Coin Carbon Cap
PoW currencies ranked by energy efficiency
Fequently Asked Questions
How is the energy usage calculated?
We calculate the total power consumption by taking the hashrate of the last 24 hours and dividing it by the efficiency of the most energy-efficient miner hardware available for each hashing algorithm:
|Algorithm||Hashrate / Watts|
The actual energy usage is probably significantly higher as only a minority of miners use the most energy-efficient hardware. However, for comparison purposes we decided to look at the best possible scenario for each currency.
How is the CO2 output calculated?
For calculating the CO2 output we used the available data on SHA256 mining distribution by country  in combination with the observed carbon intensity per country in 2016 . We came up with a global SHA256 carbon intensity of 0.25.
This may be unfair towards ASIC-resistant algorithms as ASIC mining concentrates in countries with a higher usage of coal but as there isn't much data available on the locations of ASIC-resistant mining so we are not able to factor that in. Additionally, the degrees are ASIC-resistance is often very uncertain and subject to change due to technological development.
What are the Transaction externalities?
Under the European Union and United Kingdom Emissions Trading System  individual states in Europe are auctioning off EU Allowences that permit the owning party to emit one tonne of CO2. The transaction externalities are the current price of EU Allowances equivalent to the estimated amount of CO2 emission caused by the energy production payed for using the average fee of a single transaction.
What about Proof of Stake?
It is great to see effort being put into researching cleaner alternatives. Unfortunately, there is no working PoS-based system that does not rely on some degree of centralization in its security model.
There are fundamental problems in PoS that make it difficult to impossible for it to solve the problem of distributed consensus . Maybe the future will bring further advances but as we see it today, there is no alternative to PoW for decentralized systems.
However, we are considering adding any PoS currency that can provide good, real-time data sources that can be used to calculate the networks energy consumption.
What about Ripple/IOTA/...?
As with Proof of Stake we are aware of no existing, alternative protocol that has solved the problem of distributed consensus. Usually these approaches have resulted in some form of centralized authority becoming an important factor in the security model.
Of course centralized systems can achieve a far greater energy efficiency. Here we want to compare only distributed systems and their properties.
Isn't energy usage per transaction a misleading metric?
It is important to note that it is not the transactions themselves that cause the energy usage but the monetary reward that miners get for each block. In all cases this reward is determined almost exclusively by the set block reward and price of the currency. However, we think that energy usage per transaction is a good metric to empirically measure energy efficiency. In other words, it is an indicator of the usefulness of the system in relation to its energy costs.