A

WRITE-UP

On

CONVERSION OF SOLAR ENERGY FOR USE IN BUILDINGS

By

RAUFU.T.OMOTOLA

(ARC/05/5643)

M.TECH.1

SUBMITTED TO

THE DEPARTMENT OF ARCHITECTURE,

FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE.

ONDO STATE, NIGERIA.

AUGUST, 2011

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ABSTRACT

Conversion of Solar Energy for use in Buildings presents basic information on solar

building design, which includes passive solar heating, ventilation air heating, solar domestic

water heating. The article suggests ways to incorporate solar design into multi-unit residential

buildings, and provides calculations and examples to show how early design decisions can

increase the useable solar energy.

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1.0 INTRODUCTION

This Introduction to Solar Design Issues presents basic notions of solar design and

describes different passive, active and hybrid systems and the solar aspects of design elements,

which include window design, cooling and control, and water heating. Upon reading this article,

the reader will understand:

1. The benefits of solar energy in building design.

2. The difference between passive, active and hybrid solar technologies.

3. The design opportunities available for multi-unit residential buildings

1.1 SOLAR ENERGY

Solar energy: Radiant light and heat from the sun, has been harnessed by humans

since ancient times using a range of ever-evolving technologies. Solar radiation, along with

secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass,

account for most of the available renewable energy on earth. Only a minuscule fraction of the

available solar energy is used.

Solar powered electrical generation relies on heat engines and photovoltaic. Solar

energy's uses are limited only by human ingenuity. A partial list of solar applications includes

space heating and cooling through solar architecture, potable water via distillation and

disinfection, daylighting, solar hot water, solar cooking, and high temperature process heat for

industrial purposes. To harvest the solar energy, the most common way is to use solar panels.

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Solar technologies are broadly characterized as either passive solar or active solar

depending on the way they capture, convert and distribute solar energy. Active solar techniques

include the use of photovoltaic panels and solar thermal collectors to harness the energy. Passive

solar techniques include orienting a building to the Sun, selecting materials with favorable

thermal mass or light dispersing properties, and designing spaces that naturally circulate air.

2.0 ENERGY FROM THE SUN

About half the incoming solar energy reaches the Earth's surface.

The Earth receives 174 petawatts (PW) of incoming solar radiation (insolation) at the

upper atmosphere. Approximately 30% is reflected back to space while the rest is absorbed by

clouds, oceans and land masses. The spectrum of solar light at the Earth's surface is mostly

spread across the visible and near-infrared ranges with a small part in the near-ultraviolet.

Earth's land surface, oceans and atmosphere absorb solar radiation, and this raises their

temperature. Warm air containing evaporated water from the oceans rises, causing atmospheric

circulation or convection. When the air reaches a high altitude, where the temperature is low,

water vapor condenses into clouds, which rain onto the Earth's surface, completing the water

cycle. The latent heat of water condensation amplifies convection, producing atmospheric

phenomena such as wind, cyclones and anti-cyclones. Sunlight absorbed by the oceans and land

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masses keeps the surface at an average temperature of 14 °C. By photosynthesis green plants

convert solar energy into chemical energy, which produces food, wood and the biomass from

which fossil fuels are derived.

Yearly Solar fluxes & Human Energy Consumption

Solar 3,850,000 EJ[6]

Wind 2,250 EJ[7]

Biomass 3,000 EJ[8]

Primary energy use (2005) 487 EJ[9]

Electricity (2005) 56.7 EJ[10]

The total solar energy absorbed by Earth's atmosphere, oceans and land masses is

approximately 3,850,000 exajoules (EJ) per year. In 2002, this was more energy in one hour than

the world used in one year. Photosynthesis captures approximately 3,000 EJ per year in biomass.

The amount of solar energy reaching the surface of the planet is so vast that in one year it is

about twice as much as will ever be obtained from all of the Earth's non-renewable resources of

coal, oil, natural gas, and mined uranium combined.

Solar energy can be harnessed in different levels around the world. Depending on a

geographical location the closer to the equator the more "potential" solar energy is available.

2.1 THE PRINCIPLES OF SOLAR DESIGN5

2.1.1 BENEFITS OF SOLAR ENERGY

For both new and retrofit projects, solar energy can substantially enhance building

design. Solar energy offers these advantages over conventional energy: Free after recovering

upfront capital costs. Payback time can be relatively short. Available everywhere and

inexhaustible. Clean, reducing demand for fossil fuels and hydroelectricity, and their

environmental drawbacks. Can be building-integrated, which can reduce energy distribution

needs.

