New kid in town? (A brief review of the new Enecsys micro-inverter)

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The Enecsys micro-inverter represents a breakthrough in inverter design for residential and commercial solar photovoltaic (PV) installations. Its patented technology has, for the first time, eliminated components that limit inverter life, namely electrolytic capacitors and opto-couplers. Originally developed at Cambridge University, UK, the Enecsys micro-inverter enables solar PV systems to harvest between 5% and 20% more energy over their lifetime. The electrical components of Enecsys design are also worth mentioning since electrolytic capacitors were replaced by their much more reliable ceramic counterparts, significantly prolonging the life of the micro-inverter. Shading caused by clouds or obstructions have minimal impact on overall system performance because power is harvested from each module individually, rather than from groups of modules strung together. This also means that installations can mix and match different modules and do not need to be on the same roof plane, multiple planes can be used to harvest more energy and systems are scalable. A potential single point of failure – the central inverter – is eliminated and dangerous high-voltage DC is not produced.The Enecsys micro-inverter is the only product of its kind, available in both Europe and North America that matches the operating life of solar modules (more than 25 years), operates from -40 to +85 degrees C and and has a warranty for 20 years. Enecsys micro-inverters are installed on the rack behind solar modules, either one inverter per solar module, or one for every two modules.

The following is sample systems applying two competitive micro-inverter technology and regular string size inverter.

  1. Enphase system: 20 x REC 230W , 20 micro-inverters M190-72 with Envoy; total $15,350 plus mounting and other BOS.
  2. Enecsys system: 20 x REC 230W – $9154.00, 20 micro-inverters Enecsys SMI-S240W -72 plus; total $16,343 plus mounting and other BOS
  3. Kaco with Watchdog : 20 x REC 230W – $9154.00, Kaco 5002i inverter; total $14,161 plus Mounting and other BOS.

At first regular string inverter seems to be the most economical. It will harvest the least amount of power though, since shading and other factors will have effect on the whole system, so the price per kilo watt/hr is actually higher than other two systems. The micro-inverter technology allows Enphase and Enecsys work more independent from mentioned factors since power is harvested at each and every module. It seems that Enphase has Enecsys beat in terms of pricing, but during days when maximum power output can be expected i.e. 230W per module, the Enecsys has upper hand because it can gather all energy from modules, while Enphase will cut of at 190W. It is worth mentioning that Enphase is not easily available and potential clients have to wait several weeks before they can implement the system. Enecsys on the other hand is available with no delays. So therefore buyers finally have options when it comes to their micro inverters pv projects. We predict this is just the start of an explosive sub market.

Written by
Konrad Gornicki

Enphazed? (Comparison of MPPT-per-module Options)

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Over the past year, there has been an explosion in the popularity of solar inverter solutions with MPPT tracking for each module. This technology has significant benefits in output, reliability, and flexibility over standard centralized inverter options, especially in partially shaded environments. Of course, there is a cost drawback to every new and complex entry into the market, but cost-benefit analysis will show that in some cases the extra investment will pay for itself handily.

There are three types of MPPT-per-module systems on the market: standalone MPPT controllers such as Tigo products, per-module microinverters like Enphase, and the SolarEdge system, which has a central inverter connected to MPPT trackers per module. The most popular of these by far is Enphase, and for good reason: the flexibility is unparalleled. Enphase sells microinverters in single-phase and three-phase configurations with power levels at 190W and 210W and with MC4 or Tyco connectors. Modules can be mixed and matched, and the inverters are inexpensive to replace if they fail out of warranty. Unfortunately, availability is still extremely tight, so if you are an installer or a homeowner who is looking for Enphase, you better get in line.

Let’s see what happens when we implement Enphase and Tigo solutions on a typical 4 kWp system located in central NJ with a 30˚ pitched roof and partial (50%) shading on two modules on one string and one module on another for 3 hours during the peak of the day:

  1. Enphase system parts: 18x Gloria Solar 230W, 18x Enphase M190 with Envoy and cabling: approx. $13,500 plus mounting and other BOS.
  2. Tigo system parts: 18x Gloria 230W, 18x Tigo ES050V, Tigo monitor, Kaco 3502xi: approx. $13,100 plus mounting and other BOS.
  3. Control system parts: 18x Gloria 230W, Kaco 3502xi: approx. $11,700 plus mounting and other BOS.

