Solar Water Heaters Types

Active indirect solar water heating system
Image credit: www.southface.org

Solar water heaters are also known as solar domestic hot water systems or residential solar water heaters. There are different types of solar water heaters and the choice depends on the temperature required and the climate.

Basically, solar water heaters can be either active or passive. Active systems use electric pumps, controls, and other such equipment to circulate water or heat-transfer fluids through the collectors. They also require electric power to activate pumps and/or controls.

Passive solar water heating systems require no moving parts and rely on thermodynamics rather than electric power to circulate the household water or a heat-transfer fluid through the system. Passive solar water heaters are the simplest solar water heating systems and they are also called bread box or batch heaters. These systems are most common in regions that do not experience extensive periods of below freezing temperatures.

Active solar water heaters can be further characterized as direct (open loop) or indirect (closed loop) systems. These terms explain the way the water is heated. With direct heating system household water from the storage tank is circulated through the solar collector, heated by the sun and returned to the storage tank. Direct active systems use pumps to circulate household water through the collectors. Direct solar thermal systems work best in warmer climates where the system is less prone to freezing.

Indirect systems use a heat-transfer fluid (usually a glycol-water antifreeze mixture) to collect heat and a heat exchanger to transfer the heat to household water. Indirect active systems also use pumps to circulate heat-transfer fluid through the collectors. Heat exchangers transfer the heat from the fluid to the household water stored in the tanks. Indirect systems are popular in areas subject to extended freezing temperatures because they offer good freeze protection.

Direct systems are more efficient that indirect ones but they require more maintenance to keep the pipes clear of mineral deposits.

China's Solar-Powered City Rizhao

Since I found this information interesting and inspiring I decided to publish one more post about China and solar energy, this time featuring China's solar-powered city Rizhao. China has a major problem with pollution, largely as a result of the country's rapid industrial growth and a large increase in energy consumption, which is primarily provided by coal power plants. So, I think that projects and strategies like this one in Rizhao deserve admiration and popularization.

Rizhao is a "small" coastal Chinese city of nearly three million, located at the southern end of Shandong Peninsula and bordering on the Yellow Sea. It is a rising seaport and tourist city, with golden beaches, mild climate and lots of sunshine - Rizhao receives an average of 270 days of sunlight every year. Recently, Rizhao has gained much popularity because of using sun's light and heat to provide energy, thus limiting the city’s carbon emissions and urban pollution. By using the simple, cheap solar devices that sit on the almost all of Rizhao's rooftops, the city has cut its yearly carbon dioxide emissions by about 53,000 tons. The features of a coastal city with “large green space, gardenable, open and ecological” are also obvious. The public green space per capita is up to 16 m3.

In Rizhao City, which means "City of Sunshine" in Chinese, an incredible 99% of households in the central districts and more than 30% do so in the outlying villages use solar water heaters. Also, six thousand houses have solar cooking facilities and 60,000 greenhouses are heated by solar panels, reducing overhead costs for farmers in nearby areas. Almost all traffic lights, street lamps and park illuminations are powered by photovoltaic solar cells. In total, the city has over a half-million square meters of solar water heating panels, the equivalent of about 0.5 megawatts of electric water heaters.

Rizhao Municipality has made great efforts to build Rizhao into a modern coastal Ecocity. Mayor Li Zhaoqian explained: "It is not realistic to subsidize end users as we don't have sufficient financial capacity." Instead, the provincial government heavily invested in the local solar panel industries to achieve technological breakthroughs, which increased efficiency and lowered the unit cost.

Since 2001, Rizhao City officials have been educating people and implementing building regulations to promote the use of solar panels. A combination of investment in the industry, regulations and public education spurred the broad adoption of solar heaters. The city mandates all new buildings to incorporate solar panels, and it oversees the construction process to ensure proper installation. To raise awareness, the city also ran public advertising on television and held open seminars.

Rizhao has been granted many honorable titles, such as National Model City of Environmental Protection, China’s Outstanding Tourism City, Environmentally-friendly National Model City, and National Garden City.

Sources: Renewable Energy World, Worldwatch Institute

China - a World Leader in the Solar Water Heating Market

A roof-mounted solar water heater
Photo credit: www.bcsea.org

China is by far the world's largest producer and consumer of solar water heaters. A basic models of solar water heaters in China are very cheap, starting at around 1,500 yuan (US$190). By 2006, the cumulative installed area of water heating collectors in China hit 100 million square meters, and that is roughly 80 percent of the global solar thermal capacity installed worldwide. But this number corresponds only to 78 sqm of collector surface installed for every 1000 inhabitants, which implies a large margin of market potential. So, although China is the biggest solar thermal producer and market in the world, per capita installations of solar hot water systems are still quite low compared to countries like Israel, Greece, Cyprus, Germany and many others.

