I was wondering: how costly is crypto mining for me?

I let an easy-to-use mining application run on my desktop computer (RTX 3080 GPU) for 24 hours.
After 24 hours, the miner reported that I had mined 0,00000365 BTC, and that this would earn me €0,39. The electrical power consumption of my desktop computer for that period was 13,024 kWh.

How much does 13 kWh cost me? Here in Belgium, we pay a lot of taxes on our utility bill. So just multiplying 13 kWh with the cost for 1 kWh would not produce realistic costs.
What I did instead: I took my utility bill of December 2024, with all the taxes, and created a spreadsheet that re-calculates all of the costs and taxes. That gives me a spreadsheet were I can simulate changes to my bill and see what the final result is. And with that spreadsheet, I increased my electrical power consumption for December 2024 with 13,024 kWh. That gave me an extra cost of €3,91.

Spending €3,91 to earn €0,39 is not viable at all.

But what if I would run the miner only when my solar panels produce enough power? That’s free electricity, right?

Yes, but … my electricity supplier also pays me money for the solar power I produce and don’t consume (e.g., inject).
Injecting 13,024 kWh would earn me €0,86. So that’s at least double the amount that mining would earn me.

Conclusion: as long as electricity tariffs don’t change significantly, mining is not financially viable for me. One would be better of buying BTC with the small payouts for injected power.