dtFrom= "21/02/2018"

var sumOfTheProduction = (from s in _unitofWork.statDailyRepository.Get()
                                   where s.m_date >= DateTime.ParseExact(dtFrom, "dd-MM-yyyy", CultureInfo.InvariantCulture) && s.m_date <= DateTime.ParseExact(dtTo, "dd-MM-yyyy", CultureInfo.InvariantCulture)
                                   select new DailyStatsofTurbines

                                   {

                                       m_energy_prod = s.m_energy_prod


                                   }).Sum(s => s.m_energy_prod);