EEVblog #938 - Tesla Solar Roofs - Are They Viable?

[jancumps]

It's back - maybe just a YT glitch

Mmmm. Not for me. Still shows "The video is private"

[EEVblog]

Video is showing as private

New version has been uploaded.

[Artlav]

A bit lower efficiency is equivalent to us aren't being in 2016, but are in 2010, for example. It's not a huge factor.

A huge factor engineering people tend to overlook is public appeal.
The solar installation being turned from some nerdy-hippy stuff into nice, sexy, pretty everyone-does-that stuff.
That is the key value and selling point of this, i think.

[neotesla]

Good video, thanks, Dave.

Sadly, the comments on YouTube videos, particularly this one, are becoming unreadable for unhinged swearing and aggressive stupidity. It's a good thing that they can't shoot guns in there, as there would be dead and injured. I suppose it goes with the territory of being massively popular. Note to self, avoid in the future.

[nctnico]

IMHO the concept isn't bad but what will break it are the many interconnects between the tiles which will make installation and maintenance costly (90% of problems with electricity have to do with interconnects). It does make sense to use bigger ('normal sized') solar panels to make a roof water tight because the original roof tiling underneath it is kind of redundant with solar panels on top. Then again solar panels over a roof should provide extra cooling to the house so less need to run the AC.

[EEVblog]

Sadly, the comments on YouTube videos, particularly this one, are becoming unreadable for unhinged swearing and aggressive stupidity.

I just had to ban a troll. Don't have to do that too often. I suspect it was a previously banned troll with a new account.

[nuclearcat]

While cars are often premium product, as a watch or other luxury accessory, and frequently used to show off "social status" of owner, people in such cases doesn't really calculate efficiency that much and don't go in details. Especially because Tesla cars on road is clearly different, has very nice exterior and interior. Plus, driving Tesla across the city still draw attention.
Energy product i believe a bit different. First, they took approach of making roof looking similar to existing slates, so you need to come to your neighbours, and tell look, dude, despite the usual look, actually i have fancy pancy expensive Tesla roof (and funny that Musk appealing exactly to that).  But, well, not so impressive. You can't wear your powerwall or roof as backpack for some event.
So they will come down to ground, calculating what does they spent and what they got back in return. It doesn't look so impressive: https://electrek.co/2016/07/27/tesla-powerwall-6-months-customer-review/ , or even sometimes worse: https://bryanalexander.org/2016/05/29/the-tesla-powerwall-fails-life-as-an-early-adopter/
Datasheets of Powerwall looks very rudimentary to compare with similar products in the market, no power factor info, no warranty for capacity for cycles/time, requirement to have constant internet connection (otherwise warranty void) and etc. And for now, regular AGM lead acid still looks attractive. I hope someone has done "real life" tests and calculations of efficiency, real capacity and etc.
P.S. I'm living in a country where electrical supply are BIG deal. But still, economics of solar power sucks, and even here feasibility is questionable.

[StuUK]

Sadly, the comments on YouTube videos, particularly this one, are becoming unreadable for unhinged swearing and aggressive stupidity.

I just had to ban a troll. Don't have to do that too often. I suspect it was a previously banned troll with a new account.

just read the past posts, total troll...

[digsys]

Powerwall II ? Really?  Why wouldn't you just do it with existing technology (Lead-Acid & electronics) all of which is available off the shelf right now?  The advantages of Lithium batteries for cars make a lot less sense in houses, where the lower weight and size really don't make as much difference. 

Then you missed the key point :-)
He's building a gigafactory. Sales to cars will take eons to make it worthwhile, LET ALONE provide R+D money to keep expanding technology.
There are 100+ millions houses in USA alone, just sitting there, doing nothing :-)
So, that already gives him an absolute unlimited market, which boosts R+D, plus making a cute panel 1/4 the size of Lead-acid, and no possibility of H2 or other smells.
It's like Hybrids, a pretty much waste of time (all things taken into account), BUT they progress electric technology. Otherwise we'd still be twiddling our thumbs.
Edit: Plus - who wants all that lead out there ! It's had it time.

