Power Need and Energy System

Few terms and concepts make one think about making renewable energy system and applications which can improve living.

Energy is consumed when work is done . Most machines are designed and built to do work on objects. A powerful machine is both strong and fast , can apply big force and big velocity, does a work in a short time. A small power machine can do the same work in a longer time . Work like raising water for use in house and farming, can be done slowly. Transportation in many places can be done with less speed and lighter vehicles. These need less power . Solar and wind energy can be used for these situations with less expenditure.

Few examples give a feeling of quantity of energy used for different usage. A household bulb uses electrical energy at a rate of 25 to 100 watt. For example if a 100 watt light bulb is turned on for one hour the energy used is 100 watt-hour or 0.1 kilowatt-hour. Same quantity of energy would light a 40 watt bulb for 2.5 hour. A cyclist can maintain a rate of energy use of 400 watts. To evaporate 15.5 kg of water at 100 C in one hour, energy used is 9.8 kilowatt.

Horsepower is occasionally used to describe the power delivered by a machine. One horsepower is equivalent to 750watt. On appliances, figure given for watt is for one full hour of operation. Average power usage ranges for few appliances given below.

Microoven 600-1500 watt, Washing machines 300-500 watt, Table fan 10-25 watt , Ceiling fan 10 to 50 watt, Computer laptop 20-50 watt desktop 80-150watt , Color tv 25” 100-150 watt, Cd player/Stereo 10-40 watt, Refrigerators 70-500 watt, Air conditioner 1000 watt.

Two wheelers and four wheelers engine produce mechanical energy in range 10-40 hp and 140-500 hp respectively. Diesel electric locomotive produce power of the order 3 to 5 megawatt. A motor of 250-450 watt gives enough power for a bike(cycle) for comfortable running.

To design renewable system , estimation of average total watt-hours per day and storage are made. For each item to be used, the wattage should be noted as well as whether it runs on ac or dc current. Counting average hour a device will be used , the power need is estimated. Lithium ion batteries are popular for their storage capacity and performance. Inverters are used to get current in ac form if needed.

Solar-thermal and solar-photovoltaic methods are used for solar power. In solar-thermal, mirrors are used to focus light to heat an oil or water based fluid in a black pipe. This pipe transfers heat to a heat exchanger , which makes steam to drive a turbine or direct heating. The maximum solar power delivered to the earth, surface under optimum condition is of the order of 100w/ft2. The maximum value of energy is of the order of 0.7kw.h/ft2 per day. Only a part of this is converted to useful work.

In solar-photovoltaic, two layer of semiconductor material one with extra electrons and the other with extra holes are sandwitched together in photovoltaic panels. When the material absorbs sunlight, excess electron move from one layer to the other, creating an electric current. . Devices that can reduce reflection and capture more of the solar spectrum by using one or a combination of optical methods give better efficiency.

Wind power describes the process by which the wind is used to generate mechanical power or electricity. Wind turbines (or wind generator) convert the kinetic energy in the wind into mechanical power. Turbines range in size from medium to large(kilowatt to several megawatt). Small size turbines (50-500w) are used for homes and small uses. A device called rectifier is used to convert ac output of a wind generator to dc if required.

Suitable watt solar panels , wind turbines and different storage capacity batteries can be chosen from wide ranges available in the market. One can make estimates for any system easily. In remote places, use of alternative energy system gives more benefit. Alternative energy systems are generally easy to expand. If electrical use increases one can add more solar panels , batteries or wind turbines.