Software for Renewable Energy Processes-5

Jan. 10, 2011
Bela Liptak Describes the "Battery Swap"-Based Transportation and the "Energy Free" Housing He Sees for the Future
By Béla Lipták, PE, Columnist

In this fifth article of this series, I will describe the "battery swap"-based transportation and the "energy free" housing that I visualize will be used by the end of this century. Automation and optimization of these processes will expand the role of process control beyond the present industrial applications as they will also be needed for motor, charger and fuel cell controllers in transportation and RFC, PV array, charge, back-up and bi-directional meter control and optimization to guarantee safe and efficient operation. For all the parts of this series of articles refer to or

Transportation of the Future

The car manufacturers have not yet decided if the future belongs to the all-electric car, the hydrogen fuel cell, the hydrogen-burning internal combustion engine, the multi-fuel vehicle or some combination of these, but whichever technology comes out on top, control software must be developed to guarantee its safe and efficient operation. The race comes down to cost.

The advantages of the all-electric vehicles (EV) include their relatively low fuel cost (today's cost of a gallon of gasoline buys about 100 miles of electric driving), their limited needs for new infrastructure and the fact that they emit no CO2. Their main disadvantages are their higher price (in the low $30,000s), their weight, limited driving range (Figure 1), long charging time, short battery life and small cargo space. For example, in the case of the Nissan Leaf, the price is $32,780, which is reduced to $25,280 after the U.S. federal tax rebate of $7,500 is considered, and in some case, such as in California, it is further reduced to $20,280 by an additional $5,000 tax rebate.

Figure 1: Chevrolet's Volt has a battery based driving range of 40 miles, which can be extended to 350 miles by a regular IC engine that generates added electricity. Tesla's Roadster and Nissan's Leaf are all-electric. The Roadster has several driving ranges of up to 250 miles, and the Leaf has a range of about 75 miles. Toyota is working on an electric version of its RAV4 utility vehicle and on an ultra-mini car named iQ, while Ford came out with its Transit Connect. GM has also entered competition for this market, and so has BMW, Tata and many others.

The standard charging time, if the car is charged at night in one's garage, is three to four hours. High-speed charging, using three-phase industrial outlets, can reduce the charging time to 10 to 20 minutes. "Battery swap" at service stations can further reduce this time to a couple of minutes.

It seems that after fossil fuels are exhausted, hydrogen will play a key role in transportation. It is not clear yet if the hydrogen will be charged into the individual cars at the fuel stations, or if it will fuel large fuel cells at the station that will generate the electricity to recharge the depleted batteries of all-electric cars. This will be an economic decision.

Today, economics favors the batteries, but even then, battery costs are still high, amounting to a quarter to half of the total cost of the car, depending on driving distance. In terms of energy density, lithium (Li-ion, Li-poly) and zinc-air batteries are the best today, but the availability of both of these materials is limited. For example, the lithium reserves of the planet for example are sufficient for about 4 billion electric cars.

In the long range, these reserve limitations can be overcome by using hydrogen-fueled cars. There already is a fair amount of experience with hydrogen-based transportation. In Berlin, 20% of the buses run on hydrogen. In Iceland, hydrogen-fueled rental cars are offered by Hertz. In Japan, hydrogen-fueled commuter trains are in operation. In Italy, one finds hydrogen-powered passenger ships. In Russia, hydrogen-fueled airplanes are used. And, the U.S. Air Force and NASA are jointly developing a hydrogen-fueled, earth-orbit airplane.

I visualize that by the end of the century, the filling stations might have large, underground, double-walled, cryogenic hydrogen storage tanks, supplying hydrogen to large fuel cells that will be converting the chemical energy in liquid (or high-pressure) hydrogen into the electricity needed to recharge the depleted batteries of electric cars. To reduce the refueling time to a minute or two, the depleted battery blocks will simply be swapped with recharged batteries.

Housing of the Future: The Zero Energy Homes

About half of all family homes on the planet could become fully (the others partially) energy-independent if they were covered with PV type solar collectors or solar shingles. By the end of this century, homes and other buildings are likely to have gabled roofs to maximize the south-facing roof area, and thereby maximize the efficiency of energy collection.

Solar shingles are also called building-integrated photovoltaics (BIPVs) because they are made of photovoltaic materials, and can be used to replace conventional shingles that provide only cladding for the home. Solar shingles can also be used on window overhangs, on the windows themselves (glazing), and on the siding of the home.

One design is available at 12 in. by 86.5 in., which can be nailed to the roof decking over a felt sheeting. From the underside of each shingle, 12 in. of  #18AWG wires extend, and pass through the roof deck to make the electrical connections.

Solar shingles

Figure 2: Thin-film solar shingles are encapsulated in a weather-resistant polymer and sized as conventional shingles—12 in. wide by 36 in. long.

The main disadvantages of solar shingles today are their many wire connections and their low efficiency, which is made worse by the high temperature that develops when the insolation is high. For example, the efficiency of the DOE/NREL design shown in Figure 2 is 4% to 5%. Higher efficiency designs are evolving. The efficiency of Dow Chemical's thin-film, copper-indium-gallium-deselenide (CIGS) design is 10% to 12%. The traditional PV collector efficiencies range from 20% to 30%, and nano-solar designs also hold promise. 

The installed cost of solar singles is two to three times that of regular asphalt shingles, or about $500 per sq. meter. The yearly electricity consumption of the average home is about 15,000 to 20,000 kWh, and at $0.2/kWh the yearly electricity bill today ranges from $3,000 to $4,000.

To generate this amount of electricity during the time when solar electricity is available (when the sun is out) requires a system size of over 5 kW. The yearly insolation in Arizona is about 2,500 kWh/m2/yr. Therefore, at 10% efficiency, 60 to 80 square meters of southern exposure roof area needs to be covered by solar shingles to provide 5 kW. At a unit cost of $500/m2, the installed cost is $30,000 to $40,000. In the New York area, both the area requirement and the investment cost would at least be doubled because the insolation is about half that of Arizona, and the sunny days are also fewer.

In the above example for Arizona, the system cost per watt was about $6 to $8 ($30,000 to $40,000 for a 5-kW system). This cost can be reduced if rebate programs exist in the state. For example, the rebate in New York State is $1.75/W or about 25%. In the case of large rooftop installations on commercial warehouses, the payback period is likely to be further reduced. For example, LPS industries in Moonachie, N.J., installed a 704-kW system on its 16,000 sq m rooftop for $5.7 million and, with the 30% government grant, found the payback period to be about five years.  

A key component of the control and optimization of energy-free housing is the by-directional electric meter that connects the home to the grid. These bi-directional electric meters can measure complex rates, and their soft switches allow the user to make functional changes without the need for changing any hardware. They can also be provided with recording, totalizing and a variety of logic and peak-shedding functions. In the future, the software in the intelligent electric meter might also be able to perform other control tasks, such as automatically charging the batteries of electric car(s) when the electricity is inexpensive (at night), and maximizing the amount of electricity sent to the grid (by temporarily turning off optional users) during periods when electricity rates are at a peak.  

In the next installment of this series, I will discuss the control software requirements of both the grid-connected and the totally self-sufficient, distributed and wireless energy supplies to transportation, housing and general industry, plus the methods for providing "grid-less" local back-up and energy storage.  

Béla Lipták, ([email protected]. ) process control consultant, is the editor of the Instrument Engineers Handbook.