Muenz, Straubhaar, F. Vadean and N. Vadean published one of the most comprehensive studies on the effects of European immigration and find that: (i) on demography and ageing, immigration has a positive effect, but will not be a silver bullet against population ageing; (ii) on wages and employment, the impact of immigration is on average negative, but very small. This suggests that the potential downward effect is offset by additional creation of employment due to economies of scale and spillovers (which increase productivity) as well as higher demand for goods and services (due to population growth through immigration: (iii) on public finances, the impact depends strongly upon the original ‘gate of entry’ or way of admission, the labour market access and – as a result of the former – the socio-economic characteristics of the immigrants; (iv) on balance of payments and trade, immigration has a small but positive impact on trade relations between migrant receiving and migrant sending countries. http://bruegel.org/2015/10/how-will-refugees-affect-european-economies/

Some anti-immigration groups argue foreigners are a drain on a country’s economy, as they seek to avail themselves of government services before contributing to the state themselves. But Germany has a long history of outsiders representing a net positive for the country’s economy. The 6.6 million people living in Germany with foreign passports paid $4,127 more in taxes and social security on average than they took in social benefits in 2012–generating a surplus of 22 billion euros that year, according to one report. German officials are hopeful that, in the long run, this summer’s new flood of refugees could result in a similar economic gain. http://fortune.com/2015/09/08/germany-migrant-crisis/

I would suggest reading this research paper; "The Impact of Immigration on Germany’s Society" -http://ec.europa.eu/dgs/home-affairs/what-we-do/networks/european_migration_network/reports/docs/emn-studies/illegally-resident/de-finalstudy-eng_en.pdf