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non-pv solar technology

a briefing document

New translation, the Magna Carta

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Non-pv (photovoltaic) solar technology is one of a series of briefing documents on the problems of power consumption, posed by the steady depletion of fossil fuels and most particularly of pumpable oil.
One of a grouping of documents on global concerns at abelard.org.
on energy on global warming
sustainable futures briefing documents

On housing and making living systems ecological

Tectonics: tectonic plates - floating on the surface of a cauldron

passive solar design principles
the trombe wall
purpose-built passive solar systems
commercial solar collector systems
nevada solar one
and another type of solar collector
tower power
round-up of solar thermal generation - the desert’s the place, any desert
site map

advertising disclaimer


The sun sends out heat and light towards the Earth, energy that can be collected passively and directly, and then either transformed into electrical energy or used directly as heat.

Solar collectors may be small, one-house installations, like the Sun Lizard system or the Warm Wall, or much larger commercial plants.

passive solar design principles - invincy

Using the sun's rays to heat a house.

    1. Windows south-facing in northern hemisphere, north-facing in southern hemisphere.
    2. Shade to block summer sun, with wider shading for hotter climates.
    3. Thermal mass for temperature regulation (best provided by dense materials: stone, brick, plaster,wood, concrete).
    4. Insulation.


For a warm house with minimal outlay on fuel, try the following passive solar design principles.

  • Build most windows to face south (for northern hemisphere), or north (for southern hemisphere)
  • Shade windows externally, either with adjustable shutters, or with fixed eaves or awning.
    This enables shading from the high summer sun, while allowing entry of the lower winter sun. Without shading, the house can become uncomfortably hot, and encourage expenditure on cooling.
  • Build in thermal mass to absorb excess heat, and release it during the night. The lower the thermal mass, the greater the temperature difference between night and day.

Reasons for failure of passive solar principles for heating

    • The sunny part of the house can overheat, because heat is concentrated there;
    • working in direct sunlight can be difficult
    • lack of south-facing windows in an existing house, or windows shaded by neighbouring trees or buildings.


  • Prevent the heat entering in the first place. The best way is to use external shades or shutters, so preventing direct sunlight reaching windows.
  • Heat rises, so a stack ventilation system (a bit like a tall chimney) will enable cool air be drawn through the building. A ventilation tower is part of traditional North African building design.

the trombe wall - xavier

Winter heating and summer cooling with a Trombe wall. A Trombe wall is a multi-layered construction, made up of a thick, solid masonry wall - from 8 to 16 inches/10 to 20 cm thick, with an air space of ¾ to 6 inches, and glazing. The assembly is regulated using vents through the wall at top and bottom, going into the building. The result is a large solar, thermal collector.

The arrangement works to heat the house in winter, and cool it in summer. The glazing enhances the simple passive solar heating described just above, so the wall becomes a large radiator in winter. In summer, the system allows air to be drawn out from the building, creating a cooling draft.

    1. Thick masonry wall, with exterior painted black.
    2. Shade to shield from high summer sun, with wider shading for hotter climates.
    3. Glazing, with space between glass and wall.
    4. Vents with dampers.

National Renewable Energy Laboratory Visitor's Center has Trombe walls.During summer, cooler air enters the building, replacing the hot air that escapes from the outer upper vent. If there is a window or door open at the other end of the room (or building), then a cooling air current can be created in the room/building.

During winter, cool air is drawn out of the room through the lower vent. The air is warmed, then re-enters the room through the inner upper vent. The blackened, thick wall also acts as a large thermal radiator. Because the wall holds heat, it also acts as a storage heater, taking in heat during the day, and radiating it into the building at night.

Left: National Renewable Energy Laboratory Visitor’s Center has V-shaped Trombe walls. One side of each ‘V’ is glazed, lighting the interior, the other side is black-painted concrete faced with glass, with a small air space.

purpose-built passive solar systems - invincy

Some systems have been designed to absorb the sun’s energy in the form of heat, but without the disadvantages described above in the reasons for failure.

SolarDuct shows a roof-installed example, and a wall example is described at SolarWall. These installations are also known as Active Passive solar heating systems (although the Sun Lizard may be classified as Passive Solar, as no external energy source is required to run the system). Tags helpful for further researches include 'transpired solar collectors', 'solar air heating', 'thermal wall'.

A passive solar system
Heat is collected from the sun using, for instance, a large, shallow glazed box, painted black on the interior and installed on the roof. The air heated inside the box is then transferred to the building interior. With the Sun Lizard system, a electric fan moves the hot air through insulated ducting to a low point in the room to be heated. This system incorporates a photovoltaic panel to drive the fan, which enables further self-sufficiency. However, photovoltaic panels are expensive and energy intensive to manufacture, and they are only able to convert a small proportion of the sun’s energy to electricity (typically 5-15%).

The panel for the Sun Lizard system has a maximum power output of 30W, of course, this is less when the sun is low in the sky, or it is cloudy.

Heated air is driven from the collector on the roof to a vent near floor level. This is the best position to release the warm air. Warm air rises up to the ceiling, heating much more of the room than if released at ceiling height. This does mean that longer ducting is needed, though as short as apossible to minimise spurious heat loss during transit. The ducting also needs insulating to conserve the collected heat; for aesthetics, the duct probably should be concealed.

