• Energy resources are available to supply mankind's expanding needs without environmental detriment.

• Wastes remain a major concern whether they are released to the environment or not.

• Ethical principles seem increasingly likely to dominate energy policy in many countries, which augurs well for nuclear energy.

• "When viewed from a large set of criteria, nuclear power shows a unique potential as a large scale sustainable energy source." OECD 2001

• "The competitive position of nuclear energy is robust from a sustainable development perspective since most health and environmental costs are already internalised." OECD 2001

---

Until the last ten or twenty years sustainable energy was thought of simply in terms of availability relative to the rate of use. Today, in the context of the ethical framework of sustainable development, other aspects are equally important. These include environmental effects and the question of wastes, even if they have no environmental effect. Safety is also an issue, as well as the broad and indefinite aspect of maximising the options available to future generations.

There are many who see no realistic alternative to pushing Sustainable Development criteria into the front line of energy policy. In the light of concerns about global warming due to human enhancement of the greenhouse effect, there is clearly growing concern about how we address energy needs on a sustainable basis.

Energy demand

A number of factors are indisputable. The world's population will continue to grow for several decades at least. Energy demand is likely to increase even faster, and the proportion supplied by electricity will also grow faster still. However, opinions diverge as to whether the electricity demand will continue to be served predominantly by extensive grid systems, or whether there will be a strong trend to distributed generation (close to the points of use). That is an important policy question itself, but either way, it will not obviate the need for more large-scale grid-supplied power especially in urbanised areas over the next several decades. Much demand is for continuous, reliable supply, and this qualitative consideration will continue to dominate.

The key question is how we generate that electricity. Today, worldwide, 64% comes from fossil fuels, 16% from nuclear fission and 19% from hydro, with very little from other renewables. There is no prospect that we can do without any of these.

Sources of energy

Harnessing renewable energy such as wind and solar is an appropriate first consideration in sustainable development, because apart from constructing the plant, there is no depletion of mineral resources and no direct air or water pollution. In contrast to the situation even a few decades ago, we now have the technology to access wind on a significant scale, for electricity. But harnessing these "free" sources cannot be the only option. Renewable sources other than hydro - notably wind and solar, are diffuse, intermittent, and unreliable by nature of their occurrence. The very fact that we seek the sun for our summer holidays testifies to its low intensity. Similarly, bad weather and night-time underline its short-term unreliability. These two aspects offer a technological challenge of some magnitude. It requires collecting energy at a peak density of about 1 kilowatt (kW) per square metre when the sun is shining to satisfy a quite different kind of electricity demand, - one which requires a relatively continuous supply.

Wind is the fastest-growing source of electricity in many countries, albeit from a low base, and there is a lot of scope for further expansion. While it has been exciting to see the rapid expansion of wind turbines in many countries, capacity is seldom more than 30% utilised over the course of a year, which testifies to the unreliability of the source and the fact that it does not and cannot match the pattern of demand. The rapid expansion of wind farms is helped considerably by generous government-mandated grants, subsidies and other arrangements ultimately paid by consumers. But there is often a strong groundswell of opposition on aesthetic grounds from the countryside where the turbines are located.

Renewable sources such as wind and solar are intrinsically unsuited to meeting the demand for continuous, reliable supply on a large scale - which is most demand in developed countries.

Apart from renewables, it is a question of what is most abundant and least polluting. Today, to a degree almost unimaginable even 25 years ago, there is an abundance of many known energy resources in the ground. Coal and uranium (not to mention thorium) are available and unlikely to be depleted this century.

The criteria for any acceptable energy supply will continue to be cost and safety, as well as environmental considerations. Addressing environmental effects usually has cost implications, as the current greenhouse debate makes clear. Supplying low cost electricity with acceptable safety and low environmental impact will depend substantially on developing and deploying reasonably sophisticated technology. This includes both large-scale and small-scale nuclear energy plants, which can be harnessed directly to industrial processes such as hydrogen production or desalination, as well as their traditional role in generating electricity.

Energy resources

There is abundant coal in many parts of the world, but with the constraints imposed by concern about global warming, it is likely that this will increasingly be seen as chemical feedstock and its large-scale use for electricity production will be scaled down. Current proposals for "clean coal" technologies may change this outlook. The main technology involves using the coal to make hydrogen from water by a two-stage gasification process, then burying the carbon dioxide and burning the hydrogen. Elements of the technology are proven but the challenge is to bring the cost down sufficiently to compete with nuclear power.

