Cambridge cleantech startup Polysolar is preparing for the national launch of its world first off-the-shelf solar photovoltaic (PV) greenhouse at a construction expo in London next month.ideaSpace based Polysolar has just launched the range of PV greenhouses at Cambridge building supplies retailer, Ridgeons but will gain a wider audience when the products are showcased at Ecobuild, billed as “the world's biggest event for sustainable design, construction and the built environment,” at ExceL in London.