What is the relationship between solar panel kWh and battery bank capacity?

[Datsolarboi]

For example: if I buy one server rack battery for my storage needs at 5kWh (24v/200AH eg) how to I size my solar panel array? Do I need 5kWh
of panels? Less? More?

I live in BC and here is a map of kWh/kW for the region. I live in a light orange/yellow portion of the map.

 

[upnorthandpersonal]

kWh is a unit of energy, while kW is a unit of power. A battery bank stores energy and is rated in kWh. A solar panel delivers power and is rated in kW. If you run a (hypothetical, and in ideal circumstances) 1000W (1kW) solar panel for one hour, you have generated 1kWh of energy.

So now you can start calculating how much energy you use, and how fast you need it replenished in your battery - and when during the year is your worst solar generation. Those factors will determine your battery size and solar panel needs.

 

[Datsolarboi]

kWh is a unit of energy, while kW is a unit of power. A battery bank stores energy and is rated in kWh. A solar panel delivers power and is rated in kW. If you run a (hypothetical, and in ideal circumstances) 1000W (1kW) solar panel for one hour, you have generated 1kWh of energy.

So now you can start calculating how much energy you use, and how fast you need it replenished in your battery - and when during the year is your worst solar generation. Those factors will determine your battery size and solar panel needs.

Okay so then in my worst month of December I would on average get 1.2kw per day from 1kw of solar panels. If I use 3kwh per day of battery than I should have at least 2.5kw of solar panels to replenish the battery. However if I have a day without sunlight, then my battery would be drained and not be able to replenish fully within the next day. How many days redundancy is the norm for solar set ups? If I use 3kWh per day should I have 2 extra days of power stored? Aka 9kWh and then have enough solar power to replenish them faster than they are being spent on the next sunny days (maybe 4.5kW of pv)?

Thanks for your answer!

 

[SamDeleted]

Okay so then in my worst month of December I would on average get 1.2kw per day from 1kw of solar panels. If I use 3kwh per day of battery than I should have at least 2.5kw of solar panels to replenish the battery. However if I have a day without sunlight, then my battery would be drained and not be able to replenish fully within the next day. How many days redundancy is the norm for solar set ups? If I use 3kWh per day should I have 2 extra days of power stored? Aka 9kWh and then have enough solar power to replenish them faster than they are being spent on the next sunny days (maybe 4.5kW of pv)?

Thanks for your answer!

Three days redundancy is as much as almost anyone goes for

 

[upnorthandpersonal]

How many days redundancy is the norm for solar set ups?

It completely depends. Most people off-grid have a generator to help them through winter.

 

[Mattb4]

A few things. Although a battery may be rated at a certain amp-hr or kWh you have to realize that in practice you will get less. Some of that is due to the chemistry of the battery and some is simply that there is always a degree of loss.

So if your needs are 3kWh per day you likely need a 4kWh LiFePO4 battery, a 6kWH lead acid battery.

There is also loss due to any transformation such as running an inverter to also account for. This is often called efficiency and idle power. That adds to your 3kWh daily needs. This can be quite high depending on equipment used.

On the PV side, panels are rated in watts. Often you will not ever reach the rated amount as peak but over the day in sunlight they will produce an average amount of watt-hours based on amount of sunlight they receive. Say in Winter at your location it is only 1.2 hours. You would multiply your panels rated watts by the 1.2 hours to get the watt-hours that could be used to power loads (like charge the battery).

Your batteries have requirements for acceptable and max charge amperage. These need to be kept in mind when deciding how much solar you go for.