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Solar Power

 

Whether on a solar-powered calculator or an international space station, solar panels generate electricity using the same principles of electronics as chemical batteries or standard electrical outlets. With solar panels, it's all about the free flow of electrons through a circuit.

Silicon is the raw material used to make solar cells. It's the second most abundant element on Earth.

There are three main types:

Monocrystalline or single crystal cells : The first generation of solar cells
excellent conversion rate (12 - 16%) (23% under laboratory conditions)
BUT, making them is a painstaking, therefore expensive process
another drawback - it takes a lot of energy to obtain pure crystal
Polycrystalline cells lower production costs, requiring less energy to make
11 - 13% conversion efficiency (18% in the lab)
Amorphous a more recent technology (mid-70's) lower production costs, but unfortunately also lower efficiency (8 - 10%) (13% in the lab)
This process can use very thin layers of amorphous silicon (0.3 - 1.0 microns compared to 500 microns for the other types). Using a vacuum spraying process, very thin layers can be applied on glass, metal or even flexible plastic surfaces. Amorphous silicon is usually the kind used in consumer goods such as calculators and watches.

Amorphous panels need about twice the surface area to produce the same amount of electricity, and their output deteriorates more quickly over time, but they react better to diffuse and fluorescent light and work better at higher temperatures.

 

 

 

 

A single solar cell always produces a VOLTAGE of approximately 0.5 volts, regardless of its size. For higher voltages, you have to connect individual cells in SERIES to add their voltages. The larger the solar cell, the greater the CURRENT will be. Current is measured in AMPERES.
You can also connect cells in PARALLEL to increase current.
The most common solar panels are for 12 V applications. To reach that voltage, 24 cells would be sufficient, but for charging batteries and in order to compensate for voltage drops due to various factors, a PV panel normally contains between 28 and 40 cells for a higher voltage. You don't really need to think about the individual cells. All you need to know is that they are protected from humidity and the elements inside the panel, which works as a whole.

The panel has to deliver more than 12 volts to charge a 12-volt battery. Voltage can be compared with water pressure in a hose. If the "pressure" of the electrons isn't high enough, the electricity can't "penetrate" the battery.

Voltage can drop for several reasons:

At high temperatures. (Unlike thermal solar energy, PV works less well when it's very hot! In tropical climates, choose higher voltage panels.)
As a result of long wires. It's important to keep your wiring between your panels and other parts of your installation as short as possible.
Diodes can also cause small voltage losses, as we'll see later.
Just as voltage can be likened to water pressure in a hose, current can be likened to the flow, or the amount of water (or electrons) passing through. A thin hose will take longer to fill a swimming pool than a thicker hose with the same pressure.

A panel that produces 2 amperes sends twice as many electrons as a one-ampere panel. When talking of PV panels, you usually refer to their POWER (measured in WATTS).

VOLTAGE (electrical "pressure") is measured in VOLTS
CURRENT is measured in AMPERES.
POWER (WATTS) is calculated by multiplying these two.

VOLTS x AMPERES = WATTS

How Much Will My Panels Produce?

One square meter of solar panels can produce up to 150 watts of maintenance-free power for up to thirty years. They even work on diffuse light on overcast days, albeit with less output. The voltage produced by PV panels remains roughly the same regardless of the weather, but the current (amps) and the power (watts) will vary.

The most important variable to bear in mind when planning a photovoltaic installation is the power output, which will basically depend on four factors:

the peak power of your panels (measured in peak-watts or Wp)
light intensity
the number of hours of exposure to the sun and
the angle of exposure to the sun

 

The Intensity of Sunlight

A panel's power is expressed in peak watts, the number of watts it will produce in optimal conditions, i.e. at noon in direct sunlight in cold weather. Maximum sun intensity is 1.000 W/m2.

The following factors will influence the amount of sunlight reaching the PV panels:

1.Weather conditions (cloud cover, fog etc.)

2. How high the sun is in the sky

3. The number of daylight hours

1) As to the first factor, oversimplifying somewhat, a 50 watt panel should produce 50 watts for each hour of sunshine at 1.000 W/m². It will produce about half that amount (25 watts each hour) when exposed to 1/2 the light (500 W/m²). Diffuse light passing through thin clouds might mean 300 W/m². In very bad weather conditions with thick, dark clouds, light intensity could fall to 100 W/m² with only 5 Watts produced per hour.

2) The second factor, the height of the sun over the horizon varies with the seasons. When the sun is very high in the sky (summer), its rays travel through the atmosphere more quickly over a shorter distance than when it's low in the sky (winter). Light is scattered more and becomes more diffuse when passing through fog or pollution. A spot that gets plenty of sun 9 months of the year might be shadowed from November to January due to obstacles (trees, chimneys, rooftops etc.).

3) The third factor creates the greatest problems for those who don't happen to live close to the Equator, i.e. the difference in the number of hours of sunlight between the seasons. This is a huge subject that we'll have to take a closer look at later.

 

 

 

 

Looking for the Sun

It's always best to best to have your panels facing south at the ideal tilt angle depending on your latitude and the time of year. (Magnetic south as indicated by a compass is actually 16² west of true south.)

THE SUN'S RAYS SHOULD BE PERPENDICULAR TO THE PANELS.
SUNLIGHT SHOULD HIT THEM AT A 90° ANGLE.

The ideal situation in Europe is to have a south-facing roof at an angle between 40 and 60 degrees, or, even better, a flat roof (or surface) on which your panels can be adjusted at will. You may decide to deviate from these values for convenience or for esthetic reasons, in order to fit them into the existing architectural structure. The future of PV will depend to a large extent on the harmonious integration of panels in buildings.-One example of this: In an apartment building in Denmark, where they wanted to install glass sides in the balconies (to limit heat loss), they realized that they could just as easily install frameless PV panels at a minimal additional cost. The loss in output due to the vertical position and the less-than-ideal location (facing south-west) was estimated at 30%.

Some people use sophisticated panel mounts called "trackers" that follow the path of the sun during the day. These automatic systems can increase output 50% in the summer and 20% in the winter, but this only increases the difference in output between the seasons. They are also expensive. The main reason against using them in Europe is the tremendous amount of diffuse light.

1. You can adjust your panels' position manually to get the best tilt angle for each season. Take your latitude and add 15° for the winter, and subtract 15° for the summer. At the spring and autumn equinoxes, the best angle is equal to your latitude.

2. If you leave your panel in a fixed position, you can decide to leave it at the best angle for the winter to help even out seasonal performance.

3. At the Equator, a panel can be placed horizontally for the most intense rays at noon. In Central Europe, when the sun is 30° above the horizon, however, this same position would mean a loss of about half of the sun's intensity (equivalent to 500 W/m²) compared to a tilt angle of 60°.

4. The sun is 70° above the horizon on June 21st in Belgium, but 20° in the dead of winter. (10° in Stockholm)

5. It is advisable to have at least a 15° tilt to avoid rain accumulating on your panels. A greater angle will help keep them free of snow.

6. Snow on the ground is a welcome sight in winter -it increases diffuse light considerably!

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