Needing helping very confused with energy question.......thansk:)

[starbuckscoffee]

An environmental monitoring station is battery powered. Assume that one fresh LongLife 1.35 V cells stores 1.5 kJ of
useable electrical energy before its output drops below an acceptable value. Two such cells are connected in series to
provide 2.7 volt. The monitoring station requires a current of 12 mA

(a) How many seconds will the batteries last, assuming no internal resistance?
To enable the station to run without maintenance, a solar electric panel is installed. Data provided for the solar panel
installation in that particular location indicates:
- 7 % of the sun’s energy reaching the panel is converted to electricity
- in this location the mean solar energy per day onto 1 square meter (allowing for the season and typical
weather patterns) is 12 MJ.

(b) What total electrical energy is produced per day if the solar panel has effective photovoltaic area of 0.20 m x
0.25 m?
Note: efficiency = energy output / (total energy used)

[appianway]

Woah, this is old... but here's how you do them.

a) P(energy per second) = VI. V = 2.7, I = 0.012.

If you divide 3000 (the total energy that the two cells store) by the power, you'll get the number of seconds.

b) The area is 0.2*0.25, which is 0.05 m^2 (I think). The total energy landing on this is hence 12MJ * 0.05. However, only 7% of this is converted to electrical energy. Therefore, the energy per day = (12MJ * 0.05)*0.07