trunk harness carries the electricity from all the panels through the roof usually near the ridgeline. Typically, only about 16 volts is present in each branch – although the diode trunk harness operates at a much higher voltage.

So it's like how they wire offgrid solar, low voltage panels, wires back to a diode/combiner box.
Difference is the combiner box is wired to output higher voltages.
 

Offline EEVblog

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Re: Solar Freakin' Rooftops
« Reply #10 on: February 02, 2019, 12:24:42 am »
I did a video way back:

 

Offline ConKbot

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Re: Solar Freakin' Rooftops
« Reply #11 on: February 02, 2019, 08:13:58 pm »
I always found the thin-film solar panels that fit nicely between the ridges of steel roofs to look nice, and you get the long lifetime of a steel roof.  i.e.
https://www.mcelroymetal.com/images/greensolaroverview/Residencewithsolar.jpg but I find it weird that CdTe cells are even marketable. Even if they are fine for normal conditions and low leaching in a landfill, clouds of Cd laced smoke in a house-fire situation or when wildfires sweep though neighborhoods in California seems like a valid concern.

 


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