In this talk the results of a study comparing Pb-acid and Li-ion batteries as power storage buffers for residential applications will be presented. The study is organized as an overall comparison, highlighting many production factors, in addition to the  common financial issues.  It was conducted in cooperation between the University of Landshut and California State Polytechnic University, Pomona. A cradle-to- grave life-cycle analysis of both the Li-ion and the Pb-acid battery is presented. The energy demands for production of cells in both technologies are analyzed for the single production steps. The energy needed and the CO2 generated in the production of both types of cells and batteries is compared to the energy saved and the reduction of CO2 emitted through the usage of each type of battery. The detailed analysis of these two popular technologies provides critical information as residential solar systems become

more common. They are compared to their real sustainability in a homestorage photovoltaic buffer application.

The storage of electricity generated by photovoltaics battery is performed by battery systems with a typical capacity between 5 and 20 kWh. In this application Lead-Acid an Lithium-Ion batteries are the most common storage technologies. The storage of electricity generated by a 10 kWp PV-generator in combination with a 7,5 kWh battery is analyzed on different levels. The necessary primary energies for

 

• Cell production
• Production of the Battery System
• Transport to the customer

are compared for Lithium-Ion and Lead-Acid technology. The Energy required for production of one Wh of Battery Capacity on cell level is in

Li-ion-Technology              41 kWh

Pb-acid-technology           14 kWh.

The most energy intensive aspect of Lithium-ion battery production is the coating process. The most energy intensive aspect of Lead-acid battery production is the formation process.

Lithium-ion batteries operate nearly 3-times more “energy efficient” with respect to the demand of primary energy for their production. Although Lead-acid cells require much less energy to produce, when usage and system performance are taken into account Li-ion batteries are the winner of this comparison.

It is shown that the ecological amortization in the mentioned home storage application happens after only a few months of operation. The Li-Ion storage system starts “to work green” after 0.6 years and with the Lead-acid storage system after 1.8 years of operation.