太阳能热水描述了主动式和被动式太阳能技术，这些技术利用自由丰富的太阳热能来加热水以用于所需的应用。
它是最有效的水加热方式之一（就能量/废物而言），因为它不需要能量转换，这与电阻加热或燃料燃烧不同。它是热能从一个地方到另一个地方的简单传递和集中。（参见维基百科：传热。）该技术效率的另一个例子是它运行在太阳能上，太阳能是免费的，并且仅取决于所使用的技术及其成本和效率。换句话说，能源是免费的，只有收集、转换和存储设备会增加系统的成本。话虽如此，太阳能热能的主要缺点是它只能在太阳可见的任何地方/任何时候使用。
如果您曾经感觉到热水从一直暴露在阳光下的花园软管中流出，那么您就体验过太阳能热水的作用。
从本质上讲，太阳能热水系统由太阳能集热器、隔热良好的储存容器和将热量从集热器传输到相对于流体介质的容器的系统组成，在某些情况下，水本身。
应用
由于全球有无数使用家庭、商业和工业热水的应用，因此有机会应用太阳能热技术来加热这些水。
如今，市场正在发生变化，与使用天然气和电力加热水相关的经济和环境成本正受到更高效、成本更低的系统（如太阳能热水系统）的挑战。
后台
太阳能热水并不是一个新现象。直到大约 1920 年代，它才在美国被广泛使用，当时它被可靠的化石燃料系统所取代。
一些人认为热水在适当技术领域的应用很少，主要是发达国家提供的奢侈品。一篇关于该主题的文章[需要验证]表明，“第三世界”需要什么热水可以使用木材等燃料加热，同时加热房屋和水。这种解雇有两个危险：
- 首先，适当的技术旨在减少浪费并提高自然资源的使用效率，而木材确实既能为水又能为家庭供暖，它也是许多贫困国家无法获得的自然资源。而太阳无处不在，无论我们是否使用它，它都会发出能量。第三世界国家的许多妇女和儿童死于因通风不当和烹饪火灾产生的过量烟雾引起的肺部疾病，它实际上往往是艾滋病和饥饿之上的头号杀手。
- 其次，当务之急是在需要热水的地方，有一种方法可以经济高效地在当地资源设定的参数范围内获得热水。这项技术如果得到推广，可能会导致与传统热水方式相关的区域生态足迹规模显着减少。
来自太阳
太阳辐射以每平方米 1366 瓦 (W/m 2 )的速度到达地球上层大气。[1] 地图 A显示了太阳能在不同纬度的变化情况。
在穿过大气层时，6% 的入射太阳辐射（日照）被反射，16% 被吸收，导致赤道处的峰值辐照度为 1,020 W/m²。平均大气条件（云、灰尘、污染物）通过反射进一步减少 20% 的日照，通过吸收进一步减少 3%。大气条件不仅会减少到达地球表面的日照量，还会通过扩散入射光和改变其光谱来影响日照质量。[2]
地图 C显示了根据 1991 年至 1993 年收集的卫星数据计算出的全球平均辐照度。例如，在北美，全年（包括夜间和多云天气）的地面平均日照量在 125 至 375 W/m² 之间（3 至 9 千瓦时/平方米/天）。[3]这表示可用功率，而不是输送功率。目前，光伏板通常会将大约 15% 的入射阳光转化为电能；因此，美国本土的太阳能电池板平均每天提供 19 至 56 W/m² 或 0.45 - 1.35 kWh/m² 的电量。[4]
右侧地图C中的黑色圆盘是陆地区域的一个示例，如果覆盖有 8% 高效的太阳能电池板，将以电力形式产生比 2003 年世界一次能源供应总量略多的能量。[5 ]虽然平均日照和功率可以深入了解太阳能在区域范围内的潜力，但当地相关条件对于特定地点的潜力至关重要。
穿过地球大气层后，太阳的大部分能量都以可见光和红外辐射的形式存在。植物利用太阳能通过光合作用产生化学能。人类经常使用这种能量来燃烧木材或化石燃料，或者只是在吃植物时，想象一下如果我们找到一种方法来利用这种能量而将植物和化石燃料排除在外。
A recent concern is global dimming, an effect of pollution that is allowing less sunlight to reach the Earth's surface. It is intricately linked with pollution particles and global warming, and it is mostly of concern for issues of global climate change, but is also of concern to proponents of solar power because of the existing and potential future decreases in available solar energy. (About 4% less solar energy is available at sea level over the timeframe of 1961–90,) mostly from increased reflection from clouds back into space.[6]
- Note: the Wikipedia content applies to this section only.
