What is the range of charging efficiency and discharging efficiency of solar cells and batteries?

What is the range of charging efficiency and discharging efficiency of solar cells and batteries?

Solar energy is not very clear. Let's talk about the constant current discharge of storage battery, which is 20 / 1 of the capacity of storage battery. The discharge time is 20h. For example, the discharge time of 60A / h storage battery is 20h. The voltage is 12.9v (when fully charged) and the discharge time is 11.82v. The electrolyte density is generally 1.12-1.30g/cm3

The photovoltaic panel on the surface of the car can convert 40% of the solar energy into electric energy, and the motor in the car can convert 90% of the solar energy into electric energy
If the resistance of the car is 500N, the position of the solar panel can be adjusted automatically, and the solar radiation direction is always vertical. It is known that the solar power per square meter is 1.25kw, and the total area of the solar panel is 8m ^ 2, Try to find: (1) how much solar energy is shining on the panel in 2 hours? (2) what is the mechanical power of the car? What is the maximum speed of the car when it is moving?

（1）E=1.25*8*2=20kwh=20*1000*3600=7.2*10^7J
（2）
Electric power: 1.25 * 8 * 40% = 4kw
Vehicle mechanical power: 4 * 90% = 3.6kw
Vehicle speed: according to P = FV
V = P / F = (3.6 * 1000) / 500 = 7.2m/s = 25.92km/h

Can the power of solar panel determine the number of cells on the panel?
For example, if a customer tells me that he needs a battery board of XXX watts, can I only determine the number of cells on each board based on this value? If not, what values can I determine the number of cells on each battery board? Please advise!

What you said is basically right
Dividing the module power XXX by the battery power XX is roughly equal to the number of cells
But in practical application, the voltage requirement should be considered, so the number of solar cell modules in series is relatively fixed: for example, 36 solar cell modules in series provide about 17.5V working voltage to charge 12V battery
Other common serial number, such as 54, 60, 72, 96

Know the voltage and power of electrical appliances, how to calculate the required capacity of the battery
The power of my electric appliance is 250 watts, the peak power is 2000 Watts, the current is 12 volts, and I need to work continuously for 8 hours. What capacity battery or battery should I equip this electric appliance with?
It's better to have a calculation process
Sorry, it should be 12 volts.
250 watts for 6 hours and 2000 Watts for 2 hours.
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Thank manegefen and zlj2154292 for their answers, but there can only be one answer.

The unit of a battery is ampere hour. For example, a 10 ampere hour battery discharges at the rate of 1 ampere. Theoretically, the battery can work for 10 hours. 250 watts divided by 12 volts equals 20.8 amperes. 20.8 amperes multiplied by 6 hours (you need to run for 6 hours) equals 125 ampere hour. You need 125 ampere hour battery