The value of stability in photovoltaics

It is commonly assumed that photovoltaic (PV) modules have a 25-year lifetime. Warranties last this long, and techno-economic projections use this figure when calculating system performance. Yet, PV modules do not stop functioning after this time. Many modules still perform at above 80% of their original power rating after 25 years, and there is neither an economic nor an ecological reason to retire them. In this study, we explore the implications of transitioning from a mindset with finite module-life to a long-term perspective for PV-modules. We introduce an economic model to reflect such a long-term view. Using this model, we show that degradation gains in importance compared to module price. We calculate a cost-entitlement of up to 12ct/W for utility installation when improving annual degradation rates from 0.5% to 0.2%. We show that maintenance becomes more valuable – about 33% compared to a system with 30-year lifetime - and that time-constraints for maintenance disappear. We define a new lifetime metric - the minimum economically useful lifetime of a PV module as the time the module needs to be operated before replacement becomes economically preferable. We find that modules currently installed should be operated for at least 25 years and ideally for 50 years. Our metric links module life with degradation rate and, we calculate that reducing annual degradation rates from 0.5% to 0.2% increases the useful lifetime by a factor of 1.69. Such an increase would defer module end of life by decades and reduce resources required for maintenance by 40%.