Green energy tariffs have become standard in the business energy market. Every major supplier offers one, and most describe their product as "100% renewable electricity". What this claim means in practice is more complex than the marketing suggests.
A Renewable Energy Guarantee of Origin (REGO) is a certificate issued by Ofgem for every megawatt hour of electricity generated from eligible renewable sources. The critical point is that REGOs and the physical electricity are traded in entirely separate markets. A supplier can purchase electricity from a gas fired power station and separately purchase REGOs, then legitimately describe the supply as renewable.
A Power Purchase Agreement (PPA) is a direct long term contract between a business and a renewable generator. PPAs can genuinely represent additionality: they fund renewable capacity that would not otherwise exist. They are generally suited to larger energy consumers where minimum volumes and contract lengths are justified.
Our position on green tariffs: we will explain what you're actually buying before you buy it. We won't describe a REGO backed tariff as the same thing as genuine renewable supply.