Older desktop parts can have a somewhat hefty idle power draw. According to this old review of the i7-2600k, the system idles at 74w, which at $0.12 per KWh, would cost you roughly $77 per year. Though you might want to confirm that with a Kill-a-watt meter if you can (libraries sometimes lend them out).

If that is accurate, you could potentially replace your i7-2600 with a used Dell Wyse 5070 thin client from ebay for about $40 (in the US), and that idles at 5w, which would only cost you $5 a year at the same rate, meaning it would pay for itself in a few months and safe energy (and emissions) at the same time.

Older thin clients and laptops tend to have much better idle power draws compared to desktops. For other people reading this, if you’re using a desktop for a low-power use case, it’s probably worth finding out what it’s idle power consumption is and doing the calculation, and determine if it would be worth replacing it with a more efficient used thin-client.