2.2 Applications of solar technology

Average insolation showing land area (small black dots) required to replace the world

primary energy supply with solar electricity. 18 TW is 568 Exajoule (EJ) per year. Insolation for

most people is from 150 to 300 W/m2 or 3.5 to 7.0 kWh/m2/day.

Solar energy refers primarily to the use of solar radiation for practical ends. However, all

renewable energies, other than geothermal and tidal, derive their energy from the sun.

Solar technologies are broadly characterized as either passive or active depending on the

way they capture, convert and distribute sunlight. Active solar techniques use photovoltaic

panels, pumps, and fans to convert sunlight into useful outputs. Passive solar techniques include

selecting materials with favorable thermal properties, designing spaces that naturally circulate

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air, and referencing the position of a building to the Sun. Active solar technologies increase the

supply of energy and are considered supply side technologies, while passive solar technologies

reduce the need for alternate resources and are generally considered demand side technologies.

2.3 Architecture and urban planning

Passive solar building design and Urban heat island

Darmstadt University of Technology in Germany won the 2007 Solar Decathlon in Washington,

D.C. with this passive house designed specifically for the humid and hot subtropical climate.

Sunlight has influenced building design since the beginning of architectural history.

Advanced solar architecture and urban planning methods were first employed by the Greeks and

Chinese, who oriented their buildings toward the south to provide light and warmth.

The common features of passive solar architecture are orientation relative to the Sun,

compact proportion (a low surface area to volume ratio), selective shading (overhangs) and

thermal mass. When these features are tailored to the local climate and environment they can

produce well-lit spaces that stay in a comfortable temperature range. Socrates' Megaron House is

a classic example of passive solar design. The most recent approaches to solar design use

computer modeling tying together solar lighting, heating and ventilation systems in an integrated

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solar design package. Active solar equipment such as pumps, fans and switchable windows can

complement passive design and improve system performance.

Urban heat islands (UHI) are metropolitan areas with higher temperatures than that of the

surrounding environment. The higher temperatures are a result of increased absorption of the

Solar light by urban materials such as asphalt and concrete, which have lower albedos and higher

heat capacities than those in the natural environment. A straightforward method of counteracting

the UHI effect is to paint buildings and roads white and plant trees. Using these methods, a

hypothetical "cool communities" program in Los Angeles has projected that urban temperatures

could be reduced by approximately 3 °C at an estimated cost of US$1 billion, giving estimated

total annual benefits of US$530 million from reduced air-conditioning costs and healthcare

savings.

2.4 Agriculture and horticulture

Greenhouses like these in the Westland municipality of the Netherlands grow vegetables, fruits

and flowers.

Agriculture and horticulture seek to optimize the capture of solar energy in order to

optimize the productivity of plants. Techniques such as timed planting cycles, tailored row

orientation, staggered heights between rows and the mixing of plant varieties can improve crop

yields. While sunlight is generally considered a plentiful resource, the exceptions highlight the

importance of solar energy to agriculture. During the short growing seasons of the Little Ice Age,

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French and English farmers employed fruit walls to maximize the collection of solar energy.

These walls acted as thermal masses and accelerated ripening by keeping plants warm. Early

fruit walls were built perpendicular to the ground and facing south, but over time, sloping walls

were developed to make better use of sunlight. In 1699, Nicolas Fatio de Duillier even suggested

using a tracking mechanism which could pivot to follow the Sun. Applications of solar energy in

agriculture aside from growing crops include pumping water, drying crops, brooding chicks and

drying chicken manure. More recently the technology has been embraced by vinters, who use the

energy generated by solar panels to power grape presses.

Greenhouses convert solar light to heat, enabling year-round production and the growth

(in enclosed environments) of specialty crops and other plants not naturally suited to the local

climate. Primitive greenhouses were first used during Roman times to produce cucumbers year-

round for the Roman emperor Tiberius. The first modern greenhouses were built in Europe in the

16th century to keep exotic plants brought back from explorations abroad. Greenhouses remain

an important part of horticulture today, and plastic transparent materials have also been used to

similar effect in polytunnels and row covers.

2.5 Solar lighting

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Daylighting features such as this oculus at the top of the Pantheon, in Rome, Italy have been in

use since antiquity.

The history of lighting is dominated by the use of natural light. The Romans recognized a

right to light as early as the 6th century and English law echoed these judgments with the

Prescription Act of 1832. In the 20th century artificial lighting became the main source of

interior illumination but daylighting techniques and hybrid solar lighting solutions are ways to

reduce energy consumption.

