What's the hash power requirements to solo mine and win at least one block a day?
Two cases (with 10% luck, means mining requires to iterate 90% of unsuccessful hashes),
You can mine 1 block roughly every 10 mins, hence total blocks per day is 6 x 24 = 144
The current Hash Rate in the Network is about 70000 GH/sec (Source: Blockchain.info]1
If you have 100% of the Hash power, you will get all the blocks each day.
To get at least one block a day, you will need roughly 0.7% of the current total hash power (1/144), that is about 486 GH/sec of hash power.
To get at least one coin a day, you will need at least 19.44GH/sec of hash power ( 486 / 25 coins per block)
The hash power requirement will change as the network hash rate rises with more ASIC devices shipped.
The following is assuming the difficulty has balanced with the current network hash rate (right now, the difficulty is actually about 10% low, but it will adjust in about 3 days):
Network hash rate (current) = 61 Thash/s
Blocks per day = 24 * 6 = 144
Hash power required to solve 1 block per day = 61 Thash/s / 144 = 424 Ghash/s
To get a block on average every 30 minutes, you'd need control of one third of the network's hashpower, which (unless you purchase mining equipment already in use) would require 50% of the current hashpower, or 30.5 Thash/s.
To solve a block on average every 10 minutes is only possible if you control the entire network, which you can't do unless you stop everybody else from mining.
More info available here: Equation for mining profit