Natural gas is also reasonably abundant but is so valuable for direct use after being reticulated to the point where heat is required, and as a chemical feedstock, that its large-scale use for power generation makes little sense and is arguably unsustainable.

Fuel for nuclear power is abundant, and if well-proven but currently uneconomic fast breeder technology is used, or thorium becomes a nuclear fuel, the supply is almost limitless.

Uranium is even available from sea water at costs which would have little impact on electricity prices. In any case the resource can be multiplied 60- to one hundred-fold by adopting the kind of technology which our postwar forebears thought would be necessary by now - fast neutron reactors used as breeders- See also paper on Supply of Uranium.

The Hydrogen economy

Hydrogen is expected to come into great demand as a transport fuel which does not contribute to global warming. It may be used in fuel cells to produce electricity or directly in internal combustion motors. Fuel cells are at an early stage of technological development and still require substantial, research and development input, although they will be an important technology in the future.

Hydrogen may be provided by steam reforming of natural gas (in which case CO₂ has to be taken into account), by electrolysis of water, or by thermochemical processes using nuclear heat.

Some new types of nuclear reactor such as high-temperature gas cooled reactors, operating at around 950-1000°C have the potential for producing hydrogen from water by thermochemical means, without using natural gas.

Large-scale use of electrolysis would mean a considerable increase in electricity demand. However, this need not be continuous base-load supply, as hydrogen can be accumulated and stored, and solar or wind generation may well serve this purpose better than supplying consumer electricity demand.

However, pending the development of affordable mass-produced fuel cells, a significant increase in base-load electricity demand may result from the adoption of Plug-in Electric Hybrid Vehicles. These are only a very short step from current availability (the Toyota Prius is a full hybrid, and only needs the facility to use mains power for recharging).

Wastes

Wastes - both those produced and those avoided, are a major concern in any consideration of sustainable development.

Burning fossil fuels produces primarily carbon dioxide as waste, which is inevitably dumped into the atmosphere. With black coal, approximately one tonne of carbon dioxide results from every thousand kilowatt hours generated. Natural gas contributes about half as much as coal from actual combustion, and also some (including methane leakage) from its distribution. Oil and gas burned in transport adds to the global total. As yet, there is no satisfactory way to avoid or dispose of the greenhouse gases which result from fossil fuel combustion.

Nuclear wastes

Nuclear energy produces both operational and decommissioning wastes, which are contained and managed. Although experience with both storage and transport over half a century clearly shows that there is no technical problem in managing any civil nuclear wastes without environmental impact, the question has become political, focussing on final disposal. In fact, nuclear power is the only energy-producing industry which takes full responsibility for all its wastes, and costs this into the product - a key factor in sustainability.

Ethical, environmental and health issues related to nuclear wastes are topical, and their prominence has tended to obscure the fact that such wastes are a declining hazard, while other industrial wastes retain their toxicity indefinitely.

Regardless of whether particular wastes remain a problem for centuries or millennia or forever, there is a clear need to address the question of their safe disposal. If they cannot readily be destroyed or denatured, this generally means that they need to be removed and isolated from the biosphere. This may be permanent, or retrievable.

An alternative view asserts that indefinite surface storage of wastes under supervision is preferable because progress towards successful geological disposal would simply encourage continued use and expansion of nuclear energy. This however is simply another case where ideological opposition to nuclear energy is more important to its detractors than dealing effectively with wastes to achieve high levels of safety and security, and further, ensuring that each generation deals with its own wastes. The wider question of alternative low-CO₂ means of producing base-load electricity tends not to be addressed, beyond wildly unrealistic projections for renewables.

"The scientific and technical community generally feels confident that there already exist technical solutions to the spent fuel and nuclear waste conditioning and disposal question. This is a consequence of many years work by numerous professionals in institutions around the world. .... There is a wide consensus on the safety and benefits of geological disposal." OECD 2001.