The Enphase output will only decrease by the lack of energy going out from the three shaded modules, or approximately 1.08 kWh per day at 3.9h insolation and an 80% derating factor. The Tigo system will operate slightly differently—because the output is stil DC, it will regulate the voltage and current on the affected modules until the string is uniform. Tigo calls the technology “impedance matching” since it observes and matches impedance seen at each energy maximizer connection, but the current in the string does not need to stay uniform since the maximizer will bypass current around modules as suited. As a result, the system will lose 1.08 kWh plus impedance matching losses. Unfortunately, the exact losses are rather difficult to calculate, especially since Tigo’s algorithm is proprietary. The control system, without any MPPT per module device, will lose approximately 6.5 kWh per day, or about 50% of the maximum without shading.

In this sense, both Enphase and Tigo systems are both winners because they give significantly lower costs per kWh even if costs per peak kW are slightly higher. In fact, with SREC prices at $500 per 1000 kWh, the Enphase system will pay for itself over the control system in about two years. If you or your clients have significant shading, please consider investing in one of these solutions—your mileage may vary, but in the end, you will benefit.

Are transformerless inverters worth it?

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Transformerless PV inverters have been available in ROW markets for several years now, but a change to the NEC guidelines for PV has allowed these units to be produced for use with the 60 Hz grid in the US and Canada. They are significantly lighter than their galvanically isolated counterparts and can offer a wider range of operating voltages than traditional inverters because of their advanced switching circuitry. However, there has been reluctance among installers to implement these units, mostly due to lack of necessity and perceived safety concerns. This article will explain the differences between galvanically isolated and transformerless inverters to better inform the installer.

The idea behind transformerless switching has existed long before the PV market was even developed. Device engineers have known that a pair of field-effect transistors operates most efficiently in a complete ON or OFF state, when no current flows through them, and they dissipate no power. Thus, amplifying an ideal square wave would theoretically be 100% efficient. If a signal is modulated by a much higher-frequency square wave, the result is pulse width modulation (PWM), and the corresponding circuit is called Class D. In this manner, it is possible to convert DC to DC, or efficiently switch DC to AC. For solar inverters, the technology was not available in the past because of the high cost of the switching MOSFETs and IGBTs. These, however, are getting cheaper and faster every year, so the technology has become more cost-effective than analog switching into large masses of copper and iron. The same technology is making electric cars feasible.

The downside of not having galvanic isolation is the possibility of a ground fault destroying the inverter and causing an electrical fire. With a transformer, if the secondary is shorted, then all of the current will flow through the primary and will (hopefully) be stopped by a thermal disconnect once the transformer overheats. Without one, if no protection exists or if the protection fails to detect the ground fault and trip, the large MOSFETs or IGBTs will immediately fail in a rather catastrophic manner. Fortunately, the likelihood of such an event occurring is extremely remote, and all such inverters are required to have ground fault protection as per UL 1741 requirements. The burden, however, remains on the installer to insure that backfeed current in the case of an undetected ground fault is taken into account when sizing combiner and disconnect fuses.

Thus, provided that the correct simple calculations are performed, there are few downsides and numerous benefits to transformerless inverters. Crews will certainly notice the reduced weight and size of these new inverters, and home and business owners will see increased yields over traditional designs due to increased efficiencies and wider operating voltage ranges. In short, there are always early adopters of new technologies, as well as holdouts who refuse to let go of their horse buggies when the rest of the world is already driving cars. Here, the cars are well proven.

Our New Years Solar Wish List

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On December 7, the solar industry was granted our first wish: the extension of the tax package that includes a one-year extension of the Department of Treasury's Section 1603 program. As of November 22, the Treasury had shelled out a grand total of $416,184,641 in grants for solar energy projects in the U.S., according to data from the Solar Energy Industries Association (SEIA). The corresponding minimum total investment (the basis upon which the grants were claimed) reached $1,387,282,137. The government’s investment has launched, and with the latest extension, will be sure to continue, the successful creation of jobs and opportunity in all 50 states for construction workers, electricians, plumbers and contractors that have struggled during the difficult economic climate.

Our second wish is for the Department of Energy to practically and efficiently divest funds for its loan guarantee program so that the average tax payer can reap the advantages of his initiatives. Just last month, three White House advisers expressed concern about the DOE loan guarantee program in three areas. First, there is the potential for some funds to be lost if such funds are not obligated to projects by the deadline. Second, the officials noted a risk that the program would be criticized for slow implementation. And third, they highlighted the potential for funds to be committed to projects that would have happened anyway, without government assistance.

