Greenmachines

Over 95% of all the solar cells produced worldwide are composed of the semiconductor material Silicon (Si). As the second most abundant element in earth`s crust, silicon has the advantage, of being available in sufficient quantities, and additionally processing the material does not burden the environment. To produce a solar cell, the semiconductor is contaminated or "doped". "Doping" is the intentional introduction of chemical elements, with which one can obtain a surplus of either positive charge carriers (p-conducting semiconductor layer) or negative charge carriers (n-conducting semiconductor layer) from the semiconductor material. If two differently contaminated semiconductor layers are combined, then a so-called p-n-junction results on the boundary of the layers.

model of a crystalline solar cell

At this junction, an interior electric field is built up which leads to the separation of the charge carriers that are released by light. Through metal contacts, an electric charge can be tapped. If the outer circuit is closed, meaning a consumer is connected, then direct current flows into your battery bank then inverted up to your grid tie or off grid system. And poof, free energy supplied by the sun.

Solar can be prtty expensive as it takes several years to break even, and then hope your solar cells hold out long enough to get sufficient cost/use out of them.

SOLAR

WIND

Wind Energy
Wind energy is a form of solar energy produced by uneven heating of the Earth's surface. Wind resources are best along coastlines, on hills, and in the northern states, but usable wind resources can be found in most areas. As a power source wind energy is less predictable than solar energy, but it is also typically available for more hours in a given day. Wind resources are influenced by terrain and other factors that make it much more site specific than solar energy. In hilly terrain, for example, you and your neighbor are likely to have the exact same solar resource. But you could have a much better wind resource than your neighbor because your property is on top of the hill or it has a better exposure to the prevailing wind direction. Conversely, if your property is in a gully or on the leeward side of the hill, your wind resource could be substantially lower. In this regard, wind energy must be considered more carefully than solar energy.

Wind energy follows seasonal patterns that provide the best performance in the winter months and the lowest performance in the summer months. This is just the opposite of solar energy. For this reason wind and solar systems work well together in hybrid systems. These hybrid systems provide a more consistent year-round output than either wind-only or PV-only systems. One of the most active market segments for small wind turbine manufacturers is PV-only system owners who are expanding their system with wind energy. 


Wind Turbines
Most wind turbines are horizontal-axis propeller type systems. Vertical-axis systems, such as the the egg-beater like Darrieus and S-rotor type Savonius type systems, have proven to be more expensive. A horizontal-axis wind turbine consists of a rotor, a generator, a mainframe, and, usually, a tail. The rotor captures the kinetic energy of the wind and converts it into rotary motion to drive the generator. The rotor usually consists of two or three blades. A three blade unit can be a little more efficient and will run smoother than a two blade rotor, but they also cost more. The blades are usually made from either wood or fiberglass because these materials have the needed combination of strength and flexibility (and they don't interfere with television signals!). 

The generator is usually specifically designed for the wind turbine. Permanent magnet alternators are popular because they eliminate the need for field windings. A low speed direct drive generator is an important feature because systems that use gearboxes or belts have generally not been reliable. The mainframe is the structural backbone of the wind turbine and it includes the "slip-rings" that connect the rotating (as it points itself into changing wind directions) wind turbine and the fixed tower wiring. The tail aligns the rotor into the wind and can be a part of the overspeed protection. 

A wind turbine is a deceptively difficult product to develop and many of the early units were not very reliable. A PV module is inherently reliable because it has no moving parts and, in general, one PV module is as reliable as the next. A wind turbine, on the other hand, must have moving parts and the reliability of a specific machine is determined by the level of skill used in its engineering and design. In other words, there can be a big difference in reliability, ruggedness, and life expectancy from one brand to the next.  This is a lesson that often seems to escape dealers and customers who are used to working with solar modules.


Towers
A wind turbine must have a clear shot at the wind to perform efficiently. Turbulence, which both reduces performance and "works" the turbine harder than smooth air, is highest close to the ground and diminishes with height. Also, wind speed increases with height above the ground. As a general rule of thumb, you should install a wind turbine on a tower such that it is at least 30 ft above any obstacles within 300 ft. Smaller turbines typically go on shorter towers than larger turbines. A 250 watt turbine is often, for example, installed on a 30-50 ft tower, while a 10 kW turbine will usually need a tower of 80-120 ft.  We do not recommend mounting wind turbines to small buildings that people live in because of the inherent problems of turbulence, noise, and vibration.

The least expensive tower type is the guyed-lattice tower, such as those commonly used for ham radio antennas. Smaller guyed towers are sometimes constructed with tubular sections or pipe. Self-supporting towers, either lattice or tubular in construction, take up less room and are more attractive but they are also more expensive. Telephone poles can be used for smaller wind turbines. Towers, particularly guyed towers, can be hinged at their base and suitably equipped to allow them to be tilted up or down using a winch or vehicle. This allows all work to be done at ground level. Some towers and turbines can
be easily erected by the purchaser, while others are best left to trained professionals. Anti-fall devices, consisting of a wire with a latching runner, are available and are highly recommended for any tower that will be climbed. Aluminum towers should be avoided because they are prone to developing cracks. Towers are usually offered by wind turbine manufacturers and purchasing one from them is the best way to ensure proper compatibility.

HYDRO

Conversion Factors
Handy conversion table

Determining Head
When determining head, you must consider both gross or "static" head, and net or "dynamic" head. Gross head is the vertical distance between the top of the penstock (the piping that conveys water, under pressure, to the turbine) and the point where the water discharges from the turbine. Net head is gross head minus the pressure or head losses due to friction and turbulence in the penstock. These head losses depend on the type, diameter, and length of the penstock piping, and the number of bends or elbows. You can use gross head to approximate power availability and determine general feasibility, but you must use net head to calculate the actual power available.

Determining Flow

Determining Power

Gross Head x  Flow  x  System Efficiency (in decimal equivalent) x  C = Power (kW)

 

C is a constant (the value is different in English and metric units).

1. 20 feet x 2 cfs x 0.55 x 0.085 = 1.9 kW or: 6 meters x 0.05 cms x 0.55 x  9.81 = 1.62 kW
2. 50 feet x  0.8 cfs x  0.55 x  0.085 = 1.9 kW or: 15 meters x  0.02 cms x  0.55 x  9.81 = 1.62 kW