GreenMountain Engineering

Standards for Photovoltaics

I recently returned from a week spent as one of the US representatives on the IEC Technical Committee 82 (TC82), which develops standards for solar photovoltaics. My focus is on Working Group 7, where we are working on standards including solar trackers and power and energy rating of concentrating photovoltaic modules. However, meeting with the rest of the TC82 community also gave me an opportunity to discuss issues in the design and testing of conventional wafer-based and thin-film modules.

While there are a number of groups working on standards applicable to solar (including the UL, ASTM, and NEC in the United States, CENELEC in Europe, and IEC and ISO internationally), the IEC plays an especially significant role because photovoltaics is a global market: major producers of polysilicon, cells, modules, and tools are spread across Europe, Asia, and the Americas, and customers are worldwide as well. Similarly, TC82 has members from 29 countries (including the major markets; China, Spain, Germany, the US, Japan, and France) working together to develop standards.

Standards are an important part of any growing industry.  For example, the SEMI International Standards Program is widely credited with speeding the growth of the semiconductor industry since the 1970s. Looking back, it’s hard to believe that at one point wafer sizes and shapes were not standard, and “custom-made solutions for each individual customer were the norm”[1].

For an industry whose value proposition depends on long product lifetimes in outdoor environments, standards that govern design qualification, accelerated testing, and safety of products are especially important. Additionally, standards for power rating, energy rating, and measurement are critical for allowing side-by-side comparison of different products.  This is especially apparent when trying to compare between crystalline PV, thin-film PV, and CPV.

Some of the PV standards we find most relevant in our work[2] are listed below. Where possible, I’ve also linked to free previews of the table of contents of each standard:

• IEC60904: Photovoltaic Devices
• This is a large, ten-part standard (IEC60904-1 is the numbering scheme for part 1, and so on) covering a number of device characterization areas such as measurement of I-V curves, spectral response, and solar simulators.

• IEC61215 (ed2.0, 2005): Crystalline silicon terrestrial photovoltaic (PV) modules: Design Qualification and Type Approval
• Note that a third edition is in development within the IEC.
• UL1703: Flat-Plate Photovoltaic Modules and Panels
• Note that this is also applied to thin film modules and in some cases in the past concentrating modules, though see also UL8703 below.
• IEC61646 (ed2.0, 2008): Thin-film terrestrial photovoltaic (PV) modules: Design Qualification and Type Approval
• IEC62108 (ed1.0, 2007): Concentrator photovoltaic (CPV) modules and assemblies: Design Qualification and Type Approval
• Note that for low concentration (<10x) modules, it is less clear whether they will be tested under IEC 62108 or an adapted form of IEC 61215. And some concentrating systems such as heliostats differ from the main focus (no pun intended…) of IEC 62108.
• On the IEC committee we are actively soliciting feedback on the first edition, as we work on a second edition.
• UL8703: Concentrator Photovoltaic Modules and Assemblies
• UL1741 and the just-published European standard EN50530 cover inverters
• The PV Resources web site contains a more exhaustive list of standards, though it is somewhat out of date and does not mention some of the newest standards. And the standards above cover a significant portion of what companies we work for care about.
• You may also find this UL diagram of UL/IEC PV standards by system component informative.

For anyone who was new to the industry, I hope this list of information is useful. 

That said, qualification standards only outline the bare minimum testing. It’s important to design tests to simulate other failure modes and environmental conditions not included in the standards. In addition, testing identifies certain failure modes that are more systematic (damp heat for the previous generation of thin-film modules, for example), helping guide areas for design.  Including testing early in the development path is important: we have seen some companies develop a first prototype, only to require major design revisions once they begin thinking about reliability, DFM, and qualification. 

The topic of PV module design for reliability could be a whole separate discussion, but two documents to get you started down this path are:

• NREL's "non-comprehensive summary of the most common types of failures for each PV technology", with 53 references to additional papers
• Another paper out of NREL, published in 2009: "History of Accelerated and Qualification Testing of Terrestrial Photovoltaic Modules: A Literature Review"

Standards themselves don’t necessarily inspire passion and dedication in everyone, but their purpose overlaps with the desire to design and build high-quality, reliable, cost-effective technologies that can solve some of our pressing energy supply and environmental issues. And doing that makes us at GreenMountain very excited. Come back to this blog next week for a post about the scalability of solar, examined from a variety of perspectives (land usage, capital requirements, labor, and growth rate). 

