Solar Energy for Home

Stephen Heckeroth

© 1995 Stephen Heckeroth

When it comes to resource depletion and air pollution, the automobile remains the real culprit. Transportation uses four times the energy that is used in housing and causes about ten times the air pollution because of its total reliance on petroleum. It was this realization that led me to mortgage my home and start MendoMotive, an electric vehicle company.

© 1995 Stephen Heckeroth

Karman Ghia Electric Heckeroth

(R to L) Mendomotive's crew:Stephen Heckeroth, Norm Fluhrer, Dick Hamilton, and Gary Glo with the winner of the 1995 SunDay Challenge at Daytona International Speedway.

(R to L) Mendomotive's crew:Stephen Heckeroth, Norm Fluhrer, Dick Hamilton, and Gary Glo with the winner of the 1995 SunDay Challenge at Daytona International Speedway.

Changing the image of electric vehicles from golf carts to high performance cars can easily be accomplished. A more fundamental issue is achieving mobility without pollution.

A 3,000-watt PV array, water-heating panels, and skylights make up this barn roof.

The Spyder is lightweight and good looking.

The Spyder is lightweight and good looking.

Gary Flo and Norm Fluhrer of Mendomotive show off prototype 20HP tractors converted to electric power.

Since the late 60s I have been concerned about the depletion of non-renewable energy resources and the pollution caused by their use. As an architect I have channeled my concern into refining residential passive solar design. I am now confident that with good solar access, I can design a home that will have all its energy needs satisfied by the sun.

Electric Cars

In 1992 I started converting everything I could get my hands on with off-the-shelf golf cart and forklift technology. In a search for the lightest possible vehicle, I found that a fiberglass Porsche 550 Spyder replica weighed less than 1,000 pounds. MendoMotive's first vehicles used 120 Volt at 400 Amp controllers, 9-inch advanced DC motors, and golf cart batteries. This resulted in vehicles with 50 HP drivetrains and ranges up to 100 miles. There was no regenerative braking capability and acceleration was about equal to an early VW Bug. Few chargers were available and it took 8-10 hours for a full recharge.

The California zero-emission mandate has fueled research and development around the world and new products are surfacing on the market almost weekly. Currently there is a wide variety of affordable controllers on the market with regenerative braking and up to 320 Volt and 1,000 Amp capacity, offering in excess of 300 hp. High voltage motors are also being produced that offer much higher torque than current production models.

Integrating PV and water-heating panels while re-roofing the barn is cost-effective and a relatively simple process.

A Type II Karmann Ghia plugs in while parked in the garage.

Designed and built by Stephen Heckeroth, this tower house integrates solar panels.

A Type II Karmann Ghia plugs in while parked in the garage.

Designed and built by Stephen Heckeroth, this tower house integrates solar panels.

Other battery types—Bi-polar, sealed lead-acid, nickel-metal-hydride and zinc-air—are all available on a prototype basis, offering up to four times the range for the same weight. Like any prototype, this new generation of batteries is expensive but the cost will drop when volume allows mass production. Chargers are now on the market capable of full recharge in as little as 15 minutes.

I have upgraded my Type III Karmann Ghia with a new ZAPI controller. It has a regenerative braking circuit capable of producing over 115 brake horsepower. The regenerative braking increases range by 15% in hilly terrain. It also reduces brake wear enough to make replacing the tires the only regular maintenance required on my TYP3EV.

We can now produce an electric Porsche that will outperform the original gas version in every category except range. Performance is no longer an issue. With new generation batteries and quick recharging, range will be equivalent to current polluters. Nickel-metal-hydride and zinc-air batteries are non-toxic and offer much safer energy storage than a potentially explosive gas tank. When demand takes the production of EVs to the assembly line, their cost will drop to equal or less than the cost for an equivalent gas car.

Changing the image of electric vehicles from golf carts to high performance cars can easily be accomplished. A more fundamental issue is achieving mobility without pollution. This issue can best be addressed by planning our communities around pedestrians and ultra-light vehicles. For now, this country has an infrastructure of roads designed for cars which have become less of a means of transportation and more a symbol of people's identity. Electric cars are the best transition to clean and quiet pedestrian communities.

