Go Green Stay Green

The stabilized cell efficiency of the PV laminate material is lower. Asthis spreadsheet shows, Unisolar’s best “stated” cell efficiency is 8.5%, but the tile system from SRS Energy won’t use those cells. According to their documentation, the 3-cell tile is 17 Watts, and as each Unisolar cell is 0.239 meter x 0.356 meter, it means the effective cell efficiency is 6.7%, which corresponds to 7.5% “stated” cell efficiency (the same cell used in Unisolar’s latest laminate, PVL-128). However, to make things worse, the documentation states that 30 interlocking tiles cover 100 sq ft, and since each panel is 17 W, that means 510 Watts per 100 sq ft. (actually, this and this stories claim the tiles are only rated 500 watts per sq ft). Using the 510 number and dividing by the area in square meters, the calculated “panel”-level efficiency is just 5.5% (30 * 17 W / 9.29030 sq m / 1000). Even the PVL-128 laminate (made with 22 cells) has a slightly higher, 5.9%, panel-level efficiency.

“That [cell efficiency] puts it slightly below what others in thin-film photovoltaics have been getting.” Not true. First Solar’s panel-level efficiency is at least 10.4%, thus the solar tile efficiency is not just slightly below, but 47% below that of First Solar’s thin-film modules. This is one of the reasons why First Solar sales are increasing, while Unisolar sales are declining.

“SRS Energy system’s overall efficiency makes up for the difference in sunlight to electricity conversion figures. ‘If a homeowner bought 4kW of crystalline silicon panels and then 4KW of the Solé US Tiles, they will get 10 to 15 percent more output in terms of a KWh (kilowatt hour) on their electricity’” The “make-up” statement is a red herring, of course – a 4KW solar tile system will occupy 3.5x the area of a 4KW crystalline SunPower system. The “10-15% more kWh/kW” statement is false as well, including the concocted explanations of panels waking up earlier, or better absorbing the light spectrum, etc. Several documented real-world performance records in various climates in the US and Europe demonstrate that the alleged kWh/kW advantage is a myth (I, II, III, IV, V, VI). The advantage, if any, is 5% and below. Thus, “effective” panel-level efficiency could potentially rise to only 5.8% (5.5% *1.05). Of course, that 5% advantage will be there only in the first 5-10 years, as the faster degradation of the Unisolar laminates relative to other thin-film and crystalline modules will eliminate it over time (average annual degradation for Unisolar triple-junction laminates has been shown, see page 9, to be 1.22%, while crystalline’s is typically 0.5-0.7%). But that’s not all. What makes things worse is that the tiles are curved, thus even for a roof that is south-oriented and tilted at optimal angle, the light hits the PV cells at various suboptimal angles. Even a casual simulation analysis with the PVWatts calculator indicates that, in fact, the curvature could result in less energy than a flat panel tilted at zero degrees slope. For example, a flat panel, tilted flat (zero degrees), in San Diego is estimated to generate 1314 kWh/kW AC electricity a year. A south-oriented 30-degrees-tilted flat panel generates 1500 KWh/KW, but east-oriented 30-degree-tilted panel generates just 1160 KWH/KW, while a west-oriented 30-degree-tilted one does 1268 KWH/KW (note how the east- and west-oriented tilted panels generate less electricity than a zero-tilt panel). Thus, almost certainly the tiles will underperform crystalline and CdTe panels (which, of course, both have flat surfaces) on the same roof on kWh/kW basis.

