100Green

100Green (formerly known as GEUK) was established in 2001, making it one of the oldest energy firms outside the traditional big firms. 

It was the first energy supplier to launch a tariff using a smart meter to charge customers different electricity rates depending on the time of day. In 2026 it's a Which? Recommended Provider for the second year in a row, having been included in our assessments for the first time in 2024. 

Looking for a new tariff? Use our tool to compare energy prices.

100Green score 

We combine the results of our customer survey with an in-depth assessment of companies’ behind-the-scenes practices and policies to give you an overall view. 

Take a look at our table below to see our score breakdown for 100Green:

Here's how 100Green customer and policy assessments break down:

To find out how 100Green compares with other energy companies, see our full results of the best and worst energy companies.

Which? verdict on 100Green

• Pros A Which? Recommended Provider; strong customer service, according to our survey; offers a good range of contact options.
• Cons Has not signed the Energy UK Vulnerability Commitment; scores poorly in our switching assessment.

100Green customer review

100Green was ranked first out of 17 energy companies when rated by 11,945 members of the public in the annual Which? customer survey.

It received the highest customer score of 82%, along with a four-star rating for overall customer service. It received an adequate three-star rating in all the remaining categories, including ease of contact, customer communications and value for money. No provider achieved more than three stars for value for money, perhaps reflecting generally high energy prices at the moment. 

100Green received plenty of feedback from satisfied customers in our survey. One said: 'They are efficient and reliable! Customer service is always outstanding.'

Another happy customer told us: 'Their service has been reliable, easy to use, and they provide clear communication and support when needed.'

100Green customer service

Customers in our survey gave 100Green an four stars out of five for overall customer service – a rating only equalled by its fellow Which? Recommended Providers:  E, Octopus and Sainsbury's Energy.  No supplier received the full five-star rating. 

100Green common issues and complaints 

While the majority of customers are happy with 100Green, some did experience issues. The most common issues experienced over the last year related to short-notice price increases (19%), needing a new energy meter to be installed (17%), and smart meters not sending readings automatically (15%).  

Some 19% of the 100Green customers in our survey said they made a formal complaint in the last year. This is above average when compared with other providers in our survey. 

100Green supplier assessment

In September-November 2025 we looked at five aspects of suppliers' business practices and procedures. Examples of some criteria within each category are shown below:

• Complaints – how many complaints suppliers get and how quickly they resolve them
  
• Contacting your supplier – including how and when you can get in touch, call waiting times, and the quality of self-service help online
• Help for customers who need it – including those in vulnerable situations, those who use prepayment meters, those who need materials in languages besides English, and web accessibility 
• Smart meters – including performance against 2024 smart meter targets and the proportion of customers' smart meters actually operating in smart mode
• Switching – how well suppliers handle switching.

100Green received an average score (61%) in our assessment of suppliers' practices this year.

It received high marks for its handling of complaints, and for the various methods of contact it provides to customers. It offers long opening hours on its phone line (12 hours daily on week days, and a few hours on both days of the weekend). It has equally extensive email monitoring hours and offers support through other channels too, including live chat and social media.

It did not perform well when it came to providing help for those who need it (scoring four out of a possible ten). This is primarily due to it not being a member of EnergyUK, due to its small size, and therefore not signing up for the voluntary EnergyUK Vulnerability Commitment. That means it may not be a good choice for you if you are struggling with energy debt. And it only received one out of a possible five for its switching practices. 

Does 100Green support prepayment meters?

Yes, 100Green does support traditional prepayment meters. 

With a traditional prepayment meter, customers top up a key or card and insert it into the meter to pay for their current usage and any outstanding debt on their energy account. Cards and keys can be topped up at Paypoint, PayZone, or Post Office outlets.

Find out whether a prepayment meter is right for you.

How sustainable is 100Green?

Sustainability credentials are important when choosing an energy supplier for two thirds of those responsible for choosing their provider. That’s according to our online survey of 3,000 UK adults in August 2024. 

So we factor in a range of sustainability criteria in our Eco Provider assessment. 

Here’s how 100Green fared:

• Proportion of renewable electricity sold to customers: 100%. 
• Doesn't generate renewable electricity but buys it from renewable generators which don't get government subsidies. This is important to support these generators.
• The only firm to sell 100% green gas. 
• Offers a time-of-use tariff with low overnight rates and high rates between 4-8pm on weekdays to encourage customers to use power at less popular times.

100Green narrowly missed out on being an Eco Provider this year. It's still among the best for buying and selling renewable power however.

Find out more about the differences between energy companies renewable electricity, and find out how we assessed energy suppliers for sustainability.

Based on information supplied by companies in August 2024 and their most recent published fuel mixes, where available.

Making your home more energy-efficient will save money on your bills in the long term and lower your carbon footprint. Get started with our guides to home energy efficiency.