EEVblog #632 - Solar Roadways Are BULLSHIT!

[LabSpokane]

#4

[LabSpokane]

#5

[jonovid]

if you must use solar , stack it on a roof  and do not forget the battery's .   as its useful in power outages.   a house run off battery storage and/or solar panels makes sense,  But solar on the road??, one bad idea. generating more political wheel spin then electricity!

[LabSpokane]

#6

[LabSpokane]

#7

[SeanB]

Not much power out of those panels, I would guess around 30W per panel, and at a price of around 200 times that of a 30W panel, including installation.

While you can stand on a glass panel and not break it, I would like to see those panels after 6 months of people walking across them with muddy shoes, high heels and the odd bike and street sweeper going over them. Then I would like to see the power output compared to a similar size installation on a nearby roof.

[LabSpokane]

#8

[SeanB]

#8

6 mains fed power supplies for a solar power GENERATION plant? Are they going to be used to supplant the solar panels and drive the inverter when there is insufficient sunlight? Does the monitoring circuitry require so much power that they need all those units.

[LabSpokane]

Hold on Sean, more info coming.

[LabSpokane]

#9

[LabSpokane]

OK folks, this is going to be a looong post, so bear with me.  We visited Sandpoint, Idaho yesterday evening to view the SolarRoadways demonstration.  For anyone who wishes to visit, the City of Sandpoint has a webpage with a webcam on the demo site here:  http://cityofsandpoint.com/visiting-sandpoint/solar-roadways#ad-image-11

The system as of 10:20 PDT is now installed and operating.  Watching people on the webcam is interesting because all exhibit the same behavior.  First, they place a foot on the panels to see if they are secure, then they look.  Next, they take a tentative step onto the panels and finally decide to walk across them. 

The installation commits the sin of partial panel shading.  Even at 10:00 am, the panels are shaded by the building they are installed adjacent to. 





Here are some details about the panels themselves.  We now no longer need to guess at values.  Each panel is 44W and there are 30 panels in total.  So, the theoretical maximum power generation is 1320W.  Based on the datasheets for the microinverters, I am surmising that the panels operate at 24VDC, since the lowest input voltage is 16VDC. 



Solar Roadways experienced some manufacturing problems and, if I recall correctly, only 14 of the panels are operational.  The defective ones will be replaced as they get new PCBs.  Apparently the PCBs were delaminated during the vacuum curing process. 

Each panel consists of two pieces of tempered glass with a hollow cavity to hold the cells and electronics packages.  The electronics packages are potted in some type of clear resin (silicone?) between the two pieces of glass.  There have obviously been some problems with evacuating the air out of the sandwich – as evidenced by the bubbles in the photos. 

The panels are connected together by 4-pin flat trailer lighting connectors.  The wires on these appear to be 16AWG, while the DC wiring back to the panel is 14AWG. Each panel is connected by two wires – and this is where things get interesting – by looking at the panels closely it clearly appears that each was originally intended to have an eight wire interface.  Six of the wires have been cut off at the edge of the panel.  More on this in a bit.


The installation is a bit strange in that the rated wattage of the panels exceeds the ampacity of the cabling that should be carrying the power to the panel.  The installation should generate 55A at 24VDC at peak, yet only three 14AWG cables are provided back to the panel with a rated ampacity of 15A each.  Even stranger, there are 5 microinverters for the three 12VDC cables.  Maybe two more cables were pulled during the night, but it looked like the conduit was close to full to me. 



I need to say that while I did not meet the Brusaws, the team members on site were incredibly nice and helpful.  I was given full access to photograph what I wanted and even invited to stand on a panel – which I did – and it survived my immense bulk admirably. 



I would urge people to be kind when commenting.  The SolarRoadways employees have been absolutely working their assess off with little to no sleep getting this demonstration ready.  Whatever I have to criticize technically, I certainly would not criticize the herculean efforts that good people have put forth in bringing their idea to fruition.  So, good work, SolarRoadways crew! 

