The following report focuses on EU-28 countries (plus Switzerland and Norway), for summer 2017. Click on the map to start exploring our main results
The European Union's electricity grid is the most interconnected continental power network in the world. It forms a single synchronous A/C grid  where all member states are responsible for maintaining grid equilibrium, i.e. matching total power demand with total supply at all times.
Such level of integration is made possible due to large interconnections between neighboring countries. Interconnection capacities already reach up to 40% of installed power generation capacities in countries such as Denmark or Austria. Furthermore, they are mandated to be no lower than 10% for all member states by 2020.
As a result, the impact of consuming electricity in a given EU-country depends largely on the energy policies of its neighbors: a French homeowner turning on his electric heater during peak hours in winter may contribute to increase the burn rate of a coal power plant in Germany, or a gas turbine in Denmark, albeit to a smaller extent.
Our data shows that this summer, on average, 12% of the electricity consumed by a European citizen was imported from a neighboring country. Some countries like Latvia even import more power (on average) than they actually consume due to their high export. They effectively act as "electricity highways" between distant regions. Denmark is also particularly noticeable, as it imported 54% of its consumption, using Norwegian's hydro plants as a giant back-up battery for its variable wind production. All countries imported some of their electricity from neighbors at some point during the summer, even the largest net-exporters such as Estonia or Sweden.
The physical origin of electricity consumed in a country has to take into account these imports. At first approximation, we assume that what is consumed by your power plug at any time is best represented by how electricity is produced locally together with how neighboring countries procured electricity that is being imported (model explained here). This gives us a model for the physical origin of electricity consumed.
By applying a fixed carbon emission factor  per type of power plant to the physical origin of electricity, we estimate the corresponding carbon intensity of electricity consumed in each member state, in gram of CO2-equivalent per kilowatt-hour (gCO2eq/kWh).
As shown below, Norway, Sweden, and France top the charts this summer, thanks to their high share of stable, low-carbon nuclear and hydro power. States with the largest intermittent renewable penetration, such as Denmark or Germany, exhibit a high volatility of carbon intensity, varying by a factor up to ten. The most carbon-intenstive electricity is Polish (80% sourced from coal) and Estonian (80% sourced from dirtier oil shale).
Let's focus on Denmark: A country highly interconnected to its neighbors, having the world's largest share of wind power capacity installed (~ 40%). The time serie below shows the physical origin of power consumed by Danes this summer, broken down per fuel of origin, and including imports.
As expected, a lot of Danish electricity comes from wind power (32% of electricity consumed on average this summer), but also hydropower (27%) which is mostly imported from Norway. By selecting only coal, gas, oil and nuclear on the graph legend, one can see whether Denmark is close to run entirely on renewables or not: Interestingly, zooming on the first week of July, it appears that although Denmark ran almost fully on renewables during few hours on the evening of July 2nd, it never managed to maintain this state for a whole day. Actually, not a single EU country ran exclusively on renewables during one full day: even when local renewable production would have fully covered domestic demand, thermal power plants are often maintained in order to ensure security of supply and maximize export revenues.
As for the carbon intensity of Denmark, the intermittent nature of wind power makes it extremely volatile, frequently varying by a factor 4 in less than 12 hours. The graph below breaks it down by contribution from each type of power plant: emissions appear to be almost entirely driven by the share of coal in electricity consumed, be it produced locally or imported from Germany. Obviously, what matters for the climate is not to produce more renewable electricity, but to be able to turn off fossil-fuel power plants.
This summer, the single most productive type of power plant was nuclear, supplying on average 30% of the total European power demand (305 GW). Fossil-fuels covered 40%, and renewables 30%. The resulting Europe-wide carbon-intensity of electricity averaged 280 gCO2eq/kWh, about 30% cleaner than that of the best combined-cycle gas power plants on the market. This relatively good performance on international standards could be improved much further, given that coal alone accounted for half of European carbon emissions.
To get a sense of the variability of wind and solar at the continental level, the graph below shows the part of EU-wide consumption originating from wind and solar, hour by hour. Feel free to zoom in to see more details, or add other production type by adjusting the legend to the right.
At noon on July 30, a third of electricity in Europe originated from wind and solar: an all-time high for Europe. Three weeks later, during the night of August 25, they only covered 5%: the lowest in the summer. The European Union might not be wide enough to power itself with renewable energy at all times, even with large interconnectors. In order to decarbonize Europe, dispatchable power generators such as hydro, gas and nuclear may still be required, used in conjunction with storage systems and demand-response to mitigate intermittent renewable production.