Ethical aspects of nuclear wastes

In a 1999 OECD article, Long-term management of radioactive waste, ethics and the environment, Claudio Pescatore outlines some ethical dimensions of this question. He starts on a very broad canvas, quoting four fundamental principles proposed by the US National Academy of Public Administration. They resulted from a request by the US Government to elucidate principles for guiding decisions by public administrators on the basis of the international Rio and UNESCO Declarations which acknowledge responsibilities to future generations:

• The Trustee Principle: "Every generation has obligations as trustee to protect the interests of future generations".
• The Sustainability Principle: "No generation should deprive future generation of the opportunity for a quality of life comparable to its own."
• The Chain of Obligation Principle: "Each generation's primary obligation is to provide for the needs of the living and succeeding generations," the emphasis being that "near-term concrete hazards have priority over long-term hypothetical hazards."
• The Precautionary Principle: "Actions that pose a realistic threat of irreversible harm or catastrophic consequences should not be pursued unless there is some countervailing need to benefit either current or future generations."

These can be applied to the question of nuclear wastes, and in particular to their geological disposal, a system with inherent passive safety. Referring to relevant 1995 IAEA and NEA publications, Dr Pescatore summarises the principles in this context as follows:

• The generation producing the waste is responsible for its safe management and associated costs.
• There is an obligation to protect individuals and the environment both now and in the future.
• There is no moral basis for discounting future health and risks of environmental damage.
• Our descendants should not knowingly be exposed to risks which we would not accept today. Individuals should be protected at least as well as they are at present.
• The safety and security of repositories should not presume a stable social structure for the indefinite future or continued technological progress.
• Wastes should be processed so they will not to be a burden to future generations. However, we should not unnecessarily limit the capability of future generations to assume management control, including possible recovery of the wastes.
• We are responsible for passing on to future generations our knowledge concerning the risks related to waste.
• There should be enough flexibility in the disposal procedures to allow alternative choices. In particular information should be made available so the public can take part in the decision-making process which, in this case, will proceed in stages.

Dr Pescatore points out that geological disposal is considered as the final stage in waste management. It should ensure security and safety in a way that will not require surveillance, maintenance, or institutional control.

External costs

Some energy sources dispose of wastes to the environment or have health effects which are not costed into the product. These implicit subsidies, or external costs as they are generally called, are nevertheless real and borne by society at large. Their quantification is necessary to enable rational choices of energy sources. Nuclear energy has always provided for waste disposal and decommissioning costs in the cost of electricity.

The 2001 ExternE study in Europe compared the external costs of various means of generating electricity. It showed that coal was highest (and about the same as all other generation costs), followed by gas, while nuclear and wind were one tenth or less of coal. The methodology included the risk of accidents and covered full fuel cycle. Hence if external costs are taken into account, nuclear energy becomes very competitive.

Safety

The safety of nuclear energy has been well demonstrated, notwithstanding the continued operation of a small number of reactors which are, by western standards, distinctly unsatisfactory. These include two old Soviet designs, one of which - before some very extensive modifications to the type - precipitated the 1986 Chernobyl disaster. Over 10,000 reactor-years of operation have shown a remarkable lack of problems in any of the reactors which are licensable in most of the world.

There is probably no other large-scale technology used worldwide with a comparable safety record. This is largely because safety was given a very high priority from the outset of the civil nuclear energy program, at least in the west. About one third of the cost of a typical reactor is due to its safety systems and structures, including containment and back-up provisions. This is a higher proportion even than in aircraft design and construction.

Any statistics comparing the safety of nuclear energy with alternative means of generating electricity show nuclear to be the safest. In fact, Chernobyl is the only blemish on a near perfect record, and is of very little relevance to the safety of most of the world's reactors.

Energy security

From a national perspective, the security of future energy supplies is a major factor in assessing their sustainability. Whenever objective assessment is made of national or regional energy policies, security is a priority.

France's decision in 1974 to expand dramatically its use of nuclear energy was driven primarily by considerations of energy security. However, the economic virtues have since become more prominent. The EU Green Paper on energy security in 2000 put forward coal, nuclear energy and renewables as three pillars of future energy security for Europe. The US government is clear that nuclear energy must play an increasing role this century.

Opportunity costs

Nuclear energy and renewables have one important feature in common. They give us access to virtually limitless resources of energy with negligible opportunity cost, - we are not depleting resources useful for other purposes, and we are using relatively abundant rather than less abundant energy. Probably the time is approaching when fossil carbon-based fuels will be too valuable to burn on the present scale. Particularly this is true of natural gas. Of course minimising opportunity cost would be very difficult if we preferred to "leave uranium in the ground", as sometimes urged.

Conclusion

Recent analyses fail to come up with any 50-year scenario based on sustainable development principles which does not depend significantly on nuclear fission to provide large-scale, highly intensive energy, along with renewables to meet small-scale (and especially dispersed) low-intensity needs. The alternative is either to squander fossil carbon resources or deny the aspirations of hundreds of millions of people in our grandchildren's generation.

