Is Amazon powered by 85% renewable energy? Is the wrong question
If the question is "Within the definitions, limitations and constraints that Amazon has set, is the claim that it has achieved 85% renewable energy (as defined by them) correct?" then the answer is: Yes.
I draw this conclusion because that's what the 3rd party assurance statement says.
What they are saying is not what you are hearing
Amazon sets out their Renewable Energy Methodology here. The relevant part says:
Amazon’s Renewable Energy Percentage
To calculate the percentage of renewable energy powering Amazon’s operations, we evaluate both the amount of renewable energy from Amazon’s projects and the renewable energy in the grid. This total renewable energy is then compared to
Amazon’s total energy use per the equation below:

Amazon’s renewable energy percentage is calculated on an annual basis, from January 1 through December 31 each year, and assured by an independent third-party auditor along with Amazon’s carbon footprint. We publicly disclose the results of
these audits on our sustainability website.
So, that's what they are saying when they say they are 85% renewable.
You can read for yourself what each of the terms in the equation means, but there are a few issues that, to be fair, are not of Amazon's making. For example:
- Amazon relies on "Site Energy Contracts" with energy suppliers for some of their renewables. Depending on where they are in the world, it has been known for suppliers to, shall we say, "cheat" on these. The same can be said of "Renewable Energy Certificates".
- Similar problems exist on relying on 3rd-party reporting of the percentage of renewables in the grid. Both utilities and governments have targets to meet, and while we can all hope that they will achieve those in reality rather than just in reporting, we also know what incentives do to human beings. Amazon acknowledges this by saying, "We support the need for an improved data-set that reflects a customer’s delivered electricity mix taking into account: 1. Environmental attributes owned by others. 2. The inter-grid and inter-state ownership and use of renewable energy generation."
It is also important to note that when Amazon refers to "Amazon's Renewable Energy %", they exclude transport energy. It is probably not a coincidence that this is the energy sector most challenging to make renewable. It's a significant exclusion for a company heavily involved in logistics. It's cute that they count on-site EV charging, so they get to count the energy their employees who drive EVs to work as 100% renewable while not counting those driving fossil fuel powered at all; in the scheme of things, this probably doesn't make much difference.
They also exclude anything in their supply chain and any partners outside their direct control. They also only include "financially-integrated subsidiaries" - one assumes there are non-financially-integrated subsidiaries.
I'm not bashing Amazon
This is a tricky area.
There are no internationally accepted standards for determining what percentage of an organisation is "renewable". Without such standards, there is no generally accepted methodology for measuring "renewable" and auditing those measurements.
So companies have to come up with their own: in general, they will start with what is easy to measure (buildings rather than transport, their own operations rather than their supply chain) and, when rolling things out, why wouldn't they go first to the areas that will put them in the best light?
Where things get really tricky is when you look at your customers. Are you a renewable company if you are aggressively selling to the oil and gas industry?
Notwithstanding, Amazon can do better. According to Wired, in terms of cloud services, both Google and Microsoft are doing better. Greenpeace has also raised doubts about Amazon's prognosis.