“SRS Energy’s statistics say the average homeowner with Solé Power Tiles can get 860 kilowatt hours per square foot annually living in an area with ‘5.8 peak sun hours’ per day.” SRS Energy has no such statistics, as they would contradict the real world experience of installations with Unisolar laminates. Actually, the laws of physics make it impossible for a PV solar system to generate 860 kilowatt hours per square foot annually in an area with “5.8 peak sun hours” per day. SRS Energy’s literature makes a more believable claim of 860 kilowatt hours per square (a square is 100 sq ft). But even that claim is deceptive. For the “860 kWh per square” claim to be true, the tiles must be generating 1686 kWh/KW AC electricty on an annual basis (as a square has 0.510 kW worth of solar tiles). Luckily, there are few Unisolar installation in San Diego, an area with “5.8 peak sun hours,” according to PVWatts (solar radiation hitting south-oriented 30-degree tilted panels), so the claim can be verified. SIT has installed Unisolar-based roofs at 28 schools in the area (installations and performance have been summarized in a spreadsheet). The median/average performance was below 1470 kWh/kW, or 13% less than what SRS Energy claims. A Unisolar system installed by Sullivan Solar, an installer in the area (see the same spreadsheet) has done a bit better, 1550 kWH/kW (accidentally, just 1% better than the average and median of three crystalline installations nearby). True, these Unisolar installations are on flat roofs, but as explained above, zero-degree tilt “panels” would likely outperform the curved solar tiles.

The CNET story ends with a picture of the SRS Energy’ CEO’s ice-cream parlor (sporting mostly red tiles and a row of the blueish solar tiles), which according to the story is “the first commercial buildings to implement the Solé Power Tile system.” But his store’s home page shows grey shingles and so does Google maps’ satellite image. So, SRS Energy’s CEO had to waste money and labor to tear down and replace a perfectly nice roof, so that he could install 1KW or so worth of solar? Is that SRS’ idea of “eco-nomics?”. Is that “the sustainable upgrade [made] a simple one for the homeowner, which means it is also more accessible?” (see here [cached]).
The CEO stated [cached] that “choosing to upgrade to a sustainable roof from SRS Energy puts energy savings in homeowners’ pockets immediately and delivers compelling long-term returns.” That wasn’t the case with his “sustainable” roof, but he is clearly hoping that the showcase will transfer the homeowners’ savings into his pockets, and, hopefully, deliver some return on the millions [cached] put in his venture by “angel” investors.

Before analyzing the prospects of a success for this product, let’s explore some more “marketing messages” scattered across product documentation and planted articles:

• “SRS Energy materials are UL recognized as trusted and safe solar roofing components.” (source: here). Possibly, but why is the “UL Recognized” logo missing from the “sell” sheet? The solar tile is obviously not UL certified, and using UL recognized materials means little for an electrical device. Here is an example: copper wire is UL certified, but soldering it to short the solar tile electric connector will lead to overheating and even fire under the sun. Will these tiles ever pass any UL or IEC certification? Note that Unisolar laminates’ IEC 61730 certification may still be “pending,” and the original Unisolar “residential product”, the SHR-17 solar shingles (now taken off the market), no longer carry the UL certification and were shown to degrade in likely violation of their warranty (and then Unisolar simply stopped disclosing degradation data).
• “Solé Power Tile … bringing the first building-integrated photovoltaic (BIPV) roofing product to curved roofing systems.” (sources: here [cached] and here [cached]) . This is patently false, of course, as SRS Energy’s patent application, as well as the CAD drawing indicate that the tiles have to be nailed to straight, not curved, underlayment given their interlocking design.
• Chart titled “They wake up earlier and stay up later” and footnoted “Amorphous silicon thin-film technology incorporated within the Solé Power Tile allows the system to produce an estimated 8-20% more energy than incumbent crystalline silicon panels” (source: here).

Look at the Y-axis label on the left. It is in kWh. What this chart claims, then, is that by 1 pm, “conventional” glass modules have generated 400 Wh while the tiles have generated only 350 Wh worth of electrical energy. In the afternoon, all this generated electrical energy is consumed, bringing net PV generation for the day to zero (for both the conventional panels and the tiles). Of course, the label is wrong. It should be “kW” not “kWh.” One is a measure for power, the other, for energy. But these are probably minor details for SRS Energy and their clay tile partner. Unfortunately, even if the axis were labeled “kW,” that pricture would contradict SRS Energy’s message that the Unisolar’s panels somehow do not “degrade in performance as they get hotter” [cached]. Around 1pm, a time not known for the lowest temperature during the day, conventional panels, according to this chart, outperform the solar tiles!

