Hello,
To our considerable surprise, our post from last week has been removed without notice. We really appreciate the open and insightful discussions on this forum and would like to bring the idea back for further exploration. We are aware that we introduce a very complex technical topic - it therefore may require some serious thinking to access this potential route to a sustainalble mining process.
We are naturally fully aware of the core principles of bitcoin, especially the importance of maintaining decentralization. Hardware limitations are not a good direction, we also feel they can potentially be removed or circumvented. Auditing is not attractive too, as it reduces the level of decentralization.
Our goal with this technical post is a discussion to explore potential ways to serisously reduce the carbon emissions associated with bitcoin mining. This is a growing concern for both investors and lawmakers. One potential solution we're considering is the concept of Proof of Idle, which could offer a way to mitigate bitcoin's environmental impact. If bitcoin can essentially demonstrate to be of solar energy origin, its reputation will greatly profit and a key point of critics can be removed.
Please note, this is just the beginning of a thought process, and we'd love to hear your thoughts on the pros and cons of this approach in general. How could idling be technically implemented in a way that preserves the decentralization of the network? What other principles or mechanisms might be viable to achieve the goal of decarbonization without compromising the core values of bitcoin?
# Introduction of Proof of Idle to reduce the carbon footprint of Proof of Work-based cryptocurrencies.## Introduction
Global warming is one of the key issues facing humanity in the 21st century. Research has shown that 67% of the electricity used for bitcoin mining in 2020-2021 came from fossil fuels. [1]
Bitcoin's contribution to global warming has provoked regulatory action and may keep ecologically focused investors and contributors out of the ecosystem.
That's why the idea of a Proof of Idle mechanism is introduced, where Bitcoin miners limit their active mining time to use the curtailed energy produced by renewable energy sources when it cannot be used or stored and would otherwise be lost.
## Proof of Idle
Reducing the carbon footprint of proof-of-work (PoW)-based cryptocurrencies can be achieved by time-limiting the mining process to use a higher proportion of curtailed electricity to mine cryptocurrencies.
Leveraging the correlation between curtailed electricity and photovoltaic (PV) power production profiles, bitcoin miners, who work for certain hours each day and must remain idle the rest of the time, can effectively reduce their carbon footprint by scheduling mining activities during periods of surplus renewable energy; furthermore, this scheduling is also incentivised by potentially cheaper energy prices for curtailed electricity.
## Implementation
In an implementation of the protocol, it is sufficient to limit the active time/day and let the miner decide when the best active time is, as it would be economically most attractive to mine when curtailed power is used.
Furthermore, proof of idle can be introduced as an enhancement to an existing PoW cryptocurrency, without changing its foundation behavior, by marking transactions as green transactions that are in a block mined by a miner that follows the idle criteria.
There are several ideas for the mechanism to verify a miner's idle time.
Conceivable is to integrate a Truste Execution Environment (TEE) into the ASIC chips used in the mining process. The TEE then maintains an idle log based on hardware parameters such as power consumption and hardware temperature. The TEE also timestamps and verifies the log and securely signs and transmits it to the blockchain, either at regular intervals or upon verification requests from the verifier. Regular hardware reviews and audits could enhance the system's resilience against tampering and ensure the integrity of idle proofs. Other implementations using network analysis or even physical inspection are also conceivable. Verification of green transactions does not have to be immediate and can be approved with some delay.
## Implication on resilience
A critical consideration for this system is the resilience to 51% attacks. To achieve the same level of resilience in a system that fully implements Proof of Idle, more hardware is required. The cost of this increased hardware requirement can be offset by a higher purchase price for green-verified crypto-tokens than for conventional ones.
Another effect is helping to improve the resilience: By using curtailed electricity which is available at a lower price it is financially lucrative to use hardware for a longer period, which is diminishing the mining equipment acquisition cost, and thus improves the resilience of the system. This further improves the overall ecological footprint as less new machines must be produced.
Another consideration is that curtailed power will not be available in the same way all over the world. Therefore, there is a certain risk that political policies in these countries could affect the stability of the blockchain. It is important to note that a similar risk also exists in classical PoW blockchains. In the bitcoin example, only 3 countries are responsible for over 70% of today's hash rate[2].
## References
[1] Chamanara, S. & Madani, K. (2023). The hidden environmental costs of cryptocurrency: How Bitcoin Mining Impacts Climate, Water and Land, United Nations University Institute for Water, Environment and Health (UNU-INWEH), Hamilton, Ontario, Canada,
https://inweh.unu.edu/[2] Cambridge Centre for Alternative Finance. (n.d.). Cambridge Bitcoin Electricity Consumption Index (CBECI): Mining map.
https://ccaf.io/cbnsi/cbeci/mining_map 
