Well you didn’t really tell us much about your situation, so it’s hard to answer this. For example:
· Do you drive an EV?
· What kind of sunlight do you receive in your local winter or other overcast time?
· What does your energy usage profile? Are you a minimalist? Average consumer? Have every power hungry gadget out there?
· What latitude do you live in?
· What capacity solar system do you have?
Instead of creating a shopping list of solar panels and batteries, a more practical approach to answering your question would be to follow the following steps:
1. Start out with getting your solar system. The bigger the better.
2. Once this is installed (but you are still grid tied), you will start accumulating plenty of data to determine how much energy your system is providing and how much you are using.
3. You will also be able to see how much energy you are pulling from the grid that you will have to eventually store in batteries.
4. You should collect this data over your annual solar “low point” (probably your local winter) as this will determine the worst case scenario for solar collection.
5. With this data you should be able to target your energy use and find targets for optimizing consumption.
6. Once you have this data you should be able to determine your excess solar collection (that which you are not using—maybe you are feeding back to the grid for now). This is what you have available to charge your batteries with. You can also determine how much power you are drawing from the grid. This is what you will have to use from your batteries.
7. By integrating over time (looking at the area under the curve over time) you will be able to determine (a) how much energy you will be able to put into your batteries each day and (b) how much energy you will have to draw from your batteries.
8. Hopefully your energy USE is somewhat consistent, whereas your energy collection is probably variable due to weather conditions. You will have to look at running totals over several days or weeks to determine if you have an overall energy deficit (in which case you’ll need more panels) or surplus.
9. Either way, you’ll need to count up all the energy you would draw from your batteries (that you are currently drawing from the grid) over the “overcast” period to determine the size of the battery pack you will need. Just make sure you have sufficient generating capacity during the “sunny” times to replenish the pack.
If you want to stick steps 6–9, you can just start out with a given sized battery pack and see how it goes before disconnecting from the grid or getting rid of your backup generator. If you are still drawing from grid or your generator kicks on, your batteries are too small, so add more. If you cannot fully charge your batteries during periods of clear skies in your local winter (even if it takes several days to do so), you need more solar panels or you need to cut consumption.
If cost is an issue and you have time, there is no reason you couldn’t start with a very small system (both solar and batteries) and incrementally add capacity until you are able to be self-sufficient. But even once you find that you should scale up each system another 25% as a further safety margin.