From Oil Wells to Solar Cells Primer

8/6/2019 From Oil Wells to Solar Cells Primer

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To our Educational Curriculum Listings

FROM OIL WELLS TO SOLAR CELLS:

A RENEWABLE ENERGY PRIMER

This primer provides an introduction to both renewable energy issues and technology.

For further information on specific subtopics, see:

Summary of Educational Curricula/Projects

Summary of Educational Programs/Resources

NMSEA FAQs/Primers

Other Resources:

Good periodicals on renewable energy include

Home Power Magazine and

Solar Today.

Many other good websites exist as well: See our list ofweb resources, and SolarBooks for example.

Finally New Mexico Solar Businesses can be located on our Solar Professionals

Directory.

Table of Contents

The Big Picture:

What is "renewable" energy?

What are the costs of renewable energy?

What are nonrenewable sources of energy?

What are the environmental benefits of renewable energy?

What are the practical and social benefits of renewable energy?

What are the environmental dangers of nonrenewable energy sources?


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What are the social dangers of nonrenewable energy sources?

What are the obstacles switching to renewable energy sources?

The future of renewable energy storage

The Even Bigger Picture: Recycling writ large

A Closer Look at Solar Power:

How much energy comes from the Sun?

Types of Solar Energy Technology

Solar Thermal Electricity

Stirling Dish (Solar Dish)

Solar Air and Water Heating

Photovoltaics (Solar Cells - Direct Solar Electricity)

Passive Solar Design (Solar Heating)

The Big Picture

What is "renewable" energy?

Renewable energy sources are those that are continually renewed by nature, and hence

will never run out (at least as long as the nuclear fusion processes in the Sun and fission

processes in the Earth continue). For example:

Solar Power - Capturing sunlight for:

Driving steam turbines to generate electricity ("Concentrating Solar Power",

Heating homes ("passive solar design" or "active solar heating systems"),

Heating hot water ("active or passive solar hot water systems"),

cooking ("solar ovens"),distilling water,

generating electricity directly with solar electric ("photovoltaic") cells,

other uses.

Solar Power is considered renewable because the nuclear (fusion) reactions that

power the Sun are expected to keep generating sunlight for many billions of years to

come.

The figure below shows where the most sunlight falls in the US (red indicatesthe most, blue the least).

The energy from sunlight that falls on White Sands Missile Range is roughly

equivalent to that used by the entire United States! (Specifically, the


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sunlight falling on an area of roughly 60 miles x 60 miles is equivalent to the

roughly 100 quads (a quad is 1015 btus) of energy used by the US each year. To

see more about such calculations, see our solar curriculum project Explore the

Solar Resource)

New Mexico is potentially a Solar Saudi Arabia!

Other examples of renewable energy:

Hydropower - Channeling falling water to drive turbines (generators) to generate

electricity. This is renewable because the Earth's hydrological cycle, which is driven

by the Sun, continuously replenishes lakes and rivers through rain. Hydropower is anindirect form of solar power.

Biomass - Using the heat generated by burning plants, trees, and other organic

waste. Biomass is renewable because new organic matter is always being created by

photosynthesis. Biomass is also an indirect form of solar power.

Wind Power - Using the wind to turn propellers connected to turbines. Wind power

is considered renewable because the Sun and the Earth's rotation are always

generating more winds. Wind power, like biomass and hydropower, is really another

form of indirect solar power. The wind power resource of the United States, like its

solar power resource, is huge. The dark blue areas in the map below show the areas

where "class 6" winds exist. It is estimated that developing even a small fraction of

these areas would power the US several times over, without creating adverse

environmental or social impacts. Wind power is presently the fastest growing energy

source in the world!


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Fantastic opportunities for large scale wind power exist in New Mexico, and

several projects now exist: A 200 MW facility by Public Service Company of

New Mexico, and a smaller facility consisting of several 660 kw turbines by

Southwestern Public Service Company of New Mexico. For more information on

Wind Power and renewable energy policy in New Mexico in general (and links to

the wind power world), see the website of the Coalition for Clean Affordable

Energy (CCAE), http://www.cfcae.org (NMSEA is a CCAE member

organization).

Geothermal Power - Using the heat created by the decay of radioactive elements

within the earth to heat buildings or generate steam to drive turbines (generators) to

generate electricity. Geothermal power is considered renewable because there is

enough radioactive elements in the Earth to keep it warm for billions of years to

come.

Landfill Gas - Using the methane (CH4) generated by the breakdown of garbage in

land fills (really a form of biomass). Although this is not necessarily renewable for the

long term, there is enough landfill gas to provide a significant source of energy in the

United States. This should tell us something about how much waste our society

generates!