Types
Solar hot water systems are designed to transfer the sun's solar energy to water. Finding the most efficient and effective solar hot water system for a given situation can be a challenging task. There are a number of key factors that need to be considered when choosing the most appropriate system configuration. These factors include, to a large extent, amount of solar insolation, climate, construction, installation and materials costs, location and accessibility of the system, amount of water needing heating, frequency of hot water use, availability of electricity, availability of materials, and skill level in construction.
The following classifications of systems are in three groups of two and one group of one unique system. These four main groups are:
- Open loop vs Closed loop.
- Active vs Passive.
- Uses a heat exchanger vs Does not use a heat exchanger.
- Batch system.
Any given system uses one characteristic from each group. For example, a system may be an active, open loop system which does not use a heat exchanger. Or another example, a system may be a passive, closed loop system which does use a heat exchanger. Some systems are much easier to make than others and people with a basic knowledge of tools and construction can easily make a functional system. If one desires to make their own system, this variability in complexity would influence what type of system is chosen.
Cost is another factor and each system configuration comes with a variety of different cost and benefits. The costs of any specific system can vary widely from country to country and region to region. Certain configurations using certain types of equipment are more efficient than others in specific situations. The following information gives an in depth look at these various ways of constructing hot water solar collectors.
Different types of collectors are also shown at the the end of this page as well as examples of different common solar hot water systems.
This page describes the various systems that are being used to heat up water with the sun. For a more general description of solar hot water visit the Solar hot water page.
Simple systems
A very simple solar shower, effective in sunny regions, uses a black bag full of water hung in direct sunlight.
A very simple "system" can be devised by running water through some hose or pipe that is exposed to the sun, and connecting that to a storage vessel in a thermosiphon arrangement. A thermosiphon causes heated water to displace cooler water above it and as long as the heated water can continue upward, it will do so. The pipe/hose cannot have air present as this will halt the movement. There also needs to be a minimum of a ~4ft (1.2m) rise from hose to storage vessel. A loop can set up to circulate water from vessel to hose and back, which continues the heating process. Cool water is drawn from the bottom, circulated through the hose, and returns near the top of the vessel. As long as the siphon is not broken (air present), water can be dipped or drained out of the vessel for use. This is a simple open-loop system, meaning water enters and is removed for use from the system.
Another type can be called a batch heater, since it heats a volume of water using a thermosiphon, but uses a constructed solar collector to absorb the sun energy. Its limitation is that the tank is above the collector, which is on the roof or area exposed to the sun, so the hot water must be piped to the point of use, which costs heat loss. A special Communal solar water heating system has also been proposed using a batch heater.
More sophisticated systems
More sophisticated systems exist, some still employ an open-loop system (by tapping into an existing water heater or some other vessel). A solar collector in the sunlight with a pump and power source operate to either assist or supplant the existing water heating apparatus. The water circulates from the water heater tank to the exposed collector, and back to the tank, and this will continue to recirculate the water and heat it. A photovoltaic-powered low-volume circulating pump can be used in this system, avoiding the need for external electrical power. The more efficient, the larger the collector and the smaller the volume of tank storage, the faster the water will heat. The longer it operates, the hotter the water will become, until heat loss levels off the water temperature. This open-loop system works very well in climates where freezing temperatures are absent or rare. They can work in cooler climates using a system with drains to empty the water from the portion of the system subject to freezing. The drains can be manually operated or automatically thermostatically controlled. This type of system can be widely used to assist or supplant existing conventional water heaters.
