How much a portable solar charger weighs, its size, and its effectiveness are three important considerations when buying one of these devices. This is especially true for people looking for the best solar chargers for backpacking.

Backpackers and hikers don’t want to lug around a heavy or bulky solar charger. Yet, there currently exists no common unit of measurement that will help you compare the weight, size, and output of these products.

Solar startup GreenVolts has found a friend in power giant ABB, in a very difficult solar market this year. On Wednesday GreenVolts, which makes solar concentrating photovoltaic technology, announced that it has raised another $35 million, with $20 million coming from ABB. At the same time GreenVolts has launched a new larger end-to-end solar power system.