“Small store heat and/or electricity. In general, micro generation

“Small wind”
is defined as wind-powered electric generators with rated capacities of 100
kilowatts (kW) or less. “Micro wind” is a subset of the “small wind”
classification and is generally defined as turbines with rated capacities less
than 1kW 23.

2.3.1 Micro Generation

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Micro
generation is the concept of distributed power generation using renewable
resources that exist in and around the home to generate and store heat and/or
electricity. In general, micro generation is associated with reduced carbon
emissions because it does not require the use of fossil fuels to generate
power. Micro generation technologies include small scale wind turbines,
hydroelectric, photovoltaic solar systems, ground source heat pumps, Micro
Combined Heat and Power (Microchip) installations. Small wind micro generation
is the focus of this design study.

 2.3.2 Small Wind Market Size

 The small wind global market size was $156
million in 2008, which was a 53% growth over 2007 23.

2.3.3 Small
Wind Market Share

U.S.
manufacturers contributed to 49.4% of market share for small wind systems at
the start of 2009. As of 2009, 219 small wind manufacturers were identified,
35% of which were US based 23

2.3.4
Removing the Tower from the Small Wind Turbine System

Building roof
tops have been utilized in an effort to reduce cost, and simplify the
installation of small wind turbine systems. Using building roof tops provides
the needed height above the ground to clear obstacles such as trees and other
buildings. In general, the higher the building above the surrounding
obstructions, the higher the average wind speeds. Issues arise when small wind
turbines are mounted to insufficiently tall buildings, which have low,
turbulent winds from surrounding buildings, trees, and other urban structures.
Additionally, there are other considerations with building mounted wind
turbines, such as: vibration, noise, and appearance, which are generally
exacerbated by proximity to people.The variable output produced by renewable energy induction
machines means that power conditioning and control needs to be conducted in
order to transform the produced voltage, current and frequency into an AC or DC
form that can be used by general electrical appliances. The particular
transformation of interest for this type of application is AC-DC conversion.
The renewable energy converter, in this case the wind turbine performs at
different levels depending on the magnitude of wind which varies seasonally and
at different times of the day. A 100W turbine would be most useful at supplying
charge to a battery bank which then can distribute DC power as required by the
appliances. Before defining the required circuitry to transform AC to DC, some
important terms and equipment need to be discussed.5.1 Regulator A regulator is a battery charge controller that is used to
protect the battery bank from over charging and over-discharging. The simplest
method of regulation is to simply turn off the supply when the battery is fully
charged and then to turn it on again when the battery reaches a minimum level
of voltage. There are three main groups of regulators used in battery bank
charging circuits: shunt, series and chopper.5.2 ShuntThis system dissipates the power from the renewable source,
the wind turbine, across a dump load, once the battery is fully charged. This
method is most common with wind turbines.5.3 Series The supply is
automatically switched off once the battery is fully charged.5.4 ChopperThis is a high frequency switching operation which turns the
supply to the battery on and off; once, the battery is fully discharged the
charging circuit is fully turned on. When the battery reaches a higher level of
charge, the charging circuit switches the control on and off in proportion to
the level of charge of the battery.5.5 Inverter Wind turbines that use induction generators for electrical
energy production produces an AC current. The AC supply is then rectified into
a low voltage, direct current. “An inverter is an electrical device that
changes direct current into alternating current”. (Farret 2004 Renewable Energy
Systems). Inverters are the electrical tool that enables standard house hold
items to use the power supplied by the renewable energy system. Un-directional
inverters are used when power is to be simply supplied from a generator to a
load like a battery or a kettle. If an inverter is to supply power to something
like a motor it needs to be bi-directional. If the source is to be connected to
a grid, the inverter must supply power at a similar quality to that of the
grid.5.6 AC to DC conversionThe following parameters are required to design a circuit
for AC-DC conversion. – Evaluation of AC
input limitations – Average output
voltage – Output ripple voltage – Efficiency – Circuit load, output power – Regulation to input voltage variation – Regulation to output load variation – Power flow direction if required, AC to DC In the
conversion from AC to DC a wave rectifier circuit needs to be employed. Half
wave rectifiers are generally limited to applications lower than 100 W due to
their lower power factors, their bulkiness and transformer inefficiencies.5.7 Transistor as RectifierTransistor is a three terminal semiconductor device normally
used as an amplifier or as a switch. Here the alternating current (ac)
rectifying property of the transistor is considered. The ordinary silicon diode
exhibits a voltage drop of ~0.6V across its terminals. In this article it is
shown that the transistor can be used to build a diode or rectify low current
ac (~mA) with a voltage drop of ~0.03V. This voltage is ~20 times smaller than
the silicon diode. The article gives the half-wave and full-wave transistor
rectifier configurations along with some applications to justify their
usefulness.5.7.1 IntroductionRectification of ac is normally carried out using silicon
diodes (Kasatkin & Nemtsov 1986). The silicon diode exhibits a voltage drop
of ~600mV across its terminals when forward biased. This 0.6V is very small
voltage if one wants to rectify voltages like 10V or 100V and hence the voltage
drop across the diode can be neglected. The diode for all practical purposes is
considered to conduct freely in one direction and completely non-conducting in
the other direction (reverse bias). However if one needs to rectify an ac of
amplitude 1V, the 0.6V across the silicon diode forms a large fraction (60%).
Essentially the silicon diode cannot be used to rectify low voltages like 1V ac
if one is interested in recovering the complete or almost complete (90%)
waveform of the signal. In this article the possibility of using a transistor
as a rectifier (Pookaiyaudom et.al) is explored. It is seen that the transistor
rectifier exhibits a voltage drop of 0.03V or in other words it forms a diode
with this voltage drop. This voltage is 20 times smaller compared to the
silicon diode and 5 times smaller compared to the schottky diode (0.15V). Thus
the transistor rectifier can be used to rectify ac as low as 10 times the
voltage drop across it, ~300mV. This article gives half-wave and full wave
configurations of the transistor rectifier.