Different definitions of the phrase "renewable energy": Some people argue that nuclear

power from earth based uranium should also be classified as renewable because the sun is

nuclear powered and because they claim that there is lots of earth based uranium (NMSEA

does not subscribe to this view). Others like the word "inexhaustible" instead of

"renewable" for renewable energy sources, which better conveys the important point that

renewable energy sources will neverrun out for the foreseeable future of humankind.Another useful term might be "non extracted", reflecting the fact that renewable energy

sources do not require extraction of minerals from the ground.


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What are the costs of renewable energy?

This is often the first question that people ask about renewable energy. A full answer,

however, requires a fairly detailed look at the different types and contexts of renewable

energy. We will now explore this question in some detail.

One way to express the costs is to compute the time it takes for a system to pay for itself,

relative to the prices of natural gas or electricity from the grid. In other words, how much

time does it take for the total energy savings achieved by using a renewable energy system

take to equal to the cost of the system? Relative to recent prices for gas and grid power,

payback time for renewables were (very) roughly:

Passive Solar Heating: 0-2 years

Solar Hot Water: 5-15 years

Solar Electricity (photovoltaics): 15-25 years

Utility Scale Wind Electricity: 20 years

One should keep in mind that these estimates do not include the addition savings that a

renewable energy system might provide, such as avoiding the cost of installing power or

gas lines, which can be enormous for remote sites. Nor do they take into account

occasional large jumps in gas and electricity prices, such as those that occurred in the year

2000 and more recently. These can substantially decrease payback times.

The ability of (at least some) renewable energy systems to pay for themselves relative to

utility costs means that their costs, in principle, could be included in the long termfinancing of homes and actually decrease total monthly costs, because in some cases the

savings on utility bills will more than balance out the extra cost added to payments to buy

the systems over the long term.

From another perspective, instead of dwelling on payback times, it might instead be more

sensible to focus on the fact that (some) renewable energy systems can in fact pay for

themselves at all, period! How many other appliances can do this? This is not a

requirement that we place on many other commodities, such as RV's, boats, patios, etc.

The payback of these commodities are there specific benefits (travel, etc). The paybackof renewable energy systems from this perspective is the satisfaction of using and

promoting sustainable technology, and protecting the planet for future generations.

When comparing costs of renewable electricity, one should also be careful to distinguish

retail costs from wholesale (or production) costs. The production cost of utility scale

(centralized) renewables that is commonly quoted (e.g. 4 cents/kwh for wind) should be

compared to wholesale cost that utilities pay to either produce or acquire energy from

nonrenewable sources. In contrast, the cost of home solar systems should be compared to

the retail cost of grid electricity, because the home solar system does not require

transmission and distribution of its power - the Sun takes care of that part! The Sun is

Earth's built-in transmission and distribution system!


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For example, solar electricity (in the form of photovoltaics) is about 7 times the wholesale

cost of utility scale wind power, but only about 2-3 times the cost of retail electricity.

Utility Scale Renewables: Keeping in mind the average wholesale cost of electrical power

from the grid, which is about 3.5 cents per kilowatt-hour for coal in New Mexico,

wholesale renewable energy sources rank in cost as follows:

Hydropower: 2 cents/kwh -cheapest of all, cheaper than coalWind (utility scale): 4-6 cents/kwh - just above coal.

Geothermal: 6-8 cents/kwh - twice the cost of coal.

Solar Thermal Plants: 10-14 cents/kwh - 3-4 times the cost of coal.

Home Scale Solar: Relative to an average retail cost of electrical grid power, which was

around 10 cents per kilowatt-hour in the 1990s:

Photovoltaics (home solar electricity): 19-25 cents/kwh - twice to three time the

cost of grid power.

For more on cost, see our solar curriculum project: Calculate the cost of Photovoltaic

Systems (Home Solar Electricity), or the section further on in this primer: System Costs

(for PV).

What are nonrenewable sources of energy?

Nonrenewable sources are those based on a finite amount of pre-existing "fuel". By "fuel"

we mean any substance which stores energy, for example, gasoline, kerosene, natural gas,

uranium, and firewood are all examples of fuel - firewood being the only renewable fuel is

this list. The primary nonrenewable fuels are:

Fossil Fuels: Natural Gas, Oil, and Coal - These three fuels are the leftovers from

plants and animals that lived millions of years ago - hence the name "fossil fuels".

They are all "carbon-based", that is, they consist primary of compounds made of

carbon and hydrogen derived from the bodies of ancient plants and animals. Natural

gas is the gaseous form (small molecules, consisting of one or two carbon atomseach), oil is the liquid form (several carbon atoms per molecule), and coal is the solid

form (many carbon atoms per molecule).