Opponents of electric cars argue that emissions are only transferred from the tailpipe to the smokestack or the nuclear power plant. This argument can be put to rest when photovoltaic charging stations are integrated into the roofs of our homes, and the places where we work, shop, and recreate.

Selecting the Roof-mounted Panels

Typically, a roof's main function is to keep the rain out while maintaining a comfortable indoor temperature. When photovoltaic panels are used as roofing, the roof takes on a dual function by converting the sun's rays into electricity.

Crystalline, poly-crystalline, and amorphous are the commonly available kinds of photovoltaics. Crystalline and poly-crystalline are about 10% to 12% efficient in their conversion of sunlight into electricity, compared with 4% to 8% efficiency for amorphous panels. The overall efficiency of thin film amorphous silicon panels, when compared to stationary crystalline panels, is increased by their ability to more efficiently convert indirect or diffused light. This also makes the amorphous panels very useful in areas with extended periods of overcast skies.

Another advantage of amorphous technology is that the manufacturing process is more environmentally friendly. The thin film is applied without any waste, while significant material loss results from the manufacture of crystalline panels. The energy consumed in the manufacture of thin film amorphous panels is recuperated in as little as two months of use, as opposed to up to five years for crystalline panels. Since the thin film amorphous silicon adheres to materials that also make good roofing, like metal, glass and ceramics, it becomes versatile as a building material.

United Solar Systems Corp. (Uni-Solar), is experimenting with a variety of amorphous silicon panels that, once on the market, could turn all south-facing roofs into charging stations. The modules UniSolar is developing are metal-based units. The thin film is applied to steel and covered with a protective coating for roofing uses, producing 800 Watts per 100 sq . ft.

Advanced Photovoltaic Systems [APS], until recently, manufactured laminated glass panels capable of producing 400 Watts per 100 sq ft. The panels were installed on the south-facing roof of our barn, replacing a leaky metal roof. The cost of new roofing material ($2 per sq ft) was avoided. The labor involved in putting up the panels was approximately equal to replacing the old roof with new roofing material. So the integrated PV installation cost $8 per sq. ft., when you include the avoided cost of new material.

The barn's 700 sq. ft. array produces a steady three kW for seven or eight hours a day in the summer and 1.5 kW for four or five hours on a cloudy winter day. This yields a yearly average of 15 kWh a day. Using the new California net metering law (where the utility must pay the same rate for home-produced power that is fed into the grid as they charge for electricity from the grid) and time-of-use rates, I expect the array to produce about $7.50 worth of electricity per day in the summer and a low of 75 cents per day in the winter. This means an avoided expense of approximately $4 a day or $1,500 a year. The system, including the Trace synchronous inverter and batteries, will pay for itself in less than seven years. Over its 30-year expected life, the PV roof will generate $45,000 of "avoided" utility bills even in the unlikely event where utility rates remain constant.

The 3,000-watt array is capable of providing all the power for our house and an apartment in the barn loft. Our electric car and tractor can also be charged on sunny days.

Solar charging should ideally be available where people spend their days—at work. Maybe businesses should be required to have solar charging stations the way they are required to have parking places.

Electric Tractors

While battery weight is an obstacle to performance on the road, it is an asset in the field. The batteries in a well-designed electric tractor add stability and traction. With the addition of an on-board inverter, even a small electric tractor can be used as a clean and silent mobile power source for garden and construction tools, in addition to powering most (or all) of a home. Solar charging can be accomplished over several days for use on a weekend or as an emergency power source. An electric tractor has fewer moving parts, requires less maintenance and, if mass produced, would cost the same as a comparable gas version.

MendoMotive's sister company Electrac has already converted several 20 hp tractors that are as powerful as their original diesel incarnation. We are currently seeking capital to build a production prototype—a cordless lawn and garden tractor—that will cut both pollution and the grass.

The solar age is already here, but it is individual action that will lead to a reduction in the use of non-renewable polluting energy resources. Please take action.


Stephen Heckeroth, MendoMotive, 110 W. Elm Street, Ft. Bragg, California 95437. Phone (707) 964-1331 Fax: (707) 964-6500.

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