Does the hourly schedule variate day by day or can it be predicted?
If you can predict when and how much power you will need to produce then it can be ramped up slowly, I assume.
There are electrical dispatchers who are monitoring grid supply 24/7 and instruct plants on how much they are responsible for generating on a minute-by-minute basis.
Storage batteries, pumped storage, and CAES are examples of this, though simple raw thermal banking (hot water heating, typically) is an excellent way to suck up excess Joules or GWh.
1 GWh is roughly the energy required to heat a pool of water 1 hectare * 1 m by 86 degrees Celsius. This scales to multiple GWh by increasing area, depth, or both. Conversion to steam is also possible, though that requires more engineering (pressure is A Thing). Substrates such as molten salt have a lower heat capacity per unit mass, but can be heated to far greater temperatures.
Storage at the scale of entire US generating capacity for multiple weeks using molten salt thermal storage, even accounting for Carnot cycle efficiency losses (about 20-50% depending on specifics, 30% is a good ballpark) is actually a tractable-scale concept. Existing petroleum storage facilities are roughly comperable in size, though molten salt would require somewhat more robust facilities and insulation.
Whilst it doesn't have the net efficiencies of pumped hydro (exceeding 90% round-trip storage efficiency), pumped hydro lacks sufficient developable sites, and has significant environmental impacts.
You couldn't be more Dam wrong.
Mind, where it does work, it's phenomenally effective, efficient, and responsive.
There are a few sites at which seawater-based systems might be possible, in which the ocean forms the "lower reservoir". These are dependent on suitable terrain. Matching terrain to consumption patterns is difficult: the Netherlands and much of Britain are sorely lacking. Some of the best potential sites are along the Balkan coast in Serbia and Croatia. Chile's Atacama Desert, along the Pacific coastline, is nearly ideal geographically, but is far from most use (North America, Europe, Asia). Portions of the US West Coast might be suitable, though would all but certainly face major political resistance for environmental impacts.
And: working with seawater is complex from an engineering standpoint: it's corrosive and sea life has a pronounced tendency to foul large-scale water-handling systems, though this may be tractable. There've been several pilot projects, though those have since been decomissioned, excepting Rance in France, designed as a tidal power plant, though capable of working as a pumped-hydro facility.
Terrible energy density, massive land use.
To store the energy contained in 1 gallon of gasoline requires over 55,000 gallons to be pumped up 726 feet (CCST 2012). [1]
Itaipu Dam has 14,000 MW installed power, 1,350 square kilometres (520 sq mi) were flooded. [2]
[1] http://energyskeptic.com/2015/hydropower-has-a-very-low-ener...
How many sites do we need? Why would the Netherlands need pumped hydro, isn't the European grid interconnected?
See my comment below.
https://www.energy.gov/sites/prod/files/2018/04/f51/Hydropow...
The events you may have noted in news of "negative energy prices" are often failures of prediction -- unexpectedly high availability (more sun or wind), and unexpectedly low demand. Though "pay to take my power" sounds good, it's actually a sign of mismanaged resources.
There are occasional incidental factors -- sudden demand, or more often, equipment or transmission failures which require bringing additional capacity online, or shedding load to prevent under-voltage (and hence: over-amperage), or underfrequency. Grid power frequency is generally 60Hz in the US, 50Hz in the UK, and just for grins, both in Japan, on separate and noninterdependent grids, which made generation capacity loss following the Tohoku earthquake/tsunami and Fukushima incident all the more critical. Loss of synchronisation or deviation by more than a very small fraction from the nominal frequency is considered a Very Bad Thing. Viz the recent UK blackouts.
You can read more about it at http://nordicbalancingmodel.net.