• The rest of the Performance and Savings sheet is all wrong, as well. A 4KW tile system in a “5.5 hour day” area (San Francisco or Santa Cruz) will not generate 6,022 KWh on an annual basis. Even an optimally (30 degrees) tilted and well-ventilated Unisolar laminate generates only 1500-1650 kWh/kW in Santa Cruz. A zero-degree-tilted flat laminate makes 1275 kWh/kW, on average. As discussed already, even optimally tilted curved tiles will likely generate much less than optimally tilted flat panels. Thus, the most SRS Energy can hope for is 1500 kWh/kW for their tiles. That comes to 6,000 kWh for a 4KW system, which is well below the 6,800 kWh in their “illustration.” The crystalline number of 6,022 kWh in the “example” is more plausible, by the way. Finally, the term “Efficiency” (see the third term in the calculation illustration) conventionally applies to conversion efficiency, not performance ratio.
• “The Solé Power Tile™ energy advantage allows the system to deliver more savings in the form of a reduced or eliminated electricity bill and creates value with increased homeowner equity” (source: the Performance and Savings sheet). To illustrate that bold statement, SRS Energy attaches an electrical bill that indicates 376 kWh electrical energy usage. In fact, the bill shows that electricty consumption increased from 176 kWh in the period 2/14/2009-2/28/2009 to 200 kWh in the periof 3/1/2009-3/17/2009. This surely does not look like a house with a solar system installed. It is even more weird that SRS Energy has decided to “magnify” that 376 kWh energy usage and label it 379 kWh. A Freudian slip, no doubt. The energy bill did not get reduced. It increased! The hapless homeowner will actually experience a destruction of value – more on that below.

So, setting aside the marketing propaganda, does this new product make any sense? The answer appears to be no:

1. Just two SunPower SP-315 panels (61 inch x 41 inch each, covering a combined area of 17.6 sq ft) deliver 24% more power under STC than 30 solar tiles (covering 100 sq ft). Two SunPower panels can be installed in minutes, laying 30 tiles and carefully connecting them to the underlayment circuitry may take hours. No wonder SunPower has 20%+ share in the California rooftop PV market (the first intended market [cached] for the tiles), while Unisolar’s share there is 0.1%, according to the CSI.
2. Cost will be prohibitive, even after ITC. The tiles need to sell for $6 or more per Watt for SRS Energy to break even (initial plans were for $8 per Watt [cached]). Unfortunately, thin-film solar panels can be found for less than $2 per Watt on the market these days, and all the tiles will save in terms of equipment or materials is a rack (which is only anywhere between 60c to 10c per Watt, depending on the installation size).
3. The solar tiles will not be viewed as a roofing material. Clay tiles can be purchased for $200 per square [cached]. At $6 per Watt, the solar tiles will cost $3,000+ per square ($6 x 510W), or 15x as much. Their color is attrocious, and they are made of plastic (polypropylene). There are reasons why people generally don’t put plastic tiles on their roofs that are supposed to last at least 20 years (cost, discoloration, delamination, degradation from UV radiation over time, and fire hazards [cached] come to mind). The weird rare color makes things worse – a thoughtful homeowner would wonder who will provide the dark blueish tiles in 5-6 years if breakage or loss occurs, if the sole manufacture of the Solé tiles has (god forbid) discontinued the product (the owners of the Unisolar’s SHR-17 shingles are currently in that pickle).
4. Going PV with solar tiles rather than regular solar panels will be viewed as a risky proposition by the customer, given that 99.9% of the PV market in California is flat glass panels, even ignoring the lack of certifications or ineligibility for state incentives. Jumping on the tile bandwagon won’t be an “incremental rather than monumental” decision SRS Energy wants us to believe [cached]. Quite the opposite. Of course, SRS Energy could easily “absorb the headaches and paperwork surrounding solar incentive programs” – there simply won’t be any state incentives in California for this product.
5. Plastic is not a truly “sustainable” material (as it is made from hydrocarbons) and it is not a clean way for homeowners to go “green“, despite SRS Energy’s claims [cached] to the contrary. The solar tiles may not be a truly LEED product either, despite SRS Energy’s claims – unlike ceramic tiles which absorb moisture at night, and thus cool the roof during the day, plastic does not absorb water.

CertainTeed, arguably the country’s third-largest roofing company, acquired [cached] an equity stake in SRS Energy in 2008. What were they thinking?