Title: PV System Components
1PV System Components
- Advanced Electronics
- Landstown High School STEM Technology Academy
2PV was developed for the space program in the
1960s
3What 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
4Cross Section of Solar Cell
5How 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,
6Combining 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.
7Cells, Modules, Arrays
8Photovoltaic Array for Lighting
9Telecommunications Tower
10Remote Water Pumping
11Solar Lanterns for Landscaping
12The 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.
13Other 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
14PV 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.
15Photovoltaic Array on Roof and as an Overhang
16Other 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.
17Pole Mounted PV
18Roof 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.
19Solar Roofing Shingles
20PV System Battery Sizing
- Advanced Electronics
- Landstown High School STEM Technology Academy
21Series 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.
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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,
29Connecting 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,
30Series Circuit
When cells and batteries are wired together in
series then total voltage increases, but the
current stays the same.
Series Circuit
31Parallel 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
32Sizing 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.
33Sizing 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,
34Battery 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?
35Battery 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,
36Example
- 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?
37Thinking 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,
38Sizing 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.
39Photovoltaic Systems
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.
50Photovoltaic Systems
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.
54BATTERIES
- 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.