Solar Technology Comparison

There are many solar technologies available today which range from simplest to absurdly complex. This page tries to put some of these technologies into perspective and let you compare them. When you endeavor to capture the energy of the sun, it is best to pick a method that matches your skills, budget, and needs.

First, what are the most common solar energy technologies?

1. Passive solar heating. Typically, this consists of some sort of heat reservoir that has been painted black. Usually this heat reservoir is contained in an insulating space. This approach is often applied in sun rooms, agricultural buildings or green houses.

2. Active solar heating.  This is similar to passive solar heating except that the heat reservoir is manipulated in some sort of active way. The most common form of this technology is the heating of water for domestic hot water usage. Using a fan in a sun room or storing hot water for space heating all are examples of active solar heating.

3. Concentrated Active Solar Heating. This uses some sort of mirror or lens system to concentrate the sun's light on the collecting surface. The surface then stores the heat from the sun with some sort of active system. This system is probably the oldest form of capturing the suns energy on a large scale. The concentration allows for higher temperatures to be achieved which offers higher Carnot efficiencies for mechanical engines. The higher temperatures also allow solar energy to be used in applications that exceed 60 degrees C. This includes hot water space heating, or water purification systems.

4. Photo Voltaic Electricity Generation (One Sun). This uses semiconductor materials to directly convert the energy of light to electrical energy. The "One Sun" refers to the fact that light is not concentrated in this type of application. Flat solar panels are used that are generally pointed in the noon position of the sun. PV technology is likely the most common residential application of solar electricity generation. It is also one of the most expensive methods of solar electricity generation in terms of system cost per watt of power produced. Flat panel, one sun PV systems do not typically track the sun and thus have a fairly simple installation system.

5. Photo Voltaic Electricity Generation (Many Sun). This technology uses semiconductor materials to convert the energy of light into electrical energy but uses mirror or lenses to concentrate the light on the PV panels. This systems can range for low power concentrators that put 10 suns or less on air cooled PV panels, to high power concentrators that put 100s of suns on sophisticad multi-junction PC panels that are actively cooled with water or sodium. High power systems are completely the domain of power generation companies while low power systems may be within the technical ability of some more capable "do it yourselfers". All concentrated systems need to track the sun to some degree. Parabolic trough systems need only track the sun in one dimension since the trough will maintain a focal point for a solar travel along the the longitudinal axis of the trough.

6. Thermal Solar Electricity Generation. This technology is just a special corner of the "concentrated active solar heating" technology mentioned above. Here, a lens or mirror system is used to concentrate the light of the sun on an active solar collection system. The heat collected is then used to generate electricity. The electricity generation can very. Common forms of generation include high temperature steam engines, Stirling engines, semiconductor based thermal electric power generators (Seeback effect). This technology has the advantage that it can potentially supply power for some time after the sun stops shinning. Here the relatively low cost collection and thermal storage is used to power the more expensive generation systems around the clock which offers a theoretical four times utilization improvement over PV technologies.

7. Hybrid Thermal Solar Electricity Generation. This technology is based upon its non-hybrid cousin except that it incorporates "cogeneration" techniques where the unused heat expelled after electrical power generation is then used for domestic hot water heating or space heating. These systems have a high degree of complexity, but are not particularly dangerous. Given the promise of a faster pay off, this technology may be appropriate for skilled "do it yourselfers". This is the type of system I will concentrate on developing in this web site.

8. Indirect Solar Power Generation. This is a tried and true system of power generation where the power can ultimately be traced to the sun, but is directly based upon wind or upon water based gravity systems. Some wind is developed as a result of the rotation of the earth, but most wind strong enough for power generation is the result of uneven solar heating of the earth's surface. Likewise hydroelectric systems are powered by the earth's water cycle, which is in turn driven by solar evaporation. In that sense, wind power and hydro power are forms of solar power. Novel approaches to indirect solar can be experimented with by do it yourselfers as well. So called "solar towers" can be constructed that generate small amounts of electrical power in larger green houses. Evaporative solar towers can also be built to take advantage of the water cycle. Traditional wind based turbines are well within the skills of many DIY experimenters and emerging technologies, like piezo trubulance generators are reasonable DIY experiments. We will explore some of these here as well.

The table that follows is my rather subjective comparison of these technologies from a DIY perspective. The numbers which rate the costs, complexity and payback are simply relative assesments. Many factors will affect actual costs. Thus these figures are subjective guestimates based upon material costs and typical components. I'll try to add references and additional information as time goes by to make this comparison less subjective: