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September 24-27 Long Beach, CA

All new product line for 2007

A completely new line of UL-compliant Sunny Boy inverters ranging from 700 to 7000 Watts. The new Sunny Tower simplifies commercial installations and is available in 36 or 42 kW models. Each "US" model inverter has a standard 10-year warranty and is compatible with our wireless and on-line monitoring systems. All SMA products are designed, manufactured and tested in Germany.

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Independently Published Since 1987

Independently Published Since 1987

Publishers Richard & Karen Perez

Executive Editor & CEO Joe Schwartz

Managing Editor Claire Anderson

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Senior Editor Senior Editor Graphic Artist Solar Thermal Editor Green Building Editors Transportation Editors Columnists

Ian Woofenden Michael Welch Dave Emrich Chuck Marken

Rachel Connor, Laurie Stone, Johnny Weiss Mike Brown, Shari Prange Kathleen Jarschke-Schultze, Don Loweburg Michael Welch, John Wiles, Ian Woofenden

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Customer Service & Fulfillment Jacie Gray, Shannon Ryan

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Letters to the Editor

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Rock Solid Solar F

Home Power magazine • PO Box 520 • Ashland, Oregon 97520 • USA

Extreme off-grid

with our new 5000 Watt battery-based solar inverter

Introducing the new Sunny Island 5048, designed to meet the most demanding system requirements. From remote off-grid applications to urban battery-backup systems, the Sunny Island inverter provides high efficiency, robust surge capability, and unsurpassed reliability. Our unique AC coupling system integrates solar, wind, hydro, batteries and generators, distributes power more efficiently, and extends the overall life of the batteries. See our free DVD on AC coupled off-grid systems. Call or email us today for a copy.

Call us: (888) 476-2872

Rock Solid Solar

A healthy new line ready for anything

Introducing the

Fronius IG Plus Grid-tie Inverter

Models from 4 KW to 12 KW in a single inverter

Dramatically improved efficiency

Integrated technology to maximize energy harvest even on cloudy days

Integrated DC disconnect

Enclosure allows for indoor/outdoor installation

Smart ventilation design

Field programmable to 208, 240, and 277 volts with no loss in output power

Field programmable to positive or negative ground

Removable power stage for field service

Built-in, fused six circuit combiner

Want to learn more?

Visit us at Solar Power 2007, Booth 131 in Long Beach, California for information on this exciting new addition to the Fronius family.

Fronius USA LLC, 10421 Citation Drive, Ste 1100, Brighton, MI 48116

Tel: 810-220-4414 Email: [email protected] Web:


Batteryless Hydro

I've heard of large-scale batteryless AC hydro-electric turbines for both on- and off-grid use, but are there any small batteryless hydro systems for on-grid applications? Are there batteryless grid-tied inverters that will synchronize a small hydro turbine's output with utility electricity? What does it take to set them up?

James Conklin • Manchester, New Hampshire

Coupling a batteryless inverter with a small hydro turbine in a grid-tied application is definitely doable, but there are some important system design considerations. As with a batteryless inverter using PV for input, you must correctly match the hydro turbine's output voltage to the inverter's input voltage window and maximum DC voltage limit. This can be done with low-head to high-head hydro systems, but is usually easiest with mid- to high-head systems. Low-head hydro systems might require a batteryless inverter with a DC input as low as 48 VDC nominal, which is hard to find these days. For mid- to high-head sites, I usually use an induction turbine configured for high voltage (200-500+ VDC) and 1,200 to 3,600 watts peak output.

The specifics of the turbine are very important, including the diameter of the runner (which affects rpm and voltage), output voltage, and peak output. Unlike a PV system, an important distinction of a hydro system is that it may not be able to handle running without its load. Without protection, this will occur if there is a utility failure, when the batteryless inverter is designed to shut down. In this situation, the rpm of the turbine will increase, and the open circuit voltage (Voc) of the turbine would likely exceed the inverter's maximum DC input voltage and damage the inverter—and possibly the hydro turbine too, due to overspinning.

For high-head situations (200+ feet), having a Voc that is too high for the inverter is a real concern. Fortunately, special diversion loads and controllers are available that will divert the energy fast enough to avoid damaging the inverter, while keeping the turbine electrically loaded. These diversion load/controller combinations are not cheap—they can cost more than $1,500 for 4,000 watts of diversion.

Because these small, batteryless hydro systems are still unusual, I recommend that they be undertaken with the guidance of the turbine and inverter suppliers and manufacturers to ensure optimum performance and reliability.

Jay Peltz • Peltz Power

Peak Sun-Hours

I've read that the Seattle area averages only 3.7 peak sun-hours per day. Maybe that's true in December, but April through October, I'd say it must be more like 10 to 12 hours a day, meaning that the average must be higher than 3.7 hours per day throughout the year. How are peak sun-hours determined?

Jeff Huffman • Brier, Washington

Excellent question! "Peak sun-hours" are not the same as "hours of sunlight." Sunrise to sunset represents hours of sunlight. But peak sun-hours describe how much solar energy is available during a day.

The daily amount of solar radiation striking any location on earth varies from sunrise to sunset due to clouds, the sun's position in the sky, and what's mixed into the atmosphere. Maximum solar radiation occurs at solar noon—the time when the sun is highest in the sky, compared to the rest of the day. Sunlight in the morning and evening does not deliver as much energy to the earth's surface as it does at midday because at low angles more atmosphere filters the sunlight. Besides day-to-day differences, there are also seasonal effects. In midsummer, due to the sun's higher position in the sky, an hour of sunshine packs more energy than the same hour of sunshine in the winter.

(continued on page 16)

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