Windfarms and solar power could soon lose the privilege of getting priority over other energy sources on European electricity grids, leaked documents show.

Paring back the “priority dispatch” system could increase carbon emissions by up to 10%, according to a confidential EU impact assessment seen by the Guardian. But the document goes on to model four scenarios for doing just that, in a bid to make Europe’s energy generators more flexible and cost-competitive.

Some industry sources have told the Guardian they are alarmed and think it highly likely that priority dispatch for clean energy will be scrapped from the EU’s renewable energy directive, which is currently being redrafted for the post-2020 period.

Oliver Joy, a spokesman for the WindEurope trade association, said: “Removing priority dispatch for renewable energies would be detrimental to the wind sector, which would face more curtailment across the continent. It also seems to be at odds with Europe’s plans to decarbonise and increase renewables penetration over the next decade.”

“Investors took priority dispatch into account when projecting revenues in the original investment decisions, and it could have a bearing on existing projects if they are not protected from the change.”

The issue of retroactive changes to funding rules for renewables in Europe has been a cause for disputes and cutbacks in the wind and solar sectors of several countries, notably Spain.

Senior industry sources say they will push for financial compensation and access to balancing markets to help prevent a significant industry contraction, if priority dispatch is ended.

“We have had enough instability and retroactivity in Europe and going forward, the difference between existing and future assets should be well distinguished,” said one industry source.

“I would be extremely worried if they just removed priority of dispatch and did not touch other key issues around market design. It would mean that the commission was taking measures against the same renewable industries that they defend in public.”

Fossil fuel power providers argue that renewables have the lowest operating costs and so would anyway receive priority access to the grid network.

They also say that taking the clean energy sector out of priority dispatch would prevent “negative prices” - where more energy is produced than can be sold – and eliminate anti-competitive subsidies.

The EU’s assessment views the abolishing of priority dispatch as a step towards the creation of a “level playing field” for energy generators.

But without such a system, renewable sources may be the most likely to be taken offline because of the relative ease of switching off a wind turbine compared to a coal or nuclear plant.

The energy source with the lowest marginal cost - almost always renewables - is usually the first in line to be shut down by power grid operators.

As things are, a Europe-wide trend towards ending financial support has constrained the forward march of renewables on the continent, and siphoned off investment to elsewhere in the world.

“Everyone is investing in renewables outside Europe right now,” said one industry source. “If you want to bring investors back you have to send very relevant signals.”

Removing wind and solar power from priority dispatch may be intended to help reform the capacity market system, which currently pays gas generators to remain idle. Ironically though, it could lead renewable generators to demand an extension of the same mechanism to their own sector.

“If priority dispatch is removed, then renewables must be given a fall-back option of access and renumeration in the balancing markets to help stabilise the system, or clear levels of compensation in the event that curtailment is necessary,” Joy said.

Priority dispatch is supposed to be mandatory under current EU rules, although the UK, Sweden and the Netherlands are among countries that do not comply.

The study says that “the biggest impacts on generation [from ending priority dispatch] would be observed in Denmark, Great Britain and Finland, where biomass holds a large share of generation capacity”.

But this would be felt more in terms of bioenergy’s “expensive” production costs than its carbon emissions reduction potential, which is disputed inside and outside the commission.

“The removal of priority dispatch for biomass would indeed, in the first instance, imply an increase in GHG [greenhouse gas] emissions,” the paper says.

The four scenarios for scaling back priority dispatch involve an increase in CO2 emissions of 45m-60m tonnes.