For as good as solar panels are at converting sunlight directly into usable electricity, especially for how cheap they’re becoming, they can still only gather around 20-30% of the energy that hits them. That’s fine if you have a large roof or a huge tract of land, but if you have limited space and need to do something like heat a home, there are better options available to capture more of that energy. [Greenhill Forge] has built five solar air heating panels to test this concept, and do it much more inexpensively than commercial options.

These solar heaters use sunlight to heat a fluid, in this case air, and move that heated fluid to another space. Each panel is about two square meters, insulated on all sides except the top, and configured in a way that air can flow past something that the sun has heated. The first panel, a control, does not use a glazing to help trap this heat, but the rest all have a polycarbonate window to increase the greenhouse effect of the panels. The four remaining all experiment with the way air flows around a black corrugated steel sheet to gather more of the heat, with the fifth panel using a set of black screen instead.

With the panels all set out in the sun, [Greenhill Forge] is using a set of thermocouples from a previous project to measure the efficiency of each panel. Surprisingly, he found that the panel using the layers of screen was the best at gathering energy, although he notes several times that these types of panels are extremely sensitive to changes in physical configuration, so this is not the most definitive test possible. However, at only around $100 per panel it’s quite a deal if the goal is a usable space heater that doesn’t use any fuel or grid electricity.

尽管太阳能电池板在将阳光直接转化为可用电能方面表现出色，尤其是随着其价格不断下降，但它们仍只能收集照射到其表面约20-30%的能量。如果你有一个大屋顶或大片土地，这倒没问题，但如果你空间有限，又需要做诸如为房屋供暖之类的事情，那么有更好的选择来捕获更多能量。[Greenhill Forge] 建造了五个太阳能空气加热板来测试这一概念，并且成本远低于商用方案。

这些太阳能加热器利用阳光加热一种流体（此处为空气），然后将加热后的流体输送到另一个空间。每个面板约两平方米，除顶部外所有侧面均进行了隔热，并采用一种让空气能流经被阳光加热物体的配置。第一个面板作为对照组，没有使用玻璃盖板来帮助捕获热量，但其余面板均有一层聚碳酸酯窗口以增强温室效应。剩下的四个面板则测试了空气在黑色波纹钢板周围流动以收集更多热量的不同方式，其中第五个面板使用了一组黑色筛网。

将所有面板置于阳光下后，[Greenhill Forge] 使用之前项目中的一组热电偶来测量每个面板的效率。令人惊讶的是，他发现使用多层筛网的面板在收集能量方面表现最佳，尽管他多次指出这类面板对物理配置变化极为敏感，因此这并非最明确的测试结果。然而，每个面板的成本仅约100美元，如果目标是制造一个不使用任何燃料或电网电力的可用空间加热器，那这无疑是一笔相当划算的买卖。