Although they are a form of stored solar energy (because their energy originally came

from the sun through photosynthesis), they are considered nonrenewable because

there is only a finite amount of them. Unlike renewable sources, they can't be

replaced quickly because it took many millions of years for these fuel reserves to

form, so that it takes too long for nature to "renew" them for our practical purposes.

They are so finite in fact, that it is thought that oil production may peak during thefirst few decades of this century (the famous "Hubbard Curve"), and that coal and

natural gas will last only a few hundred years more (at the current rate of usage).

There are also a number of environmental reasons for not using these fuels that we


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will discuss later.

Nuclear Power - Nuclear power is the generation of heat (say, to drive steam

turbines to generate electricity) by the nuclear reactions involving radioactive

substances such as uranium 235, an "isotope" of the element uranium. There are two

kinds of nuclear power:

Fission: In this process, radioactive elements split apart to release energy.

There are currently about 1100 nuclear "reactors" that use fission. About 430 of

these are used to generate electricity in nuclear power plants (the rest are for

research or production of special radioactive materials used in medicine, food

processing, and scientific research).

Fusion: In this process, radioactive elements (usually hydrogen nuclei) are

combined to release energy. This is the source of the Sun's energy. At this point

in time, successful fusion reactors have not been achieved, but there is much

research on them.

Nuclear power is not classified as a renewable by many people in part because there

is only a finite amount of uranium 235, and this cannot be renewed by nature for us.

However, the amount of uranium may be quite large. Many are reluctant to classify

Nuclear power as renewable because of its associated social and environmental

problems (discussed further below). Many people consider fusion nuclear power to be

fundamentally safer and cleaner than fission nuclear power, and hope that researchers

will succeed soon in developing it as an energy source. The feedstock for the fuel for

fusion is abundant on the Earth's surface - water!

What are the environmental benefits of renewableenergy?

No mining or drilling for the fuel source - the energy is provided from the sky,

or via heat in the ground not materials in the ground.

Keep in mind that we must still obtain materials for manufacturing the collection

devices for renewable energy, and this may include mining. But these materials aremuch less than the amount of fossil fuel we extract. For example, photovoltaic solar

cells are very thin, so the volume of material relative to the energy they produce is

very small. Related to this is the fact that they pay back the energy used to

manufacture them in 2 to 3 years in sunny climates. Moreover, they're recyclable and

therefore can be used indefinitely!

No paying for the fuel source itself - The energy is free!

One must still pay, however, for the initial manufacturing and maintenance of thecollection devices.

No net emissions (such as those from burning fuels) - There are either no


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emissions associated with fuel at all (solar, wind, hydropower), or the emissions

from burning fuel are compensated by photosynthesis initially (biomass, landfill

gas), so that the emissions are closed-cycle (at least to a large degree). Thus we

avoid many of the environmental problems associated with nonrenewable

energy (see below).

Keep in mind that there may be emissions, or other pollution associated with

manufacturing the collection devices. Some of these emissions (those associated with

energy production at least) could be avoided in the future if new collection devices

are manufactured in factories that actually use renewable energy in the first place.

Careful attention will always be necessary, however, to minimize the impacts of

pollutants associated with manufacturing.

What are the practical and social benefits of renewable

energy?Economic development! Switching to renewable energy sources is estimated to

create at least several times as many jobs as traditional energy sources (some

estimates suggest as much as 10 times or more). These jobs would include both

manufacturing jobs and the maintenance of collection and energy storage devices.

This is possible because one is paying for the manufacturing and maintenance of the

collectors, which is labor intensive, and NOT a fuel supply.

Renewable energy is flexible! Because renewable energy generation can be de-

centralized - that is, many small collection devices can be widely distributed insteadof having only a few large centralized power plants, the need for transmission lines

can be reduced, and the resulting system will likely be more robust with respect to

civil disturbances, natural disasters, etc.

Freedom from Exploitation! Because renewable energy generation can be owned by

the end user, switching to renewable energy would put more power, and ultimately

money, in the hands of the general public, instead of into the hands of monopolistic

energy companies.

What are the environmental dangers of nonrenewableenergy sources?

Air pollution - Burning fossil fuel emits a number of noxious chemicals into the

atmosphere:

Carbon Dioxide (CO2): CO2 is emitted when burning any carbon based fuels (as

all fossil fuels are), and is widely thought to be the primary greenhouse gas

causing global climate change (which includes global warming). For more info,see our primer materials on global climate change.

Carbon Monoxide (CO): CO is emitted when carbon based fuels are burned

inefficiently, is poisonous, and contributes to the air pollution in cities


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associated with automobiles. A malfunctioning furnace can also produce carbon

monoxide.

