You can model this as (cost per kWh of cheapest alternative) / (cost of rentable per kWh) = marginal oversupply you want. So, if hypothetically Solar was 2c/kWh and peaking natural gas was 6c/kWh then you would want to add more solar until 3kWh of new Solar only offset 1kWh of natural gas with the other 2kWh being wasted.
Which does not mean 2/3 of total solar energy would be wasted. Further, storage and energy markets also complicate things. However, it does illustrate why you want an over supply of the cheapest option even if not all of it gets used.
Though when selecting individual locations for wind, different locations favor different time of the day. And of course solar output varies significantly east/west and based on local weather conditions. That all gets modeled ahead of time and in practice get reflected in market rates.
Even then, I do really expect a category of "peak demanders" to appear soon (storage is one kind, but there are other things one can do with intermittent almost free electricity). That will help increasing the spare capacity.
I suspect an outgrowth of oversupply is storage will ramp up based on consistent access to very cheap rates. It makes a huge difference if you’re paying 0.4c/kWh or 4c/kWh to charge, especially when storage is significantly less than 100% efficient.
That said, consistent very low prices will likely result in someone using most of that power for something even if the power plant operators aren’t making money during that period.
I don’t think any of these solutions are viable to prove we can be reliant on renewables, and this one especially would not resonate with a populace.
Just at a consumer level, think of everything you use power for on a daily basis. It’s a cornerstone of modern life, and you can’t expect society to backtrack.
Before I left the UK, the flat I lived in had two electricity rates, with the night rate being significantly cheaper then the day rate [0]. This meant the water heater and the (electric) storage heaters [1] were powered at night, when schools and offices used no power.
[0] I’m not certain, but I think it was: https://en.m.wikipedia.org/wiki/Economy_7
Also, storage heaters are a real pain to deal with. They're inefficient and not very controllable in terms of the amount of heat they produce.
Not so; when the problem is bad weather rather than the diurnal cycle, even weather forecasting gives more forewarning than emergency stop buttons in power stations, and (given the geographical distribution) the change itself is smoother. On the scale of a continental grid, do you even need to care about anything besides diurnal storage/demand-shifting (as preferred) and seasonal issues?
The result for individuals: many people just subscribe to a flat rate from the electricity companies to avoid the uncertainty and pay the same predictable price each month (but of course, this predictable price comes at a significant markup with respect to the "free market" price). The rest of us go with the fluctuating price but just don't bother, because we are not going to spend substantial amount of time every day looking at how the prices evolve to decide when we turn stuff on or off. So we just read the bill every two months, not even making an effort to understand it, grumble a bit and go on with our lives. I suppose there may be some people who actually try to optimize, but I don't know any - from what I know, people short on income tend to go with the flat rate because they can't afford the uncertainty.
I don't know how it works in industrial applications. I do know that some industries (e.g. steel) complain about the fluctuating prices because they operate 24/7, and basically they reaction is that if the government doesn't subsidize their electricity bill, they'll just close and go to some other country. So my guess is it's not really working either.
In fact, practically the only facilities being built for the last decade have been wind and solar and in massive quantities. If you look in the generation queues of the various RTO/ISOs (organizations that manage which units run and at what level for large parts of the grid) the only thing expected to be built is even more wind and solar along with storage. Multiple GW of wind capacity is being added each year, so it isn't slowing.
Why is this happening? It's complicated, but it's basically economics at this point.
What problems do we face? Well, sometimes wind and solar aren't available. You can solve this in three ways. The first is to have thermal generation respond when the wind/solar dips. This can be tricky as thermal generators (outside of natural gas) weren't designed to move that fast. They were designed to run near max for most of their life. Natural gas peakers are more effective here. Another option is storage, which can hold you over until you get more wind/solar again. However, we would need a massive amount of storage built for this to be effective. A third option would be to increase demand response at the industrial and customer level. Meaning, power isn't generally expected to be 100% available in that scenario. If there isn't enough generation capacity, those that aren't willing to pay the high prices are shut off (or something along those lines). That is generally how supply/demand is supposed to work anyway, but practically speaking, the demand doesn't participate today. In actuality, I expect a combination of all of that to become common place and it is what the Federal Energy Regulatory Commission has been pushing for.