[1] The SEMI International Standards Program – History, Successes and Lessons Learned to Address Compound Semiconductor Manufacturing Challenges, http://www.csmantech.org/Digests/2006/2006%20Digests/4A.pdf

[2] I'm putting the "about us" blurb down here in a footnote as many readers may already be familiar with us: We offer design engineering for hire, including engineering of products, automated tools, and software for many companies in the cleantech sector. This includes extensive experience in the solar industry (we’ve done design engineering for dozens of solar companies). The product-related standards I mention in this post are less relevant when we develop manufacturing tools, but do come into play when we design solar modules, encapsulation, interconnects, CPV receivers, or a range of other solar components.

Highlights from the 5th Conference on Clean Energy in Boston

Matt, Jon, and I went to the Conference on Clean Energy at the Hynes Center in Boston today. This morning, I watched a series of investor pitches from a group of cleantech startups. The mix was interesting-- smart grid startups were dominant, which is a big change from the last few years, where solar, wind, and biofuels were the big players.

To my ear, the most interesting pitch was from the least clean of the startups-- Silicon Basis. They're an integrated circuit company; the "clean" angle is that their chips will have lower power consumption.

Dave Richards, a charming Englishman from the University of Bath, spoke in place of CEO Rob Beat. Silicon Basis is trying to implement a new type of chip that has lower power consumption and better performance (600 MOPs/mW) than the typical chips used in cellphones, ipods, and the like, but with a reconfigurable technology that will reduce development time and cost substantially below the usual 18-24 months and $10M. In technical terms, they say they've figured out how to manufacture FPGAs that reconfigure themselves between clock cycles. If they have actually pulled this off, they are insanely smart. About 2 months ago, they were issued patent GB2457912 in the UK. Silicon Basis also announced a partnership with Actina Imaging, who will help them test their first chips.

Here are brief summaries of the other startups that pitched.

Jason Hanna, President and Founder of Coincident Smart Energy Technology

Jason is a computer engineer out of EMC. I talked with him for a few minutes after the talk; he seemed like a smart engineer. Coincident is developing two things: an online marketplace for HAN devices and services and a hardware gateway. From my perspective, the hardware gateway was more interesting-- an embedded Linux board with a Zigbee wireless module. On looking at their website, I realize that I had found it a few months ago-- I'm impressed that they managed to get coincident.com.

Steven Filler, Director of Business Development, Prism Solar

Prism Solar is building holographic concentrators for solar panels by replacing 70% of the silicon with strips of holographic film. I was inclined to like Filler's presentation because it included a lot of numbers. Their holographic film selects part of spectrum for efficient heat rejection, which results in 10 C cooler cells at high noon in Tucson as compared to a conventional solar panel. Filler claimed that their holograms have better acceptance angle and can use bifacial cells. He claimed a 70% increase in energy production. Prism is selling modules domestically, but really wants to sell holographic film under license. They think they can hit 1.04 $/W by 2012.

Rory Gaunt, CEO, Lifecycle Renewables

The most interesting part of Rory Gaunt's presentation was the bullet: "negligible technology risk." Lifecycle Renewables' plan is to convert waste vegetable oil into fuel for commercial electricity and heat.
Whole Foods Market will be their first oil supplier and customer in 2010 when they bring up a 500 kW station, taking a 45,000 ft² kitchen facility off the grid. Their claimed advantages over other biofuel heat/power startups are low cost processing, efficient logistics technology, and state and federal incentives. They're seeking $750k and plan to be profitable in year 2. I like Mr. Gaunt's straight-forward style: "Funds will be used to get the oil."

Roselyn Romberg, Electronic Housekeeper

Founded in Denmark in 2005, Electronic Housekeeper launched in Europe in Q1 2008. They plan to establish a new headquarters in the US shortly. They make smart grid hardware hub for apps and services with backend database. They've had $1M in sales so far, and they claim that their customers' have seen usage reductions of 10-15% in electricity, 15-25% in gas, and 20-40% in water. I thought it was interesting that Ms. Romberg emphasized their device's passive nature: "We don't rely on behavior modification."

Roger Faulkner, Electric Pipeline

Cost-effective underground power transmission. I'm afraid don't know much about power transmission, so I didn't listen to Roger carefully. Sorry, Roger.

