import re
text="Energy (kWh/m²)"
print(re.sub(r'([²³¹⁰ⁱ⁴⁵⁶⁷⁸⁹⁺⁻⁼⁽⁾ⁿ])|\W', lambda x: '' if x.group(1) else '_', text))
print(re.sub(r'[\W²³¹⁰ⁱ⁴⁵⁶⁷⁸⁹⁺⁻⁼⁽⁾ⁿ]', '_', text))