class Order(models.Model):
    placed_at = models.DateTimeField()
    amount = models.DecimalField()

Order.objects.annotate(year=TruncYear('placed_at'))
             .values('year')
             .annotate(total=Sum('amount'))

Order.objects.annotate(year=TruncYear('placed_at'))
             .values('year')
             .aggregate(total=Sum('amount'))

<QuerySet [{'year': 2016, 'total': Decimal('20000.00')},
           {'year': 2017, 'total': Decimal('30000.00')}]