Nuclear energy's opponents have yet to credibly suggest how we should produce most of our future electricity. Certainly all the reputable energy scenarios show the main load being carried by coal, gas, and nuclear, with the balance among them depending on economic factors in the context of various levels of greenhouse constraints.

The notion of sustainability needs to be supported politically so that all external costs are factored in. Then it can start to drive the economic choices among fuels for electricity production.

The sooner substantial solar and wind capacity is operating on grid systems the sooner their advantages and limitations will become widely evident. That will help focus public discussion on the real options for continuous, reliable (base-load) electricity generation on the large scale required. Nuclear power can contribute significantly to sustainable development.

Sources:
OECD NEA Newsletter # 1/99, (the 1995 principles referred to are quoted in Appendix 3 of Nuclear Electricity).
OECD IEA, 1998 & 2001, World Energy Outlook.
OECD NEA, 2000, Nuclear Energy in a Sustainable Development Perspective.
IAEA, 1997, Sustainable Development and Nuclear Power.
World Energy Council, 2000, Energy for Tomorrow's World - Acting Now!
World Energy Council 2002 statement.
OECD NEA 2001, Trends in the Nuclear Fuel Cycle.

---

Uranium Information Centre Ltd
A.C.N. 005 503 828

GPO Box 1649N, Melbourne 3001, Australia
phone (03) 9629 7744
fax (03) 9629 7207

History
Solar cell technology dates to 1839 when French physicist Antoine-Cesar Becquerel observed that shining light on an electrode submerged in a conductive solution would create an electric current. In 1941, the American Russell Ohl invented a silicon solar cell.

Improved solar cells became a reliable source of electricity for satellites, but their price horrified electric utilities, so they were only used when cheaper alternatives were unavailable. Sure, if you lived three miles down a dirt track -- or in the outback of Australia -- PV could be cheaper than stringing a new power line. To many users of PVs, the decision was environmental -- they wanted to avoid fossil and nuclear power.

A 4-kilowatt photovoltaic system powers The Nature Conservancy's Red Canyon Ranch in Wyoming.Utility PhotoVoltaic Group.

The oil crises of the 1970s came and went without PV playing a significant role, although other uses of alternative energy sources, such as wind-powered electric generators and solar water heaters, did make a slight impact. But as PV prices enter a freefall, it is being used for much more than powering isolated homes. One promising application is to beef up sagging voltage near the end of utility transmission lines. "You can put small increments of power right where it is needed with PV, rather than spending large sums on infrastructure development," says Gibson of the Utility PhotoVoltaic Group. Still, he admits, despite studies proving the feasibility of this use, "real progress... may still be five years off."

Today, the demand for PV is not limited to environmentalists. "The market has come up significantly in the past two years," says John Bigger, technical director at the Utility PhotoVoltaic Group. "We're seeing a significant increase in demand, most all of the large manufacturers are looking at a waiting list of three to six months or more."

As worldwide PV manufacturing capacity grows by a steady 15 percent per year, the overseas market "has taken off," says John Thornton of the National Renewable Energy Lab. Over the next decade, North America, with its excellent electric grid, will represent a small percentage of global sales. U.S. exports in 1996 were $800 million to $900 million.

PV could be a godsend for the 2 billion-plus people who don't have access to electricity, Bigger says. "There's not enough money to extend existing grids to them right now, so the major alternative is diesel fuel" running generators in isolated villages. Far better, he says, would be to install some solar panels, and gradually build village-based systems powering lights, radios, refrigeration and water pumps.

How big is the market for cells that can provide juice at $3 per watt? Just looking at South Asia, where electricity is in short supply or nonexistent, "You are dealing with one-third of the world population right there," Thornton says. Already, he adds, demand for PV systems is "insatiable." And with each decrease in cost, demand perks up, feeding back to increase manufacturing volume and further reduce costs.

Thin-film technology

One long-heralded cost-cutting technology -- thin film cells -- is set to enter the market in 1997. Today's PV cells are made of crystalline silicon, which require expensive, highly pure silicon. Thin-film cells are cheaper, not just because the material costs roughly 1 percent as much as crystalline cells, but also because they're easier to manufacture. "It's a little analogous to a glass plant," says Thornton. "It's conceivable that you could build plants where it rolls off in sheets."