Sulfur dioxide (SO4): SO4 is emitted mostly by the burning of coal, and is the

principle cause of acid rain.

Nitrous Oxide (NO2): NO2 , or "nox", is created when fossil fuels are combusted

in the presence of air (which is 80% nitrogen). Nox is another greenhouse gas,

and also an principle contributor to smog v ia automobiles.Particulates: Particles of ash are emitted from the smokestacks of coal fired

power plants. These particulates are a serious threat to human respiratory

health in many parts of the US.

Mercury: Coal contains significant amounts of mercury, a highly toxic element,

that is emitted when coal is burned. Mercury from coal plants is thought to be a

major pollutant of land and water in the US. The Environmental Protection

Agency is beginning to regulate mercury emissions more stringently.

Radioactive Uranium: Both coal and nuclear power plants can emit uranium(coal deposits often contain significant amounts of uranium).

Water Pollution/Usage:

Coal-fired power plants use large amounts of water to:

Transport the coal (in some cases)

Wash the coal

Cool the coal (to prevent spontaneous combustion)To absorb and carry away heat in the form of steam to complete the

thermodynamic cycle of power generation.

Nuclear power plants use enormous amounts of water to:

Refine uranium ore into nuclear fuel rods

To absorb and carry away heat in the form of steam to complete the

thermodynamic cycle of power generation.

Land/habitat impacts of mining, drilling, and spilling:

Coal mining and oil and gas drilling disrupt and pollute hundreds of square miles

of land per year. Moreover, many of our largest fossil fuel resources are located

in environmentally and socially sensitive regions, such as the Four Corners Area,

the Cumberland (Appalachian Mountains) region, and the Artic National Wildlife

Refuge, to name a few.

Mining underground can lead to poisoning of streams because water seeps

into the coal mines and becomes acidic from the sulfur associated with

coal seams.Coal seams are on average only a meter thick, so vast areas must be

either tunneled or strip mined to obtain the coal. Coal companies

nowadays sometimes demolish entire mountains (called "mountaintop


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removal") to get at the coal underneath.

Oil spills from grounded tankers regularly contaminate vast areas of the

ocean, killing enormous numbers of sea animals and birds.

A good report on energy-related pollution issues and renewable energy in New Mexico

can be found at http://www.nmpirg.org/reports/renew_energy/index.html

What are the social dangers of nonrenewable energysources?

Dependence on foreign sources - Dependence of foreign sources can greatly corrupt

a nation's good intentions towards its neighbors, and also make it more susceptible to

foreign exploitation.

Nuclear Weapons Proliferation - Developing nuclear power can put the technologyand know-how for building nuclear weapons into the hands of more and more

countries and who knows who else.

Energy Company Monopolies - Dependence on fuel sources that require large scale

extraction and power production facilities tends to encourage the formation of

corporate monopolies which can overcharge consumers, flaunt environmental

regulations, and corrupt the moral integrity of a society.

What are the obstacles to switching to renewable energysources?

Upfront Cost: While some renewable energy sources such as hydropower, wind

power, and geothermal are now competitive or almost competitive with fossil fuels,

solar electricity is still several times more expensive than coal-fired electricity, and

the financial mechanisms needed to avoid this problem (to allow renewable energy

systems to pay for themselves naturally) do not commonly exist yet.

Stranded Cost: US citizens have already paid about a trillion dollars for our fossil fuelinfrastructure. Some argue that this investment would be "stranded" if we switched

completely to renewables, unless ways to incorporate much of that infrastructure

could be found. Thus, this investment would seem to create a considerable economic

disincentive to switch to renewables. Others argue that gradually abandoning this

infrastructure would actually save money because a more distributed infrastructure

would be so much cheaper that it would more than make up for stranding the old

infrastructure.

Politics: People who make money from traditional energy sources simply don't want

to lose their profits, and often work hard to avoid doing so. See our pages onpolitical advocacy for more info. NMSEA is an active member organization of the

Coalition for Clean Affordable Energy (www.cfcae.org).

Environmental Impacts: All major sources of energy have significant environmental


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fundamental difference that they allow an energy economy with no net emissions of

pollutants from the combustion of fuels, i.e, a true closed-cycle economy. This should

remain true even if synthetic fuels are eventually introduced to store renewable energy -

for example, if production of say, methanol, from atmospheric carbon dioxide and water

using renewable electricity as an energy source becomes available. This is because such a

fuel, while carbon-based, can be neutral with respect to emissions of greenhouse gasses:

the carbon dioxide used to manufacture them could be absorbed from the air (via acollector of via natural biomass growth processes), and then simply released back into the

air at the point of use (and similarly with the water used to generate the hydrogen).

Thus, what we are really talking about is recycling writ large: new processes whichcould eventually lead to closing all of our material cycles.

