Passive solar membrane distillation (MD) is an emerging technology to alleviate water scarcity. Recently, its performance has been enhanced by multistage design, though the gains are marginal due to constrained temperature and vapor pressure gradients across the device. This makes condenser cooling enhancement a questionable choice. We argue that condenser heating could suppress the marginal effect of multistage solar MD by unlocking the moisture transport limit in all distillation stages. Here, we propose a stage temperature boosting (STB) concept that directs low-temperature heat to the condensers in the last stages, enhancing moisture transport across all stages. Through STB in the last two stages with a heat flux of 250 W m⁻², a stage-averaged distillation flux of 1.13 L m⁻² h⁻¹ S⁻¹ was demonstrated using an 8-stage MD device under one-sun illumination. This represents an 88% enhancement over the state-of-the-art 10-stage solar MD devices. More notably, our analysis indicates that 16-stage STB-MD devices driven by solar energy and waste heat can effectively compete with existing photovoltaic reverse osmosis (PV-RO) systems, potentially elevating freshwater production with low-temperature heat sources.

被动式太阳能膜蒸馏（MD）是一项缓解水资源短缺的新兴技术。最近，它的性能通过多级设计得到了增强，尽管由于整个设备的温度和蒸汽压力梯度受到限制，增益是微乎其微的。这使得增强冷凝器冷却成为一个值得怀疑的选择。我们认为，冷凝器加热可以通过解锁所有蒸馏阶段的水分传输限制来抑制多级太阳能 MD 的边际效应。在这里，我们提出了阶段升温 (STB) 概念，将低温热量引导至最后阶段的冷凝器，从而增强所有阶段的水分传输。通过最后两级热通量为250 W m ^-2的STB，使用8级MD装置在单太阳光照下证明了1.13 L m ^-2 h ^-1 S ^-1的级平均蒸馏通量。这比最先进的 10 级太阳能 MD 设备提高了 88%。更值得注意的是，我们的分析表明，由太阳能和废热驱动的 16 级 STB-MD 设备可以有效地与现有的光伏反渗透 (PV-RO) 系统竞争，从而有可能利用低温热源提高淡水产量。