SBIR-STTR Award

For both utility-intertied and stand-alone photovoltaic (PV) systems, the DC wiring and its associated issues is always,except for the smallest of systems, a major problem. AC powertransmission techniques will be used to completely eliminate DC interconnection. This will be done by incorporating a small DC-AC inserter on the back of each PV module so that the module output is standard 120 Volts, 60 Hz, AC current. AC power transmission can be used for both utility-interactive and stand alone systems. A major advantage of these systems is compatibility - the 120 VAC bus provides a common ground for all components to interconnect. The benefits of maximum power point tracking on an individual module basis, the elimination of DC wiring, custom string combiners, blocking diodes, series string losses and the standardization offered by a common 120V AC bus voltage can outweigh the additional cost of the inverted In Phase I of the effort, a proof-of-concept 50 Watt DC to AC inverter that is designed to mount on the back of a photovoltaic module will be developed. It will deliver 120 Volt 60 Hz AC power to the utility grid or to a local stand-alone grid. Appropriate manufacturing techniques (e.g. Application-Specific Integrated Circuits, hybrid circuits, monolithic and "smart power" approaches) will be examined, estimates of inserter size and the cost and efficiency for various scales of production will be prepared, and the feasibility of incorporating storage elements with the inserter on the back of the PV module to make truly modular stand-alone PV power systems will be studied.Anticipated Results /Potential Commercial Applications as described by the awardee:This device could bring photovoltaics to the "appliance level", both for utility-interactive and for larger-scale stand-alone systems. In fact, this concept blurs the boundary between the two, as stand-alone systems effectively gain their own mini-AC grid. The main commercial market should be utility-interactive power systems, followed by support of diesel power grids in remote areas, with smaller stand-alone systemsstill being a significant market. The emergency power/disasterrelief market could also be well served by this product.

One of the major costs in photovoltaic (PV) systems is the direct current to alternating current (DC-to-AC) inverter. This project addresses new design options for distributed, highly-integrated modular inverters for PV power systems which are well suited to low-cost, high-volume production. In Phase I, a small, modular, innovative, 2100 watts, utility-interactive PV inverter was developed. The prototype inverter measures just 11.75 x 3.72 x 1.5 cubic inches which is small enough to mount directly on the back of a PV module. The measured efficiency of the prototype inverter was 96% peak, significantly higher than any current commercial units. In Phase II, the inverter's control hardware (microcontroller, communications, timing clock and dividers, sine-generation memory and addressing counter, and inverter control) will be integrated into a mixed-signal (i.e. both analog and digital) Application Specific Integrated Circuit (ASIC). Since about 30% of the cost and size of the inverter is in this control area, considerable savings are possible. The combination of logic and power switches is known as "Smart Power". This will be the first application of Smart Power for PV applications. The Phase II goal is an inverter design that, in mass production, can be manufactured for under $0.25 per peak watt.Anticipated Results/Potential Commercial Applications as described by the awardee: The effort should lead to the development of an "AC Module",a potentially new product which integrates the PV module and the inverter. This AC module should lead to simpler and lower cost PV systems. The AC module, as a new consumer product, has the potential to revolutionize the PV industry.