Control Software and Renewable Energy, Part 3

While the first cost is still higher, the operating costs already favor the electric car over the ones using internal combustion (IC) engines. At a gasoline cost of $3/gallon and at an average fleet mileage of 30 mpg, the cost of driving a conventional car is about $0.1 per mile. The energy content of a gallon of gasoline is about 10 kWh; therefore, the per mile energy consumption of the average IC vehicle is about 0.33 kWh/mile (10 kWhpg/30 mpg = 0.33 kWh/m). The cost of driving an electric car is about half of that, because at an electricity cost of $0.15 per kWh the cost of the energy needed per mile energy (0.33 kWh/mile) is $0.045 (0.15 x 0.3 = $0.045) instead of $0.1 for the IC engine driven one. Naturally, as the cost of gasoline rises and as the cost of batteries drop, the economic advantage of driving electric cars will further increase.   

Figure 3: Electric Cars

The race between fuel cells (FC) and batteries is not yet over. Today, economics favor the batteries, but the long-range outcome is yet undecided. As electric cars replace today's vehicles, the availability and cost of the materials needed for fuel cells and batteries will become important factors. The critical cost factor in the case of fuel cells is the cost and availability of the catalysts, and the critical cost for the batteries is the cost and availability of lithium, although other materials (nickel, manganese, antimony and the use of multiple miniature carbon terminals) and other designs (asymmetric super-capacitors, MEMS, etc.) are also being considered.

As will be discussed later, extensive research efforts are in progress to develop inexpensive catalysts and to increase the efficiency of fuel cells by exploiting nanotechnology.

Solar Battery Charge Controllers

The larger the solar electricity collection system, the more sophisticated the battery charge controllers become. They usually are provided with digital interfaces and interactive displays, which can be integral with the controller or can be provided with wireless connection to the user's PC. In either case, the human-machine interface allows the home's owner to check the charging voltage and the amount of electrical energy stored at any time and to modify the limit settings for each mode of operation. Some of the charge controller suppliers include Xantrex, Morningstar. Outback Power, Blue Sky Energy and Steca.

For very small systems, a 30-ampere controller with LCD display costs about $50, while the solar inverter needed can be as inexpensive as $10. Even these least expensive voltage controllers are usually provided with such features as:

1. Overload protection
2. Short circuit protection
3. Reverse discharge protection
4. Reverse polarity connection protection
5. Thunder protection
6. Low voltage protection
7. Overcharge protection
8. Battery stop and charge voltage HVD (high voltage differential) features
9. Charge and low voltage LCD (liquid crystal display)
10. Display the capability of the battery SOC (state of charge)
11. Loads and comeback features
12. Temperature compensation
13. Store, calculate and display of the charged AH (ampere hour) on the LCD screen.
14. Store, calculate and display the discharged A (amperes) on the LCD screen.
15. Temperature range: from -25 to +55°C.