Electric energy is a very important resource in human daily life. Solar cells and wind turbines are different machines that generates electric power for people, however, there are difference and similarity between the solar cells and wind turbines in turns of the working principle and the efficiency; which the cost, environmental issues, land area taken and production of energy will be included for both machines. The wind turbine is a machine that converts kinetic energy from wind into mechanical energy then converts to electric energy to power many homes and cities. The built structure of wind turbine is three blades connect to the rotor and a nacelle sits on a tower, the nacelle is the box that contains all the machinery that generates electrical energy. When the blades spins by the wind, the low speed shaft that connects to the rotor starts spinning at a low rate of 30-60 rpm which is not enough for generating power, where the lower speed shaft connects to the high speed shaft inside the gearbox and increase the rotational speed up to 1000 -1800 rpm which have enough speed to generate power, the high speed shaft connects to the generator and convert mechanical energy to electric energy to generate power for people; the controller of the wind turbine is also very important, it limits the speed at about 55 mph to prevent it to be damaged. This is how wind turbine generates power. According to research, the efficiency of wind turbines is about 35%, the operating and maintenance costs of wind turbines, the wind power in different season, the production taxes and the land taken are some of the factors that affects the efficiency. The operating and maintenance costs of wind turbines are as high as $0.043/kWh in Switzerland and as low as $0.019/kWh in United States. The wind power in winter is stronger than the other seasons which increase the production and the efficiency. United States Production Tax Credit $0.022 USD/kWh of electricity generated by the wind farm. Wind turbines are also in a wind farm which takes a lot of land space and affects the efficiency as well. The solar cells always combines together as solar panels to generate electric power, and they are some of the newest way to generate power for people. The solar cells are made up of two slice of silicon which is a type of material called a semiconductor that allows electricity to flow through very easily, there are two types of silicon layers, the lower layer silicon p-type (positive type) and the upper layer silicon n-type (negative type) to form a “sandwich”. When the sunlight shines on the solar cell, the photons hits the upper surface n-type, the photons carries the energy to electrons in the lower layer p-type layer, the electrons use the energy to move to the upper n-type layer and runs into the circuit then runs back to where it begins. The efficiency of the solar cells are about 15%, the temperature, weather, time and the land taking are some of the factors. According to research, solar cells perform better in a low temperature, when the temperature is at 70°C, solar cells produce 25% less power than 25°C. When the weather is windy and cloudy, sunlight could not shine at the solar cell which produce less power as well. The sun doesn’t shine for 24 hours so that it would not produce power all day long. Solar cells takes up a lot of space and affect the efficiency. In comparison, the wind turbine and the solar cell both performs better in a cold climate or a low temperature; they use renewable energy such as wind and sunlight to generate power which is very environmentally friendly, at the same time, because of the renewable resources, the resources of energy in unstable, the wind doesn’t stay at the same speed and the sun doesn’t always shine which affect the efficiency of both machines, furthermore, the wind turbine takes up a lot of space as well as solar cells, these factors lowers the efficiency of the machines. In contrast, the wind turbines’ efficiency is about 35%,but solar cells’ efficiency is only about 15%, wind turbines are definitely more efficient than the solar cells, additionally, although the wind and the sunlight are not very stable resources, the wind turbine can still work at night time but solar cell couldn’t. However, solar cells can be extracted at anytime while wind turbine couldn’t. Solar cell can be used for smaller operations such as watches, bikes and calculators, wind turbines are mostly used for generate large amount of electricity for homes and city. These are the compare and contrast for solar cells vs. wind turbines.