These particular panels are installed on a sand base in nearly the same manner one would install concrete pavers.  The panels are locked together with metal strips top and bottom which are screwed together.  The edges that border the concrete have aluminum strips that are attached to the concrete to lock the panels into place.


Here is the third panel being laid down:

I also managed to look inside the control panel / kiosk, and this is where things get interesting.  Solar Roadways has kept its topology of using EnPhase micro inverters.  These inverters are the M215-IG models.  I was told that the inverters connect directly to the local utility.  I’m not sure that this is correct, since these are 120/240V inverters, but perhaps the utility has enabled some type of net metering. 


Where things get really interesting is in the upper right hand side of the panel.  One finds a total of six MeanWell 500W power supplies.  This does not mean they are supplying 3000W constantly, but the fact that the power supply is more than double the rated wattage of the power generation side, should lead one to some obvious conclusions.


What I do not know at this time is what wattage the heaters are rated at. 

Here are some calcs with what I know about the installation:



SolarRoadways has conducted demonstrations of the panels using a power supply to light the LEDs – even in daylight.  This is surprising to me because one would think that each solar panel, at 44W, would be able to provide its own power for the micro and a couple watts of LEDs.  I saw several panels that were ostensibly functional, but saw none operate under natural or artificial lighting.  I have a suspicion that these panels operate as only powered devices at the present time.  I will know more next week once the meter goes on line.  I will be contacting the City of Sandpoint on this as well. 

I honestly think SR was overly ambitious with this installation.  If they had simply confined themselves to solar generation only, without worrying about microcontrollers and blinky LEDs, that this may have gone better.  What the city of Sandpoint has at this time appears to be a piece of artwork, more than a power generation system.

[LabSpokane]

Site

[LabSpokane]

Shading

[LabSpokane]

Not much power out of those panels, I would guess around 30W per panel, and at a price of around 200 times that of a 30W panel, including installation.

While you can stand on a glass panel and not break it, I would like to see those panels after 6 months of people walking across them with muddy shoes, high heels and the odd bike and street sweeper going over them. Then I would like to see the power output compared to a similar size installation on a nearby roof.

44W each.  They pay a huge price in capacity for the hexagonal design.  Theoretical output should be 2100 W if they had used 150sqft of conventional solar panels. So, they are losing about35% in capacity in the design alone.

I'm looking for a comparable site in the Sandpoint area with online data.  Not sure I will find one. 

[ataradov]

That webcam will be a hit in the winter time, when this things gets covered with ice and people start slipping and falling.

Overall - topic title says it all. And taking public money for this is a total scam.

[amspire]

That is an odd assortment of parts.

I assume they are providing a 3 phase output with the 3 inverters, but they are 215W continuous each so very underrated for the panels. I do not quite see the point of a test like this if you are using inadequate cables and inadequate inverters - unless they know that the panels will only output less then a total of 600W absolute maximum.

The inverters will only switch on at 22V and the optimal working range for the inverters is 27V-39V so maybe the panels are wired for more then 24V.

And what are they doing with the 6 x 12V supplies from the mains? 12V is too low as a backup for the inverters and if they as putting a pair in series to get 24V, why wouldn't they buy 24V supplies? It does seem to suggest that they are using 10 panels per phase rather then pooling all the panel outputs together. It sounds like they are just making do with bits and pieces they had available.

It would be disappointing if this is just a stunt instead of a proper test to gather data.

If the idea is to gather data, then I do not mind the shadows - that it the reality of Solar Roadways unless you are going to ban cars, people, trees and all buildings anywhere near the roadways.

[LabSpokane]

That is an odd assortment of parts.

I assume they are providing a 3 phase output with the 3 inverters, but they are 215W continuous each so very underrated for the panels. I do not quite see the point of a test like this if you are using inadequate cables and inadequate inverters - unless they know that the panels will only output less then a total of 600W absolute maximum.

The inverters will only switch on at 22V and the optimal working range for the inverters is 27V-39V so maybe the panels are wired for more then 24V.

And what are they doing with the 6 x 12V supplies from the mains? 12V is too low as a backup for the inverters and if they as putting a pair in series to get 24V, why wouldn't they buy 24V supplies? It does seem to suggest that they are using 10 panels per phase rather then pooling all the panel outputs together. It sounds like they are just making do with bits and pieces they had available.

