GreenField Solar (GreenField) is a developer of high-intensity photovoltaic concentrators, which offer the potential to drive low-cost solar energy into mainstream adoption, using readily available materials and technology that is capital efficient.

GreenField Solar Drives Low-Cost Solar Energy to Mainstream Adoption

Interview with | Greenfield Solar

Can you give us an overview of GreenField Solar’s technology?

The key to GreenField’s technology is a unique solar cell design and an advanced sun tracking and control system which gathers every available ray of sunlight to generate power more effectively than traditional solar panels. 
GreenField’s PhotoVolt™ cell is a rugged, low-cost, high-voltage and low-series-resistance silicon solar cell. It is designed for high-intensity operation and uses a greatly reduced amount of semiconductor material compared with flat-panel cells. This innovative cell is designed for efficient operation at high intensities – that is under conditions hundreds of times more intense than normal sunlight – a unique feature compared to other solar cells. This feature enables the PhotoVolt™ cell to generate extraordinary amounts of usable electricity as well as heat.
Additionally, GreenField has developed the StarGenTM solar concentrator, which is a Concentrated Photovoltaic (CPV) system, precisely tracking the sun from dawn to dusk, and concentrating sunlight at high intensity using parabolic mirrors onto proprietary PhotoVoltTM high performance solar cells.
GreenField created the StarGenTM solar concentrator system to maximize the advantages of the unique characteristics and features of its proprietary PhotoVolt™ cell, with the goal of delivering a highly cost-effective solar energy solution. The design involves a rather large optical dish (with over 12 m2 of mirrors) that focuses sunlight onto two dense arrays of PhotoVolt™ cells under high concentration, and uses active cooling (liquid cooling) to remove the heat generated on the solar cells. 
The StarGen™ solar concentrator can generate up to 50 percent more electricity than one-sun non-tracking panels in good solar conditions.

How does the StarGen™ solar concentrator work?

The StarGenTM solar concentrator is based on a line-focus dense array configuration that focuses the light from multiple flat mirrors onto a receiver where the PhotoVoltTM solar cells are closely spaced and commonly cooled. To do this, each flat mirror is curved in one axis and held into a parabola along a mounting beam. This mirror assembly forms the central building block of the StarGenTM solar concentrator design.
Twenty-eight of these identical mirror assemblies are precisely attached to a "backbone" main beam, angling each mirror assembly so the focused line of light from each mirror overlays the others, creating a highly concentrated, line focused beam of concentrated light at two focal points onto the densely packed array of PhotoVoltTM solar cells. The mirror assemblies, mast and receiver beam together make up the StarGenTM solar concentrator’s optical system.

What makes GreenField’s solar cell unique?

The PhotoVoltTM solar cell is unique because it possesses inherent characteristics that make it suitable for dense array Concentrated Photovoltaic (CPV) system designs. Dense array CPV systems are concentrator systems with a large optical element focusing light onto an active region with many, densely packed solar cells, as opposed to distributed array CPV designs which incorporate a single solar cell for each optical element.
Because of its dense array design, the StarGen™ solar concentrator has an inherent ability to co-generate both thermal and electrical energy with an active cooling system extracting the thermal energy from the solar cells. As a result, the StarGen™ solar concentrator is capable of harvesting both forms of energy with overall solar conversion efficiencies exceeding 60%, by essentially utilizing the heat extracted when cooling the cells at high intensities.

What are the advantages of the technology?

