Many Types Of Solar
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Solar energy is one form of renewable energy available to most home and building owners.  New structures and devices designed to use solar energy are usually designed and built to be much more "energy efficient" from the get-go. They often include strategies to store solar energy, because of the noncontinuous and intermittent availability of sunshine, especially in the Midwest USA.  Structures and devices which are remodeled to use solar energy are typically "retrofitted" to upgrade energy-efficiency substantially.

There are 2 major categories of solar energy, passive and active, which can be further divided into applications as follows:

PASSIVE (no mechanical parts, works by shape, orientation and design) 
- Winter heating & summer shading 
- Daylighting
- Solar Cooking
- Solar Drying & Ventilation
- Water heating
- Photovoltaics (electricity generated from light, mounted stationary)

ACTIVE (collectors, blowers, pumps, heat exchangers & controls) 
- Winter heating 
- Solar Cooking
- Solar Drying & Ventilation
- Water heating
- Photovoltaics (mounting structure follows the sun’s path)
- High-temperature solar electric
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In passive solar, solar heat and light are collected and delivered with little or no hardware.  Instead, a passive solar floorplan, its building geometry and its envelope materials do all the work of collecting, storing, retaining and distributing the solar energy.

In passive daylighting, optimally positioned windows and roof apertures admit daylight without movement.  In a passive solar electric device or structure, solar electric components are integrated into intentionally oriented exterior surfaces such that they collect solar energy automatically, without movement to track or reflect the sun.  A passive solar water heater not only is positioned to capture the sun's rays without movement, but it is also positioned relative to the water heater or other storage tank such that hot water rises, or thermosyphons, up into the tank, instead of relying on a pump.  Most such passive solar structures and devices are designed from day one to perform this way, but some are remodeled to incorporate their passive solar features later. Sometimes this is called "integrated" solar.  Integrated solar electric systems in a building are sometimes called "building integrated photovoltaics" or BIPVs.

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Although some passive solar homes appear very unconventional compared with traditional housing, passive solar features and various levels of passive solar design can be incorporated into homes which appear fairly traditional.  A passive solar home design starts by admitting sunbeams in winter, but keeping out those sunbeams in summer.  This is accomplished not just by windows, but by optimizing exterior and interior building geometries.  Most glass faces south. Windows are few and small in other directions, especially east and west.  They are carefully placed for daylight and natural ventilation.  Floorplans are usually as open as possible to allow daylight and solar heat to permeate throughout the main living spaces.  Materials in some inside walls and floors store heat from the sunny times until later when there's no sun.  Special glass may be used to minimize UV sunlight or to fine-tune solar heat transmission. Overhangs, baffles and summer shading strategies are common to prevent summer overheating and sunglare. 
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Another form of passive solar heating is solar cooking.  A solar oven has a specific solar collection and insulation design which permits it to heat to temperatures as high as 300-400F when optimally positioned in full sun.  Like a passive solar home or building, there are no moving parts, although they are usually designed for portability.  However, the solar oven must be properly aimed to achieve its high temperatures.  This is commonly done during initial setup.  Sometimes an operator must reposition the oven's solar face if cooking duration is longer than a couple hours, so a solar oven can also be considered "active solar."
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The term "active solar" is used when hardware collects, converts and delivers the solar energy from where it's collected to where it's used or stored.  Solar collectors on roofs or other south-facing surfaces heat water or air, or even generate electricity.  Active solar systems can be incorporated into most new and existing structures.  Active solar systems typically require some periodic inspection and maintenance. 
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A solar water heating system can significantly lower water-heater energy bills, especially when the water heater is electric and hot water usage is high. Besides one or more collectors outside, a system includes a heat exchanger, usually 1 or 2 pumps, some controls and gauges, and a well insulated storage tank.  For small systems, this storage tank can sometimes be the water heater, since it is usually needed to supplement the solar heat.  One pump usually moves antifreeze from the heat exchanger to and from collector.  Another circulates water from the tank through the heat exchanger and back to the tank after it's heated.  All the pipes should be insulated.

An active solar water heating system can also be used to heat a swimming pool so that it is useful earlier in the spring and later in the fall than normal.  In most northern climates, there's usually enough sun in spring, summer and fall that a backup heater is not needed for 3-season pool use.  A solar pool heater for 3-season use may not need heat exchangers or antifreeze.  It is possible to have a single system to heat domestic water and the pool or spa.

Solar electricity, called "photovoltaics" or PV, also relies on collectors.  PVs produce about 10 watts per square foot in full sun, starting out as DC voltage. More power is produced the longer and more directly the panels are exposed to the sun.  PVs are usually very expensive in the short-term compared with utility electricity.  However, PVs can be cheaper, even sometimes in first-cost, when locations are far enough from power lines that there are major costs to extend utility lines.  After initial purchase, PV electricity costs almost nothing, except occasional battery replacement.  PV panels can last 40 or more years.

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All but the smallest and grid-intertied PV systems may have as many batteries as collectors.  There are many other specialized accessories, including a charge controller to protect batteries from overcharging, an inverter to convert DC power to AC, fuses and disconnects to protect people and devices as with utility electricity systems, amp and volt gauges, and special synchronizing equipment if the system is grid-intertied (or tied to the electric utility's power system).

Finally, when considering all the various solar design and technology options, unless cost-effectiveness is not important, it’s advisable to value and implement the simplest and cheapest kinds of solar energy first, like daylighting and outdoor clothes drying before solar electric-powered lights and dryers. Applying the simplest, least-cost and most energy-conserving solutions typically results in much lower costs for our energy supplies.

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John F Robbins, CEM / CSDP 
859.363.0376
john@johnfrobbins.com
www.johnfrobbins.com
3519 Moffett Rd
Morning View, KY USA
41063-8748

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