Why don't people just buy solar panels from any of the multiple suppliers out there?
Isn't competition a great way to drive innovation and pricing improvements?
Why does it beget questions about storage of energy? Are people planning to buy much bigger solar systems than they actually need so they can then buy a 6.5k or 13k battery system to store the energy?
(if a 2 bedroom house requires a 6.5k system for just the refrigerator and lights for a day, how many batteries do you need if you have 2 electric cars, and run the rest of your house, like the tv? Oh, and how many solar panels do you need to get that much incremental power into the batteries?)
They do. Many Tesla owners already have solar on their homes, acquired from SCTY or another source. Either way, if it is a logical place for Tesla's customers to go as a next step, then it follows for it to be a logical place for Tesla to go as a next step. If my customers all want the same ancillary product once they've bought my flagship product, why should I let them buy it from someone else when I could instead become a one-stop shop?
It begets questions of storage for obvious reasons. As someone who said you own solar panels, I'm flabbergasted that you can ask such ridiculous questions. Do your solar panels produce electricity for you at night? How do you continue to run your electrical gizmos at night when they don't? How do you pay for that electricity you use at night? I assume you're on one of any number of net metering schemes where you pay for the excess you do not produce, or the power company pays you if you're a net producer. Either way, such schemes treat the grid as though it is an unlimited capacity battery. This is not true, and completely not the case.
When power is generated and put onto the grid, the generating station runs at some nameplate capacity, lets say 100MW. If the load on the grid is exactly 100MW, then everything is fine.
If the load placed on the grid by the end users totals 80MW, then you have 20MW of excess that has to be bled off. It doesn't magically stay there for later (unless you have utility-scale storage in the system a la PowerPack), and if you don't bleed it off (usually with big resistors to ground converting it to heat) then it will damage equipment.
If the load on the grid by the end users is 120MW, then you have an overload condition, which will lead to brownouts where all customers don't get enough juice (and voltage sags) or (more likely, as that condition is dangerous to end users and their equipment, so power companies don't allow it) rolling blackouts, where the extra 20MW of users get cut off and get no power.
This is a simple example - the real grid has many generating stations (and solar is adding many more) and many users, and the numbers are bigger, but the principle is the same. The real grid has baseload plants, and peaker plants. Baseload plants are like the 100MW plant in the above example, they are slow to start up and run optimally at one speed, generating a constant amount of power. Nuclear plants are a great example. The CANDU6 reactors at the Pickering generating station near me are rated at 660MW each. When they're running, that's what they run at, and there isn't a way to make them only generate 330MW if that's what you need. Since these plants can't respond to changes in demand for power quickly, the grid also has peaker plants. Peaker plants are smaller, more agile plants that can react to changes in the total grid load quickly, but at the cost of poor efficiency and greater cost.
The load placed on the grid by users varies throughout the day and with the seasons. In the summer, in hot climates, solar power is a pretty decent match - Solar makes the most power at high noon, right when everyone is maxing out their air conditioners. In cold climates in the winter, not so much - solar still makes the most power at high noon, but the highest demand is in the morning and evening when users need their lights on because its dark outside, and they're heating the building (some of them with electricity). The power companies around the world are increasingly trying to change their customers habits with time-of-use billing. I pay more for electricity I use during peak times, and so maybe I choose to not do my laundry until off-peak times. If you want to use solar power as your primary generation source (and I believe we will ultimately get there someday in the not-too-distant future) then you need some way to store the power you generate for use during the time that you can't generate. This is also true for wind and other renewable energy sources. They don't align with the load pattern, and so you need some way to shift the load in time - storage.
Eventually, the power company is going to stop allowing you to treat the grid like its a big battery, because it isn't, and solar will eventually reach a point where if they continued allowing everyone to do that, they'd be buying electricity from you just to burn it up in those resistors I talked about above.