Our third wish is for PV module prices to decrease starting from Q2 2011, setting the stage for grid parity and a broader acceptance of grid tie PV. Beginning in 2008 and continuing into 2010, wholesale module prices began a steep downwards trajectory, in response to expanded manufacturing capacity and the global financial crisis. Due to strong investments from the Chinese to boost total capacity of cells, ingots and module assembly operations, more capacity than ever before will be available for export to familiar markets. At present, the majority of production is dependent on exports, accounting for up to 40-50%. With photovoltaic cells, for example, China’s total output of 2008 2300MW (megawatts) comprised 97% of the Chinese products exported is relatively small. Moreover, with exports totaling more than 10 billion US dollars, the Chinese domestic market for its production is underdeveloped. Moreover, the halting or deep reductions to the Feed in Tariffs (FITS) in France, Spain, Italy and the 900 lb gorilla, Germany, will surely alter the pricing landscape next year. Therefore, all the excess capacity should yield lower prices for the 2011 solar season.

In connection with our third wish, we would like to see a continued downward push towards lower installation costs. Unfortunately, the reductions in module prices from 2008 did not translate into a noticeable reduction in average installed costs for PV systems in 2009, perhaps reflecting a natural lag between the time that PV system installation contracts are signed and the time that PV systems are installed. Currently, a California PV installation costs USD$6.5/watt and a New Jersey PV installation costs USD$6.3/watt. Preliminary evidence does suggest, however, that the average costs for PV systems installed in 2010 will be substantially lower than in 2009.
My last wish places the onus on the elected officials to continue their important work of ratifying aggressive RPS, and fair grid tie standards in their respective operating areas. Getting all the foundation work completed on the more than 3,273 traditional electric utilities in the United States will set the stage for a larger market for PV and not regional markets confined to 10 solar consuming states.

One wish has been granted; if the other wishes come true this will undoubtedly ensure another 30% annual growth rate for our industry.

Nice Rack! A Review of Various Residential Solar Roof Mounting Types

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Installers and system integrators alike can easily be confused by the myriad of solar roof mounting styles and types available on the market. There are several reputable manufacturers, and they have become favorites in the industry due to availability and performance. Others, such as no-name brands or new, proprietary solutions should be used with caution or not at all. This article will act as a short review to aid the selection of a mounting configuration with an ideal mix of cost, reliability, and aesthetics.

The bread and butter of residential roof-mounting is, of course, Unirac SolarMount. There is no other product on the market available so broadly and with so many potential configurations. The mounting rails themselves come in regular and heavy-duty versions (with a thick support added to the rail) in polished aluminum, mill finish, and anodized black. Additionally, installers can choose between top mount and bottom mount module clamps, although most go for the top-mount versions for ease of installation. In dry climates and well-insulated shingle roofs, it is sufficient to simply screw down the SolarMount L-feet directly to the roof rafters for a solid hold. However, for homeowners that are more concerned about water leakage or aesthetics, or for tile roofs, Unirac provides standoffs of varying heights, to be used together with flashings for waterproofing. For systems where roof pitch is insufficient or nonexistent, there are also tilt legs available to increase module insolation. The downside to Unirac’s SolarMount is the expense—systems such as Pro Solar may not be as versatile but are an excellent now-cost alternative.

Professional Solar is a direct competitor to Unirac, and offers high value roof mount and ground mount products. Three heights of rails are available: regular (1.5”), deep (2.5”) and extra deep (3”), each with the appropriate accessories. The rails are of a somewhat simpler construction and offer less aesthetic appeal than the SolarMount counterparts, but as long as extreme winds are not involved, they work just as well mechanically. Unlike Unirac, Pro Solar’s method of attaching to tile roofs does not require the removal or breaking of any tiles. A sliding member is concealed under a set of tiles, and the rails are screwed down to it from above. The usual kind of standoffs, flashings, and tilt legs are available, although the tilt legs’ length is not adjustable, as Unirac’s is.

Iron Ridge also offers high-quality roof mounting in regular (XRL) and heavy-duty (XRS) styles, and they are worth exploring as well. While the product construction quality is a notch or two above offerings from Pro Solar, Iron Ridge’s system is not as versatile as Unirac’s. Additionally, it is more difficult to supply customers with these products due to availability and the lead times from major suppliers. Other module-specific or proprietary products such as Sharp’s SRS and Lumos’s PowerMount are also on the market, but do not garner the same level of respect as long-time favorites Unirac and Pro Solar. Conceivably, the tried-and-true is that for a reason.

