豆腐卤水有望降低太阳能成本

    两项新研究提供的迹象表明，这种状况有可能会迅速发生改变。其中一项研究提供了一种全新的太阳能电池生产方式，它要比现有方法更便宜，更安全。另一项研究显示，聚焦式太阳能发电系统（即使用太阳的能量来加热液体，以驱动涡轮机，简称CSP）能够满足“目前相当大一部分能源需求。”

    《自然》杂志(Nature)上周三发布的一份研究报告中，利物浦大学(University of Liverpool)的乔恩•梅杰和其他几位研究人员宣称，氯化镁可以取代生产第二代薄膜太阳能电池所用的氯化镉。氯化镁是制作豆腐和浴盐的原料，还可用来融化冬季道路上的冰雪。

    梅杰在哥本哈根参加一个电视电话会议时表示，氯化镁源自海水，每克成本仅为0.001美元，远低于每克0.3美元的氯化镉。此外，它还能够消除处理氯化镉的挑战和费用——氯化镉是一种剧毒化合物，需要复杂的安全措施来保护生产工人，废弃的电池板也需要一道特殊的处理程序。

    “所以，我们完全可以用一种完全良性而且成本低得多的物质来取代这种昂贵且带有剧毒的原料，而且无需承受任何效率损失，”梅杰说。“对于各种太阳能电池的生产商来说，这是一项巨大的成本收益，有可能推动生产过程发生巨变。”

    由硅制成的面板目前在太阳能市场占据着主导地位。为了提升太阳能的竞争力，诸如第一太阳能公司(First Solar)这类企业对开发碲化镉制成的太阳能电池越来越感兴趣。这种材质更有效率，更加灵活，可应用于包括窗户在内的更多表面。

    生产碲化镉电池需要给太阳能电池添加一层薄薄的氯化镉，然后在炉中加热。梅杰说，这个环节被视为激活过程，可以有效推动电池的效率从大约1%提高到20%。

    寻找更安全的替代材料时，梅杰和他的团队最初考虑的是氯化钠，但他们发现它的效率大约只有氯化镉的一半。另一种选择是氯二氟甲烷，但它跟臭氧层枯竭有关，已被国际协议限制使用。

    然后，他们转向氯化镁，发现这种物质的效率完全可以跟氯化镉相媲美，而且不需要昂贵的安全设备。

    梅杰说，氯化镁目前还没有得到应用，但他希望“一旦这项研究工作获得关注，就能获得产学界的认可。”

    第一太阳能公司企业沟通部主任史蒂夫•克鲁姆仅仅表示，氯化镉仍然是该公司生产过程的“重要组成部分”，它并非“生产过程中主要的成本驱动因素。”

    《自然气候变化》（Nature Climate Change）杂志本周发表的另一份太阳能研究报告显示，CSP系统可以解决世界大部分地区很大一部分电力供应。来自奥地利国际应用系统分析研究所(International Institute for Applied Systems Analysis)的研究人员模拟了CSP系统在全球四个地区的建设和运营情况，并充分考虑了天气、电力需求和成本等因素。他们发现，CSP系统可以满足地中海地区当前70-80%的电力需求，而且跟燃气电厂相比，它无需支付额外费用。

    Two new studies offer signs that this could be changing quickly. One offers a new way to produce solar cells more cheaply and safely than current methods. The other indicates that concentrating solar power, which uses the sun’s energy to heat up a liquid that drives a turbine, could supply “a substantial amount of current energy demand.”

    In a study released Wednesday in journal Nature, University of Liverpool’s Jon Major and several other researchers announced that they had found that magnesium chloride, which is used in making tofu, bath salts and applied to roads in the winter could replace cadmium chloride in the making of second-generation, think-film solar cells.

    Speaking in a teleconference from Copenhagen, Major said magnesium chloride, which is extracted from seawater, would cost $0.001 per gram compared to $0.3 for cadmium chloride. It would also eliminate the challenges and expense of handling cadmium chloride, a highly toxic compound that requires elaborate safety measures to protect workers during its manufacture and a special disposal process when panels are no longer needed.

    “So what we have done without any loss of efficiency is to replace expensive and highly toxic material with one that is completely benign and much lower cost in the process,” Major said. “This offers a great cost benefit for production of these kinds of solar cells and could help make a step change in the production of them.”

    The solar market is currently dominated by panels made with silicon. In a bid to make solar more competitive, there is growing interest from companies like First Solar in developing solar cells using cadmium telluride, which is more efficient and more flexible so it could be applied many more surfaces including windows.

    To make these cadmium telluride cells, a thin layer of cadmium chloride is applied to the solar cell, and then heated up in a furnace. This is considered the activation process, Major said, helping boost a cell’s efficiency from around 1 percent to as much as 20 percent.

    In a bid to find a safer alternative, Major and his team first looked at sodium chloride, but found the efficiency was about half of cadmium chloride. Another option was difluorochloromethane but that has been linked to ozone depletion and its use has been restricted by international agreements.

    They then turned to magnesium chloride and found that it was just as efficient was comparable and could be applied without any expensive safety equipment.

    Major said magnesium chloride isn’t being used at the moment, but was hopeful it “would be taken up by research and hopefully by industry once this work is publicized.”

    Steve Krum, the director of corporate communications for First Solar, would only say cadmium chloride remains “critical part” of its production process and that it was not a “major cost driver in our manufacturing process.”

    In the other solar study, researchers writing in Nature Climate Change this week said concentrating solar power or CSP could supply a large fraction of the power supply in much of the world. The researchers from the Austria-based International Institute for Applied Systems Analysis simulated the construction and operation of CSP systems in four regions around the world taking into account weather, electricity demand and costs. They found that CSP in the Mediterranean region, for example, could provide 70-80% of current electricity demand, at no extra cost compared to gas-fired power plants.