Daylighting systems collect and distribute sunlight to provide interior illumination. This

passive technology directly offsets energy use by replacing artificial lighting, and indirectly

offsets non-solar energy use by reducing the need for air-conditioning. Although difficult to

quantify, the use of natural lighting also offers physiological and psychological benefits

compared to artificial lighting. Daylighting design implies careful selection of window types,

sizes and orientation; exterior shading devices may be considered as well. Individual features

include sawtooth roofs, clerestory windows, light shelves, skylights and light tubes. They may be

incorporated into existing structures, but are most effective when integrated into a solar design

package that accounts for factors such as glare, heat flux and time-of-use. When daylighting

features are properly implemented they can reduce lighting-related energy requirements by 25%.

Hybrid solar lighting is an active solar method of providing interior illumination. HSL

systems collect sunlight using focusing mirrors that track the Sun and use optical fibers to

transmit it inside the building to supplement conventional lighting. In single-story applications

these systems are able to transmit 50% of the direct sunlight received.

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Solar lights that charge during the day and light up at dusk are a common sight along walkways.

Although daylight saving time is promoted as a way to use sunlight to save energy, recent

research has been limited and reports contradictory results: several studies report savings, but

just as many suggest no effect or even a net loss, particularly when gasoline consumption is

taken into account. Electricity use is greatly affected by geography, climate and economics,

making it hard to generalize from single studies.

3.0 USES OF SOLAR ENERGY

Solar energy can be used in houses in many ways ranging from heating and cooling to

cooking and electricity production.

Space heating: Solar energy for heating of buildings through using the building as a collector or

the use of special building elements or collectors.

Space cooling: These can be achieved through mechanically driven compression type

refrigeration or by using absorption type refrigeration. The energy to run these plants is obtained

from the sun.

Water heating: This is used for domestic usage or in swimming pools is done using the thermo

siphon principle. The water is heated in the collector, rises and is replaced by cooler water.

Cooking: Solar energy can be used for cooking using either the direct (focusing) cooker or the

box (oven) type solar cooker. In the focusing cooker the pot containing the foodstuff is placed at

the focus of a parabolic mirror. The solar oven is an insulated chamber with a window on one

side to admit radiation. Solar cookers use sunlight for cooking, drying and pasteurization. Solar

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cooking offsets fuel costs, reduces demand for fuel or firewood, and improves air quality by

reducing or removing a source of smoke.

The simplest type of solar cooker is the box cooker first built by Horace de Saussure in

1767. A basic box cooker consists of an insulated container with a transparent lid. These cookers

can be used effectively with partially overcast skies and will typically reach temperatures of 50–

100 °C.

Concentrating solar cookers use reflectors to concentrate light on a cooking container.

The most common reflector geometries are flat plate, disc and parabolic trough type. These

designs cook faster and at higher temperatures (up to 350 °C) but require direct light to function

properly.

Drying: This deal with various agricultural products is achieved by exposing them to the sun in

a covered tray of some sort or by blowing hot air through or over them.

Distillation: This is used by the process of non-potable water for drinking using the box type

distiller. Solar stills can be used to make drinking water in areas where clean water is not

common. Solar distillation is necessary in these situations to provide people with purified water.

Solar energy heats up the water in the still. The water then evaporates and condenses on the

bottom of the covering glass

Expansion engines and steam engines: This process is based on solar energy may be used for

water pumping.

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Electricity: These can be produced from solar energy in two ways. The first direct conversion by

photovoltaic or thermoelectric processes. Alternatively, solar energy may be used to produce

mechanical work which will then be used to drive electric generators.

4.0 PASSIVE, ACTIVE AND HYBRID SOLAR

Solar buildings work on three principles: collection, storage and distribution of the sun’s energy.

A passive solar building makes the greatest use possible of solar gains to reduce energy

use for heating and, possibly, cooling. By using natural energy flows through air and materials

radiation, conduction, absorptance and natural convection. A passive building emphasizes

passive energy flows in heating and cooling. It can optimize solar heat gain in direct heat gain

systems, in which windows are the collectors and interior materials are the heat storage media.

The principle can also be applied to water or air solar heaters that use natural convection

to thermosiphon for heat storage without pumps or fans.

An active solar system uses mechanical equipment to collect, store and distribute the

sun's heat. Active systems consist of solar collectors, a storage medium and a distribution

system. Active solar systems are commonly used for: Water heating, Space conditioning,

Producing electricity, Process heat and solar mechanical energy.

Hybrid power systems combine two or more energy systems or fuels that, when integrated,

overcome limitations of the other, such as photovoltaic panels to supplement grid supplied or

diesel-generated electricity. Hybrid systems are the most common, except for the direct gain

system, which is passive.

Terms

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Absorptance: - The ratio of absorbed to incident radiation.

