Question: when was the first solar powered calculator invented
[{'answer': 'end of the 1970s', 'provenance': [{'wikipedia_id': '32261445', 'title': 'Solar-powered calculator', 'start_paragraph_id': 1, 'start_character': 137, 'end_paragraph_id': 1, 'end_character': 153, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '32261445', 'title': 'Solar-powered calculator', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 153, 'bleu_score': 0.9214109120166031, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 8593430638479156907}, 'section': 'Section::::Abstract.'}]}]