* Brussels debate on 2030 targets likely to be very tough
* Many in business want fewer targets
* Environmentalists say strong targets crucial to change
BRUSSELS, Feb 14 (Reuters) - One-hundred percent green energy for the European Union is realistic by the middle of the century provided the bloc signs up to ambitious energy policy goals for 2030, conservation body WWF said in a report on Thursday.
Debate has begun in Brussels on targets for 2030 to replace the existing set of 2020 goals, which are to cut carbon emissions by 20 percent from 1990 levels, improve energy savings by 20 percent compared with projected use, and increase the share of renewables in the energy mix to 20 percent.
Targets for 2030 should include energy savings of at least 38 percent compared with business as usual, obtaining 40 percent of fuel from green sources and cutting carbon emissions by 50 percent, the WWF report says.
"Our report clearly shows that the EU has untapped potential for cutting energy use, taking full advantage of renewable sources that could deliver cheaper and more secure energy and ensuring that a 100 percent renewable system by 2050 remains within reach," Jason Anderson, head of climate and energy at WWF European Policy Office, said.
The report is based on analysis by Dutch consultancy Ecofys, which judged 100 percent renewables by 2050 to be realistic, although it would require big improvements in energy efficiency, as well as accelerated development of wind, solar and green transport fuel.
Debate on the 2030 EU targets is likely to be protracted. While many in business agree on the need for a carbon target, they tend to be more reluctant to couple that with other legislative goals.
Advocates of natural gas also say the fuel, which is only half as polluting as coal, must retain a role in ensuring reliable power and that carbon capture and storage, which entails burying greenhouse gas emissions, can offset its emissions.
If the EU Emissions Trading Scheme, currently overwhelmed by surplus allowances, could be made to function, some argue that renewable energy targets should not be necessary because market forces would naturally shift investment towards carbon-free energy, such as wind and solar.
The existing efficiency target, the only non-binding target of the 2020 goals, has proved very hard to meet. Months of discussion on an Energy Efficiency Directive last year stopped short of enforcing the full 20 percent savings. (Reporting by Barbara Lewis; Editing by Mark Heinrich)