Against this backdrop, the Sacramento utility district's estimate of $3 per watt of installed cost by 2002 seems reasonable, Thornton says. And at that price, he anticipates that 9 gigawatts (billion watts) PV capacity will be installed in the United States. That would allow the sun's rays to account for roughly one percent of the U.S. generating capacity of 700 gigawatts).

However, Thorton says the actual price of PV will depend on the world market, and if demand exceeds supply, the $3 price may not be reached on scheduled.

And while $3 is cheap, it's not the end of the road, Bigger adds. "In the long term, some people see costs dropping below $1 per watt, although that would be well after 2010."

But what about a traditional drawback of solar power -- its limited availability? The projected 9-gigawatt increase in capacity in the United States would not require nighttime storage, Bigger says, since many utilities get their peak load during peak daylight, around mid-day or in the early afternoon. Clearly, systems in places where alternative electricity is not available would need storage, probably batteries, for nighttime power.

Physics
Sunlight is composed of photons, which can be thought of as "packets" of energy (the amount of energy in a photon being proportional to the frequency of its light). When photons strike a solar cell, the vast majority are either reflected or absorbed (some really high-energy photons will blow right through, but they're of no concern here). When a photon is absorbed, its energy is transferred to the semiconductor -- in particular, to an electron in an atom of the cell. If enough energy is transferred, the electron can escape from its normal position associated with that atom. In the process, the electron causes a hole (i.e., an empty spot where the electron used to be) to form. Each photon with enough energy will normally free exactly one electron, and one hole. Note that both electrons and holes are mobile, and as such can be current carriers.
Figure 1. The effect of the electric field in a PV cell (diagram courtesy of How Stuff Works )

The simplest solar cells have 3 active layers -- a top junction layer (made of N-type semiconductor ), an absorber layer (a P-N junction), and a back junction layer (made of P-type semiconductor). Thanks to the P-N junction, the cell has it's own built-in electric field. This electric field provides the voltage needed to force electrons and holes freed by light absorption to flow in their own directions (the electrons to the N-type side, and the holes to the P-type side). If we provide an external current path, electrons will flow through this path to their original (P-type) side to unite with holes the electric field sent there, doing work for us along the way. The electron flow provides the current, and the cell's electric field causes a voltage. With both current and voltage, we have power, which is just the product of the two.

Figure 2. Operation of a photovoltaic cell (diagram courtesy of How Stuff Works )

After a moment's thought, you can see that two additional layers must be present in a solar cell --electrical contact layers -- to allow electric current to flow out of and into the cell. The electrical contact layer on the face of the cell where light enters is generally present in some grid pattern and is composed of a good conductor such as a metal. The grid pattern does not cover the entire face of the cell since grid materials, though good electrical conductors, are generally not transparent to light. Hence, the grid pattern must be widely spaced to allow light to enter the solar cell but not to the extent that the electrical contact layer will have difficulty collecting the current produced by the cell. The back electrical contact layer has no such restrictions -- it need simply provide an electrical contact and thus covers the entire back surface of the cell.

Additionally, an antireflective coating is generally applied to the top of the cell to reduce reflection losses, and a cover plate of some kind is often installed to protect the cell from damage while out in the real world.

Materials
The most common material used in solar cells is single crystal silicon. Solar cells made from single crystal silicon are currently limited to about 25% efficiency because they are most sensitive to infrared light, and radiation in this region of the electromagnetic spectrum is relatively low in energy.

Figure 3 -- Single crystal solar cells (image courtesy ACRE )

But single crystal silicon isn't the only material used to build solar cells.

Figure 4 -- Polycrystalline solar cells (image courtesy ACRE )

Polycrystalline ("many crystals") solar cells are made by a casting process in which molten silicon is poured into a mould and allowed to cool, then sliced into wafers. This process results in cells that are significantly cheaper to produce than single crystal cells, but whose efficiency is limited to less than 20% due to internal resistance at the boundaries of the silicon crystals.

Figure 5 -- Amorphous solar cells (image courtesy ACRE )

Amorphous cells are made by depositing silicon onto a glass substrate from a reactive gas such as silane (SiH₄). This type of solar cell can be applied as a thin film to low cost substrates such as glass or plastic. Thin film cells have a number of advantages, including easier deposition and assembly, the ability to be deposited on inexpensive substrates, the ease of mass production, and the high suitability to large applications. Since amorphous silicon cells have no crystal structure at all, their efficiencies are presently only about 10% due to significant internal energy losses.