My Grownup (Solar) Christmas List

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Q3 and Q4 of 2010 has been fairly tumultuous as far as product offerings and availability. Though the US market has seen the arrival of new products such as SMA’s TL line of grid-tie inverters and an expansion in availability of Sanyo HIT high-efficiency modules, pending installations have been hampered by constant shortages of American-made modules (Sharp and SolarWorld) as well as near non-availability of Enphase microinverters and accessories. Furthermore, the US market has seen a rise in pricing from most Tier 1 Chinese module manufacturers, which has led tenser relations with installers and suppliers buying direct. Many (if not most) of these issues were the result of market fluctuations and were not the result in human error in supply chains. However, some issues, especially the microinverter shortage, were caused by miscalculations of demand. No market is perfect, but the following list is what Aten Solar (and other distributors, no doubt) would like to see from the industry in Q1 2011 forward:

  • An increase in inventory of American-made modules. Although Chinese goods are almost always lower-priced, many publically-funded projects require ARRA-compliant components
  • More availability on Enphase inverters. The backlog of 4-6 weeks on Enphase products has become difficult to handle, especially when customers already have modules and other BOS components on the ground
  • Debut of Sanyo HIT 225/230W modules and Yingli Panda Series modules for the US. Sanyo already has small form-factor modules up to 235W available in Europe, but offerings in the US only rise up to 220W. The high-efficiency Panda Series were announced early Q2 2010 and still have not arrived stateside
  • Debut of Kaco large residential inverters in the US. Kaco is currently losing the opportunity to compete with its larger counterpart SMA by not releasing any residential inverters larger than 5kW. The larger inverters were promised by late Q4 2010 or early Q1 2011, and are not arriving yet.

Despite the above shortcomings, the steadily rising demand for solar products is keeping the industry very successful as a whole. As a result, established module and inverter manufacturers have all had to increase production volumes and allocations significantly. Aten Solar’s business flow has grown fivefold since the early part of 2010, and we are confident that such growth will continue onward into next year.

So with all that being said Happy Holidays and Season's Greetings to All!

High Efficiency Solar Panel Considerations

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New, high-efficiency solar modules such as the Sanyo HIT line or Sunpower are becoming more common in the PV marketplace and are considerably more expensive than the average solar module. The question is, are they worth it to the average homeowner? This depends on the goal the property owner is trying to achieve with a PV system. If there is a glut of unshaded roof space and only a certain yearly energy output is required, then high-efficiency modules can be a waste and the owner’s investment will take longer to pay off, if ever. Alternatively, if there is a deficiency of roof space or the owner wants to generate as much power as possible, then such modules may be beneficial. Let’s explore the issue on two different roofs:

Roof A: 37° pitch, 50ft wide, 12ft deep, unshaded
Roof B: 37° pitch, 30ft wide, 12ft deep, unshaded

Let’s assume that our power requirement on Roof A is 6 kW AC (assuming 95% inverter efficiency). If we use CentroSolar modules on Roof A, we can mount two rows of 14 modules and get 6.118 kW AC, close to our target. The CentroSolar modules are relatively inexpensive at $2.19/W for this quantity, so the panels would end up costing $14,082. If we mount Sanyo 220W modules on the same roof in two rows of 14, we get 5.852 kW AC. Here, the improved temperature performance of the Sanyo system would make up for the difference in nominal power. However, the Sanyos cost $3.54/W, meaning that the buyer will spend almost $22,000 on modules without much benefit over the CentroSolar option.

Now, let’s assume that the owner of Roof B wants to maximize his output. He can use two rows of 9 Centrosolar modules to get 3.496 kW AC and spend $9053, or he can go with two rows of 11 Sanyo modules and produce 4.598 kW AC, costing him $17,130. The extra 1.2 kW AC may sound welcome, but the homeowner must realize that the margin will actually cost him close to $7 per watt. Naturally, there is no “correct” choice here, but any homeowner should be well-aware of the additional burden on his or her pocketbook as well as the return (or lack thereof) on investment.

For more information on which system is right for you please contact Aten Solar at 800-310-7271 or feel free to use our contact form and a representitive will get back to you right away.

One Size Fits All

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Yes, the renewable energy industry has literally exploded since project financing for larger commercial and utility scale was made available here in the U.S. Also in 2009 solar module prices fell between 30% and 50% compared to an average 5% to 10% drop in previous years. In just 10 years something called a feed in tariff, or what’s better known as a FIT allowed for investments in both private and commercial owned electricity generated to be fed into the public power grid. This allowed for investors to receive reimbursement in a form of a fixed price for a Kwh of electricity. As you probably heard numerous times, Germany has demonstrated to the rest of the world how to make solar energy feasible and from inverters manufacturers to EPC’s, German companies continue to pave the way in all aspects of this industry. All told, Germany has installed about 10 GW since FIT inception and has created at least 15,000 jobs.

In 2009 Gainesville, Florida Regional Utilities (GRU) announced they were going to lead the nation and announce the first fit in the USA which allowed rate payers who sign up within the 1st two years of the program a guaranteed fixed rate of $.32 per kilowatt for 20 years. GRU estimates that investors will see a 5-percent return on investment for large-scale projects.