[rrinker]

 I really wouldn't even need the 'fake' ones on my house, the way it is oriented, the sun rises on the right front corner and sets on the left rear so throughout the day, the entire roof gets some solar exposure - exactly where depends on the season.

[Jeff_Birt]

If you want to put a solar roof on your house I have no issue with that. If Musk want to spend millions of his own and his investors money to make them that is fine too. The only thing that will make it viable is government handouts to the factories and the rich people who have the money to blow on a solar roof. If the technology was actually viable on its own then it could stand on its own without tax breaks. This is just a slightly more practical version of solar roadways.

The best PV cells made are less than 30% efficient, and those are the high dollar ones used on satellites. The rectangular silicone cell PV modules you see on roof tops are about 15% efficient. The solar roofing materials are typically in the 5%~8% efficient range. Some PV materials produce usable power in lower light than typical silicon panels, thinking specially of the Uni-Solar flexible panels, which can mean that you can get more usable power in low light conditions. Still the amount of power that you get from 'solar roofs' is really low.

Back in 2004 I advised our university's solar house team on the construction of a small, very efficient house using a custom hybrid roof made of copper seamed roofing with heat collection attached to the bottom and uni-solar panels on the top. With 80% of the roof south facing and the ENTIRE roof covered with Uni-Solar panels the house could not produce enough power to be self sufficient. We were one of the first homes in the state of Missouri to be grid tied, the first in our city, and the process of getting it approved was expensive and time consuming. The city credits the wholesale rate when net metering so the payback just for the grid tie expense would be on the order of 10 years.

Notice also that in the entire length of time Musk is blathering on there are NO technical details given. There was however a lot of BS about the different tiles ascetic appeal and other marketing wank.

The solar heating of water is very efficient and even in colder climates you can use the evacuated tube type collectors. A solar water heater is by far the most efficient and cost effective way to harness solar energy but it is not sexy.

[DH2ID]

I see this more from a technical/engineering/experimental point of view:

Hey, we've got the technology, we should just find some guys who want a new roof on their
regular houses (not especially built, and in various cities and in the countryside, in say
Pennsylvania/Oregon/Texas/California) and give it to them for free in exchange for
measurement equipment and internet access to their roof output.
Then watch what happens in summer/winter/heat/freezing cold, inspect the tiles and
improve them.

My main concern at this moment is

a) interconnection of the tiles (in salty air/dust)
b) efficiency (in cold/heat/low sun angle)
c) durability (ice/hail/fire/storm/micrometeorites)
d) safety (electrical current should be shorted to ground in a fire or while walking on the roof)
e) cleaning the roof (California/water supply)

[lpickup]

Thanks for the video Dave.

I get the desire to achieve the best possible solution when it comes to efficiency, and agree that a conventional rooftop solar would be more efficient & cost-effective WHERE a conventional rooftop solar could be installed.  But consider the situation I was in in my last house, and will be in my future house:  I'm in the northern hemisphere and the FRONT of my house faces south, meaning I'd have to install solar panels on the front of the house.  I can forget about getting homeowners association approval to do such a thing, much less get my wife's approval.  Plus the style of my house has a more vertical layout in the front--the best sloped roof is in the back (north facing) side of the house.  So effectively the efficiency we are comparing it to is 0.  The idea of solar shingles is very compelling to me (provided it meets the HOA/wife approval).

My primary concerns would be how all those tiles/shingles are actually connected together, and what is the installation cost?  I know Elon made the statement that the price point he was aiming for was to be cost competitive with a traditional roof + the cost of electricity.  I don't imagine he took installation costs into place, and I also suspect he was comparing the material cost to more high end roofing materials (i.e. those slate tiles he was so proud of).  Plus, electricity is actually very cheap in my area, so meeting that cost goal would be a pretty tall order.

