Eli5: Call company that installs solar panels. Give them a bunch of money (thousands to tens of thousands depending). Wait 20 years to get that money back on the lower energy bill. Replace the whole system because it is obsolete. Rince repeat.

For real totally disconnecting from the power grid is a bad idea. That means you need a lot more equipment and battery storage. This increases the investment significantly, without much upside. It also prevents you from selling the power you generate but don't need back to the power company (but depending on where you live this might not be a thing due to overproduction).

Also depending on you latitude and local climate it may be nearly impossible to go fully off grid without a huge system. Where I live we have about 6 weeks of very little to no sun (low sun combined with a lot of clouds and snow). That means all the power you need during that time needs to be collected previously and stored. This during a time it's cold af so the power usage is high (using heat pumps for warming the house, which is very efficient). This means a lot of batteries and a lot of solar panels, just to get through these 6 weeks. It could easily triple the costs or more, even if you have the room for it to begin with.

I would analyse the power usage and see where you can save money on. 300 per month seems very high. Where I live energy is much more expensive than in the US and my bill is closer to 100 per month.

Just call a company, have some panels installed for say 2500-5000 bucks depending on how much room you have on the roof and if you need upgrades to your power system. This will save you at least 50 per month on the bill. But be aware the ROI will be on the order of 10-15 years at least and more if you are unlucky. Saving energy is free and means money in your pocket right away.