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How cheap is coal? The API 2 benchmark for imports CIF Rotterdam specifies a calorific content of 6,000 kcal/kg, which works out to be almost exactly 7 MWh/tonne. Prices adjust mainly for calorific content, with minor adjustments for other parameters such as residual ash and sulphur that has to be scrubbed in the exhaust chimneys. Multiply by plant conversion efficiency to get MWhe/tonne: so an old plant like Ratcliffe on Soar with efficiency of about 33% has a fuel cost of $140x3/7 or $60/MWh produced, or £45/MWh. A modern HELE (high efficiency low emissions) plant approaches 50% efficiency operated as baseload at 2/3rds the fuel cost, or £30/MWh.
Capital cost for HELE plants is significant: this article quotes $3.6-4.5bn/GW, but for the UK let's assume £4bn/GW.
As our old cold fleet proves, plant life is over 50 years: RATS was commissioned in 1968. So we can use a capital charge rate of say 7% to cover depreciation and financing, or £280m p.a. Annual output depends on load factor. On a merit order basis such coal would rank behind cheap nuclear (but way below the current Hinkley Point CFD price of £130,79/MWh), so to keep the arithmetic simple, let's assume 80% load factor or output of 7TWh/a/GW. That adds £40/MWh to the cost.
At £70/MWh it is clearly much cheaper than offshore wind, and on a par with onshore wind and solar at the point of grid connection. However, using previous coal power station sites eliminates huge costs fore More Grid. The EGL4 2GW link has recently tendered £5bn in contracts for HVDC cables and converters, with more to spend on hooking it into the onshore grid. However, being based on use only from higher wind outputs in Scotland it will struggle to achieve good utilisation. It might not even manage a 7TWh/a throughput, which would only be highly intermittent anyway.
Saving the transmission cost more than pays for the HELE plant. Renewables can't compete.