It would be disappointing if this is just a stunt instead of a proper test to gather data.

If the idea is to gather data, then I do not mind the shadows - that it the reality of Solar Roadways unless you are going to ban cars, people, trees and all buildings anywhere near the roadways.

As far as I could tell, this is single phase 120/240VAC.

The power supplies must be for the heaters - all I can figure. Between the automotive connectors and the 12VDC power supplies, I thought it was a 12VDC bus until I looked up the inverter datasheet like you did. Good catch on the 22V startup voltage.

I doubt this is a 120VDC system. Anything over 48VDC is not compatible with people safety.

Like I said, I will be in touch with the right people on the generation side.

[Mr.B]

The power supplies must be for the heaters...

If there is only a pair of wires to each panel as shown in your photos, where does the heater bit come in?
Is there a separate heater pad under the panels... 

[LabSpokane]

The power supplies must be for the heaters...

If there is only a pair of wires to each panel as shown in your photos, where does the heater bit come in?
Is there a separate heater pad under the panels... 

I *think* it's sandwiched in the stack up. The PCBs are labeled with some type of temp sensor. But, unless the wiring is dramatically increased in gauge, it's unclear to me how the power will be transmitted without melting the insulation. Each power supply can deliver 40+ amps.

[Mr.B]

I'm confused...
Two wires are required for the transmission of power from the panels to the inverters.
There doesn't appear to be any electrical connection for heaters, unless I am missing something from your photos.

[LabSpokane]

I'm confused...
Two wires are required for the transmission of power from the panels to the inverters.
There doesn't appear to be any electrical connection for heaters, unless I am missing something from your photos.

I'm saying the heaters seem to be internal to the panel. It's all very puzzling to me as well.

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Disco floor mode.


Don't ask me how ANY of the lighting displayed corresponds to creating the yellow and white lane marking used on roadways. I haven't even seen what resembles an attempt to do so.

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7:26 pm PDT - Less than 12 hours after unveiling, two of the working panels have already had some type of electrical failure.

[amspire]

3000W of heating to keep a 600W maximum solar panel/inverter system running. It is still only 100W of heating per panel - is that enough? At a guess, it is probably enough to raise the panel temperature by 10 deg C if there is no snow or water. It will be interesting to see if historic and live data is available when the system is running.

[LabSpokane]

3000W of heating to keep a 600W maximum solar panel/inverter system running. It is still only 100W of heating per panel - is that enough? At a guess, it is probably enough to raise the panel temperature by 10 deg C if there is no snow or water. It will be interesting to see if historic and live data is available when the system is running.

You're correct assuming what I saw was the final install.  To be fair, if all the panels were operational *and* connected to the inverters and assuming similar efficiency to rooftop solar, it would be a 1320W system. 

[Mr.B]

7:26 pm PDT - Less than 12 hours after unveiling, two of the working panels have already had some type of electrical failure.

A successful marketing campaign. Not.
I wonder if they went to the Roo Brothers School of Marketing.
Second thoughts, they can’t have, they delivered something…

[LabSpokane]

7:26 pm PDT - Less than 12 hours after unveiling, two of the working panels have already had some type of electrical failure.

A successful marketing campaign. Not.
I wonder if they went to the Roo Brothers School of Marketing.
Second thoughts, they can’t have, they delivered something…

Look at the live video feed.  Whatever I think as an engineer, this system has been an absolute success from a PR standpoint.  Kids love it. They have every kid in town coming by to play electric hopscotch. 

From the people that I've spoken to, I predict that absolutely no one will make a critical evaluation of this system from a "does it actually do what it was promised" standpoint.  Nobody cares if it generates a net surplus of power, cost per kW of power delivered, installed cost per kWe, cost per mile of road, if it will stand up to studded snow tires, whether it can produce legible road markings that are visible from a long distance during daylight hours.  Nobody cares.  And I'm talking about even the people that should know better.

All you need are blinky LEDs.  Nothing else matters.