Moving towards a truly closed-cycle economy will require a fundamental shift in our

approach to both energy and manufacturing in general. We therefore urge you to take

recycling and renewable energy very seriously: Recycling is not just a nice thing to dofor the environment - its really the whole baliwag!

A Closer Look at Solar Power

How much energy comes from the Sun?

The sun provides about 1000 watts per square meter at the Earth's surface in direct

sunlight (this reference intensity is often called "one sun" by solar energy scientists). This is

enough power to power ten 100 watt light bulbs, or 50 twenty watt compact fluorescent

light bulbs! Contrary to what is sometimes repeated by those who oppose solar energy,

solar power is really not very diffuse or weak. In fact, the sunlight falling on a very small

fraction of a home's roof is typically more than enough to provide all the energy needs of a

home. Or put another way, covering less than one percent of the land area of the United

States with solar panels could provide all the energy we currently use. For more on this

topic, see our solar curriculum project "Exploring the Solar Resource".

Another way to look at this is to consider the enormous energy in the geophysical flows

around us as a whole - the sunlight, ocean currents, wind, clouds - the energy in these

systems is simply enormous, and dwarfs the scale of human energy usage. Most of this

energy ultimately originates from solar power, which drives the hydrological cycle,

thermal upwelling of air, and heats the ocean's surface.

As an example that's even more close to home, you, the reader, are solar powered! All

the energy you obtain from your food originates with solar power, via the photosynthesis

of sugars in plants.

Types of Solar Energy Technology


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There are several primary solar energy technologies, most of which are discussed further below,

including

Photovoltaics (solar electricity),

Passive Solar Design (solar heating, natural cooling, and can incorporate hot water

systems very nicely)

Active solar thermal (Solar Hot Water/Air collectors)

Solar thermal electricity (large and small scale electricity generation from solar

heat)

Solar cooking

Solar distillation

Solar water pumping

A passive solar system is a solar water-heating or space-heating system that captures and moves

sun-heated air or water just by the configuration of the building, without using explicit

collectors, pumps or fans. An active solar system, on the other hand, is a system that uses

collectors of various sorts and moves sun-heated air or water using pumps or fans. Many homes

incorporate several aspects, such as passive solar design and photovoltaics, and sometimes other

renewable energy forms such as wind systems. Many off-grid homes are totally energy and water

sufficient and are not connected to or dependent upon utility power lines, and city water supplies

and sewers.

Our solar curriculum has both solar thermal and solar electric projects.

Solar Thermal Electricity

Solar thermal electricity, also called "Concentrating Solar Power" or CSP by many, is the

solar power variant on the traditional power plant: Solar energy is focused onto either a

central receiver using mirrors (the "power tower" approach) or onto pipes using parabolic

troughs (called the "troughs" approach) to heat a working fluid, usually either water or

molten salt, which is then used to drive a turbine to generate electricity. This technology

is only now beginning to become commercialized (Spain plans to build a large solar thermal

electricity plant soon).

Here is a picture of the experimental Solar II plant, near Barstow California:


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This 10 megawatt (ten million watt) experimental solar plant, the largest of its kind, used

molten salt as a working fluid, which it stored for several hours in order to contour output

to demand (including extending power generation well past sunset). This plant could supply

power for approximately 10,000 homes from morning until well into evening, at a

production cost of 10-14 cents per kilowatt hour (about three to four times the wholesale

production cost of coal-fired electricity). Over the period of several decades, this plant

uses less land area, and uses it less destructively, than a coal-fired power plant that

produces the same power (assuming we including the land area that needs to be mined for

the coal).

Sandia National Laboratories, located in Albuquerque New Mexico, built an earlierprototype of Solar II (the Sandia "Power Tower"), and conducted much of the fundamental

research embodied by Solar II. See http://www.sandia.gov/Renewable_Energy/ for more

information on their solar thermal program.

Stirling Dish (Solar Dish)

Another form of solar thermal electricity generation, or concentrating solar power, is the

"stirling dish", or "solar dish" approach. These systems consist of a concave parabolic solar

concentrator, which focuses sunlight onto a stirling heat engine. Stirling engines use air as a

working fluid, as opposed to water, and therefore may be quite useful in arid climates.

These units are also smaller than power tower or trough systems (they usually fall in the 20

to 30 kilowatt range), and may therefore be useful for more distributed applications, such

as remote water pumping, or neighborhood systems.


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For more info on these see the Solstice pages on solar dishes.

