# B Power question

1. Dec 26, 2016

### brycenrg

So im trying to figure out how much Wh I would have with these solar cells I have. Each solar cell is rated to have 2.8w. Does this mean if I have 40 of them I would have 112 wh? I am going to be putting the solar cells in series. Does this affect the power? I know adding in series is good because it boost your voltage but.. im not sure if that affects your power. If it does then, How do i figure out what my power would be?

2. Dec 26, 2016

### BvU

Power is energy/time. Here it can be simply added up. So with 40 x 2.8 W you have 112 W, not 112 wh .
112 W is 112 Wh per hour. Wh is a practical unit for energy. 1 Wh = 3600 Joule.

Power is simply Voltage x Current. Placing the 40 cells in series you get 40 times the voltage from one cell at the same current.
Placing them parallel you get 40 times the current of one cell at the voltage of one cell for the whole lot.
Product Voltage x Current is same in both cases.

3. Dec 26, 2016

### brycenrg

Thank you, isn't W and Wh the same thing but just Watt over that hour which gives it practical application? Ok so putting them in series or parallel doesn't effect the power. Interesting. Now i'm wondering why people prefer to use series to obtain higher voltage.

4. Dec 26, 2016

### BvU

Are speed and distance the same thing to you ?
So am I. Any reference ?

5. Dec 26, 2016

### brycenrg

Whoops, i mean series. Yeah i'm wondering why its better to make a solar panel with high voltage than high current. People prefer to put in series to get the higher voltage out of the system. Maybe it depends on the item?

Oh sorry, so W = Joule/second , Wh = joule? makes sense now. Wh is total energy given out in one hour

6. Dec 26, 2016

### BvU

Yes. And therefore Ws = Joule, Wh = 3600 Joule
Transporting the energy goes at the cost of losses due to resistance. The higher the voltage and the lower the current, the better: the power dissipated in a resistor is I2 R so 10 A at 0.1 $\Omega$ is 10 W loss. With 10 V and 10 A that is 10 %. With 100 V and 1 A you lose only 0.1% of the same 100 W of generated power.

7. Dec 26, 2016

### Staff: Mentor

In addition to BvU's reply which mainly applies to distance transmission of AC power, even in small installations like solar power panels in a home, you minimize switching FET and diode losses when you have a higher working voltage. Solar panel systems need to convert the DC voltages from the panels to 12V or 120Vrms (or whatever AC Mains voltage your household is using), and the switching losses from the FETs or IGBTs and diodes become higher when the voltages are lower.

Last edited: Dec 29, 2016