Kudos to Gainesville for truly setting the stage for an incentive program that is easily understood, bankable, mandated by a state authority and most importantly replicated. As solar professionals, Aten Solar understands that it is difficult or downright impossible to get the more than 3,273 traditional utility companies to agree to any incentive program. In the US solar industry, we are riddled with an alphabet soup of acronyms and catch phrases such as SREC, PBI, MassCEC, Sunsense, Sunshine to the point it is madding. Understanding and financially modeling the myriad of incentive programs and relevant state and federal tax incentives and rebates will cause the U.S. to adopt solar at a slower pace than many European markets and the 47 other countries that have adopted FITS.

Industry lobbying from SEPA, SEIA and regional trade associations need to put the pressure on the law makers to adopt a national incentive schema for solar to be more mainstream. If a FIT is accepted in the U.S, adjusted on state by state basis, more installs would occur therefore pushing the module, components and install prices down further in order for most U.S. states to reach the coveted grid parity market. Undoubtedly, if this is truly “our prize”, then it only makes sense to have one or two incentive programs nationwide.

Solar Cells Printed on Paper

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The three big challenges are that solar cells are expensive to produce, they’re not very efficient, and you need some means to store the energy collected. What if you could simply staple solar panels to your house rather than hiring a professional installation team? That’s not as far-fetched as it sounds — MIT researchers have figured out a way to print thin film solar cells on paper using a process that resembles a standard inkjet printer. If they’re able to gear efficiencies up to scale, the development could revolutionize the production and installation of solar panels.

MIT’s new semiconductor-coated paper features carbon-based dyes that give the cells an efficiency of 1.5 to 2 percent. That’s not incredibly efficient (typical solar panels are 20-40% efficient), but the convenience factor makes up for it. In the future, researchers hope that the same process used in the paper solar cells could be used to print cells on metal foil or even plastic.

Of course, paper solar cells are a long way from commercialization. MIT researchers say that the technology is still in the research phase and it could take years before being commercialized. And once it is? There’s no telling how it could revolutionize the home solar industry, which currently relies on pricey professional installers to set up panels.

Unfortunately we haven’t heard any word on new battery technologies to go with these new solar cells. But we are sure there’s some group of really smart people working to tackle that aspect of solar energy.

Affordable Solar Power from a weed?

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Believe it or not weeds can provide a very positive effect on global warming. Thepokeberry weed – native to North America, South America, East Asia and New Zealand and whose red dye was once used by American Civil War soldiers to write letters home – may now hold the secret for revolutionizing the next generation of low-cost photovoltaic cells, making widespread, affordable homegrown solar power a real possibility. Especially for countries who find themselves in unfortunate economic circumstances.

Researchers at Wake Forest University’s Center for Nanotechnology and Molecular Materials were able to create a more efficient fiber-based solar cell by coating the solar cell’s fibers with the pokeberry dye, which helps the fibers absorb more sunlight. This, together with the humble pokeberry’s red dye, the fiber-based solar cells generate twice as much power than current thin-film technology. And what’s even better is that the pokeberry can grow anywhere, including dry and inhospitable places.

“They’re weeds,” says the center’s director Dr. David Carroll. “They grow on every continent but Antarctica.”

With their spin-off company FiberCell Inc., Wake Forest is now developing these fiber-based solar cells for the commercial market.

So how does a fiber-based solar cell work? Made of millions of tiny, plastic cylinders or fibers that trap sunlight until it is absorbed, this configuration means that a fiber-based cell can collect light at any angle, from sunrise to sunset because there is much more surface area available.

To manufacture these highly-efficient ‘hybrid’ cells, the plastic fibers are stamped onto plastic sheets and the absorber dye (this is where cheap and locally-grown pokeberries come in) is sprayed on. The sheets are flexible, which means that manufacturers can make them and ship them at a low cost to developing countries. Once there, local factories can spray the absorbent pokeberry dye on the cells.

Dr Carroll points out that compared to a plant making flat-cell solar panels, which would cost about $15 million, a fiber-based solar cell finishing plant would only cost $5 million, which would make this kind of solar power much more accessible. “We could provide the substrate,” says Carroll. “If Africa grows the pokeberries, they could take it home. “It’s a low-cost solar cell that can be made to work with local, low-cost agricultural crops like pokeberries and with a means of production that emerging economies can afford.”

Weeds may have been given a bum rap with everything they do to grow in the cracks of our sidewalks and driveways, but perhaps one day we will all be fortunate enough to also have them on our roofs.

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