[coppice]

My main concern at this moment is

a) interconnection of the tiles (in salty air/dust)
b) efficiency (in cold/heat/low sun angle)
c) durability (ice/hail/fire/storm/micrometeorites)
d) safety (electrical current should be shorted to ground in a fire or while walking on the roof)
e) cleaning the roof (California/water supply)

It might be interesting to match that list up with the long list of failed solar roofing tile ventures, and try to identify the most common cause of their failures. Elon Musk showed nothing more than their ability to make glass roofing tiles that look OK, and I'm not even sure if that was genuine. The tile he held seemed to have no electronics (there are two nail holes at the top, and apparently no other features) and looked like they had sprayed a dark rectangle on a conventional tile.

[lpickup]

If you want to put a solar roof on your house I have no issue with that. If Musk want to spend millions of his own and his investors money to make them that is fine too. The only thing that will make it viable is government handouts to the factories and the rich people who have the money to blow on a solar roof. If the technology was actually viable on its own then it could stand on its own without tax breaks. This is just a slightly more practical version of solar roadways.

It probably could stand on its own no problem if we properly accounted for the "hidden" costs that the incumbent solutions (i.e. fossil fuels) incur (i.e. damage to the environment, GHG emissions and the resultant damage caused by climate change, health care costs due to airborne and water-borne pollutants) not to mention the very generous subsidies and tax breaks that oil, gas and coal companies receive for their exploration costs.

Even so, I don't necessarily have a problem with offering incentives to change behavior and help advance a technology that we need to get to to create a sustainable energy source that significantly reduces our impact on climate change.  Almost by definition it won't be the cheapest solution, and I can tell you that most people will not be willing to put the greater interest of society and the planet first without some kind of incentive.  Unfortunately I feel it is a very selfish attitude to take that our generation should be entitled to consume a finite source of energy at a very rapid pace and meanwhile destroying the environment, leaving nothing but problems for our descendants.

[nixfu]

Of course.... if they actually also provided a superior, stronger, and longer lasting ROOFING material than traditional materials that could offset some of the costs of using them even on shaded parts of the roof compared to traditional materials.


Prediction, Coming in 2017

- Solar freaking FLOOR TILES!  Tile your entire house in solar, great for the bathroom/shower too!
- Solar freaking DRIVEWAYS!
- Solar freaking POOLS! Put solar panels at the bottom of your pool, after all it has a built in lens effect to magnify the solar radiation!  Hmm that might not be a terrible idea on first thought. I should patent that.

[Jeff_Birt]

It probably could stand on its own no problem if we properly accounted for the "hidden" costs that the incumbent solutions (i.e. fossil fuels) incur (i.e. damage to the environment, GHG emissions and the resultant damage caused by climate change, health care costs due to airborne and water-borne pollutants) not to mention the very generous subsidies and tax breaks that oil, gas and coal companies receive for their exploration costs.

You mean oil companies get to deduct their business expenses? How is that different than any other company/industry on the planet? On the other hand billions of dollars are handed out to companies worldwide to fund this 'renewable' mania. These billions of dollars are of course taxes. Spain really jumped off the deep end and wasted precious money and resources (taxes again) to fund these boondoggles.

If private companies and individuals want to invest their own money in this stuff then I'm all for it. If it really is a winning proposition then investors would be lining up.

I'll give you a prime example of government logic. The university I work for had a central steam generating plant, it has been in operation for decades burning coal and waste products from local wood processing. New EPA regulations made it too costly up refit the plant so the university has spent millions and millions installing a ground source system and touting how green it is. Meanwhile all of the old buildings on campus have leaking windows and doors wasting a tremendous amount of energy. In addition a few perfectly functional dormitories had to be torn down as there was no practical way to add a local steam generation source to them. Two more had a temporary boiler installed but they too will be torn down in a few years after new buildings are constructed.

