But in reality it probably doesn't matter, I doubt you can get a search warrant based on "they use a lot of power and have great internet connection"
While looking for that story, I came across a wiki article about a similar story in the US, although the police there used thermal imaging to identify the farm from outside the home. That was ruled that constitutes a search w/o a warrant in the US. https://en.wikipedia.org/wiki/Kyllo_v._United_States I would suspect observing suspiciously melted roof snow in the US wouldn't violate the law like using thermal imaging would.
I don't know German law, but I could see how that could get you a search warrant if Dutch and American law are any indication.
A lot, but probably less than you think. To provide one kilowatt of power continusly for 10 years you need about 23 million liters of diesel, which fits in a cube with 28 meter long walls.
A railway car of diesel can provide ~3W continously for 10 years. A tank the size of the Hindenburg could provide ~8kW for 10 years. The world's largest supertanker could carry enough diesel to provide ~22kW for 10 years.
https://www.bp.com/content/dam/bp-country/en_au/media/fuel-n...