Active Solar Thermal

Although solar air and water heating systems gained a bad reputation in the 1980s, largely

due to overly generous tax credits and the immature and sometimes disreputable industry

that these credits created, these systems can function beautifully, especially in the sunny

southwest, and are still one of the most economical forms of solar energy if properly

implemented. They can easily provide between 40% (Seattle) to 80% (Phoniex) of the hot

water heating needs of a typical US family. Here is a photo of a solar hot water panel: Thistype of collector is called a "flat-plate collector":

Active systems such as this involve pumps (for water) or fans (for air) and collect sunlight

with flat plate collectors (as pictured in the photo above). The flat plate collector is

essentially an insulated box that allows sunlight in on one side through a glass covered

window and absorb it with dark colored metallic surfaces. The collected (and trapped)

heat is then transferred by conduction into a working fluid (typically water with orwithout antifreeze, or air), which is continuously pumped through pipes in contact with

the collecting surfaces. The working fluid is then routed either to a storage medium, such

as a hot water tank, rock bed, or radiant floor, or transferred directly into the air.


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Active hot water systems themselves come in several basic types: one type uses

antifreeze to keep the water in the collector from freezing on cold winter nights. The

other, so-called "drain-back" systems, let the water drain out of the collector at night, so

that antifreeze is not needed. The latter can be an "open system", that is the water that

flows through the collector can be used directly.

A disadvantage of active solar thermal systems is that they typically need moremaintenance than passive systems, and have a higher upfront cost ($3000 to $5000 - passive

systems are usually around $2000).

One form of solar water heating that tends to require less maintenance and upfront cost,

and which might be characterized as the passive form of active solar thermal is called

batch solar water heating. In this approach, the collecting surface is the darkly covered

surface of a water tank itself (see picture below). The tank is usually insulated and covered

with glass just as is the case with a flat plate collector. Pumps are not generally necessary

in this kind of system. Instead, the tank-collector is simply used to pre-heat the waterbefore it goes into a supplemental hot water heater. That way, if the sun has heated the

water, the hot water heater need not. Otherwise, the hot water heater kicks in. Another

variation on this approach is to have a hot water tank located at the top of, or underneath

a flat plate collector. In this approach, cold water naturally flows downwards into the

collector, and hot water flows back upwards into the tank, in a convection driven process

called thermosiphoning. These systems are called "integral" systems.

Batch systems may be conveniently located underneath skylights or clerestories, with or

without insulation on the sides and back sides, giving great flexibility to how they are

integrated into a home. For example, here are photos of a batch hot water tank mounted

in a clerestory (photos courtesy of Karlis Viceps):

Here is what the tank's insulated mounting box looks like from below:


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Finally, some hot water systems are integrated directly into sunspace or clerestories, as hot

water pipes running just underneath the glazing and attached to metallic collectors. Here is

a picture of one such system, made by Zomeworks, located in a sunspace:

The long white strips across the slanted ceiling are the bottoms of the metallic collectors

(manufactured by Zomeworks). The hot water pipes can be seen emanating from the right

hand ends of these strips.

Photovoltaics (Solar Cells - Direct Solar Electricity)

Photovoltaics, or "PV" for short, and more commonly known simply as "solar cells", are

special semiconductor devices which convert sunlight directly into electricity. The word

photovoltaic derives from the words "photo" which means light (Greek for light is "phos"),

and "volt", the fundamental unit of electrical energy potential. Therefore, "photovoltaic"

literally means "light-electricity".

Many individual solar cells can be packaged together into "pv modules" which can then be

placed on a rooftop, carport roof, in stand alone arrays, and many other convenient places.

'


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pioneering program (see http://www.smud.org/pv/) where homeowners volunteer to pay

a small premium on the electric bill to host a PV system:

PV cells, as we know them now, were first developed in 1954 by Bell Telephone

researchers and first applied to power satellites in space.

Our solar curriculum has several projects related to solar electricity, including:

dc electricity,

solar cell demonstration project,exploring the history, science, and components of PV systems,

calculating the cost of photovoltaic systems.

Good educational materials on PV can also be found at http://www.eren.doe.gov/pv/.

Photovoltaics System Components

The basic components of a complete home PV system are:

PV panels: These produce the electricity from sunlight. There are typically 10 to 20

of these.

Batteries: Used to store the energy. A typical (off-grid) installation uses 10-20 deep-

cycle lead acid batteries.

Charge controller: To regulate the charging of the batteries

Inverter (pictured below): Converts the low voltage DC (direct current) power from

the batteries into 110 volt AC (alternating current) for use by appliances .


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The following diagram shows they are connected together:

First, the Sun shines on the pv modules to produce electrical power. That power is routed

through a charge controller to the batteries. The charge controller regulates the charging

of the batteries: The voltage on the batteries needs to be increased slowly, because

charging them too fast or routinely overcharging the batteries quickly degrades them.