Because an Active Passive Solar system like Sun Lizard is a closed loop system, the air that is heated in the ‘black box’ on the roof is sourced from inside the room being heated (or a connecting room).click to return to index on fossil fuel 

commercial solar collector systems - xavier

These are large systems, based on directed mirrors that rely on boiling materials to drive generators. Unlike PV systems, these systems are not scalable for domestic use. There are some cheap devices for focusing the sun to cook food and boil water in remote or poor regions. These solar concentrator systems are currently [2007] about half the price of the equivalent power-rated photovoltaic system, but PV is expected to close (and more) this gap fairly rapidly.

A 64-megawatt, 400-acre, solar concentrator plant is being built near Boulder City, Nevada by Spanish company, Acciona:

“The 64-MW Nevada Solar One will generate up to 134 million kW hours of electricity per year.”

An aerial view of Nevada Solar One - 300 acres and 760 mirror arrays. Image courtsey of ACCIONA
An aerial view of Nevada Solar One - 300 acres and 760 mirror arrays. Image courtesy of ACCIONA

“ [...] roughly 184,000 mirrors installed at Nevada Solar One, a solar thermal plant that will go live next month in Boulder City, Nev. The mirrors direct sunlight on an oil-filled tube. The oil is then used to create steam, which turns a turbine.”

Length of parabolic mirror with oil-filled tube (purple in sun ray diagram). Photo credit: Michael Kanellos/CNET News.com
Length of parabolic mirror with oil-filled tube (purple in sun ray diagram).
In this photo the mirror is facing the ground for inspection, and is reflecting the ground and people.
photo credit: Michael Kanellos/CNET News.com

marker at abelard.org

A world map showing where solar thermal plants would work best.  Credit: Solar Millennium
A world map showing where solar thermal plants would work best. Credit: Solar Millennium

“Acciona Energy is the largest wind developer in the world with a portfolio of more than 4,500 megawatts installed in 169 wind farms in 10 countries. In solar energy, the company’s Nevada Solar One project represents the largest solar thermal electric power plant (64 MW) built in the world in the last 16 years, in addition to the company’s 29 MW installations of photovoltaic power and a 46 MW photovoltaic solar plant under development in Portugal. In the area of biomass, Acciona maintains three biomass plants (33 MW) and small hydro power plants (59 MW). In biofuels, the company produces biodiesel from vegetable oils and bioethanol from surplus wine.

“Acciona is one of the premier international corporations working in the development and management of infrastructure services and renewable energy sources, employing more than 38,000 people worldwide. Acciona is listed on the IBEX-35 in Spain with a market capitalization of approximately $17.27 billion.”

marker at abelard.org

and another type of solar collector

“Solar thermal gets less attention than its sexier cousin -- high-tech photovoltaics -- but has two big advantages. First, it is much cheaper than PV. Second, it captures energy in a form that is much easier to store -- heat -- typically with mirrored surfaces that concentrate sunlight onto a receiver that heats a liquid (which is then used to make steam to drive a turbine).”

The Solucar Tower, the collecting point for the sun's energy reflected from mirrors.
Solar thermal collector - the Solúcar Tower.
below: the concentrating mirrors around the the Solúcar Tower.

marker at abelard.org marker at abelard.org marker at abelard.org

tower power

A more speculative project is the Solar Tower, first publicised in 2003, but a full-size tower has yet to be built. By the end of 2007, EnviroMission Ltd had failed to receive a $A57 million grant from the Australia government and failed to complete a merger with a US concern. The most probable future for the Solar Tower appears to be:

“the first solar tower may well be built in China. EnviroMission's joint venture with a Chinese development and construction company is close to receiving approval to build a kilometer-high solar tower outside Shanghai [...]”. [Quoted from green wombat]

marker at abelard.org

tower power [first reported in January 2003]

EnviroMission Limited intended to build one-kilometre-tall towers in New South Wales as part of a large-scale solar-thermal generator system. Each tower would produce 200 megawatts of electricity, enough to supply 200,000 households and estimated to cost $A800 million.

round-up of solar thermal generation - the desert’s the place, any desert

“But solar thermal’s time may now have come — and mirrored arrays of solar thermal power plants may soon bloom in many of the world’s deserts.”click to return to index on  non-pv solar technology briefing document

Related further documents
On energy
1 Replacing fossil fuels—the scale of the problem
2 Nuclear power - is nuclear power really really dangerous?
3 Replacements for fossil fuels—what can be done about it?
3a Biofuels   3b Photovoltaics (solar cells)
3c Non-pv (photovoltaic) solar technology
3d Tar sands and shale oil    3e Wind power
5 Energy economics—how long do we have?
6 Ionising radiation and health—risk analysis
7 Transportable fuels    7a Fuel cells
8 Distributed energy systems and micro-generation
8a Geothermal systems and heat exchangers
8b Combined energy systems   
8c Energy storage
9 Fossil fuel disasters   
Fossil fuels are a dirty business
11Books on energy replacements with reviews

On global warming
4 Global warming
4a Anthropogenic global warming, and ocean acidity
4b Energy pricing and greenwash
4c How atmospheric chemistry and physics effects global warming
4d Antarctica melting ice, sea levels, water and weather implications
4e Gathering data to test global warming
4f Arctic melting ice, sea levels
4g Shifting global and local weather patterns
4h Dendroclimatology

On housing and making living systems ecological

Tectonics: tectonic plates - floating on the surface of a cauldron

sustainable futures briefing documents

email abelard email email_abelard [at] abelard.org

© abelard, 2007, 27 december

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the address for this document is https://www.abelard.org/briefings/non-pv_solar_technology.php

1290 words
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