Naked Science Forum

Non Life Sciences => Technology => Topic started by: Donnah on 13/11/2010 15:02:34

Title: How do solar panels work?
Post by: Donnah on 13/11/2010 15:02:34

Solar panels convert light (but not heat?) into DC electricity and an inverter converts it to AC.  Does the battery pack store it as DC or AC, and how do ohms, amps and watts fit into the picture?  I don't even understand ohms, amps and watts.  Are they considered attributes of electrical current?

Please make explanation simple, since I am a simpleton when it comes to electricity.

Title: How do solar panels work?
Post by: Geezer on 13/11/2010 19:24:43

The water pipe analogy is one way to understand the flow of electricity.

Water pressure is analogous to voltage.
Water flow rate is analogous to electric current.
Restriction to flow (caused by a narrow pipe) is analogous to resistance.

Electric current is the measure of the number of electrons that are flowing in a circuit. In a photocell, when high energy photons encounter the cell, the action releases electrons in the material and allows them to flow through a circuit, so an electric current is produced. The more electrons, the greater the current. A voltage is also produced, so there is also an electric "pressure" (similar to a battery).

Heat from the Sun also arrives on Earth in the form of photons, but, because they are at lower frequencies, they have insufficient energy to trigger the photoelectric effect.

Title: How do solar panels work?
Post by: SteveFish on 13/11/2010 20:46:22

A minor correction. The largest percentage of heat from the sun is in the form of visible light. When visible light is absorbed by the earth (not reflected) it heats the earth. The atmospheric greenhouse effect works because greenhouse gasses are transparent to incoming visible light, but the heat it creates is re-radiated as outgoing infra red radiation that is absorbed by greenhouse gasses.

Title: How do solar panels work?
Post by: Geezer on 13/11/2010 21:18:38

Quote from: SteveFish on 13/11/2010 20:46:22

A minor correction. The largest percentage of heat from the sun is in the form of visible light. When visible light is absorbed by the earth (not reflected) it heats the earth. The atmospheric greenhouse effect works because greenhouse gasses are transparent to incoming visible light, but the heat it creates is re-radiated as outgoing infra red radiation that is absorbed by greenhouse gasses.

True, that does heat the atmosphere, but there is still a very substantial amount of direct infrared heat energy received from the Sun.

Title: How do solar panels work?
Post by: Donnah on 13/11/2010 23:58:00

Here's what I've summarized so far:

ohm = resistance
amp = level of electric charge (electrons passing a given point/second) or speed
watt = rate of energy conversion
volt = force/power (the level of  force/power the conductor is at when it takes 1 amp to create 1 watt) 

Photons (light particles) from the sun hit a solar panel and interact with silicon to create electrical current. That current level may vary, depending on the number of electrons released by the interaction (would this be measured in watts?).  The speed at which the electrons travel along the wire to the battery is measured in amps (thus the expression "amped up").  Direct Current (DC) means the electron current is allowed to flow unimpeded.  The electrons are then stuffed into the battery until it reaches a voltage (power level/force) where the battery is considered full (of electrons).

Have I got that right?  [???]

Title: How do solar panels work?
Post by: Geezer on 17/11/2010 00:17:44

Quote from: Donnah on 13/11/2010 23:58:00

Here's what I've summarized so far:

ohm = resistance
amp = level of electric charge (electrons passing a given point/second) or speed
watt = rate of energy conversion
volt = force/power (the level of  force/power the conductor is at when it takes 1 amp to create 1 watt) 

Photons (light particles) from the sun hit a solar panel and interact with silicon to create electrical current. That current level may vary, depending on the number of electrons released by the interaction (would this be measured in watts?).  The speed at which the electrons travel along the wire to the battery is measured in amps (thus the expression "amped up").  Direct Current (DC) means the electron current is allowed to flow unimpeded.  The electrons are then stuffed into the battery until it reaches a voltage (power level/force) where the battery is considered full (of electrons).

Have I got that right?  [???]

A couple of details.

The speed at which electrons travel is a function of the nature of the conductor and it is independent of the current and voltage. The current (measured in Amperes/Amps) is a measure of the quantity of electrons flowing in the conductor. Electrons might flow in a conductor at around 1/3 the speed of light.

Think of volts as potential or "electric pressure" (not power). Voltage is the potential to cause electrons to flow (producing a current) in a conductor. The water analogy works here. If there is no pressure, water won't flow in a pipe.

Power (measured in Watts) is the product of voltage and current. So, if you have a resistor and there is a voltage of 10 volts across it and a current of 100 amps flowing through it, it dissipates 1000 Watts of power.

The photoelectric electron flow is a current flow, so it is measured in Amps. More photons means more electrons means more amps. The electrons are indeed stuffed into a battery where they produce a chemical reaction to store the energy.

Title: How do solar panels work?
Post by: Donnah on 17/11/2010 04:37:42

And the second summary says:

speed = how well the conductor conducts
   (What is the measure for speed?  Water is measured in GPM or PSI.)
ohm = resistance
volt = force/pressure
amp = density of electric current
   (quantity of electrons passing a given point/second (maybe 1/3 light speed))
watt = power (rate of energy conversion) (voltage (pressure) x amp (current) = watts (power))
 

Photons (light particles loaded with electrons) from the sun hit a solar panel and interact with silicon to create electrical current (amps).  Direct Current (DC) means the electron amp current is allowed to flow unimpeded.  The electrons are then stuffed into the battery until it reaches a voltage (pressure level) where the battery is considered full (of electrons).

Where does the voltage come from that pushes the amp current from the solar panel to the batteries?  Or does the current just flow into the battery ?

I sure appreciate your help.  This is actually starting to take shape in my mind.  [:0]

Title: How do solar panels work?
Post by: Geezer on 17/11/2010 05:07:40

Uh oh! The water analogy is no good when it comes to speed.

Speed is not related to how well a conductor conducts. For now, it's probably best to just assume that speed is a constant.

Title: How do solar panels work?
Post by: Donnah on 18/11/2010 02:25:11

So if I take out the part about speed is the rest correct?