Impax Asset Management Group Plc (<a href="https://www.londonstockexchange.com/stock/IPX/impax-asset-management-group-plc/company-page" target="_blank">LON:IPX</a>) and Bullfinch Asset AG have bought a portfolio of around 3,500 decentralised solar plants and battery storage systems spread across Germany from local rooftop solar rental company DZ-4 GmbH (DZ4).