PV Gap

Sarah Said:

photovoltaic/ solar cell help?

We Answered:

The first link doesn't work, but that's not necessary.

Timing motors are pretty rugged. The 3.9V shouldn't hurt it. In addition, the motor will run a very-low percentage of the time, and probably not under full mechanical load, so overheating should not be a problem.

The alternative panel is a possibility, but you might need more than one. Its maximum power output is 3.9V at 64mA at one standard sun. However, you typically won't achieve the full output as useable energy for the following reasons:
1. Most of the time, there will be less than one standard sun of illumination. Energy output is directly proportional to the amount of sunlight falling on the cell. At solar noon on a cloudless summer day at moderate lattitudes, sunlight can exceed one standard sun but less than 1.5x as I recall. When the sun is lower in the sky, less light gets through the atmosphere.
2. You may have power losses in circuit components, especially if the power passes through a transistor or diode. Those devices will dissipate some of the energy.

If your load is 100mA, then you will need at least two of those panels, if not more.

Alternatively, you can use the panel to charge a battery during sunlight hours. The battery can accumulate the energy, then provide large current for short periods to the motor.

Hope that helps. Give it a try. Add more PV cells if needed.

Reginald Said:

How do i use the average solar radiaton into a nominal photovoltaic cell.?

We Answered:

I think that should be 4.9KWh/m^2.d. i.e. KWh not KW. This means that the energy from the sun is 4.9KWh per square meter per day, with the day meaning one day of a yearly average. The power from the sun available to a solar panel is more like 1000W/m^2.

If your nominal solar panel is rated at 50W it means it produces 50W if connected to an ideal load, with "standard sun" of 1000W/m^2. The figure is at 25C, but the panel will heat up to around 60C, reducing the output. The ideal situation is easy to calculate...

To determine the energy produced per day or per year:
4.9KWh/m^2 x .050KW = 0.245KWh (or 245Wh) per day. Multiply by 365 days for a year.

As the power from the sun available for a solar panel is nominally 1000W/m^2, the figure above also means there is the equivalent of 4.9 hours of "standard sun" per day. The regional figure corrects for latitude, day/night period, summer/winter period, sun's angle to a properly oriented panel, and to some extent the cloud, rain, dust etc. These are all taken as the average for a day over a year.

The figure above is for an ideal situation, where the panel converts the sun's energy and that is used by an ideal load connected to the panel.. What is not allowed for are losses due to dust and leaves on the panel, variations in individual panels, aging, panel temperature, wiring losses, battery charging and non-ideal matching of the load to the panel. Note that a panel produces nothing if no load is connected. Also the efficiency of a battery means about 40% of the energy to charge the battery is lost. Using a battery system with a proper power matching (MPPT) controller, probably about half the energy available from the panel is lost.

Connecting to a grid (inverter but no battery), probably something like 10% of the energy from the panel is lost, but this figure is difficult to determine properly when feeding into the grid.

Claire Said:

Why does heat negatively affect a photovoltaic cell's efficiency in solar panels?

We Answered:

What makes photovoltaic cells produce electricity is light (especially in the ultra violet spectrum), not heat.
Where you use heat are so-called solar water heaters, where water is actually pumped through (black) panels and thus heats up by the absorption of the sunlight's energy by the metal panels.
Most electronic components work less efficient in higher temperatures than lower ones. Something to do with electrical resistance increasing with heat. Super-computers are cooled with some liquid gas, in order to avoid loss of processing speed.

Jeremy Said:

Is a photovoltaic cell (Solar Cell) active or passive any why? (please give a source)?

We Answered:

An active voltage source is any device or system that produces an electromotive force between its terminals OR derives a secondary voltage from a primary source of the electromotive force.

ACTIVE : Active voltage sources provide the electromotive force directly.
PASSIVE: Passive voltage sources provide the electromotive force by acting as switches.

There is no requirement that the active voltage source have no external energy input itself.

e.g., generators driven by wind, water, motors, transformers etc. are all classed as active voltage source, as are automobile batteries, etc.

Photovoltaic cells fall within the above definition.

Passive voltage sources, e.g. wall switches, transistor switches, etc, which do not transform the primary energy in any way but simply allow it to pass, or block it.

I don't know if there is a clear definition of this on-line.

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