Hi new with questions

[Tominrm]

Another new member posting first question.

Hello, I just signed up because I was looking for an answer to my question.
I am trying to help a friend who lives in a island in Greece. I am new to solar electricity, but my background includes electrical systems.
My friend is building a small off-grid solar system that is sufficient to run a small refrigerator, two or three lights and a computer. He has a diesel generator to use when he runs his washing machine.
Obviously cost is the most important factor.

The first question : if the installed solar panels is not sufficient due to demand is greater than expected, is it possible to use the diesel generator to charge the battery a few minutes/hours a day until more panels are added? If so, is there anything bad about using the generator other than the cost of fuel and inconvenience?

If the refrigerator is rated 750 watts(not sure yet, but was told that it is a small with a freezer compartment. No ice maker. I would expect a smaller one compared to most American household. 2-3 fluorescent lights and a computer, how many solar panels would be needed?

In that design, what kind (and rating) of battery would you recommend?

Who makes decent inverter ?

[jony101]

it is best to rely on voltage as an indicator of your battery condition. For 24 volt system 25.46 volts equals 100 percent charge and 24.20 equals 50 percent charge (dont go below 50 percent and your battery will last longer). When you get to 50 percent you need to turn on the generator.
I have a 12 volt system and rely on my LED meter to know when i'm getting too low, it works great for me. Worst case you can just use a multimeter to see what your battery voltage.

The other thing mentioned about your controller, which is pwm is that it is not giving you the most amps that your panels can deliver. That why someday you might want to upgrade to mppt controller. With pwm and your large number of panels you are losing alot of useful amperage. That is the weak area of your system.

actual results that I got using 2 different controllers on my 240 watt solar panel with
pwm controller I get 7 amps of charging power
mppt controller I get 12 amps of charging power

with the limited sun available every day (especially in winter) , you want to charge your batteries quickly, more amps means faster charging especially for your large battery pack.