PV System Components

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PV System Components

• Advanced Electronics
• Landstown High School STEM Technology Academy

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PV was developed for the space program in the
1960s
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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

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Cross Section of Solar Cell
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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,

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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.

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Cells, Modules, Arrays
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Photovoltaic Array for Lighting
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Telecommunications Tower
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Remote Water Pumping
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Solar Lanterns for Landscaping
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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.

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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

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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.

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Photovoltaic Array on Roof and as an Overhang
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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.

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Pole Mounted PV
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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.

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Solar Roofing Shingles
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PV System Battery Sizing

• Advanced Electronics
• Landstown High School STEM Technology Academy

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Series Parallel Circuits
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• 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.

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

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

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

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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,

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Series Circuit
When cells and batteries are wired together in
series then total voltage increases, but the
current stays the same.
Series Circuit
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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
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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.

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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,

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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?

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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,

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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?

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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,

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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.

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Photovoltaic Systems

• Charge Controllers

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

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

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

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

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

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

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

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• 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.

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

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

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Photovoltaic Systems

• Inverters

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

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

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

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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.