Much Better Solar Photovoltaics On the Way

Startup Enphase Energy of Petaluma, CA, is now making its first micro-inverters.  The small inverters can be bolted to the racking under each of an installation’s solar panel to convert DC power into AC for each panel individually. The company claims that the devices will increase a PV system’s efficiency by 5 to 25 percent and decrease the cost of solar power.

Enphase has already teamed with various distributors and partners, including solar module manufacturer Suntech Power Holdings and installer Akeena Solar, to bring its device to customers.  The micro-inverters can be used on residential, commercial, or even utility-scale photovoltaic systems.

There’s much more to solar power than black glassy panels glistening on rooftops.  Perhaps more important now that installations and real world testing is well underway and understood is the inverter performance that convert DC power created by the solar panels into grid-ready AC power.

Currently all the panels in a rooftop photovoltaic system are connected to one large inverter mounted on the side of a house from which the AC power is off loaded to the house or grid.  This is being done as solar panels are wired together in series, and their combined high-voltage DC power is fed to the inverter. From that current flow the inverter’s logic circuit optimizes the total current and voltage levels. But if one panel’s current drops, it becomes the limit of the overall output of the system.

SolarPanel Microinverter by Enphase
SolarPanel Microinverter
by Enphase

Leesa Lee, director of marketing at Enphase points out the problem, “Something as simple as a leaf blowing over a module, or dust or debris or shade on one module, will affect the entire array of all those modules that are connected in series.”  Think bird poop and all the other things falling out of the sky as major problems, but mostly canceling the equality of each panel, that forces production to the least efficient module.  It’s a bigger problem than many realize.

But Enphase’s micro-inverters individually optimize the voltage-current levels at each panel. That uses the most power from each panel and then adds the panels together, increasing the system’s efficiency. “Any problem on a module is limited to that module alone,” Lee says. In addition, the equipment cost for micro-inverters is about 15 percent less than the cost for a traditional system, she says, because expensive DC components, such as signal combiners and disconnects, can be replaced with off-the-shelf AC parts.

Enphase Micro Inverter Points. Click image for a larger view.
Enphase Micro Inverter Points

The problem has been known for decades so the concept of small inverters has been around for more than a decade, but there have been technical challenges to making practical devices. Enphase’s Senior Director for Systems, Mary Dargatz says,  “One of the biggest stumbling blocks to micro-inverter technologies in the past has been conversion efficiency.” So, Enphase has converted many analog parts in the circuits to digital to make the inverter smaller without sacrificing efficiency. The conversion efficiency of an individual micro-inverter is 95.5 percent, on par with efficiencies of traditional large inverters, which range from 94 to 96 percent.

Seems odd, doesn’t it?  The most costly part of a system is hooked up in a 40 year old design that cuts down on the output.  It’s a habit from the 1960s when inverters were very expensive.  Now with micro-inverters on can add to a system without making the inverter, the second most expensive part obsolete. It may be that the micro inverters can be used to upgrade older systems as well.  Enphase offers a long list of downloads to assist owners and installers with analyzing and assessing how the new micro inverter can be used. Its well worth looking over.

Going partway in an attempt to address a broader voltage range, National Semiconductor is making a power-optimizing module for individual panels.  The device only has the logic circuit for optimizing current and voltage levels–it doesn’t do the DC-to-AC power conversion.  What it offers in conversion efficiency looks to be meant for existing installations.

Enphase uses its AC output and ease of connection to offer another service to backup the sale.  The full kit would allow a consumer to send data in for analysis and receive reports via the Internet.  Beyond that, the potential exists for rationing power, if the situation allows, to divide one’s output say for use in the home and for sale.

It all makes for a much more practical implementation of solar arrays with photovoltaic collector panels.  A drop in panel costs, now a drop in inverter cost and a simpler installation should help get home and small commercial arrays more deeply down into the economy where more people can afford the investment.  That more mass market, which should reduce prices as well.

Which brings us to what might be the most important advantage of all.  With the Enphase micro-inverter one can start small and add modules or panels as the budget (or incentives) allow.  Now that’s a path to help build more market, too.  Growth looks good for photovoltaic.

Here is the original post: New Energy and Fuel

Building a Much Lower Cost Solar Cell

Jason Karp an electrical engineering Ph.D. student at the University of California, San Diego and his colleagues at the UC San Diego Jacobs School of Engineering are developing an inexpensive optical concentrator and assembly to offset the high cost of very efficient solar cells. The development should lead to solar concentrators that are less expensive and require fewer photovoltaic cells than existing solar concentrators or photovoltaic solar cell panels.

