Stand-alone PV systems with battery storage represent the largest market share and will continue to be the most important type of PV applications in the next decade. How could the cost of such systems be decreased and their reliability be further increased ? This proposal aims at giving some answers to this problem.
The battery is the component which most strongly influences the cost and reliability of a P.v system
A cost-analysis of installed PV systems is helpful in order to highlight the relative importance of each component of the installation. Considering the initial investment cost, the modules represent the first part of the cost and the battery the second part, almost at the same level for the smaller installations, in the range of 25 to 30 %.
But considering the total costs over the lifetime of the systems, therefore including the replacement of the failed components such as lights or batteries, the relative cost of the modules decreases as they are usually supposed to last 15 or 20 years, and batteries, which may have to be replaced 2 to 4 times, become the major cost, in the range of 30 to 45 %.
An analysis of the failures of PV installations also shows that batteries play a leading role as a source of problems. All these observations result from field experience on large programmes.
The characteristics of the batteries are very different from one model to another, even within the same category of batteries.
Observations at the laboratory level show that batteries are the only component of which the main characteristics (efficiencies and lifetime) are variable, rarely mentionned by the manufacturer and often not known by the system installer. Even among batteries of the same type (automotive, stand-by or traction) but coming from different manufacturers, tests have shown significant variations in the performance: the efficiency may be measured at 75 or 85 %, and the lifetime may be doubled. Such "unknown" variations are unacceptable for the PV system designer or the end-user. The normal solution would consist in initially testing the batteries in order to determine their long-term characteristics regarding the specificities of PV installations: energy efficiency and evolution, yearly capacity decrease, long lifetime. But the main difficulty is in fact in the possibility of rapidly quantifying long-term evolutions. An additional difficulty is due to the different operating conditions between conventional battery systems (automotive, UPS, electric vehicles) and photovoltaic batteries, in other words batteries used in photovoltaic systems o. PV batteries are the only ones to encounter large temperature variations, prolonged periods at low states of charge, stratification of the electrolyte, short periods of overcharge. Therefore, research and development in other fields of applications are not directly usable.
To address these problems, the main objective of this project is to allow the wisest possible selection of the most appropriate batteries for PV use, by developing appropriate test methods.
One of the remarkable points of this proposal is the high involvement level of a major European industrial partner in a relatively fundamental research subject.
Funding SchemeCSC - Cost-sharing contracts
19009 Raphina (Pikeermi)
M27 8LR Manchester