Rectification of alternating current with a single
transistor has been considered. This simple circuit consisting of a transistor, a
biasing diode and a few resistors can rectify a.c as low as 0.3V or even less.
The rectification can be for positive half cycle or negative half cycle
depending on the type of transistor (pnp/npn respectively) chosen. The
schematic circuit of the rectifier is as shown in Fig-1. The quiescent forward
biasing (Kasatkin & Nemtsov 1986) of the base-emitter junction of the
transistor is taken care by the voltage drop across the silicon diode (1N4148).
The base-emitter junction of the silicon transistor and the silicon diode being
similar the voltage drops across them are also more or less equal. The ac to be
rectified is introduced in the emitter circuit as shown in the Fig-1. Under
this situation to the first order any low negative voltage (NPN-version)
appearing at the emitter would set up an emitter current which would mostly
flow to the collector. However a small voltage drop (~0.03V) across collector
and emitter of the transistor is required to maintain a current through it.
Essentially any additional voltage in the base-emitter loop other than the
balanced out voltage drops of the silicon diode and the base-emitter junction
will be transferred to the collector circuit, as most of the emitter current
flows through the collector. The Fig-1 shows 1 both types of rectifiers which
can rectify either the negative phase or the positive phase of the ac signal.The wind energy is a rapidly expanding field. Extensive
research activities are being conducted across the globe in this area, with the
goal of improving the efficiency of wind turbines. Several configurations of
wind turbines have been proposed and the modern horizontal axis wind turbines
are at this juncture very efficient with the power coefficient up to 45 % to 50
%. In spite of all the efforts, as reported in chapter 1, the overall contribution
of wind power in the global total electricity generation is still a small
fraction. One of the main reasons for the low success rate of wind turbines is
the high rated wind speed. The low wind speed small scale wind turbines are
generally ignored because of their poor performance that does not allow
justifying their installation and operational cost. The aim of this thesis was
to develop the wind energy harvesters that can operate near the ground level
where wind speed is very low (5 m/s).CONCLUSIONThe 6 blade turbine feeds power directly to the generator.
Up to 100 watts of continuous power can be produced by the permanent magnets
rotating inside “heavy duty” windings that safeguard the generator from
burn-out and eliminate the need for thermal cut-outs, chokes or ‘complex
electronics.’ Electrical slip-rings and brushes allow the Ampair 100 to seek
the wind and feed the simple two-wire battery connection.