04-02-2015, 08:13 PM

Solar panels are the key ingredient for an electric boat.

They are conceptually quite simple, but in fact getting the most out of them isn't so simple.

Let's review some real basics of electricity, volts, current, and watts.

Watts are a unit of power, defined by volts * current. All the voltage in the world does nothing without current flowing. Similar to horsepower = torque * rpm, if a motor isn't moving, all the torque in the world produces no power. Voltage is like a electron force, and current is movement of those electrons.

The higher the voltage, the easier current flows. The more current (amps) that flow, the more power you get.

So consider a 100 watt solar panel. It can output 12 volts at 8.33 amps (12 * 8.33 = 100),

or it could output 24 volts at 4.16 amps. They are equivalent in power.

Solar panels are made up of solar cells.

A typical solar cell is about 3 watts. It outputs less than a single volt, usually .5 volts, and thus for 3 watts,

it would output 6 amps of current. One half a volt is not much, even the lowest voltage microprocessors need about 1 volt to operate. So cells are connected in series to get higher voltage. So just like three 12v batteries can be connected in series to get a 36v battery, solar panels connect many .5 volt cells in series to get say 12v, which would be 24 cells in series. A typical 100 watt solar panel connects 36 cells in series to output 18 volts with 6 amps of current (18v * 6a = 108 watts).

Then things start to get more complicated. Because the cells are connected in series, the output current from one cell is flowing through the next cell in series, which adds its voltage to the flow. This is all good until one of the 36 cells can't produce the same amount of current as the other 35 cells. This will occur if one cell is not getting the same sunlight as the others. The current is now limited to only what this one cell can pass through. So a 100 watt solar panel would be reduced to a 33 watt solar panel if a single cell can't output its 3 watts, but can only output 1 watt. If it is completely shaded, and can output .1 watt, the entire panel is limited to 3.6 watts. But it gets even worse, because all the power from the other cells that isn't going anywhere is generating heat that can destroy the panel. So what to do?

They are conceptually quite simple, but in fact getting the most out of them isn't so simple.

Let's review some real basics of electricity, volts, current, and watts.

Watts are a unit of power, defined by volts * current. All the voltage in the world does nothing without current flowing. Similar to horsepower = torque * rpm, if a motor isn't moving, all the torque in the world produces no power. Voltage is like a electron force, and current is movement of those electrons.

The higher the voltage, the easier current flows. The more current (amps) that flow, the more power you get.

So consider a 100 watt solar panel. It can output 12 volts at 8.33 amps (12 * 8.33 = 100),

or it could output 24 volts at 4.16 amps. They are equivalent in power.

Solar panels are made up of solar cells.

A typical solar cell is about 3 watts. It outputs less than a single volt, usually .5 volts, and thus for 3 watts,

it would output 6 amps of current. One half a volt is not much, even the lowest voltage microprocessors need about 1 volt to operate. So cells are connected in series to get higher voltage. So just like three 12v batteries can be connected in series to get a 36v battery, solar panels connect many .5 volt cells in series to get say 12v, which would be 24 cells in series. A typical 100 watt solar panel connects 36 cells in series to output 18 volts with 6 amps of current (18v * 6a = 108 watts).

Then things start to get more complicated. Because the cells are connected in series, the output current from one cell is flowing through the next cell in series, which adds its voltage to the flow. This is all good until one of the 36 cells can't produce the same amount of current as the other 35 cells. This will occur if one cell is not getting the same sunlight as the others. The current is now limited to only what this one cell can pass through. So a 100 watt solar panel would be reduced to a 33 watt solar panel if a single cell can't output its 3 watts, but can only output 1 watt. If it is completely shaded, and can output .1 watt, the entire panel is limited to 3.6 watts. But it gets even worse, because all the power from the other cells that isn't going anywhere is generating heat that can destroy the panel. So what to do?