This interest rate should in theory be lower than all other rates in the economy, which have higher risks. Nobody should lend to a company or individual at a rate lower than the risk free rate. The Lightning Network RateThe first and most obvious example of a possible risk free rate in Bitcoin, is providing liquidity in the lightning network. Therefore, it is possible the market for lightning channels could represent a non-custodial risk free Bitcoin rate of return. Therefore, JoinMarket perhaps offers more of a genuine candidate than lightning for Bitcoin’s risk free rate.