The average person spending their worn money would first say, "lets fix the doors and windows and maybe add some more insulation". That would reduce energy consumption and reduce cost. The amount of pollution from the steam plant would also be reduced. The 'green' government funded solution mandated tearing down a perfectly functioning steam plant, and a tearing down a total of four dormitories, spending millions of dollars on a new ground source system and doing nothing about the crappy doors and windows. What is the total 'environmental footprint' of these two options? Tearing down large structures and building new ones is very costly and uses a LOT of resources and energy. But those hidden costs are not factored in.

[jonovid]

My main concern at this moment is
a) interconnection of the tiles (in salty air/dust)
b) efficiency (in cold/heat/low sun angle)
c) durability (ice/hail/fire/storm/micrometeorites)
d) safety (electrical current should be shorted to ground in a fire or while walking on the roof)
e) cleaning the roof (California/water supply)

It might be interesting to match that list up with the long list of failed solar roofing tile ventures, and try to identify the most common cause of their failures.

one idea maybe the use ozy colorbond corrugated roof sheets and conductive printed paint. the idea is you cut-off the length you need. 
steel roof sheets with  layers of laminated solar cell material, with conductive strip cut gaps on the roofing tin. think corrugated pcb with a steel back.       http://www.abc.net.au/tv/newinventors/txt/s3008638.htm 

also the idea of printed solar cell material as roof sheets came from here-

[MisterDiodes]

Every time I see these big fashionable Tesla galas about how great solar is - I cringe.

Being involved in the critical production processes of the business end of a silicon wafer - mono or amorphous - I can tell you those government reports of a payback time of 2 to 3 years is far too low.  When you count in the cost of hazardous waste generated, toxic water and the cost of the production of precious metals and acids:  Several of us engineers at a production plant calculated that a solar panel connected to the grid would have to run 10 to 15 years before it comes close to offset the impact of energy and hazardous waste it took to build the module.

IN short: Solar power is not quite as "green" as people think - and generates quite a lot of waste.  Take a look at the tanker trucks carrying away spent acid and various other junk leaving the production plant.   Take a look at the power required to run the silicon furnaces 24/7... The power required to process the aluminum frames, glass, the cost of fuel shipping the heavy & fragile panels around, etc.

And NOW look at the cost of recycling spent solar panels.  The ones built in the 80's are becoming useless now, and will create even more waste - and is a looming problem you don't hear a lot of discussion about:

http://news.nationalgeographic.com/news/energy/2014/11/141111-solar-panel-manufacturing-sustainability-ranking/

Does it make sense to put a solar array for electricity on every roof?  Not here in the Pacific Northwest USA for instance - typically in winter you're looking at 3 or 4 usable hours / day for PV production, maybe less.  If you're near a power grid, it is far less expensive and far more efficient to just connect to the grid for juice.  IT DOES make a LOT of sense to use a hot water heating system - especially with vacuum glass collectors - because heating water directly with a standard electric heating element is not the most efficient - and most energy used in a home is for hot water.  Depending n the cost of propane for a gas water heater, a rooftop heat collector can be a real increase in efficiency and quick payback on the energy used to produce the collectors - much more so than a PV array. It just depends on where you live, and cost of various fuels.  Where I live, we have very cheap electricity in the first place, and very cold water from the well - so solar hot water makes a lot of sense on payback time.   A house in a sunny location will make better use of a PV array.

Also - be careful of the cost of lead-acid batteries for storing energy - they have a very limited lifetime and create waste hazards of their own - and use up a lot of fuel shipping back and forth from China.  If you live where it's not TOO cold during the winter, nickle-iron and related old battery technologies are a good choice:  They are not space efficient but are cheap to build and last virtually forever.  They have to be kept warm though during the cold months.

There is no one perfect answer for every house - and solar PV arrays will not be the answer for all energy needs.  Every location needs to make the best use of power sources that are appropriate to that locale.

