SOLAR ENERGY

Does the solar panel or motor have storage capacity?

The solar panel is a direct power source - switch it on, put it in the sun and it will generate electricity (given a sufficient level of sun intensity - the intensity can be measured using one of our Calibrated No.10 panels). Neither the panel nor the motor has any storage capacity.

What can I use as a light source for the solar panels?

Ideally, the best thing is the Sun itself. However, when it’s winter or overcast, to test your car or boat indoors a good substitute for sunlight is a powerful halogen lamp. Mains powered halogen flood lamps of about 500 watts are readily available from lighting shops or hardware suppliers.

A 500 watt lamp directly facing the panel and about 300mm away, will produce a light level equivalent to about 50% Sun.

Another option for testing a car or boat in winter is using a battery pack delivering the correct voltage. This at least tests that the car or boat is assembled correctly and functions.

CAUTION: The lamp puts out more heat than the Sun, so to avoid panel damage only illuminate the panel for about 40 seconds, then allow the panel to cool down.

A safer option is a low voltage 100 watt handheld halogen spotlight. This type of lamp is available from automotive accessory stores and is usually 12 volt rated. You will need a suitable battery or power supply. This lamp is suitable to demonstrate power generation (that is – to turn the wheels when the car is off the ground) but is not sufficient to run a vehicle.

Note: In the classroom, the light may appear very bright to our eyes but the car does not run as the light level is far too low for the solar panel to produce useful quantities of power. Fluorescent lights are a poor substitute for sunlight, as the frequency of light they produce is very different from the sun. Incandescent lamps are much better. However, remember that full sunlight is around 1000 Watts per square metre. In a typical room at home you might have 500 Watts of light in a room of 15 square metres, this is only about 3% of the energy provided by full sunlight, so it is no wonder solar panels do not work well inside.

SOLAR BOATS

We want to introduce Solar boats to our programme. We do not have a large budget. What do you suggest?

You can buy the motor and small solar panels from us separately. Alternatively, you might like to consider our "Intro Solar Boat kit". This is specifically aimed at schools that want to try making solar boats but don’t have the budget for hundreds of dollars per boat - those are for class efforts, not individual students.

The "INTRO SOLAR BOAT KIT" is aimed at school classes who are interested in trying out solar powered concepts. The Intro Boat allows students to gain experience and learn while developing the boat - without competing in Model Solar Challenges. It is great value for money as it includes a normal “hobby type” motor, our No. 4 Solar Panel and other parts.

The JUNIOR SOLAR BOAT KIT is designed to provide the basis of a solar boat for use in the Junior Solar Boat Challenge. It includes a motor (that complies with the regulations for that level, and is well matched to the competition panels), a different guide tube and bearings (to reduce friction on the propeller shaft), 2 shafts and 2 propellers etc. No panel is provided as this allows the school to re-use previous years’ panels, or share panels between boats.

We have deliberately kept the price for these kits low (compared to the individual prices of components). We work with the Victorian Model Solar Vehicle Challenge organisation to further the aims of ensuring our youth / future citizens are learning about responsible energy consumption.

Which solar panel you would recommend for the Junior Solar Boat kit (STBJUN)?

The Junior Solar Boat kit is designed to be used in the Junior Solar Boat Challenge (Primary). When competing we suggest using our No. 26 solar panel which is designed for the competition. It is a light weight, fibreglass enclosed panel (it weighs approx. 50 grams) and conforms to the 350 square cm regulation.

Note: If you don’t intend to compete, but want to introduce solar concepts to your students, our Intro Solar Boat would be more suitable as it comes with our No. 4 panel.

Which Solar Power Panel Controller is suitable for the Model Solar Boats?

The Automax or the low voltage Solar Panel Power Controller is suitable for a single Boat Panel connected in series as it will function from about 5.3 Volts up to about 10 Volts, ideal for the boat panel maximum power voltage when it is connected in series.

Note: The standard Solar Panel Power Controller will not function below about 10 Volts so consequently is not suitable for use with a single Boat Panel.

