I got acquainted with solar energy systems in the mid-1970s when the first Arab oil embargo led many people to start looking to the sun as a source of free energy (as the slogan went, "Four billion years without a shortage."). I participated in the development of the solar energy industry in California over the next decade, first directing the state's landmark solar-industry commercialization programs, then as a private sector participant, marketing, selling and installing solar systems for water, space and pool heating. The current upsurge of interest in solar energy systems is the first in 20 years. The domestic solar thermal industry collapsed in the mid-1980s, the victim of falling oil prices, low natural gas prices and the expiration of federal and state tax credits first enacted in the 1970s.
During the period 1975-1985, solar thermal technologies were thoroughly explored. In California I estimate that more than 250,000 solar water heating systems were installed for homes, apartments and factories, along with tens of thousands of pool heating systems (one part of the industry that never collapsed) and thousands of solar home heating systems. In almost all cases, conventional heating systems were used as backups during winter and periods of low sunshine and cloudiness. In fact solar thermal technology has been used in some form for more than 100 years in the US and elsewhere.138
The federal Energy Policy Act of 2005 gave new impetus to the solar thermal industry, providing (currently through the end of 2008) federal tax credits of 30% for residential and commercial solar water heating and space heating systems. In most parts of the US, solar water heating systems can easily supply 50% or more of annual requirements for a family home, apartment house or business.
During this past decade of growth in green building, I have wondered why more explicitly sustainable projects don't use solar thermal systems. They work quite well, there are plenty of local suppliers, the economic benefits are reasonable (with federal tax credits, along with many state incentives, you get typically a 10% or better annual return on investment), and they represent a visible symbol of commitment to renewables that most people can readily identify. Perhaps the reason is that architects and engineers doing commercial work are simply unfamiliar with them and reluctant to experiment.
From the standpoint of basic physics, using a very low-intensity energy source such as solar is intuitively appealing. With a single-glazed, metal-finned collector, the sun can easily heat water to 160°F, more than enough for a typical water heater (usually set about 125°F to 135°F), and protecting the collector against freezing is not difficult in most climates. Many of you may have used an elevated black-plastic water bag as a way to have a hot shower while camping. The technology is that simple. Many parts of the world that have to rely on diesel or heating oil (or even wood) for water heating have used solar water heating for decades, including a good part of the Mediterranean and Australia. On a trip to Greece a couple of years ago, I saw many solar water heaters atop apartment buildings in Athens, a testament to the basic utility of this technology.
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Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.