Dave Howell, COO of Practical Solar

Practical Solar is making heliostats with a total cost of $200/m². Howell viewed the proprietary firmware in their controller as a strength, and he boasted about how difficult it would be to reverse engineer it, taking more than a year and a million dollars to do so.

Mitch Wondolowski, Grid Solutions

Weather, market prices, and utility rates integrated into a residential demand response system.
"Enabling residential load balancing for the grid"

Richard Chase, Future Solar Systems

If I understood Mr. Chase correctly, Future Solar will install solar panels using an arrangement similar to that used by the City of Berkeley in California-- they put up the capital to put solar panels on your roof, and then you pay them for the electricity over the next 20 years. (Not exactly the same as Berkeley, but similar.)

That was all in the first session on Thursday. If i have the time, I'll add more summaries from the rest of the conference tomorrow.

Rooftop testing station site goes live

John Lawler mentioned our rooftop testing station back in April. We've undertaken a fun project over the last couple of weeks, and I'm pleased to announce our web site that shows data from the instruments in our rooftop solar testing station. You can check it out at http://roof.greenmountainengineering.com/.

Data is recorded whenever the sun is up in San Francisco and is displayed "live" (well, actually updated every 60 seconds) for the current day. If you select a day in the past from the calendar, you'll see data from that day. You'll also get a fancy time-lapse video showing the weather conditions for that day.

Although the setup is explained in much more detail on the actual site, the very short version of how this all works is that we have a computer in a weather-proof case on the roof. The computer collects data from all of the various instruments and sensors (including a Trac-Stat SL1) and sends it off to our web server. Our web server stores that data, processes it, and sends it to you in the form of a web site.

This whole arrangement is a simple analogue for a number of projects we've done for our clients. Although our rooftop testing station site shows off a publicly-accessible, read-only interface to a single set of equipment, we've built secure systems to control and monitor hundreds of discrete pieces of equipment simultaneously, log hundreds of gigabytes of data per year, and provide convenient access to equipment in remote locations.

Please let us know if you have any questions about the site or if you'd like to learn more about the kinds of things we can do to develop monitoring and control systems for you.

Hello smart grid, goodbye stupid grid

The east coast office of GreenMountain in Cambridge, Massachusetts, has a reasonably impressive array of electrical meters. They're all Elster A3 "Time-Of-Use" meters, meaning that they record not just the amount of electricity used, but also the time it was used. In theory, the utility can then use a rate structure to encourage their customers to use less electricity at peak times. The meters have the typical ANSI optical port, so you can hold an ANSI reader up next to the meter and read data locally. The meters in our building also have Itron's 50ESS ERT radio transmitter, which is a separate module that slides into the side of the stock A3 meter. I'm not sure how NSTAR (the local electric utility for most of the towns around Boston) is actually reading the meters, but they're probably driving around with vans containing short-range radios to read the data. That's about as smart as our grid gets in 2009.

I first worked on smart grid hardware in 2002. (We didn't call it "smart grid" back then.) Now, we'd say that I was working on AMI, "automatic metering infrastructure." At the time, I worked on a line of power distribution units for data centers.

We used an embedded processor with no operating system, just our own firmware written from scratch in C. Early on, we decided to use a proprietary TCP/IP stack; the next closest competitor was an IC called "i2chip," which implemented TCP/IP entirely in hardware and cost $12 in quantity 100. (This is now the Wiznet W3100; I believe in a box somewhere I still have a sample from the first batch of silicon the gentlemen from Wiznet made.)

Our web-based monitoring interface used Javascript in a hidden iframe to refresh the interface automatically without reloading the entire page. We measured current with PCB-mounted current transformers; I remember looking at datasheets for the first high current Hall effect sensor ICs and thinking that our upgrade path had finally been invented.

Less than a decade later, the same system would hardly be recognizable. Our latest remote monitoring deployment (actually for use in the photovoltaics industry, not smart grid) uses an entirely open source stack. We run Python on Linux with the Yahoo User Interface library to make the front end smooth. That all the components are open source is a sign that we're working in a domain where the benefits of interoperability outweigh the costs of open development.

I suspect that the same transition to open technologies developed to interoperability standards will occur in the larger world of smart grid, but it needs help to happen. The development of such standards has been underway for years, but since NIST received a mandate to coordinate the development of smart grid interoperability standards in the Energy Independence and Security Act of 2007, it has accelerated. In a roadmap workshop in late April, 2009, NIST released the first draft of the list of smart grid standards they will recognize in their framework. The revised release is expected at Gridweek this Thursday.

