Download Photovoltaic Solar System Components

PV System Components
Advanced Electronics
Landstown High School STEM &
Technology Academy
PV was developed for the space
program in the 1960’s
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
Cross Section of Solar Cell
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,
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.
Cells, Modules, Arrays
Photovoltaic Array for Lighting
Telecommunications Tower
Remote Water Pumping
Solar Lanterns for Landscaping
The PV Market
• As prices dropped, PV began to be used for standalone home power.
• If you didn’t 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.
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
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.
Photovoltaic Array on Roof and as an
Overhang
Other Mounting Systems?
• If it is impossible or you don’t 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.
Pole Mounted PV
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.
Solar Roofing Shingles
PV System Battery Sizing
Advanced Electronics
Landstown High School STEM &
Technology Academy
Series & Parallel Circuits
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.
Secondary cells
– Cells that can be recharged.
• Lead-acid battery or wet cell.
• Nickel-Cadmium cell or Ni-Cad.
Connecting Cells and Batteries
– Series
• Series-aiding:
– IT = I1 = I2 (current stays the same),
– ET= E1 + E2 (voltage is added together)
– Parallel
• Current expressed as IT = I1 + I2 , Current is added
together,
• Voltage expressed as ET = E1 = E2, Voltage stays the
same,
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,
Series Circuit
When cells and batteries are wired together in series then total
voltage increases, but the current stays the same.
Series Circuit
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.
3A
3A
6A
Sizing a PV System
Solar 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.
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,
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?
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,
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?
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 earth’s surface
facing the sun will intercept about 1 kw-hr of solar
energy,
• What you collect depends upon surface
orientation and collector efficiency,
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.
Photovoltaic Systems
Charge Controllers
Charge controllers manage interactions and energy flows
between a PV array, battery bank, and electrical load.
Single-stage battery charging is
simpler, but multistage battery
charging brings batteries to a
higher state of charge.
•Charge controllers protect batteries from overcharge by
terminating or limiting charging current.
•Charge controllers protect batteries from overdischarge by
disconnecting loads at low battery voltage.
Most charge controllers include displays or LEDs to indicate battery
voltage, state of charge, and/or present operating mode.
Shunt charge controllers regulate charging current by
short-circuiting the array.
Series charge controllers regulate charging current by
opening the circuit from the array.
•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.
•Diversionary charge controllers regulate charging current
by diverting excess power to an auxiliary load when
batteries are fully charged.
•Controllers designed for
hybrid PV systems must
manage multiple current
sources simultaneously.
Photovoltaic Systems
Inverters
Inverters are available in many different configurations
and ratings. Usually converting 12 volt DC power to AC.
Stand-alone inverters are connected to the battery bank
and supply AC power to a distribution panel that is
independent of the utility grid.
Interactive inverters are connected to the PV array and
supply AC power that is synchronized with the utility grid.
BATTERIES
• Batteries can be used to provide long-term or shortterm 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.