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PV System Components

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Adapted from a presentation by Dr. William J. Makofske in August of 2004. ... Advanced Electronics Landstown High School STEM & Technology Academy ... – PowerPoint PPT presentation

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Title: PV System Components


1
PV System Components
  • Advanced Electronics
  • Landstown High School STEM Technology Academy

2
PV was developed for the space program in the
1960s
3
What is a solar cell?
  • Solid state device that converts solar energy
    directly into electrical energy
  • Efficiencies from 10- 80
  • No moving parts
  • No noise
  • Lifetimes of 20-30 years or more

4
Cross Section of Solar Cell
5
How Does It Work?
  • The junction of dissimilar materials (n () and p
    (-) type silicon) creates a voltage,
  • Energy from sunlight knocks out electrons,
    creating a electron,
  • Connecting both sides to an external circuit
    causes current to flow,
  • In essence, sunlight on a solar cell creates a
    small battery with voltages typically 0.5 volt DC,

6
Combining Solar Cells
  • Solar cells can be electrically connected in
    series (voltages add) or in parallel (currents
    add) to give any desired voltage and current,
  • Power (Watts) output is calculated P I x V
  • Photovoltaic cells are typically sold in modules
    (or panels) of 12 volts with power outputs of 50
    to 100 watts.
  • These are then combined into arrays to give the
    total desired power or watts.

7
Cells, Modules, Arrays
8
Photovoltaic Array for Lighting
9
Telecommunications Tower
10
Remote Water Pumping
11
Solar Lanterns for Landscaping
12
The PV Market
  • As prices dropped, PV began to be used for
    stand-alone home power.
  • If you didnt have an existing electrical line
    close to your property, it was cheaper to have a
    PV system (including batteries and a backup
    generator) than to connect to the grid.
  • As technology advanced, grid-connected PV with
    net metering became possible.

13
Other System Components
  • While a major component and cost of a PV system
    is the array, several other components are
    typically needed. These include
  • The inverter DC to AC electricity
  • DC and AC safety switches
  • Batteries (optional depending on design)
  • Monitor (optional but a good idea)
  • Ordinary electrical meters work as net meters

14
PV On Homes
  • PV can be added to existing roofs.
  • While south tilted exposure is best, flat roofs
    do very well.
  • Even east or west facing roofs that do not have
    steep slopes can work fairly well if you are
    doing net metering since the summer sun is so
    much higher and more intense than the winter sun.
  • The exact performance of any PV system in any
    orientation is easily predictable.

15
Photovoltaic Array on Roof and as an Overhang
16
Other Mounting Systems?
  • If it is impossible or you dont want to put a PV
    system on your existing roof, it is possible to
    pole mount the arrays somewhere near the house as
    long as the solar exposure is good.
  • Pole mounted solar arrays also have the potential
    to rotate to follow the sun over the day by
    installing a sun tracking system,
  • Sun tracking systems can provides a 30 or more
    boost to the PV system performance.

17
Pole Mounted PV
18
Roof Integrated PV
  • If you are doing new construction or a reroofing
    job, it is possible to make the roof itself a
    solar PV collector.
  • This saves the cost of the roof itself, and
    offers a more aesthetic design.
  • The new roof can be shingled or look like metal
    roofing. A few examples follow.

19
Solar Roofing Shingles
20
PV System Battery Sizing
  • Advanced Electronics
  • Landstown High School STEM Technology Academy

21
Series Parallel Circuits
22
  • Battery
  • A combination of two or more cells.
  • Negative terminal is also called the cathode,
  • Primary cells
  • Cells that cannot be recharged.
  • A dry cell also referred to as a carbon-zinc
    cell.
  • Alkaline cell.
  • Lithium cell.

23
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26
  • Secondary cells
  • Cells that can be recharged.
  • Lead-acid battery or wet cell.
  • Nickel-Cadmium cell or Ni-Cad.

27
  • Connecting Cells and Batteries
  • Series
  • Series-aiding
  • IT I1 I2 (current stays the same),
  • ET E1 E2 (voltage is added together)

28
  • Parallel
  • Current expressed as IT I1 I2 , Current is
    added together,
  • Voltage expressed as ET E1 E2, Voltage stays
    the same,

29
Connecting batteries
  • When cells and batteries are wired together in
    parallel then the amount of current increases,
  • When cells and batteries are wired together in
    series then total voltage increases,

30
Series Circuit
When cells and batteries are wired together in
series then total voltage increases, but the
current stays the same.
Series Circuit
31
Parallel Circuit
All the positive terminals are connected
together, and all the negative terminals are
connected together. The total current (IT) is
the sum of the individual current of each cell or
battery.
6A
3A
3A
32
Sizing a PV SystemSolar Panels
  • Solar modules/panels are typically sold by the
    peak watt.
  • That means that when the sun is at its peak
    intensity (clear day around midday) of 1000 watts
    per m2,
  • a solar module/panel rating at say 100 Wp (peak
    watts) would put out 100 watts of power.
  • The climate data at a given site summarizes the
    solar intensity data in terms of peak sun hours,
  • the effective number of hours that the sun is at
    that peak intensity on an average day.
  • If the average peak sun hours is 4.1, it also
    means that a kw of PV panels will provide 4.1
    kw-hr a day.