NIST's list gives only a few words to explain what the standards are, so for those of you new to the industry, here's a summary with a little background on each item.

There are 16 standards on the list so far, but the upcoming revision will probably add more. The links that start each section point to the canonical source. You'll notice that the Open Smart Grid subcommittee is a big player.

AMI-SEC: A task force was formed in 2007, but they haven't released a standard yet. The standard will relate to security for advanced metering infrastructure, i.e. how do you prevent miscreants from sniffing your meter data, while still allowing the power company to do it? At first blush, this seems like an inconsequential problem, but it's not. For example, if you wanted to figure out whose house was ripe for burglary because they're on vacation, and you could read data from electric meters, you could do it with a few trips through a neighborhood with a van that records usage data and compares it to the past. Hey, looks like the folks in Suite 100 of 5395 Pearl Parkway aren't home; let's rob them!

ANSI C12.19: This is a standard that describes structure of data that can be transferred by the ANSI optical port I mentioned above. The standard was originally released in 1997; a revised version, ANSI C12.19-2008 was released last year. This standard isn't likely to play a big role in smart grid because optical ports are slow and short-range.

BACnet: BACnet is a standard that specifies a communication protocol for building automation and control. The standard was created by ASHRAE, the HVAC experts, in 1995. The most recent release is ANSI/ASHRAE 135-2008. By now, there are open source implementations of BACnet in at least three languages: C, Python, and C#.

DNP3: A protocol for communication between SCADA equipment at electrical substations. If you're interested, the DNP User's Group has a good primer.

IEC 60870-6/TASE.2: Protocol for communication between electric utilities.

IEC 61850: Covers automation within individual substations.

IEC 61968/61970 These standards define APIs for use by utilities. The former is for automatic meter reading, the latter for energy management systems.

IEC 62351 Parts 1-8: A security standard for power systems, published in eight parts. The first 6 parts have been released; part 7 is expected in 2010; and part 8 is aimed at late 2013.

IEEE C37.118 This standardizes communication about phase information between different parts of the grid. The title is "IEEE Standard for Synchrophasors for Power Systems." The word "syncrophasor" refers to the concept of using absolute time references for phase information, rather than just assuming that two systems are operating at exactly 50.0 or 60.0 Hz. The standard also mandates minimum reporting frequencies. The standard is managed by the IEEE Power System Relaying Committee Working Group H11. NIST would like to see IEEE C37.118 harmonized with IEC 61850, mentioned above, which covers phase information relaying within substations.

IEEE 1547 Standard for connection of distributed resources, meaning small, non-centralized power producers like solar panels or wind turbines (though they need not use renewable sources of energy), to the grid.

IEEE 1686-2007 Security for the ill-named intelligent electronic devices (IED's) in substations. This standard is produced by the IEEE Power Engineering Society Committee on Substations. (Alarmingly, the password used to secure the committee's "Protected Files" is stored in plaintext in the webpage source code, and the files are hidden with only an obfuscated URL. Perhaps even more alarmingly, the only document they've seen fit to secure is an announcement about a Halloween costume party. And they're generating a secuity standard?)

NERC (North American Electric Reliability Corporation) CIP 002-009: Another security standard, CIP 002-009 lays out 8 different topic areas that must be addressed when setting up network equipment for bulk electric systems. These range from what hardware can be used, to how to train personnel, to physical security of the site. For the purpose of the standard, NERC has defined the "Bulk Electric System" to be the electrical generation resources, transmission lines, interconnections with neighboring systems, operated at or above 100kV.

NIST Special Publications SP 800-53 [PDF] and SP 800-82 [PDF]
These NIST special publications are also security standards. The first, SP 800-53, makes recommendations about security controls for computer systems used by federal executive agencies. The second, NIST SP 800-82, is broader, covering industrial control systems. It's not specific to smart grid, though certainly all grid systems use industrial controllers. Further, the standard does list the SCADA controls of the grid as the primary example of an industrial control system that needs security.

Open Automated Demand Response: OpenADR is a communication protocol for transmitting demand response signals from utilities to electric customers' appliances, which presumably will react to use electricity at off-peak times. The refrigerator that Tendril announced today with GE at GridWeek uses price signals to figure out when it should make ice (at night, when it's cheap); based on an earlier press release, I'd bet it's using OpenADR.

