You're making the same mistake again. You're equating complexity to impossibility/improbability. They are not causally related.

We know that brains work. You and I having are having this disconnected conversation using an incredibly deep stack of technological infrastructure, all created with human brains over decades and centuries. Brains are physical things, not metaphysical. The physics of the universe we live in allow matter to interact in particular ways that let brains exist.

The physics that lets brains exist is the same physics that describe relativity. We have 100+ years of thousands upon thousands of experiments and acquisition of data that backs up relativity. Its very unlikely to go anywhere.

I'll agree that the physical structure of an adult brain (not just human) is very complex. Its not mind boggling though. Much of the brain is just repeated neural structures. There are what, a few trillion connections? In 1950 that was a mind boggling huge amount of data. Now? That amount of data fits into a thumb drive with room to spare.

The tricky part up to now, and a couple years into the future, is building the right tools to pick it all apart. Its just like the solar panel problem. Low efficiencies, high cost. Same with Moore's Law and cpu's. But we have, if not the highly refined eventual versions, but the basic and functional tools to brute force through figuring out the its & bits of the brain. Actually, a lot of the work is already done. Neuro chemistry, effects of different neurotransmitters, effects of various drugs on the brain, FMRI, etc and etc.

Don't forget that Obama recently announced a brain initiative. Its the along the same line as the human genome project in the 1990's. Detractors said that it would take hundreds of years to finish with technology in the early 90's. Was done under budget and on time within 10 years. By 2020, just 7 short years away, everything computer-related is going to have doubled a little over 3 more times.

With all of this in place, the subsystems of the brain are complicated but not insurmountably. Even without initially having a sound mathematical description of how the brain works, we are/will have enough data to brute force a detailed simulation. If that's the route we have to go, then the mathematics will come later. Indeed, this is how much of the relationship between engineering and science/math has been for thousands of years. People were using arches in buildings long, long before understanding the math behind weight distribution.

In terms of energy, we can easily calculate how much energy it takes to simulate a brain. Let me put some numbers together. I was born 1/30/1980. I am 12,149 days old. Lets say that on average, it has taken 2200 calories a day for me to survive from birth to the current moment. Roughly, it has taken 26,727,800 calories for my body and brain to survive and prosper. To keep this simple, I won't even try to calculate the energy spent on everything else like clean water, electricity, transportation, entertainment, etc. In general terms, since I live on Earth with you and billions of others, its not an insurmountable amount of energy since we're all here. Plus, I'm a big guy so its safe to say it takes less calories to raise a human-class sentience to adulthood.

So, lets sum up your arguments and my counters:

1) Uploading (understanding) a brain is too complex:
-> There's already a large understanding of the biochemistry and mathematics behind brain function. Its not a mystical black box. Given current and in-development tools, combined with massive data storage and analysis systems, picking apart all the bits of the brain will be done in a few years.

2) Too much energy:
-> We're already well on the way to reverse engineering the brain. The energy required to finish the task is marginal. To simulate a brain, we already grow billions of real brains for less calories than it takes for a fat guy in San Francisco to write everything you've been reading. Convert those thermal calories to heat in the world's most efficient sterling engine, and that's one thing you can use to power your simulated brain. I dare say that it will cost less power to run a sentient AI than it does to support my love of bacon.

3) We'll find a way around relativity before understanding the brain:
-> Brains exist. So does relativity. The physics of the universe support reverse engineering brains. They don't experimentally support breaking relativity at the moment. However, I too am hopeful that some loophole or something is discovered that lets relativity be less of a barrier than it appears. However, given practical real-world data, that isn't likely any time soon.

4) Physics is difficult to simulate:
-> I didn't hit on this point explicitly above, but yes and no. Yes in that creating a simulation of universe from particles on up is daunting. Even with today's and near-future doubling growth, doing massive particle simulations will be very hard. No, in that you don't have to simulate every atom in a brain to understand how it works. You create mathematical models detailing how the tiny little structural bits of the brain work (neurotransmitters for example) and perform calculations based at that. Still a large computational problem, but one that is already with our grasp as of this minute and only easier to do going into the future. So basically, you don't actually have to simulate physics. You just have to simulate the mathematical interactions of the subsystems that make up the brain to get comparable results.

5) Germans
-> That's the great thing about solar power. Its everywhere. During the day in most parts of the world, even when its overcast, you still get enough sunlight hitting the ground to provide lots and lots of power. Sure, you'll get more in the desert on the equator, but that's the maximum and not minimum useful amount. People that make the statement you did have the argument backwards. You have to ask, "What is the minimal amount of solar energy we can collect to be useful and economical?"

Man, this took a lot longer to write than I thought it would.