Solar and Wind Energy Basics

Solar Energy

The Sun (a.k.a. Sol, latin for Sun) produces approximately the equivalent of 384 billion billion megaWatts per second (384 x 10**24 watts/s). Through nuclear fusion, in the time it takes to say, "Boy, it's hot today!", the sun has crushed and cooked 700, 000, 000 tons of hydrogen, resulting in 695, 000, 000 tons of helium plus 5, 000, 000 tons of pure energy (3.86e33 ergs in the form of gamma photons). Radiating in all directions, our nearest star has steadily churned out energy at this rate for 4.5 billion years (give or take 0.1% during each eleven year solar cycle) and estimates are that it will continue doing so for at least another 4.5 billion years.

Only a very very tiny fraction of solar output lands on Earth. Yet, it is the primary source of energy for our planet (99.8%). It grows our crops, heats the oceans, produces clouds and generates the wind. For Earth, the Sun is "The Source" of energy that makes life possible.

Solar Energy has several forms:

1) Primary Solar Form: This is the energy we receive in the form of light and radiant heat. The visible light portion can be converted into electricity using Photovoltaic Technology. The radiant heat portion (Solar Thermal Energy) can be collected and stored as simple thermal energy (i.e. hot water, steam, etc.). More on these technologies later.

2) Secondary Solar forms: Most other forms of energy we see on earth can be traced back to solar energy translated from its primary form. For instance:

2.1) Wind energy is the result of the sun unevenly heating the land, oceans and/or atmosphere.

2.2) Hydro energy (typically utilized in hydroelectric dams) is the result of gravity forcing water to flow from a higher level to a lower level. The flow can power anything from a turbine, a dynamo or a water wheel for milling brain. However, continuous hydro energy would be impossible unless solar radiation evaporated the water from lower areas into clouds (thereby over-coming gravity). Water, from rain and melting snow deposits at high elevations, can then flow into rivers to begin the cycle anew.

2.3) Fossil fuel energy is energy derived from crude oil, coal and natural gas. These substances are nothing more than the remains of plants and animals that died some 300 million years ago. Under geothermal pressure and heat, the remains of those plants and animals eventually transformed into the substances we know today. However, the energy in the compounds that made up their remains, were originally derived by plants through biological processes that stored energy from the sun as food (photosynthesis --> glucose).

2.4) Biomass Energy essentially this is energy produced from organic refuse (dead plants, trees, manure, even tires).

Solar Energy Technology Basics -

The solar cell (or photovoltaic cell)

At the heart of current solar energy technology is the solar cell. Also referred to as the photovoltaic cell, (PV cell) this device has the ability to convert sunlight into electricity. There are several types of PV cells. The cheapest and most common being based on cadmium sulfide technology. These cells have a conversion efficiency of about 7%. This means that on a clear sunny summer day, (at around noon or so) when typically one square foot of sunlight contains approximately 100 watts of energy (about 340Btu/hr), a cell based on this technology could be expected to produce about 7 watts of electricity per square foot (the cells are typically arranged in multi square-foot panels). An eight unit bank (or array) of 3 ft. x 6 ft. solar panels would produce electrical power at the rate of 8 x 18sqft. x 7 watts = 1008 watts per hour or 1.008 kilowatts/hr of power. Of course, this rate of power production decreases as the sun moves across the sky and changes its angle of incidence relative to the array. Realistically, over an 8 hour day the total power output might be at most no more than 5kWhrs (depending on location and time of year). Potentially, it will produce more if the array is able to track along the solar path, keeping its collection surface pointed directly at the sun in similar fashion to a sunflower.

Solar Thermal

Easily the oldest and cheapest form of solar technology, solar thermal technology utilizes collectors to capture the sun's radiant heat energy. After capture, the heat energy (in the form of steam ) can be used to drive electrical generator turbines or simply stored as hot water for use later. The collectors themselves are of four general types, solar plate collectors, batch collectors, parabolic and hyperbolic trough and compact linear fresnel reflector (CLFR), heliostat and tower. Plate and batch collectors are common for residential use.The reflector type collectors are common to commercial and industrial applications, including large scale power generation. However, there are individuals that have established specialized reflector applications for residential installations.

Wind Energy Technology Basics

As mentioned earlier, wind energy is simply the result of uneven atmospheric heating by the sun. Warmer upward expanding air masses flow toward cooler downward contracting areas in a spiral pattern because of the earth's rotation. These shifting patterns of atmospheric movement are further modified by terrain irregularities (i.e. mountain ranges, oceans, lakes, etc..).

Wind Technology Basics -

The wind turbine - At the heart of wind technology and its application to power generation is the wind turbine. A wind turbines is essentially a device that inverts or reverses the function of an aircraft propeller. Instead of an engine that spins a propeller to move air, the wind turbine spins due to the force of the air pushing on its blades (as in a windmill). It converts the rotational mechanical energy into electrical energy using a generator (or perhaps, an alternator).

Types of wind turbines - There are basically two types of wind turbines, horizontal axis wind turbines and vertical axis wind turbines. Both come in various sizes and therefore electrical power generating capacities. The horizontal type resembles, as mentioned before, a windmill where the propeller, (or rotor, as it is commonly referred to) can reach a diameter of 350ft. or more with tower heights in excess of 40 stories. Commercial machines of this type can produce power in excess of 6MW (megaWatts) supplying energy to many thousands of homes. A horizontal residential turbine might have a rotor diameter of up to 30 feet mounted on a 25ft. tower and supply pretty much all of the homes power requirements (typically less than 50kW). Vertical wind turbines are less frequently used commercially, but are gaining popularity in residential markets (for more information see our Residential Wind Power page).