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Note that stop and start operation (ramp-up and turndown) reduces efficiency per MW of power, increases maintenance, and shortens life of turbines, generators, bearings etc as metals expand and contract with the heat caused by operation. Manufacturers are improving this aspect where possible.

Single-cycle turbines are typically used for peaking generation and to compliment intermittent generation from renewables, skewing the overall efficiency and CO2 production attributed to renewables. "Efficiency of a turbine at part load can be substantially below the 30-40% efficiency at full-power," while continual stops and starts degrade a turbine more rapidly ... causing more non-recoverable losses and more maintenance to repair recoverable losses. Gas turbine failure modes .pdf     Read advancements in turbomachinery

Thermal efficiency is not same as total efficiency. "Total efficiency is defined as the sum of the net electricity generated divided by total fuel input to the system." Total efficiency is lower percent than thermal efficiency depending on factors such as degradation of equipment, temperature, humidity, type of fuel, start-and-stop losses, transformer losses, electricity used for cooling pumps and electromagnet etc..

Peak electric consumption (maximum usage on hottest day) in US in 2020 was about 800 GW per hour, and expected to increase with economic growth, government mandates for 'all-electric' homes and buildings, plus manufacturing goals for electric vehicles, higher global temperatures etc.

Using 2021 for example, the 1.6 GW energy capacity of electrochemical batteries in US would equal .2% of total power needed for 1 hour of 800 GW peak, or equal to .12 minutes of electric consumption before all battery capacity would be depleted. Calculation Afterwards, batteries would need to be re-charged before dispatching another 7.2 seconds out of a 24 hour day. If battery construction could be afforded and sustained 1000 fold, to 1600 GW, it would supply 120 minutes, or 2 hours of a peak day in the US. Usage of power is less than peak most days, but continually growing.

Wind, solar and hydroelectric rely on weather to produce electricity. Weather is unpredictable, making it a poor choice to meet reliability goals, if intent is to supply power to all users ... particularly since batteries cannot energize the grid nor meet current usage nor sustain growing demand.
Renewables are experiencing a building boom as costs, media promotion, investors seeking long-term pay-out and science push government and business toward the “sustainable development scenario” (SDS) outlined by IEA.
Forecasts show that challenges are present: Chart   Article   Read

Job losses from closing coal plants etc are offset by growing need for workers to upgrade and automate the grid, upgrade substations and distribution, with better energy forecasts, improved batteries, etc, plus build new transmission lines to keep up with building boom in solar and wind.
However, as demand increases, and the grid becomes more complex, and increasing amounts of intermittent renewables and DERs and microgrids come on-line, the challenge shifts to grid reliability ... specifically to maintain stable frequency and keep voltage "within ±10% of nominal at all points across the grid." Keep in mind the grid is cris-crossed over millions of square miles, with millions of poles and transformers and customers ... comprising a system that might not be fully mapped at the local distribution level in 2021. Read

If voltage drops below nominal, then your 115 volt refrigerator and 240 volt AC cannot run without damaging the motor.
Why? Two reasons. 1) Lower volts reduces the magnetic field needed to spin rotor. Motor slows down and overheats. 2) Volts and amps are inversely proportional. If volts drop, then loads will draw more amps to meet the amount of watts (power) shown on product label. Wires are rated by amperage, and are generally not oversized (larger wire carries more amperage but costs more).
Exceeding the amp rating means too many electrons are moving through the matrix (atomic structure) of the conductor (wire), causing more resistance from wire which causes heat which overheats design parameters of wires, motors etc... affecting substation relays that will trip off ... and can affect power plant generators that will automatically shut down to avoid damage.

-Power lines and towers are designed to withstand load factors such as heat, ice and high wind.

Suspension clamp U bolt type
Preformed armor grip suspension clamp

Note also that 3-phase, or the use of 3 wires per circuit, allows more amperage to flow along smaller wires vs single-phase that uses 2 wires instead of 3. This is the reason why 3-phase is more efficient for delivering power to end users and for running commercial motors etc than single-phase.
Resource: Difference 3-phase and single-phase

 The high cost of building and updating transmission lines might cause undersizing, or the use of less-than-best materials. For example using polymer insulators today that don't last as long as porcelain, but are lighter weight and cost less. Over time, as demand for power grows, an undersized or poorly-designed transmission system could lead to shortages, requiring local generation from solar panels, batteries etc (microgrids). The result would be a fragmented grid where some areas might not have power, or only receive power a few hours per day as experienced in some countries.
Resource: Cost comparison transmission construction

Let's suppose, if all homes in a neighborhood install solar panels. In Hawaii, it was determined that just 50% of homes feeding PV-generated power back to the grid on a good day posed problems that required updating distribution lines and substation transformers. If a neighborhood has underground distribution lines, then updating for rooftop solar would be more expensive than above-ground distribution. In any case, the cost of distribution improvements should be included when calculating the value of rooftop solar.

3-phase 7200 volt distribution lines arrive at building service

Fig-A is called 'concentric round' since each strand is identical, each is round, and cable is round. Diameter 0.795." or .455 square inches.
This wire was lying on the ground as part of the installation of new Distribution lines along the freeway.

Note: "each layer in a conductor is wound in the opposite direction"

''Air space between strands can be reduced by compacting the aluminum conductor into trapezoidal shape for a more compact wire size."
Wire in Fig-B was lying on the ground as part of the installation of new Subtransmission lines along a local highway.

Color difference added for clarity