Types of Solar Power

From the dawn of mankind, the sun has served as both a religious and psychological symbol of strength, energy and almost everything labeled good by the multi-cultural populations that have lived their lives under its rays.

Over the past three decades, researchers discovered that translating the laws of physics into practical solar applications often turned out to be as challenging a task as the original task of discovering those same laws.

The pace of research and development in the area of solar energy, slow compared to the current energy needs of the global population, need not necessarily cast an umbrella's shadow, let alone rain on the renewable energy parade.

From an optimistic perspective, the promise of solar power technology deal with two very simple sun observations that a sunny day walk confirms. The sun provides both heat and light.

Photovoltaics (PV) technology explains solar power's popularity on a micro scale. In addition to the solar roof top systems, photovoltaic products powering gadgets from calculators to tablets, continue to attract consumer attention.

For organizing purposes, todays three part PV market consists crystalline panel, thin-film and solar concentrator PV firms.

The crystalline and thin-film firms produce the familiar looking flat panels for the smaller scale residential and industrial sectors of society. Solar Concentrators produce large scale PV products intended for commercial electricity production.

PV conversion levels, or the amount of sun a PV product can convert into energy, continue to incrementally increase. Recent efficiency statistics for products on the market show that crystalline solar panels (single crystal and multiple crystal PV) exceed the efficiency levels for the thin-film photovoltaic technologies, which use non-crystallized silicon, in conjunction with an addition substance(s).

Solar Concentrator systems, which use a light gathering object, such as a mirror, to collect a large amounts of sunlight and redirect it at a PV cell or module, do increase PV efficiency.

However, the most recent efficiency statistics for concentrator PV cell/modules on the market is 34 percent. The efficiency rating coupled with the cost of constructing a large scale concentrator project, partially explains their relatively small portion of the PV market.

A recent NREL report, Concentrating Photovoltaic Power Industry documents technologies that produce PV modules with a 40% efficiency rate. In an era where utility scale, 300-400 megawatt concentrated solar thermal power plants are becoming common place, concentrated photovoltaic (CPV) proponents still seek their first 100 megawatts of commercial construction.

What's the CPV hold up?

While CPV technology harnesses the power of the sun directly onto compact, electricity producing photovoltaic materials, thereby reducing the need for expensive silicon, land and water use requirements of their concentrated solar thermal rivals (even taking solar thermal dry cool technologies into account), the CPV industry is still fraught with new industry growing pains.

To date, only a few scattered, small scale CPV demonstration projects are on the books, and thus far, small scale production has translated into higher production costs.

Absent a successful large scale operational track record, investments for large scale material production are still considered high risk, mostly because of questions regarding the reliability of the the triple junction solar cells.

The use of triple junction cells for CPV also introduces an efficiency conundrum. While the current triple junction cells can reach a record 40% efficiency level, they are only one portion of the CPV efficiency equation.

The efficiency of the surrounding concentrators, often called optical efficiencies, (currently at the 85% - 90% mark) reduces the benchmark efficiency level.

System inefficiencies from electricity generation to electricity use, via the electricity transmission system, further reduce system efficiency levels to the 25% range.

Taken together, CPV hardware costs plus CPV efficiency levels translate into a product with double the costs of concentrated solar thermal projects.

A recent National Renewable Energy Laboratory (NREL) publication, Opportunities and Challenges for Development of a Mature Concentrating Photovoltaic Power Industry presents some high-concentration CPV industry goal metrics for 2015:

• $/W installed cost=<$2
• System reliability=20 years
• Commercial system efficiency=29% to 36%

Despite its current drawbacks, projected future technology improvements along with the situational advantages offered by CPV, make it a utility scale solar technology of the future.

The NREL report expands the definition of CPV to include medium concentration systems (typically 10X to 20X concentration) and low concentration systems (2X to 3X enhanced PV modules).

With a bit of human ingenuity, these lower concentration technologies could translate into the creation of simple enhancing covers that double or triple today's roof top installations, thereby giving a big boost to both utility scale and distributed CPV.

Solar thermal technologies, those that use the sun's heat as an energy source, currently out compete CPV technologies for utility scale electricity projects.

A quick historical review finds that water heating dominates the short history of solar thermal technologies. Recent statistics from the Energy Information Agency (EIA) highlight the market importance of low and medium temperature collectors used for either heating swimming pools or residential water heaters.

These solar thermal systems typically consist of a solar collector, which gathers the sun's heat and transfers it to water passing thought the plumbing system on its way to a storage container.

Solar water heating systems save money by reducing the electricity costs associated with traditional water heating.

The latest generation of solar thermal technology, concentrated solar power, used for the large scale production of electricity, offers the promise of even larger scale environmental benefits.

In its simplest form, a concentrated solar power plant consists of solar collectors (mirrors or parabolic dishes), that collect heat to transform water to steam, which in turn provides force to move electricity generating turbines.

Environmental benefits include cleaner emissions from steam generated electricity compared to emissions from fossil fueled generated electricity plants.

Storage and use of solar power after the sun sets continues to interest the solar community. Molten salt storage technology enables solar plants to operate on either a twenty-four hour/day basis or as reliable peak electricity providers.

Excessive water use to generate steam for turbines also raises concerns for plants planned in the water scarce desert southwest, leading to both dry cooling and wet cooling technologies.

© 2001-2012 Patricia A. Michaels.