How does the propeller fit on the motor?

The boat propellers don't fit directly on the motor - the motor shafts are 2.0mm diameter, and the propellers have a 2.4mm hole.

The motor is connected to a 2.5mm steel rod via a silicon rubber tube coupling. The propeller is a press fit onto the 2.5mm steel shaft.

When making boats, most people run the steel shaft through a guide tube (the basic one has a 2.7mm inner diameter).

If you want to minimise friction, we recommend that you use the 2.5mm steel rod with the 4.5mm inner diameter guide tube, together with the driveline bearings. That way if the guide tube is not mounted perfectly straight, the shaft shouldn't touch the guide tube’s inside wall.

SOLAR CARS

What is the difference between the Solar Car kits?

We have four Solar cars in our range. They cater for different audiences:

The Basic Solar Car (Code: SOLARB) is aimed at introducing the concept of solar power generation, and utilises a single one piece panel (No. 4 panel) and the SM17 motor combination. This is popular amongst the younger students as it can have quite decent performance (i.e. it goes quickly). Useful to demonstrate that solar power generation works (a quick vehicle in full sun).

Note: this kit is also available in a No-solder variant Code: SOLARB-NS).

The Solar Car V2 (Code: SOLARv2)  is aimed at the next level of teaching (solar and electricity). It not as quick as the Basic Solar vehicle, and it uses a two-piece panel (No. 11) and utilizes the MOTJ2 motor. This panel has a lower total power output than the No. 4 panel. Instead of providing only power, this panel is used to allow the teacher and student to experiment with wiring panels in series and parallel and how the power generated is affected by those changes, under changed lighting conditions (as the sun goes down, or on an overcast day).

The Advanced Solar Car (Code: SOLDV) - uses a larger (4 piece panel) and has electronics (a Solar Panel Power Controller). This kit allows more complexity and versatility for experimentation.

The Intro Solar Car (Code: SCRINT) is used to introduce concepts that are needed to participate in Model Solar Challenges (but is not suitable for competition). This car uses 2 No. 4 Solar panels (usable in series and parallel) and has wheels with a low rolling resistance.

Which motors operate using only a small amount of current?

The MOTJ2 motor has a low current-usage suited to work with small solar panels (starting current being the issue). If using solar panels, the MOT17 and the MOT30 are both powered by solar panels in different kits (respectively one No. 4 panel and 2 No. 4 panels). The real the question comes down to matching the motor to the panel, in this case, not just which motor has the lowest current consumption.

The MOT22 is the motor with the next lowest current consumption and is a part of the Versatile gearbox assemblies, in either Jouster or Bubble variants. If the motor suits, you still need to consider if the gear ratios are acceptable for your usage.

How do I test the electronics on the Solar car?

For testing the electronics on the car there are a couple of really simple functional tests that will prove the system is OK or not as the case may be. They are detailed below. (NB. ** All tests should be performed at the same panel illumination level).

  1. Test the open circuit voltage of the panel it should be above 6 Volts. If not, there is a panel fault. 
  2. Check the short circuit current direct out of the panel with nothing else attached to it but the Amp meter directly across the panel output terminals. Remember this reading.
  3. Now connect the electronics unit to the panel and connect the Amp meter directly to the output terminals of the electronics (motor connections) adjust the electronics according to obtain the highest current reading. This reading is expected to be over three times the current measured in 2 above. **

** All tests should be performed at the same panel illumination level. We obtained the following test results in Sun at 4% Sun level.
a)         Open circuit volts 6.2 Volts
b)         Short circuit current from panel 0.006 Amps
c)         Current out of electronics unit 0.035 Amps

How do I decide what gear ratio to use for my model car?

We can make no suggestions as you need to work out the desired gear ratios for your own car. The gear ratio depends on your car's wheel diameter and the solar panels power as well as other factors. Please check the Victorian Solar Association’s website for a simulator. That will allow you to calculate gear ratios.

ADVANCED SOLAR CAR

What motor upgrade would be suitable for the Advanced Solar car?