[cavac]

Solar Freakin' Roofs!

Dave, maybe you could do a video on a DIY solar system with those slightly damaged but functional reject solar cells from Ebay. Something like a 12 Volt/5 Volt system thats not connected to the grid.

Not the "mounting in a frame" part, which there are lots of youtube videos. But the wiring stuff, the maths, how to select the correct wire gauge and things like that. For example, how to wire a single panel, but also how to correctly wire up multiple panels to a single charge controller? How does one calculate the values for the protection diode? That kind of video.

[f4eru]

Several of us engineers at a production plant calculated that a solar panel connected to the grid would have to run 10 to 15 years before it comes close to offset the impact of energy and hazardous waste it took to build the module.

Just give us numbers.

The EROI of solar PV panels is generally shown to be around 5, but if you have better numbers, just give them to us.

Concerning hte recycling : let's assume panels will be recycled in 30 Years, on average.
The copper, aluminium is straightforward and easy to retrieve. The glass, silicium, interlink ( probably also mainly copper) will probably be wasted, which is not a big deal, silicium is cheap and very low relative weight, glass also. Interlink copper is a small portion of the total copper.

[f4eru]

Concerning the solar shingles, this will probably be a fad.
Conventional panels are just easier to manufacture, sturdier, easier to mount, more efficient, and cheaper.

Concerning efficiency, regarding the sole change in linking technology:

Warning : these are ballpark calculations.

let's assume they have a single cell that outputs 0.6V @ 5A in one of these shingles.
let's assume the resistance of the interconnection to the next cell is 10 mOhm, (a 25cm wire @60°C 1mm² is 4.8mohm, plus 5.2mohm for a connector). Cable loss : 0.01*5 = 50mV
Now you already have a loss of 8.3% of the generated electricity only in the shingle to shingle link.......

le's see on a small traditional glass panel : 24V @ 5A
The cells are very close together, there's only a few mm from cell to cell, the end of the string is looped back to the start of the panel.
The same 1mm² wire with 1m length @60°C -> 19.3mOhm
The same connector @5.2mohm
the interconnects drom cell to cell can be estimated at nearly zero (the loss of the cell to edge interconnect and the few mm from cell to cell are the same than in the shingle solution )
cable loss : 0.0245*5 = 0.1225V  --> 0.5% loss

Now that's much better !!


Now let's consider the ressource "copper" in this link :

40 shingles(24V) : 40*0.25m = 10m of copper wire@8.9g/m, 40 connector pairs @ 2g    total : 169g of copper
single 24V panel :  1*1m of copper wire, 1 connector @2g  total : 10.9g of copper

So you have roughly 15x the power loss in the link despite investing 15x more in the copper, just because you want to space the cells for aesthetic reasons.

[kevyk]

Everyone is forgetting a most critical limitation to the engineering for ANY solar panel including the Tesla / Solar City ones. This issue alone makes almost all rooftop solar panels completely unviable once you do the actual calculations. And no one ever talks about this.

The issue is, for at least on one evening every year, the weight of Santa's sleigh would obviously crush any solar tiles placed upon the roof. This makes rooftop solar panels impractical.

Now, when Santa finally implements anti-grav, then we can talk about solar again, but until then don't waste your money on an obviously flawed technology.

[f4eru]

The problem is, there are people also in nuclear power stations, so sometimes the roof collapses at nuke power stations when santa passes :
http://media.gettyimages.com/photos/snow-storm-in-isere-the-roof-of-in-warehouse-at-the-nuclear-plant-of-picture-id162568841?k=6&m=162568841&s=594x594&w=0&h=iWRnFUXLd9WwgoukcN4GTfR1DL2YIZ_rtI1ana_33Xo=

[f4eru]

Strange! BBcode strips the final "=" sign in the URL. Some bug in the parser probably..

Here's the picture :