Aside from the various forms of silicon, a number of other materials can also be used to make solar cells -- gallium arsenide, copper indium diselenide and cadmium telluride to name a few. Note that solar cells are sensitive to different wavelengths of light (i.e., photons of different energies) as a function of the materials they are built from. Accordingly, some cells are better performers outdoors (i.e., optimized for sunlight), while others are better performers indoors (optimized for fluorescent light).

Newer, high-tech solar cells have yielded improved energy conversion efficiency by incorporating two or more layers of different materials with different wavelength sensitivities. Top layers are designed to absorb higher energy photons while allowing lower energy photons through to be absorbed by the layers beneath. Double-junction cells are commercially available to BEAMers on occasion (surplus shops often call these "spacecraft cells"). Spacecraft and other mass-sensitive applications have now started to make use of triple-junction cells (but don't expect to find these in surplus shops any time soon).

Cell Packaging
Solar cells also are available in a variety of packages. Most common are "raw cells," often with some cover sheet attached. One popular line of cells, the Panasonic Suncerams, consist of amorphous silicon cells, deposited on the back of a glass substrate (in this case, the glass functions as both substrate and cover sheet). These are durable and cost-effective cells, if a bit heavy due to the thickness of the glass. Encapsulated solar cells are also sold -- as the name implies, an enclosure (often plastic, often with some sort of concentrator lenses built into the cover sheet) contains a regular (generally multicellular) solar cell or cells. These are extremely durable, if heavy and none too efficient. Recently, flexible solar cells have become available. These are amorphous cells on a thin plastic substrate -- low efficiency, fairly high cost, but light and a very useful package for some applications.

Performance

An important feature of solar cells is that the voltage of the cell does not depend on its size, and remains fairly constant with changing light intensity. However, the current in a device is almost directly proportional to light intensity and size¹. Figure 6 shows example I / V curves for a single cell as a function of light input:

Figure 6 -- Single-junction solar cell I/V curves (diagram courtesy ACRE )

A solar cell's power output can be characterized by two numbers -- a maximum Open Circuit Voltage (Voc, measured at zero output current) and a Short Circuit Current (Isc, measured at zero output voltage). Remember that power can be computed via this equation:

P = I * V

So with one term at zero these conditions (V = Voc @ I = 0; V = 0 @ I = Isc) also represent zero power. As you might then expect, a combination of less than maximum current and voltage can be found that maximizes the power produced. This condition is called, not surprisingly, the "maximum power point". BEAM solar engine designs attempt to stay at (or near) this point. The tricky part is building a design that can find the maximum power point regardless of lighting conditions².

Note that single junction silicon solar cells produce approximately 0.5 - 0.6 Voc, so they are usually connected together in series to provide larger voltages. In some cases (like the Panasonic Sunceram cells), multiple cells are built onto a single substrate in order to yield the convenience of higher output voltage from a single package.

Some more subtle properties of solar cells also need to be accounted for in their use. In particular, when connecting solar cells in series, care needs to be taken to give all cells roughly equal access to light -- the weakest solar cell in series (or one that is shaded) will determine the total current. Normally this is not an issue in BEAMbots, and will only rear its ugly head if you spread solar cells around on the surface of your 'bot. In a pinch, reverse Schottky diodes can be wired across each cell to automatically bypass any cell that may get shaded.³

Similar issues can occur when wiring solar cells in parallel. In that case a shaded cell can act as a short circuit to the output of its more active neighbors. Here, a germanium diode in series with each separate cell can be used to mitigate problems, if 'bot geometry can't be adjusted to avoid them (although at the cost of a few tenths of a volt).

This work is licensed under a Creative Commons License.

As part of the chassis design, you will of course have worked out what type of suspension to use. It may have come about the other way. You may have chosen your suspension, positioned your driver and motor, then joined up all the bits with a frame. There are indeed many ways to achieve a design. I sometimes start with the aerodynamics, get a body shape, then try and fit in the best suspension, motors and batteries, etc, around the driver.

Whichever way you go about designing your solar car, the mechanical systems should be simple in concept, but designed to minimize friction and weight while maintaining the strength needed to handle the various road conditions. You should take a good look at existing state of the art. You will learn a lot from this research and then you can apply your own ideas. Lightweight metals like titanium and composites are commonly used to maximize the strength-to-weight ratio needed to build efficient components. The mechanical systems include the suspension, brakes, steering, wheels, and tires. Regulations from most events set minimum standards that mechanical components must meet, but as mentioned elsewhere there are no standard designs used in solar cars.

