1. Solar vacuum tubes typically dissipate heat 24 hours a day and only collect heat for about 10 hours. When the ambient temperature decreases in winter, the temperature becomes lower and lower. 57% of total heat loss %above.
Second, the insulation layer of the water tank accounts for more than 23% of solar heat loss. So, if the temperature drops, it must be because the vacuum degree of the vacuum tube has decreased or the film layer has fallen off. Or the water tank is poorly insulated.