The Advanced Solar Car kit will not produce flashing performance as it was really intended to demonstrate solar panel and motor performance variations under differing Sun conditions and panel wiring configurations i.e. changing between series and parallel. Then, when using the Electronic Panel Controller, the value of matching the solar panel output to the load is clearly demonstrated by the performance increase.

Unfortunately, just changing the motor will not improve performance as the limiting factor is the panel power. The panel only puts out 1.2 watts in full Sun.

If you wish you can put together an upgraded version of this car using an MOT30 motor and two No. 4 panels (2.0 volt 0.8 amps at full sun) with these panels connected in parallel you could expect the car to start running at about 15% Sun and for faster running with the panels in series the car should start running at just over 30% Sun. Obviously, you need a larger chassis to mount these larger panels and they do not have sufficient voltage to run the electronics unit which requires > 6 volts. It is also still necessary to keep weight low as these panels together in full Sun still only produce fractionally over 3 watts in full Sun.

Note: this is effectively our Intro Solar Car kit (although that doesn't have an electronics kit)

Is the SM403 motor suitable for the Model Solar Car?

No, the SM403 will not work well due to the large diameter of the motor casing.

The ST403 motor is designed to fit into the Junior Solar Boats’ market (it is not a Senior class winner but works well in the Junior boat segment).

-       The ST-403 motor has a large body diameter, which is not an issue with boats but for cars that won’t work well with our normal range of gears.

What gears should I use with a Faulhaber motor?

At the moment the only company supplying pinion gears to suit the Faulhaber motor are R.I. Gear. They make pinion gears which are attached to the motor’s shaft by a grub screw –that way there is no risk of damaging the Faulhaber motor by pushing the gear onto the shaft. Note: our pinion gears are all press fit.

How can I improve the performance of the Model Solar Challenge Car?

The use of Electronics is one way to harness the solar panels power better. We have two units available:

The AUTOMAX (Maximum Power Point Tracker - MPPT):

This holds the solar panel’s output voltage at its Maximum Power Point (MPP) voltage regardless of the load conditions, thus transferring all the available panel power to the motor.  The AUTOMAX does not require tuning or setting up. It has an inbuilt computer which continuously reads the input power, and tracks for the maximum power point all on its own.

Note: the unit as supplied is fully assembled and then tested.

The Solar Power Panel Controller (SPPC)

This is a simple cost effective way to significantly improve the performance of your Model Solar Car. At the same time you will reduce set up time and complexity.

Note: this unit is only available in kit form. A student familiar with electronics assembled one of these units in less than 20 minutes.

The SPPC operates by rapidly switching the motor on and off to maintain the solar panel Voltage at the point where maximum power is produced. This switching action causes the inductor in the output section of the circuit to modify the current and voltage provided by the solar panel to a value that exactly matches the motors requirements.

This results in the maximum power available from the solar panel being constantly transferred to the motor thus maximising the drive available to the car.

This action of modifying voltage and current to suit the motors requirements has the added advantage of increasing the motor torque by up to 500% as the motor starts from stalled. Consequently, the car performs as though it has an automatic transmission exhibiting much greater acceleration that a car without electronics.

Interestingly, we have found that generally one gear ratio suits all conditions, so gear changing is a thing of the past.  Just put your car on the track and turn it on, no matter what the sun level is.

MODEL SOLAR CHALLENGES

Why are there different motors in the Solar Catalogue than in the Technology Catalogue?

The two motors listed in the Solar catalogue are different types of motors, and are suited to the Model Solar Challenges, as these have a much higher efficiency than the “hobby” type motors in the Technology Catalogue.

  • The Faulhaber motor is an industrial motor which is seen by many as “the” motor to use in competition
  • The SM403 was developed by a motor manufacturer for us, to get an affordable motor with good efficiency that matched in with the Junior Solar competition or Sheridan car needs.

You now only offer one No. 26 solar panel in your catalogue?

