If solar panels can be turned off, why are utility companies having to sell excess power at a loss? Why can’t they tell the solar farms to reduce their output by the required amount?
It's worst actually, at least in France, if you inject to the grid you have to pay an "energy transport fee", even if you inject for free (only recently self-made systems are allowed to sell energy, before they can only donate or not inject at all) and the injected energy is now paid less than the cheapest price to the customers (6 cent/kWh for ground based p.v., 10 cent for on-roof p.v.). So well, we do not harm large utility business.
What harm on scale is the variable output especially from small p.v. utilities built out of incentives NOT personal power plants, the grid is sized with some large power plants serving a large set of customers, their absorption vary but if the grid is vast (and not too vast) enough variation tend to be slow on average, let's say 50MW PP experience 100-200kW demand variation in very short time. They can compensate easily keeping the grid frequency stable. With a significant amount of grid injecting p.v. variation might be MUCH bigger creating significant stability issues where injection goes up too quickly making the frequency skyrocketing and large PP can't decrease their output fast enough risking disconnection witch in turn might put large p.v. plants offline suddenly creating a cascading effect of large blackouts.
That's the real issue with grid-connected and tied renewables and another reason why we need to go toward self-consumption NOT injection.
As I understand it: because the incentives are wrong.
Owners of small scale solar panel installations are payed a fixed price per kWh in many EU countries, regardless of the market price. The taxpayers pick up the tab I guess.
In theory someone somewhere should be incentivised to spend money on building storage systems so that they then have to pay less money in the future in excess days.
Solar power does get curtailed pretty often, but there isn't one uniform solution to the problem, different utilities / markets / grids have chosen different solutions to this.
as far as I understand there's a market based solution. producers bid prices for time slots (consumers too, but that's less important from the perspective of a solar power plant) and if they win the contract is live, they need to input for that slot. if they miss (go over or under) they get paid less (and of course a penalty is possible too, theoretically it's the same)
this incentivizes better capacity and availability forecasting for solar installations, and preserves the usual dynamics of the open energy market.
..
the problem is with these super small ones, where initially states just let people connect it, because it's green, yey. (but now DSOs started to make connecting waay harder. and regulators are investigating, eg. in Spain. [0])
of course the non-residential installations already usually need aFRR capability. (eg. this is the case in Hungary.)
and there's already a market for "reserves" in the EU. (but the interconnection rate is below the target 15% as far as I know. but still, there are intra-state markets, etc.) and we can see that when solar is high the reserve prices are surging. [1]
What harm on scale is the variable output especially from small p.v. utilities built out of incentives NOT personal power plants, the grid is sized with some large power plants serving a large set of customers, their absorption vary but if the grid is vast (and not too vast) enough variation tend to be slow on average, let's say 50MW PP experience 100-200kW demand variation in very short time. They can compensate easily keeping the grid frequency stable. With a significant amount of grid injecting p.v. variation might be MUCH bigger creating significant stability issues where injection goes up too quickly making the frequency skyrocketing and large PP can't decrease their output fast enough risking disconnection witch in turn might put large p.v. plants offline suddenly creating a cascading effect of large blackouts.
That's the real issue with grid-connected and tied renewables and another reason why we need to go toward self-consumption NOT injection.