ROI
Return On Investment (ROI) is the typical approach to justify the spending to acquire asset.
For the sample solar renewable energy illustrated, this is simple:
One-off cost like equipment purchase & installation
Recurring cost like maintenance, insurance, administrative (if trading to grid is involved)
In a 5 or 10 years total cost model, how much energy charges could be saved, or how much revenue is generated if energy is sold back to the grid vs how much expense to paid.
However, there are risks that might affect the net gain:
Sufficiency of sun light intensity
Weather condition at the location
Physical security of equipment against theft or sabotage
In cyber protection technology, stake holders normally expect cyber-security is the baseline and integrated with the asset. Adding extra cost won't be seen as ROI. A slightly adjusted model is to calculate the avoidance cost of a single cyber-security incident vs investment. Therefore, the justification is to be:
If we invest $X, then we could avoid spending...