Closed-loop systems are best in climates which freeze and reach lower temperatures, but are more sophisticated and therefore more expensive. In the closed-loop system a coolant, usually propylene glycol, is circulated through the collector then to a heat exchanger, where the heat absorbed is transferred from coolant to water. The propylene glycol remains liquid at much lower temperatures and will continue to absorb heat and transfer it to the water. The propylene glycol also remains in the system, hence the "closed-loop" name. The heat exchanger is either external to an existing water heater tank, or replaces the existing tank. A PV-powered low-volume circulating pump can also be used in this system.
These systems and associated technologies are arranged basically in order of cost, sophistication, and energy. The simple systems are certainly "appropriate technologies" and could be used with minimal investment, and with guidance, can be used by practically any culture, regardless of perceived sophistication. The open-loop systems can be used in developing societies in original construction or retrofitted, and as with the simple systems, the types of installation can greatly reduce energy costs, GHG, and allow greater focus on other needs. The closed-loop systems are more expensive, therefore more restricted to wealthier cultures, but their benefits are similar to the others. Based on per capita energy use, the more expensive systems can probably reduce more fossil fuel use than the others.
Modern mass-produced evacuated tubesW collect heat even below freezing. The tubes themselves are best suited for mass-production, but the rest of the system is more flexible in its manufacture. Evacuated tubes use a vacuum sealed space to separate the collector tube from the outside elements. When solar radiation is absorbed by these collectors and converted to heat, the vacuum barrier prevents most of this energy from escaping. Essentially, this method operates in a similar manner to a thermos.
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The ability to contain captured solar radiation while preventing loss to the outside environment is what allows evacuated tube systems to continually heat water, even if the temperature outside of the system is frigid.
Solar hot water pools
Energy derived from the sun drives and sustains life on earth. So why can't it heat your pool?
Swimming pools... your skin tingles in anticipation of diving in clear cool water on those ridiculously-roastingly hot summer days. This precise moment of contact makes all the hassle of cleaning and caring for your pool worth it, does it not? Now if only the scorching days lingered longer so you could laze a bit more in your backyard tropical-wannabe paradise. Alas, the seasons don't listen to you, and inevitably fall, winter and spring attack your precious pool, chilling it to its tiled bones, making it completely unusable to you. Much of the year your pool sits, unused and unloved, like a dog eagerly awaiting the return of its owner, like a dormant daffodil bulb waiting for the snow melt, like a ... Just as surely as we weren't sent here to Earth to suffer, surely we can all get what we want. And if for you that includes a heated pool without the financial and environmental expenses of fossil fuels, then welcome to the wide world of solar hot water systems.
Related projects
![[4]](#cite_note-us_pv_annual_may2004.jpg-4){kind=link}
References
- ↑ Solar Spectra: Standard Air Mass Zero NREL Renewable Resource Data Center
- ↑ Earth Radiation Budget NASA Langley Research Center
- ↑ Solar Maps NREL: Dynamic Maps, GIS Data, and Analysis Tools
- ↑ us_pv_annual_may2004.jpg National Renewable Energy Laboratory, US
- ↑ Homepage International Energy Agency
- ↑ Liepert, B. G. (2002-05-02) Observed Reductions in Surface Solar Radiation in the United States and Worldwide from 1961 to 1990 GEOPHYSICAL RESEARCH LETTERS, VOL. 29, NO. 10, 1421
See also
- Green tuning of space heating systems: besides heating water for using it as is, it can also be used for circulating it through radiators, in affect making a space heating system (see also: Heat pump system#Fitting a heat pump system to a house in practice)
- DIY solar thermal collectors
External links
Full Text Thesis
- Experimental Analysis of an Indirect Solar Assisted Heat Pump for Domestic Water Heating by BRIDGEMAN, A.G.
- Evaluation of a Stratified Multi-tank Thermal Storage for Solar Heating Applications by Cruickshank, C.
- Central Solar Heating Plants with Seasonal Storage for Residential Applications in Canada: A Case Study of the Drake Landing Solar Community by Wamboldt, J.