Not all cryptocurrencies are deflationary. Yes the deflationary model encourages holding/discourages spending however for some projects this is a desired outcome based on the utility the coin/token is aiming to provide.
Additionally deflationary crypto can act as a hedge against inflation, hyperinflation, and stagflation. The decreasing supply can counteract inflationary pressure caused by externalities like government policies and economic shake ups.
IMO it seems RECs are a better solution than carbon taxes at least in situations like this. With RECs you're buying renewable energy to offset non-renewables, with a carbon tax the company is just giving the government money for use of non-renewables. Only funds spent on RECs in this case actually go to supporting the renewable energy sector. I'm no expert in this stuff so I could be off, just how I understand it.