Active solar: - A solar heating or cooling system that operates by mechanical means such as

motors, pumps or valves to sort and distribute the sun's heat to a building.

Energy rating (ER):- A rating system that compares window products for their heating season

efficiency under average winter conditions.

Evacuated tube collectors: - Solar collectors that use individual, sealed vacuum tubes are

surrounding a metal absorber plate.

Flat-plate collectors: - The most common type of solar collector. Can be glazed or unglazed.

Hybrid power systems: - Combines active and passive solar power systems or involves more

than one fuel type for the same device.

Latent Heat: - Also called heat of transformation. Heat energy absorbed or released by a

material that is changing state, such as ice to water or water to steam, at constant temperature and

pressure.

Low-emissivity (low-e):- Coatings applied to window glass to reduce inside heat loss without

reducing outside solar gain.

Passive solar: - A solar heating or cooling system that operates by using gravity, heat flow or

evaporation to collect and transfer solar energy.

Photovoltaic (PV) system: - System that converts sunlight into electricity. It can be autonomous

or used with another energy source. (It can be connected to the main power grid, for example).

R-value (imperial), RSI-value (metric):- A measure of resistance to heat flow through a

material or assembly a numerical inverse of the U-value.

Solar balcony:-An enclosed balcony that acts as a solar collector.

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Solar constant 1,350 W/m2:- The average amount of solar energy reaching the earth’s upper

atmosphere.

Solar Domestic Hot Water (SDHW):- A supplement to traditional domestic hot water heating.

The most common system uses glazed, flat-plate collectors in a closed glycol loop.

Solar Heat Gain Coefficient (SHGC):- Equal to the amount of solar gain through a window,

divided by the total amount of solar energy incident to its outside surface.

Solar south: - This is 180 degrees from true or grid (not magnetic) north.

Solar wall: - A proprietary system that uses perforated metal panels to pre-heat ventilation air.

Switchable glazing: - Glazing materials that can vary their optical or solar properties according

to light (photo chromic), heat (thermo chromic) or electric current (electro chromic).

Thermosiphon solar collector: - A system in which the circulation of hot water in the loop is

based only on buoyancy.

U-value: - A measure of heat flow through a material or assembly. Measured in Watts/m2/°C.

Warm-edge spacers: - Separate a window's glazing layers with thermal break or a low

conductivity material.

5.0 CONVERSION OF SOLAR ENERGY FOR USE IN A BUILDING

There are basic ways in which solar energy may be conversion for use in buildings:-

biochemical, electrical and thermal conversion.

Biochemical conversion: - This is the conversion of solar energy which involves photo-

biochemical processes. Photosynthesis which involves the use of solar energy in the conversion

of carbon dioxide and water into carbohydrate and oxygen. The carbohydrate is consumed by

humans and other animals for energy. Solar energy can be in production of biogas. Sunlight is

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used to grow algae which are then fermented an aerobically to produce methane for the operation

of internal combustion engines and for cooking.

Electrical conversion: - These can of solar energy be done directly using thermoelectric or

photoelectric processes. Thermoelectric conversion is the direct conversion of solar energy into

electrical energy by means of thermocouples. A potential difference for the generation of

electrical energy is achieved by cooling one and heating the other junction of the thermocouple.

A thermopile is made up of thermocouple joined in series. Photoelectric or photovoltaic

conversion is the production of electricity using the light content of solar radiation. Photovoltaic

cells made from silicon are commonly used.

Thermal conversion: - this is when radiant energy falls on a surface, some of it is absorbed. The

nearer the surface is to a matt black surface, the more the radiation absorbed. Some of this

energy is transmitted to other parts of the body by conduction and some re-emitted by conductive

and radiant processes. The solar energy is thereby converted to heat energy. The heat produced

can be trapped by covering the absorber plate with a sheet of glass thus creating a greenhouse

effect.

6.0 RECOMMENDATION AND CONCLUSION

The goal of sustainable architecture is to efficiently utilize energy especially in the built

environment thus, the introduction and intensive use of solar designs can be easily achieved this

goal. But careful integration of the technique in a way that harmonizes the culture, behavioral

pattern and socio- economic tendencies of the people and importantly not neglecting the climatic

conditions of the location. However to sustain this solar technique in the developing country like

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Nigeria , there is need for cooperation of all stakeholders and the interest groups to ensure that

mutual agreement is reached.

Enlightenment on the usage is vital and the training of expertise to resolve and maintain

the facility is crucial.

Finally the government must assume the responsibility of moderating the cost of the service by

giving subsidies that will guarantee mutual use by all and sundry.

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