OpenHAN: First released in 2008, OpenHAN describes a framework for secure communication over a network with consumers' devices to implement, among other features, load-shedding and metering. The acronym HAN is an unpleasant bastardization of the already-odd "local area network" (LAN) into the truly nonsensical "home area network." (Not as bad as the bizarre SAN, "storage area network.")

ZigBee/HomePlug Smart Energy Profile Zigbee is a standard for wireless communication based on IEEE 802.15.4. Implementors must pay a fee, not just for a copy of the standard, but $3500 annually for a membership in the Zigbee Alliance, plus an additional fee for each Zigbee product released. The smart energy profile allows wireless devices to adjust to price signals and deliver usage statistics, among other features.

Those are the 16 NIST-approved standards we've got so far. We'll see what Commerce Secretary Gary Locke announces on Thursday.

Two Opportunities to See Us

Two Mountaineers will be speaking at events in the Bay Area in the next few days.  We hope you can join us for one of these engaging discussions!  On Thursday, Brian Atchley is speaking on the changing landscape of renewable energy infrastructure at a one-day seminar presented by the Society of Manufacturing Engineers, An Engineer's Guide to Green: New Rules - New Tools.  Then next Wednesday, David Hague will be participating in a panel exploring innovation and financing for clean technologies, Clean Tech Companies in Growth Mode: Challenges, Opportunities, and the Competitive Landscape in a Global Marketplace. Full details and registration information are included below.

An Engineer's Guide to Green: New Rules - New Tools
Thursday, May 21 8:30 AM - 3:30 PM
Santa Clara, CA

Clean Tech Companies in Growth Mode
Wednesday, May 27 6:30 PM - 9:00 PM
San Francisco, CA

Slides from Business and Society Conference

David Hague and Brandon Stafford spoke at the Business and Society Conference at Dartmouth on Thursday, the 15th. After the panel, there was some interest in slides Brandon presented. Some thoughts from Brandon:

The panel on which I spoke was intended to focus on sustainability in supply chains, but my presentation covered the Jevons paradox and the relatively low power density of renewable energy as compared to the high power density requirements of contemporary civilization (click images below for full size).

The other gentlemen on the panel-- Peter Girard from Timberland, Chris Hacker from Johnson and Johnson, and Paul Ligon from Waste Management Upstream-- were from large companies that are faced with the enormous challenge of figuring out how to square their genuine interest in reducing the environmental impact of their businesses, with the reality that they operate in market sectors where their impact scales directly with their sales. (Arguably, this is not the case for Waste Management, but it's certainly true for J&J and Timberland.)

I was heartened to see the leaders of industry professing genuine environmental concern. I was particularly struck by Johnson and Johnson's credo (PDF), which is even more impressive given that it was written in 1942. Even the most honorable of sentiments do nothing to reduce the impact of commerce based around the sale of newly-manufactured goods, but those sentiments are certainly a prerequisite for developing more sustainable business models. I look forward to continuing the debate about how we can balance our need for jobs and consumable goods against the finite supply of resources available.

Images above are based on charts in Vaclav Smil's Energy At The Crossroads, 2003.

Recommended Reading

Looking for something to read over the holidays?

We've compiled a list of our favorite books on a variety of interesting  topics.

You might not be surprised to see that more than half (but not all!) of them are engineering books, so I hope you can find something helpful on a technical topic or otherwise engaging and though-provoking on Our Bookshelf.

Copper disks on a rotary table

One of our clients asked us for help heating a moving tungsten wire to around 1000 C during a manufacturing process. We need to apply around 250 W/m to the wire, and the wire can't withstand a tight bend without breaking. To that end, Matt Dorson has been prototyping a rolling contact system that will use electrified copper disks to run current through the wire. Yesterday, Matt was down in the shop in our Somerville office using a rotary table and the mill to manufacture the copper disks from a sheet of rectangular stock.

This is one of the things I like about GreenMountain-- instead of sending the part out to a machine shop, adding administrative overhead and shipping time, Matt just makes the part. If he realizes while he's making it that the diameter is wrong, he can change it without issuing a new set of CAD drawings. It also means that he becomes intimate with the design; he notices what elements of the design are hard to manufacture and how the design could be improved. For commercial production, this would be horrendously slow, but it lets us prototype and test as fast as we can design. Instead of producing a new prototype every two or three weeks, Matt iterates on a 3-4 day cycle.