Start with the tariff type, not the price
Every supplier in this group sells both electricity and gas, so the fuel on offer does not separate them. What does is the kind of tariff. Powerpeers is the only one of the four offering a dynamic contract, sitting alongside fixed, variable and green options (dynamic, fixed and variable). Octopus Energy lists fixed, variable and green (fixed, variable and green), and Vattenfall lists fixed, green and variable (fixed, green and variable). A dynamic contract is the category worth reading most carefully, because the price moves during the term rather than being fixed in advance.
100Green's published detail is a fixed term of 12 and a green supply, which leaves less to weigh up than the three suppliers above. The practical order is to pick the tariff shape you can live with, then compare the money attached to it.
Unit rates, where the spread is widest
A unit rate is the price of each unit of energy you actually consume, and it is where the gap between suppliers is widest. Across the plans tracked here, unit rates run €0.11 to €6.29, and a reference annual cost runs €953.30 to €1,932.71, with Vattenfall quoted at €953.30.
On a single published figure, Octopus Energy charges €0.17 and Vattenfall €0.33. Powerpeers lists €0.11 to €0.30 because its dynamic contract moves within that band, so the figure describes a range rather than a locked price. 100Green does not publish a unit rate, so its cost has to come from a quote rather than from a table you can line up against the others. Note the currency too: 100Green quotes in sterling and the other three in euros, so any rate you are handed should be converted before you compare it.
Do the arithmetic with your own usage. The lower unit rate wins on a home that runs heating, an electric car and a tumble dryer, and it matters far less on a small flat where most of the bill is fixed.
Standing charges, the quiet decider
A standing charge is the cost of being connected, and it appears on every bill whatever you consume. Across the plans tracked here, standing charges run €0.09 to €144.
Within that span, Powerpeers sits at €0.21 to €0.39, Octopus Energy at €6 and Vattenfall at €10.90. This is the line that quietly decides small households. If your usage is low, you will spend more on the standing charge than on energy, and the supplier with the smaller standing charge is the better match. If your usage is high, the arithmetic flips and the unit rate takes over. Working out which side of that flip you sit on is more useful than ranking suppliers on a single number.
Contract length and the cost of changing your mind
All four sell on a fixed term, and the lengths differ. Powerpeers offers 12, 24 and 36, Vattenfall offers 12 and 24, and Octopus Energy offers 12 alongside 100Green at 12.
Pair the term with the exit fee, because the two move together. Across the plans tracked here, exit fees run €0 to €131.54, while 100Green charges £0 and Octopus Energy charges €0. A longer commitment can hold a lower unit rate, and it is also what makes an exit fee worth reading. If you expect to move, start or expect to generate, or simply think your usage will change, read the exit fee before the unit rate. If you are confident you will stay, a longer term is worth the rate it may carry.
Support, because a switch can go wrong
Most tariff differences are settled in a call or a message, and that is where reliability shows. Powerpeers and Octopus Energy both list email, chat, phone and a help centre (email, chat and phone and email, phone and chat), while Vattenfall lists phone alone (phone). One channel means one queue, which matters most when a meter reading is disputed or a direct debit goes wrong in the first month.
Terms only tell you what is promised. The Powerpeers review, the Octopus Energy review and the Vattenfall review set out how the day-to-day experience lines up with those published terms.
Green credentials, and who you actually sign with
Three of the four put their whole supply on renewables: 100% for Powerpeers, 100% for Octopus Energy and 100% for Vattenfall. The mechanism behind those claims is where the reading is worth doing. Octopus Energy relies on certificates, while 100Green buys its green power under a power purchase agreement, so the two are not making the same kind of claim even where the headline looks similar. If you generate your own electricity, 100Green pays £0.12 for power you export, and no comparable export rate is listed for the other three.
The company on the other side of the contract also belongs in the file. 100Green contracts as Green Energy (UK) Limited and serves the GB market, Octopus Energy as Octopus Energy Italia Srl and serves the IT market, and Vattenfall as Vattenfall AB from its SE base. Vattenfall reports 12,000,000 customers and was founded in 1909, while 100Green was founded in 2001. An operating history is a modest comfort rather than a price signal, but it is a real one.
A comparison order that works
Run the same order every time, so you compare like with like. Tariff type first, because it decides what the price can do. Then unit rate, then standing charge, then contract length, then exit fees, then support, and read the green claims last. Our green energy supplier rankings do the sorting, and the 100Green review covers what a fixed green contract in the GB market involves.
Whichever supplier you settle on, work through the same order again as your renewal approaches. Every one of these figures can move, and the cheapest-looking rate on a renewal quote is not always the one you were on before.