Charge controllers must also control the voltage that the pv modules output power at to

operate at them at their maximum power output (this is called "power point tracking").

Next, the inverter converts the dc (direct current) electrical power from the batteries (or

directly from the modules in a grid-tied system) into ac (alternating current) electrical

power at 110 volts. This can then be fed to household appliances via a wall socket.

System Costs

The costs of typical PV system range from anywhere between a few thousand for a

vacation cabin size system, to about ten thousand for a small home, and upwards of$35,000 for a large home (for more details on home PV system costs, see our curriculum

project "Calculate the cost of Photovoltaic Systems"). Component costs break down roughly

as follows:


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About $4-6 per watt for the panels, so for a typical 2 kilowatt system the panels cost

about $8,000-12,000.

Several hundred dollars for the charge controller.

About $1 per watt for the inverter: a typical 2 kilowatt system typically uses a 2400

watt to 5000 watt inverter: therefore the inverter cost will be $2400 to $5000.

About $100 per kilowatt-hour (kWh) of energy storage: a typical 2 kilowatt system

might require 20 kWh of storage (only 10 kWh in active use to extend battery life)

and therefore about $2000 worth of batteries.

Today's crystalline PV panels have a very long lifetime, at least 25 years, and possibly much

longer. Today's batteries typically last 3-10 years before they need to be replaced.

Fortunately, US law requires that the batteries be recycled, and over 99% are. Many solar

enthusiasts are hopeful that energy storage systems using hydrogen fuel cells will become

available in coming decades to replace the need for short-lived batteries.

A commonly repeated myth is that PV panels take more energy to manufacture than they

produce. In fact, PV panels typically pay back their energy in 2 to 3 years in a sunny

climate, as the National Renewable Energy Laboratory (www.nrel.gov) has documented.

New Mexico has many small businesses that specialize in PV installation and maintenance

(see our Professional's Directory).

Sandia National Labs in Albuquerque (see http://www.sandia.gov/pv/), and the National

Renewable Energy Laboratory in Golden Colorado

(http://www.nrel.gov/photovoltaics.html), both have active photovoltaic research and

development programs.

There are also several PV cell manufacturers in Albuquerque: Matrix Inc, Emcore Corp., and

Advent Solar.

Passive Solar Design (Solar Heating)

(For additional depth after reading this section, see the guidlines listed on our FAQs/Primerpage.

Perhaps the most cost-effective and sensible form of solar energy,passive solar design, is

the idea of designing buildings to take advantage of the natural sunlight for heating in the

wintertime, andto properly block sunlight for cooling in the summer.

The three principles of passive solar design are:

Gain: Getting enough sunlight in at the right time (and blocking it at the right time as

well).

Thermal Mass: Having enough thick masonry surfaces to store the energy from

sunlight to keep the home warm at night, and from overheating during the day.

Insulation: Having good insulation (and low air leakage) to keep the heat in during


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the winter, and heat out during the summer.

The key to getting solar gain at the right time (winter), and not at the wrong time

(summer) is to take advantage of the fact that the path taken by the winter sun is much

lower in the southern sky than the path taken by the summer sun (which passes nearly

overhead at high noon:

The way to take advantage of these differing paths is to place most of the windows on the

south side of the home, and add overhangs over these south-facing windows for additional

summer shade. Here are some pictures of passive solar homes in New Mexico, showing the

south-facing side:

Both of these homes were designed by NMSEA member and past president Karlis Viceps of

Taos, New Mexico. Both have rainwater harvesting, cisterns, trombe walls (a masonry wall

with glazing that stores solar energy for night time use), direct gain (many southern

windows), and passive "batch" solar hot water.

Passive Solar Design History: Passive solar design has a fascinating history, stretching at

least back to the Greeks, who planned entire cities to take advantage of the Sun's energy.


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great oo on t e story o so ar energy s o en rea - years o so ar

architecture and technology", by Ken Butti and John Perlin, Cheshire Books, CA, ISBN 0

917352 08 4.

Native American tribes of the southwest, as well, have long applied these techniques.

Their cliff dwellings, for example, those at Mesa Verde, faced south, so that they take

advantage of the low winter sun during winter, but were shaded by the overhanging rock

during summer. Likewise, the thick rock and adobe walls of these dwellings served asthermal mass to store the Sun's energy and keep the buildings warm at night:

The term "passive solar" was coined in New Mexico during the 1970's by passive solar

pioneer Benjamin "Buck" Rogers.

Passive solar design techniques were experimented with and widely implemented in NewMexico in the period 1970-1985, by people such as Peter Van Dresser, Bill Yanda, Ed

Mazria, Wayne Nichols, Doug Balcomb, Bill Lumpkins, Mark Chalom, Keith Haggard and

Michael Reynolds. Several of these people also founded the New Mexico Solar Energy

Association, the oldest solar association of its kind in the US. Several books by some of

those listed appear in our book list.