The design is an optical innovation. After the surface lenses focuses the light with a two-dimensional lens array a secondary optic, multimode slab waveguide is used as a secondary to collect and homogenize the sunlight.

Reflective facets fabricated on the backside of the waveguide act as fold mirrors to couple sunlight into the waveguide at angles, which exceed the critical angle for total internal reflection. These facets occupy a small fraction of the total waveguide surface and enable high geometric concentrations despite decoupling loss if light strikes a subsequent coupling region.

This geometry yields a thin, flat profile for moderate concentration systems that may be fabricated by low-cost roll manufacturing. The analyses of tradeoffs show optimized designs can achieve 90% and 82% optical efficiency at 73x and 300x concentration, respectively.

Karp and his group may be in the money – for concentrator photovoltaic (CPV) to be cost-effective, the complete cost of the optics, assembly and mechanical tracking must not exceed the cost savings gained from using small area PV cells.  The team gets it; the place to shave expense is in the collection of the light, saving a big share with reduced photovoltaic cell counts.

Sunlight collected by each aperture of the arrayed primary collector is coupled into a common slab waveguide using localized injection features such as prisms, gratings or scattering surfaces. Rays that exceed the critical angle defined by Snell’s Law propagate via total internal reflection (TIR) within the waveguide to the exit aperture, typically at the edge of the slab.  TIR is a complete reflection with negligible spectral or polarization-dependent losses, which enables long propagation lifetimes.  The waveguide transports sunlight collected over the entire input aperture to a single PV cell placed at the waveguide edge. PV alignment becomes trivial since comparatively large cells are cemented to the waveguide edge(s).  Fewer PV cells reduce connection complexity and allow one heat sink to manage the entire system output.

Planar MicroOptic Solar Concentrator. .

As illustrated, the innovation is going beyond a lens that concentrate an area to a PV, Karp’s waveguide collects several lenses to one or more PVs.  This has to dramatically cut costs and allow budgeting for extremely efficient PVs.

The goal was to design a concentrator optic, which could be fabricated at an extremely low cost per unit area. Constraining the design to be compatible with a continuous roll process-manufacturing platform, as opposed to injection molded and assembled elements, maximizes the cost advantage of CPV.  Roll processing can perform a range of functions on rigid or flexible substrates such as embossing of refractive or diffractive structures, dielectric and metallic deposition and the joining of multiple processed layers.

The team’s paper, in the January 2010 issue of the journal Optics Express, available in a pdf download, covers in detail concentrator geometry, coupling the waveguide, optimizing the system, and the building of a prototype.  The paper also discusses the method Karp and his team use to self align the concentrator during fabrication. At 12 pages and lucid for the non-optic expert, it’s a worthwhile read.

Prototype Planar MicroOptic Solar Concentrator. .

The team took their prototype outdoors for testing to find the prototype system reached 90% of its maximum optical efficiency with  ± 1° angular acceptance.  The optical efficiency of the prototype system was significantly lower than the optimized simulations using custom optical elements.  Despite its relative inefficiency the experimental measurements were in close agreement with the optical model and support the notion that optimized designs would also perform with high efficiency. The team is currently pursuing variations of the basic structure to increase both concentration and optical efficiency.

The team has demonstrated self-aligned fabrication using off-the-shelf components to create a 37.5x prototype concentrator with 32.4% optical efficiency. Systems with greater than 80% efficiency are expected when using a custom lens array with a 100% fill factor and minimal aberrations.  A CPV with multimode waveguides opens a new design space for large-scale concentrator optics with the added benefits of flux uniformity and fewer PV cells in a thin, planar geometry.

OK.  That’s all real technical.  But it works, the lens array and the waveguide beneath can be roll to roll process manufactured.  Mount some photovoltaic cells along the selected edge and you have a low cost high efficiency solar panel.  One has to like this, especially if the savings can justify the cost of a solar tracking system to keep the panel squarely facing the sun.

Something has to be done about solar panel costs – it looks like Karp and his team have a very good shot at helping build a much larger market.

The original post is created by: New Energy and Fuel

Falling Panel Prices could bring Solar closer to Grid Parity

Rising inventory levels of photovoltaic (PV) panels and new production capacity coming online is driving solar PV prices lower and thereby, bringing solar energy closer to grid price parity. With the release of the latest earnings of solar energy companies, Wall Street’s keen attention to revenue guidance, inventory levels and pricing are paramount in diagnosing the health of the solar energy industry. Expectations call consolidation of the solar industry with some key players gaining market share and for others it becomes more challenging. However, despite the turbulence in the industry, consumers will benefit in the near-term as solar PV prices fall and government incentive fuel growth in solar PV deployment.