GreenField’s technology employs high concentration to improve both the scalability and the capital efficiency of PV.
High concentration allows the StarGenTM solar concentrator to utilize only a small fraction of the expensive semiconductor material utilized by conventional one-sun silicon modules. This expensive semiconductor material typically represents a significant component of the cost for conventional silicon modules (as well as other PV technologies). However, concentration dramatically reduces the amount of semiconductor material needed.  Concentrating sunlight 500 times in the StarGen solar concentrator (or at 500 suns) means that only 1/500th of the expensive semiconductor material used in a one-sun module is needed to produce the same power. 
GreenField replaces the expensive semiconductor material with readily available, low cost glass mirrors and metal supports. So, material costs are dramatically reduced per installed watt due to high concentration.
Another factor contributing to the low system cost is the PhotoVolt™ solar cell’s design simplicity which lends itself to high volume, low cost production – no complex photolithography or sophisticated epitaxial growth processes are required!
Furthermore, at 500 suns concentration, for roughly the same capital investment, 500 times the production capability, as measured in terms of watts, is achieved. The low capital investment requirements mean that the PhotoVolt™ solar cell is highly scalable. Adding to the scalability of the technology, the PhotoVoltTM solar cell is silicon based, and does not utilize any of the rare earth materials
sometimes found in competing solar cell designs. By utilizing the most widely available semiconductor material and high concentration, the StarGenTM solar concentrator can scale both in production capacity and in raw material supply to deliver the world’s future PV supply needs.

How can GreenField ensure low cost electricity on a large scale?

Critical to delivering low cost solar electricity is achieving high energy production per each installed watt. The StarGenTM solar concentrator’s dual axis tracking ensures that near peak energy production is achieved throughout the course of the day. Compared to today’s market-dominant flat-panel silicon modules, the StarGenTM solar concentrator generates significantly more electricity per installed watt over the course of a year in average sunlight regions, and the advantage only increases in above-average sun conditions.
Low installed system costs, and high energy production means that solar electricity costs of less than 10 cents per kWh are achievable.

What is the outlook for GreenField Solar and how can it impact the future of PV and clean energy?

 Although there is mounting motivation to make the transition to clean energy, significant barriers remain, including finding an alternative energy source that is both cost effective, and has the large-scale potential to supply meaningful worldwide demand.
Solar energy is recognized as the renewable energy source that is well positioned to satisfy these needs, and eventually become a dominant form of future energy supply. However, in order to make the transition, PV technologies must be able to compete on cost with fossil-fuel based electricity, without subsidies. Furthermore, PV must utilize raw materials that are in abundance not only to keep raw material costs down, but also to ensure that as the global demand for PV grows, the technologies deployed have the ability to scale with the demand.
GreenField Solar can provide the world with a low cost, scalable and capital efficientPV solution, helping to transition the world to a renewable energy economy. The company currently has several demonstration products in the field and will have 20 StarGen™ solar concentrators operational at a location in Northeast Ohio in summer 2011.

Where do we go from here?

 The need for advanced energy continues to accelerate with increasing demand and rising costs of conventional energy sources. The race is on to develop less expensive and more efficient solutions to meet the complex challenges associated with developing and deploying new forms of advanced energy.
Greenfield Solar is one of many pioneering companies based in Ohio, many of whom will be participating in the 2011 Advanced Energy B2B Conference & Expo to be held September 14 – 15 at the John S. Knight Center in Akron, Ohio. 
The conference and expo will provide a venue to showcase the region’s assets in advanced energy and provide the opportunity to make business connections. The overall theme of the conference and expo is to explore the commercial opportunities in advanced energy for regional, national and international collaborators interested in doing business in Northeast Ohio or with partners in Northeast Ohio. In addition to a robust program and exhibition, conference attendees will have the unique opportunity to arrange business-to-business meetings with organizations in which they are interested. 
The event is geared to companies and researchers already engaged in the advanced energy industry, supply chain manufacturers with an interest in advanced energy opportunities, and national and international collaborators interested in doing business in Northeast Ohio or with partners in Northeast Ohio. Stephen Crolius, senior director of the Clinton Climate Initiative, will deliver the keynote address. Complete details on the conference and expo can be found at
The exhibition and conference will be co-produced by NorTech and the Summit County Mayors Association. NorTech is a leading nonprofit technology-based economic development organization serving 21 counties in Northeast Ohio. As a catalyst for growing Northeast Ohio’s emerging technology industries, NorTech is leading efforts to develop regional innovation clusters that create jobs, attract capital and have a long-term, positive economic impact.

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