Steering & Suspension

Front wheel steering has many advantages since it tends to be more stable and safer. A solar car uses energy frugally if it is to be competitive. If there are two front wheels, it is therefore advisable to work out the geometry so that they run parallel when the car is going straight ahead to eliminate scrub, but when the car is turning, the front wheels turn at different radii. If the car is turning left, the left front tire is making a smaller circle than the right front tire. If the tires remain parallel while turning, they will cause unnecessary drag because the angles will not describe scrub free attack to the road, decreasing tire life and overall performance. The principles overcoming this problem were solved by Ackerman, hence the Ackerman Steering geometry employed on most production cars.

Brakes

Disc brakes are desirable as they are predominantly hydraulic. Having hydraulic lines running to the wheels can be easier than mechanical brake arrangements. The most significant problem with disc brakes is that the brake pads do not back away from the brake rotors when pressure is released, they just relieve braking pressure. Because the pads don't normally back away from the rotors, they continue to have a small amount of drag. While this drag may not be noticeable on the family car, it is very inefficient on solar cars. Go kart shops now have brake calipers that are spring loaded to move the pads away from the rotors. These very worthwhile.

Motor driving single rear wheel

Solar cars typically have three or four wheels, where the rules require at least three, or the vehicle falls into a cycle category. The common three wheel configuration is two front wheels and one rear wheel (usually the driven wheel). Four wheel vehicles are sometimes configured like a conventional vehicle (with one of the rear wheels driven). Other four wheel vehicles have the two rear wheels close together near the center (similar to the common three wheel configuration). In theory, three should be more efficient, since there are less moving parts and rolling resistance may be lower.

A wide variety of suspensions are implemented on solar cars. This is partly due to the fact that the body and chassis designs are so different between cars. The most common type of front suspension used in solar cars is the double A-arm suspension, similar to those used on conventional vehicles. Typically, trailing arm suspensions similar to those found on motorcycles are utilized in the rear. Teams design their suspension components to move freely and smoothly for maximum efficiency. The design must also be adjustable so as to maintain proper alignment and functionality.

Disc brakes cycle parts

One of the great things about solar cars, is that you have a free hand to let your imagination roam. That is one of the reasons for the incredible diversity, although I think you may agree, the monocoque designs are beginning to look a bit samey.

Safety should be high priority for any designer. For this reason, solar cars must meet stringent braking performance standards and every solar car is required to have two independent braking systems, much like the dual braking systems on production cars. Disk brakes are most commonly used in solar cars because of their adjustability and good braking power. Some teams use mechanically actuated brakes while others use hydraulic. Mechanical brakes tend to be smaller and lighter than hydraulic, but don't offer as much brake force and require constant tuning. To maximize efficiency, the brakes are designed to move freely by eliminating brake drag, which is caused by brake pads rubbing against the brake surface.

Double wishbone suspension and steering

The steering systems within a solar car, much like suspensions, vary greatly. The teams must meet turning radius and handling requirements, but are free to use any design. The major design factors for steering are reliability and efficient performance. The steering system is designed with precise steering alignment because even small misalignments can cause significant losses and increase tire wear. Many teams now use long uprights mating onto high mounted wishbones. This reduces the thickness of the wheel spats or fairings, hence lowers drag. The object of employing suspension is obviously to cushion the vehicles passage. It should be soft enough to protect the car and solar array from unnecessary jolts and firm enough to provide a stable ride. A good suspension will also ensure the wheels stay in contact with the road surface, by controlling bounce and re-bound. A spring allows movement and a shock absorber, or damper, prevents oscillation.

Tires

In early racing events, bicycle wheels and tires were commonly used because of their lightweight and low rolling resistance (minimal friction). These wheels and tires were generally overloaded when supporting the weight of a solar car, which effected the performance and safety of the vehicle. Event Regulations do not allow overloaded tires and wheels. Fortunately, the popularity of solar car raycing has prompted some tire manufacturers to construct tires designed for solar cars. Most teams are taking advantage of these low rolling resistant, lightweight wheels and tires that increase both safety and performance.

Leading arm suspension and steering

Republished unchanged from :
http://www.speedace.info/solar_car_mechanics_suspension_steering_and_brakes.htm