33
Sizing and Calculating
  • To determine the number and size of the batteries
    we will need, there are some thing we need to
    determine,
  • Load (number of kw being used),
  • Battery capacity,
  • Location of the panels,
  • Type of mounting system,

34
Battery Sizing I
  • If your load is 10 kw-hr per day, and you want to
    battery to provide 2.5 days of storage, then it
    needs to store 25 kw-hr of extractable electrical
    energy,
  • Since deep cycle batteries can be discharged up
    to 80 of capacity without harm, you need a
    battery with a storage of 25/0.8 31.25 kw-hr.
  • A typical battery at 12 volts and 200 amp-hour
    capacity stores 2.4 kw-hr of electrical energy.
  • So how many batteries would you need?

35
Battery Sizing II
  • To calculate how many batteries
  • We use the relationship between battery energy
    (E) in kw-hr and battery capacity (amp-hr),
  • E(kw-hr) capacity(amp-hr) x voltage/1000
  • E 200 amp-hr x 12 volts/1000 2.4 kw-hr
  • So for 31.25 kw-hr (2 ½ days) of storage we need
  • 31.25 kw-hr/2.4 kw-hr/battery 13
    batteries
  • How many batteries would you need for only one
    day of storage? 13/2.5
  • 5.2 batteries
  • If we are happy with one half day,
  • we need only 2 or 3 batteries,

36
Example
  • Typically, Landscape lights are rated at 20w,
  • If we wanted to design a PV system to run these
    lights for 30 days per charge how many batteries
    would we need?
  • 12 volt battery
  • E 200 amp-hr x 12 volts/1000 2.4 kw-hr
  • Load 20w x 30 days 600w/1000 .6 kw-hr
  • .6 kw-hr/2.4 kw-hr .25 batteries
  • So how many batteries do we need?

37
Thinking About Solar Energy
  • When the sky is clear and it is around midday,
    the solar intensity is about 1000 watts per m2 or
    1 kw/m2, or
  • In one hour, 1 square meter of the earths
    surface facing the sun will intercept about 1
    kw-hr of solar energy,
  • What you collect depends upon surface orientation
    and collector efficiency,

38
Sizing a PV System to Consumption
  • A PV system can be sized to provide part or all
    of your electrical consumption.
  • If you wanted to produce 3600 kw-hr a year at a
    site that had an average of 4.1 peak sun hours
    per day,
  • PV Size in KWp 3600 kw-hr
  • 4.1 kw-hr/day x 365 days/yr x 0.9 x0.98
  • 2.7 KWp
  • Note the 0.9 is the inverter efficiency and the
    0.98 represents the loss in the wiring.

39
Photovoltaic Systems
  • Charge Controllers

40
  • Charge controllers manage interactions and energy
    flows between a PV array, battery bank, and
    electrical load.

41
  • Single-stage battery charging is simpler, but
    multistage battery charging brings batteries to a
    higher state of charge.

42
  • Charge controllers protect batteries from
    overcharge by terminating or limiting charging
    current.

43
  • Charge controllers protect batteries from
    overdischarge by disconnecting loads at low
    battery voltage.

44
  • Most charge controllers include displays or LEDs
    to indicate battery voltage, state of charge,
    and/or present operating mode.

45
  • Shunt charge controllers regulate charging
    current by short-circuiting the array.

46
  • Series charge controllers regulate charging
    current by opening the circuit from the array.

47
  • Maximum power point tracking manipulates the load
    or output voltage of an array in order to
    maintain operation at or near the maximum power
    point under changing temperature and irradiance
    conditions.

48
  • Diversionary charge controllers regulate charging
    current by diverting excess power to an auxiliary
    load when batteries are fully charged.

49
  • Controllers designed for hybrid PV systems must
    manage multiple current sources simultaneously.

50
Photovoltaic Systems
  • Inverters

51
  • Inverters are available in many different
    configurations and ratings. Usually converting 12
    volt DC power to AC.

52
  • Stand-alone inverters are connected to the
    battery bank and supply AC power to a
    distribution panel that is independent of the
    utility grid.

53
  • Interactive inverters are connected to the PV
    array and supply AC power that is synchronized
    with the utility grid.

54
BATTERIES
  • Batteries can be used to provide long-term or
    short-term electrical supply in case of grid
    failure.
  • Many grid-connected houses choose to have a small
    electrical battery system to provide loads with
    power for half a day in case of outage.
  • Larger number of batteries are typically used for
    remote grid-independent systems.
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