For me, the objective of MCP is to obtain heating autonomy in winter, for example by storing 15 days of heating with a single day of sun in winter (20 to 50m² of solar thermal panels).
It can be done with paraffin or palm oil, and / or an equivalent whose phase change T ° turns around 35 ° C
Now the balance sheet alone is not necessarily profitable
question of choice, budget, comfort or voluntary approach.
just like when you replace your simple glazing, the financial profitability is around 30 to 40 years, while the gain in comfort is immediate.
Now, a 150m² house perfectly insulated and treated in double flow for example only needs less than 5kw of heating power at -7 ° C which can be supplied by a very small heat pump, see a thermodynamic DHW tank or a wood insert in addition to a reasonable surface area for solar hooders
So why seek autonomy, you say? well, for fun, or in case of a serious energy crisis why not
there are many who set up "blockhouses" in their basement
There, you know everything