Passive solar design was placed on a firm scientific footing at Los Alamos National

Laboratory in the 1970s by Doug Balcomb and others. Doug has made his vast experience

available to passive solar designers by developing a passive solar design software called

Energy-10: See http://www.nrel.gov/buildings/energy10/.

From the enormous experience acquired by passive solar builders and researchers over the

years, many good rules of thumb have been developed. Unfortunately, few architects

nowadays apply them, or even know them. Moreover, some buildings that are claimed to

be passive solar are not designed carefully. To give you a flavor, here are some of the

more important ideas (See our Passive Solar Guidelines for a complete presentation).

Right Placement and Sizing of Windows: Windows on the non-south sides should be

sharply limited in their surface area to prevent heat loss. Windows on the south side, on

the other hand, should have quite large surface area, but not too large:


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Orientation Percent of total floor area

East 4

North 4

West 2

South7-12 (depending on whether additional thermal

mass is present)

Right Sizing of Overhangs: Overhangs are strongly encouraged for south-facing windows

and trombe walls in Northern New Mexico. The following overhang angles were suggested

by Doug Balcomb. These angles are not the angles one would get from most books

corresponding to the winter and summer solstices. Rather, they have been adjusted by

five degrees or so for the climate of New Mexico, such that they provide eight weeks of

full solar gain on either side of the winter solstice (as opposed to just on the winter

solstice), and a full eight weeks of shade on either side of the summer solstice (as opposedto just on the summer solstice).

Right Surface Area and Thickness of Thermal Mass: The usual sheet-rock, studs,

furniture, etc of a house represent a certain baseline amount of thermal mass:

Without additional thermal mass, direct gain (south-facing windows) should not exceed

7% of floor area.

A house that has 7% direct gain is sometimes called a "sun-tempered" house.

Even if adequate additional thermal mass is added to the house, for example, by adding

internal masonry walls or floors with masonry thicker than an inch, then direct gainsouth-facin windows can be u to but should not exceed 12% of the total floor area


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unless you are careful to avoid, or live with, a large degree of glare.

If adequate additional thermal mass is added to the house, an additional indirect gain(e.g. Trombe walls) may also be added to with a glazing area up 8% of the total floor areain addition to the 12% direct gain without overheating the house during the day.

Total solar gain area for a house with added thermal mass can therefore be up to butshould never be more than 20% of total floor area.

The simplest rule of thumb is that thermal mass area should have at least 6 times the

(uncovered) surface area of the direct gain glass area. More detailed mass sizing info is

contained in the guidelines.

Thermal mass effectiveness increases proportionally to thickness up to about 4 inches.

After that, effectiveness doesn't increase as significantly. So concentrate on getting the

surface area and the first four inches of thickness, and not on excessive thickness andvolume.

Contrary to common belief, it is not important to have all the mass in the direct gain path

- so don't worry about trying to arrange for this! Rather, strive to have thermal mass in

line of sight of sunlit surfaces.

Right Arrangement of Thermal Mass: Once light enters through the windows, reflection

and thermal re-radiation can transmit energy from the sunlit surfaces to other thermal mass

surfaces which are in line of sight of the sunlit surfaces. Non-sunlit floor area, for example,will not function well as thermal mass with respect to sunlit floor area because it is not in

line of sight with sunlit floor areas.

Contrary to common belief, it is not advisable to color all thermal mass surfaces darkly

(with the exception of indirect gain surfaces such as Trombe walls and water walls, which

need to be verydark). Walls lit by clerestories, for example, are better painted white,

such that they reflect the light to other thermal mass surfaces, such as the floor. If the

wall becomes too hot, a thermal-siphon airflow can be set up that effectively heats the air

and overheating the space.

In general, wall and ceiling thermal mass surfaces should be light-colored, while floors

should be dark. Making the floor dark helps keep the floor warm and easier to clean, in

addition to providing good adsorption of thermal radiation.

Right Arrangement of Rooms:

Room layout should take advantage of morning sunlight for the kitchen, and possibly a

bedroom, winter sunlight for the living room, and make use of buffer spaces and garages asadditional northern and western shielding, as the following diagram suggests:


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A sunspace might be added with advantage in front of the living room.

These rules of thumb should give you a good feeling for what is required. Nowadays,

computer software, such as "Energy-10" exist to assist the architect with perfecting the

thermal performance of a building. Every effort should be made to take advantage of

these new tools, and of these design principles for energy efficient building.

From Oil Wells to Solar Cells Primer

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