To get a better perspective on the solar PV industry, let’s examine inventory levels for some of the leading solar PV suppliers. The following chart, Figure 1, compares inventory levels in relationship to sales volume. While inventory levels have increased, the level of inventories to sales is not egregious

Figure 1 Sales and Inventory levels install

While it is important to control inventory levels in relationship to sales, revenue growth is predicated upon price, performance, and return on investment for prospective customers. Thin-film PV has emerged as the low-cost solar solution even with its lower efficiency levels in comparison to mono-and poly-crystalline PV panels. Thin-film still offers a lower cost/watt than crystalline PV, see Solar Shootout in the San Joaquin Valley , but prices for crystalline PV are falling as a result of rising production capacity and inventory levels.

Figure 2 Market Value Market Value

In Figure 2 Green Econometrics is comparing the market value of some of the leading PV suppliers as measured by their respective stock prices. In the valuation of solar PV suppliers, the stock market appears to be betting heavily on thin-film PV, as First Solar (FSLR), the leading thin-film PV supplier, enjoys a market value that accounts for over half the value of the entire solar industry. FSLR is positioned as the low-cost supplier in the solar industry with its announcement of $1 per Watt reducing its production cost for solar modules to 98 cents per watt, thereby braking the $1 per watt price barrier. However, new panel suppliers, mainly from China are pushing prices lower for poly-and mono-crystalline panels suppliers. ReneSolar (SOL) is seeing average selling prices for wafers at $0.93 per watt and bring PV panels prices to under $2.00 per watt.

There appears to be a lot riding on the success of thin-film PV and as prices fall for crystalline PV, the closer we get to grid parity. In the following chart, Figure 3, price for crystalline PV have declined quite dramatically in the last 30 years. According to the Energy Information Administration, in 1956 solar PV panels were $300 per watt, and in 1980, the average cost per solar modules was $27/watt and has fallen precipitously to approximately $2/watt in October 2009. As the installed cost of solar PV falls closer to $4/watt, pricing per kilowatt-hour (KWH) (depending on your climate and geography), equates to approximately $0.16/KWH that would be inline with utility rates after rates caps are removed.

Figure 3 Solar PV Prices econ

The bottom line is that despite the lower PV panel costs; we are still not at parity with hydrocarbon fuels such as coal and oil. Carbon based taxes or renewable energy incentives as well as more investment into alternative energy should improve the economics of solar and wind and bring us to grid parity.

Original post: Green Econometrics

Solar Energy Limits – Possible Constraints in Tellurium Production

Solar energy is gaining considerable attention from Wall Street and countries looking to achieve energy independence. Solar energy represents one of the most significant energy solutions to help eradicate our addiction to oil. Despite the tremendous success offered with solar photovoltaic (PV), more research is required to sustain further deployment and achieve energy independence. Some semiconductor materials used to develop photovoltaic devices are scarce and may limit PV from achieving mass penetration. Let’s review the current solar PV market to better understand the dynamics of this market.

Figure 1 PV Production by Year
PV Production

Figure 1 demonstrates the rapid market growth of solar PV and Solarbuzz is astute to point out some critical data points: cumulative PV deployment is still less than 1% of global electric usage, PV industry faces capacity constraints, and Germany and Spain account for 47% and 23% of total PV deployment in 2007. With the significant growth in both the production and deployment of solar PV devices, the stock price of some of the leading PV suppliers have appreciated dramatically even despite a recent pull back in the beginning of the year.

Figure 2 PV Production of Leading Suppliers
MkPV Suppliers

Despite the turbulence on Wall Street in 2008 with the NASDAQ down 14% year-to-date, and Dow Jones Industrial Average down 7.3% YTD, investor appetite for clean technology stocks remains robust. First Solar (FSLR), a leading supplier of thin film solar PV remains in positive territory and is up nearly ten-fold from its IPO in November 2006. Thin film PV offers a cost advantage over traditional crystalline PV cells. PV devices employ various elements with different band gap properties to achieve improving solar efficiencies. (See our post on semiconductor band gaps: What’s Pushing Solar Energy Efficiency?, October 1st, 2007)

Figure 3 Market Capitalization Solar PV Suppliers
Mkt Cap

There are several elements used in thin film PV production. Among the elements used include cadmium and tellurium (CdTe), copper, indium, and selenium, (CuInSe), and copper, indium, gallium, and selenium (CIGS). These various elements are used to improve operating efficiencies and lower production costs of PV devices. In general, crystalline PV devices have higher solar efficiencies, but cost more due to their material thickness of 200-to-300 microns. Whereas, thin film PV are usually about 3 microns deep offering significantly lower production costs. However, SunPower (SPWR) the leading polycrystalline silicon PV supplier offers the highest solar efficiency a rating of 22.7% that started shipping in 2007.

