A new low-cost solar collector based on thick (4.5′′) vertical tubes related to the previous design based on long 1.5′′ plastic hoses connected directly between water-grid supply and consumption is presented. This novel design could noticeably improve its performance for temperate locations mid and high latitudes, as was demonstrated by dynamic thermal modeling. This tool has been useful for understanding the particular characteristics of this kind of water-pond collector and besides, for noticeably improving its performance by optimizing its parameters, like tube diameter and number of glazing layers. By this way, the optimized design could fully satisfy the household demand up to midnight along the whole year for Buenos Aires (35°S) and during summers (remaining as a useful preheater for the whole year) for Ushuaia (55°S). Besides, its high simplicity makes it available for user’s own construction, costing down 50 dollars for a single-family unit. 1. Introduction The demand of sanitary hot water in tropical developing countries can be supplied by locally manufactured cheap solar collectors, considering the low difference of temperature involved. Following this idea, many solar enthusiasts have often proposed hose-based solar collectors (e.g., by using a plastic hose coiled within a glazing box), but mostly they have achieved poor results [1, 2]. However, the hose collector has been recently studied by dynamic thermal and hydraulic modeling, showing the huge potential of this concept. Their particular behaviors were discussed and therefore its performance was noticeably improved for tropical low-latitude locations [3] and for temperate mid-latitude locations [4]. Although these studies have demonstrated that this collector is not suitable for cold high-latitude locations, they give us a good background for understanding their special characteristics, which is convenient to summarize here. The simplest hose-based design consists in one long LDPE hose wrapped with several transparent layers of a low-cost plastic material (preferably bubble wrap made by LDPE transparent film) simply resting onto the roof, as is illustrated in Figure 1. Here, the hose is connected directly between water-grid supply and consumption, using the district-grid pressure as driven force for pumping hot water through the whole hose. The thermal-hydraulic modeling has shown that, by choosing a diameter between 1′′ and 2′′ of a 100？m in length hose, this system can provide the desired consumption flow together with a reasonable storage capacity (50 liters to 200 liters) and enough
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