More than 30 million Chinese households now have one solar water heater installed, and the popularity is due to the efficient evacuated tubes which allow the heaters to function even under cloudy or smog-choked skies and at temperatures well below freezing. The evacuated tube technology was initially developed by Qing Hua University in Beijing in the early eighties, with pilot manufacturing in 1985.

A report from the China's top planning authority predicted that by 2010, the coverage of solar water heating systems in operation in China will reach 150 million square meters. It is also estimated, that by utilizing solar energy, China can save more than 50 million tons of coal in 2010.

"Green Olympics" - Beijing 2008

Beijing National Stadium - 'Bird's Nest'
Photo credit: Guo Lei/Xinhua

The 2008 Summer Olympics in China are in their apogee and they are drawing a lot of attention. Taking into account a massive global audience, the Beijing Olympic organizers are hoping to focus our attention to climate changes and popularize the idea of using eco-friendly technologies. The "Green Olympics" may help change peoples attitudes and set standards for future building projects in China and around the world.

The Olympic organizers are trying to make the Olympic Games environmentally friendly and Beijing a model city for using green technologies, zero net emissions and sustainable architecture. As a part of these efforts, more than a quarter of the energy used at Olympic venues is coming from renewable sources.

Beijing's Olympic Village is a great example of sustainable community development. All seven main Olympic stadiums are equipped with solar generators capable of outputting 480 kilowatts of energy at any given moment. The entire hot-water supply for the Olympic Village will be powered by solar energy. Photovoltaic panels are incorporated on the stadium walls and roofs for most of the outdoor lighting. Also, the main stadiums will receive power from Beijing's first wind farm.

Beijing National Stadium - 'Bird's Nest' includes a rainwater collection arrangement, a natural ventilation system and its upper surface is clad with Ethylene Tetrafluoroethylene (ETFE) roof panels, that let in natural light. The stadium is referred to as the ‘Bird’s Nest’ because of its saddle-shaped steel roof and interwoven façade

The spectacular-looking structure called "Water Cube" looks like a building made of bubble-wrap. It is officially known as the National Aquatics Center and is completely surrounded with ETFE pillows. It is expected to cut energy use by 30 percent and has been built so that after the Olympic Games to be converted easily to a shopping area and leisure center.

The idea for the Beijing's "Green Olympics" makes perfect sense because China sees its energy costs rising and energy sources dwindling, as well as significant damage to the environment. And the so-called "Green Olympics", although will not solve China's environmental issues, they could point the way to a more sustainable future, according to officials and experts.

China is already a world leader in many renewable energy technologies, but so far many of the green technologies have been for export only, because they are too expensive for the country to use itself. China, for example, led the world in manufacturing and utilisation of solar water heaters and energy efficient light bulbs. It is also on the way to becoming the world leader in wind turbine manufacturing and installation.

Going Green with a Solar Water Heater

Utilizing energy of the sun to heat water is one of the oldest forms of solar technology available. The first commercial solar hot water heater was patented by Baltimore inventor Clarence Kemp in 1891 (he called his solar water heater the Climax), and since then improvements in performance, design, and level of complexity have made solar water heaters the perfect choice for homeowners looking to go green and create more sustainable home.

There are several different types solar water heaters, including those with pumps and those that work passively. Basically, solar water heating systems have two main parts: a hot water storage tank and some type of collector that absorbs solar energy. The most modern solar water heaters mount flush with a home's roof and resemble skylights. Geographic location, collector orientation, and collector size will determine how much energy can be provided for domestic hot water heating.

On an average single-family residence, there will typically be one or two solar collector panels on the roof. Some homeowners use the solar water heating system exclusively (sometimes with a gas or electric tankless water heater as a backup energy source), while others pair them with other systems as pre-heaters.

Solar water heating systems cost depends on a number of factors, such as the size of the system and the particular system manufacturer, the number of people in the household, the current hot water usage, the type of roof it is going to sit on, trees causing shadows, etc. The typical solar heating system costs in the range of $2,000 - $6,000. Any solar rebates and other incentives available in your area will reduce the total cost. You can find more detailed information about it at www.dsireusa.org (for USA customers).

Using solar energy to meet part or all of your home's domestic hot water needs have a good economic payoff and can be a valuable and cost effective option to invest. When correctly installed, a solar hot water system can reduce your water-heating bills 50-80%, depending upon water consumption. With a solar water heating system, you'll get the hot water your household needs, save electricity which means saving money, reduce your dependence on coal-fired power and benefit the environment. Saving electricity means reducing emissions created by burning fossil fuels and water consumption at power stations, thus taking steps to save the environment. When a water heating system is combined with an electric water heater, pollutant emissions are reduced by about 2,800 pounds per year. A solar system replacing natural gas will reduce pollution by 1,200 to 1,600 pounds annually.

Solar water heaters pay for themselves in four to eight years and should function for 20+ years.