Figure 4 FSLR and SPWR Solar PV Production
Mkt Cap

FSLR and SPWR are the two leading PV players as measured by Wall Street in terms of market valuation. The cost-efficiency tradeoff between these two PV suppliers offers an interesting framework to evaluate the solar PV market.

Figure 5 PV Cost-Efficiency

The stock market appears to be betting on FSLR given its market capitalization of $22 billion and trading at 43 times 2007 revenues of $504 million. FSLR employs CdTe in its solar modules. In several postings on Seeking Alpha starting back in November 2007, Anthony and Garcia de Alba have provided valuable insight into material constraints in the production of PV devices.

Tellurium is a rare metalloid element that is used in producing semiconductor materials because it does not conduct electricity. Tellurium is recovered as a by-product in refining and processing of gold and copper as well as other ores. Tellurium was primarily used to create metal alloys that enable easier machining of end products.

Because of its unique properties, Tellurium and cadmium (CdTe) have been used in thin film PV production since the 1980’s. According to a comprehensive study by Fthenakis and earlier work by Moskowitz “The Life Cycle Impact Analysis of Cadmium in CdTe PV Production”, CdTe is deposited on a thin film substrate using electrodeposition, chemical surface deposition, and vapor transport deposition. FSLR reports in their 10K that they employ a proprietary vapor transport deposition process for CdTe PV production.

A thin film of CdTe is deposited on a substrate at a thickness of 3 microns. According to the Fthenakis and Moskowitz, back in the 1980’s, a 10 megawatt (MW) PV facility employing vapor transport deposition of CdTe uses 3,720 kilograms (kg) of CdTe to achieve a10% efficiency at 3 microns. A one-one bond of CdTe with an atomic weight of Cd at 112.41 and Te at 127.60 suggests Te comprises 53% of the weigh of CdTe. With 3,720 kg of CdTe used at 10MW, the amount of Tellurium used is estimated at 1,978 kg or 197.8 kg/MW.

The electrodeposition CdTe process using a mixture of cadmium sulfate and tellurium dioxide used 880 kg of tellurium dioxide, which amounts to approximately 696.8 kg of Te for 10 MW PV productions. The electrodeposition CdTe process would equate to about 69.7 kg of Te per MW. For a 100 MW PV production approximately 7 tons of Te are consumed.

One would assume the PV production process would improve significantly from the 1980’s and the amount of Te consume would decline with improving efficiencies. This would suggest that FLSR at 200 MW PV capacity in 2007 would consume somewhere between 14 and 38 metric tons of tellurium. This figure is significantly higher than the estimates derived from the FSLR tellurium posts on Seeking Alpha that are closer to10 tons per 100 MW (100 kg/MW).

Figure 6 Global Tellurium Production

Let’s proceed with the conservative figure of 100 kg/MW (10 tons at 100 MW) to assess the tellurium constraints. Tellurium production is a by-product of gold, copper and other ores. We have found Te production estimates ranging from 132 metric tons (MT) to 300 MT per annum. In a National Renewable Energy Laboratory (NREL) report Assessment of Critical Thin Film Resources in 1999 estimated Te production between 200 and 300 metric tons per year in 1997 and indicated under utilization of capacity for the production of tellurium.

Let’s compare our conservative estimate of 100kg/MW Te usage for FSLR to the optimistic production forecast of 300 MT to evaluate capacity constraints for FSLR. With 300 MT (300,000 kg) global Te production and FSLR using 80% of the Te production, capacity of PV tops out at 2,400 MW (2.4 GW).

The U.S. electric energy usage in 2006 was 4,059.91 billion kilowatt hours (KWH) which translates into 463,460 MW (divide 4060 by 365 days x 24 hours). So without significant investment into research and development for PV FSLR could be constrained at 2,400 MW representing only 0.5% of the U.S. electric usage in 2004. Further more, if FSLR were to be constrained at 2.4 GW annual production, revenues ($2.60 per watt Q4/07) would peak at approximately $6.24 billion, a price-to-sales multiple of 3.4x with its market capitalization of $22 billion.

However, in comparison to leading companies in energy, pharmaceuticals, technology and finance, FSLR’s market capitalization is relatively small. Perhaps with improving production processes, FSLR could reduce the amount of Te per panel and improving mining and metal refinement process could increase Te production to expand the market for CdTe thin film PV devices.

Figure 7 Market Capitalization of Leading Companies
Mkt Cap

The bottom line is that more research and investment into alternative energies is required to ameliorate the world from being held hostage to oil and hydrocarbon fuels that are directly linked to rising CO2 levels and climate change.

Original post created by: Green Econometrics