In a Proof-of-Work blockchain, new blocks are created by mining, but in Peercoin’s Proof-of-Stake, new blocks are created by staking.
In a Proof-of-Work blockchain, the act of mining involves using computer processing power to solve blocks. The miner who solves the block first has the privilege of adding that block of transactions to the blockchain, earning them new coins as a reward for their service to the network.
Ultimately, miners are responsible for validating and processing transactions on a blockchain network, and electricity is the scarce resource they use to do this work.
Naturally, miners will attempt to solve and produce blocks faster than their competitors in an effort to earn more rewards for themselves. Becoming faster than the competition requires more processing power, which inevitably requires more electricity to be burned, an incredibly wasteful process.
This process works to secure a blockchain, however it ends up centralizing power over the network with pool operators, as most miners will lend their hash power to a few large mining pools in an effort to continue earning rewards.
Economies of scale also play a factor in centralizing Proof-of-Work blockchains, with miners who manage to grow so large that they are able to get better deals on hardware and negotiate better energy prices. They will always outcompete the small home users and drive them out of profitability.
In Peercoin’s Proof-of-Stake system, the scarce resource used to secure the blockchain is not electricity, but time. Basically, the older your coins are, the more time they’ve accumulated sitting in your wallet. Coins with a higher time accumulation have more power to participate in producing blocks and securing the network.
Let’s say you own 100 peercoins, and you want to start minting new blocks. After sitting in your wallet for 30 days, you will have accumulated 3000 “coin days”, because each of those 100 coins is 30 days old. These coin days are the actual minting power of your coins. You can think of your coin days as being similar to your hash rate from traditional mining. Accumulating more coin days means you’re more likely to produce a new block on the chain.
There are a number of rules in place to make this a fair system. 30 days is the minimum time you need to hold your peercoins in your wallet before they can become eligible to start minting. If you transact with your coins, that timer will reset.
Every time you produce a block, you will earn new peercoins as a reward (about 3-5% annually) and the age of the participating coins will reset to zero. After 90 days, peercoins will hit their maximum minting power. These time limits are all security features designed to decentralize minting power and keep the process fair.
Using time as an integral part of Peercoin's security means that blockchain security becomes inexpensive. It no longer becomes necessary to consume some scarce resource (like burning electricity), which could be used in a more beneficial way.
Why waste electricity at all when a green alternative exists that can perform the same function? Time is also a scarce resource. It is limited. You can't create more of it, and you can't manipulate it, or speed it up to benefit yourself. All you can do is wait, and waiting doesn’t cost anything except your patience.
The main costs for staking in Peercoin are an investment in the coins and time necessary to participate in the staking process. As a result, Peercoin staking is energy efficient, sustainable, and can even be done on low powered devices like the Raspberry Pi.
Peercoin has proven over the past decade of continuous operation that the energy wasted to secure Proof-of-Work blockchains is completely unnecessary.