Yes. We order a quantity of panels to one specification, and when they arrive we test them for power output. They are graded according to their wattage, and offered for sale. When ordering the best thing is to specify car or boat panels, as we will pick the most suitable panels for your application from what is in stock.

Our panels are amongst the best / most suitable panels for being competitive in the Model Solar Challenges, as they were especially designed for the car and boat challenges - over the years a lot of development has gone into these panels.

Are the highest power SOLAR26 always the best panels to use?

Not always.

For the BOAT Challenge, the regulations stipulate maximum surface area of 350sq. cm. In that case the higher Performance panels will provide more power.

For the CAR Challenge, the regulations stipulate maximum power output of 10Watts. That means that 2 of the lower rated panels are adequate, as the scrutineers will mask off some of the panel to bring the power down to the specified power output! Andthe car design, gearing and other factors also influence performance.

Pros and Cons of using Competition solar panels

Unless competing in the Solar Challenges, we would not suggest using the competition panel. Why?

  • The competition panel is expensive
  • The competition panel is fragile (lightweight construction - especially for the challenges, where weight can be an issue)
  • Students are not always careful when removing them and can easily damage the panels internals (solar cells)
  • All of our "normal" (small hobby style) panels are robust - they have a backing board
  • To make it worth using a competition panel, you need to match it with a suitable motor etc. (these were purpose made for the challenge, to match in with the Faulhaber motor used by many teams)

Model solar competition guidelines

The basic intent of the Model Solar Competition is to engage students in Science and Technology. To ensure they fully engage and get the maximum educational benefit it is essential the students actually do the work. This ensures deeper understanding and maximum educational outcome. 

Considering the feasibility of providing a kit of parts for cars competing in the Model Solar Car Challenge it is acceptable to offer a kit of components say for running gear, solar panels and electronics. However, any pre designed chassis or body would not be eligible to compete as these must be the work of students. See the appropriate section of the regulations copied below (Note:  Always check your state’s current Model Solar Challenge regulations).

Original work

All teams must be able to provide evidence to the scrutineers that the car is the original work of the team members in both design and construction, performed in the current year, and not simply a restyling of a previous existing car.  This will include both the chassis and the body of the car.  Solar panels, motors, drive systems, wheels, suspension, guide systems and other similar components will not be included and may be reused.  If any school has more than one car entered, the cars must be significantly different in both chassis and body to indicate to the scrutineers that the cars are the work of different teams. This work will be verified by submission of a poster (3.6) and discussions with delegated committee members in an interview (3.7)

There is significant help already available to students in preparing their own designs and constructing a car in the form of the Scorpio Solar Car and the Sheridan kit car. Having undertaken the construction of these cars students should have gained sufficient knowledge and skill to design and construct their own car.

The Model Solar Challenge Victoria website shows details of a past winning car, assembly of components and even a Mathematical Simulation to allow students to evaluate the probable effect on performance of various design choices.

Link to Model Solar Challenge Victoria

The most important design features of a car in order of importance are:

  1.  Quality components
  2.  Build accuracy
  3. Aerodynamics, comparing identical cars except for aerodynamics running in full sun, a car with the best aerodynamics reasonably possible compared to a car with the worst aerodynamics would win a one lap race by 9 metres and a two lap race by 22 metres.
  4. Power to weight ratio.

INTERESTING INFORMATION

Currently we do a year 7 project that is a model helicopter from timber that has a solar panel powering a 1.5v round motor that turns an ornamental rotor. What motor should we use?

This question is both easy and a little complex. As you correctly pointed out it depends very much what performance is needed. Firstly, as to just drive a rotor for show we need practically no power so just about any motor would do.

Now the problems. How fast do you want it to run? These permanent magnet motors have the characteristic that RPM varies with voltage so if we have a 6 volt motor rated at 5000 RPM when we run it on 1.5 volts it will spin at 1250 RPM (or round about that speed).

Next how big a solar panel can you accept, and at what Sun level do you want it to start running? These questions either dictate the required no load running current required of your motor. Or, conversely, the no load running current of the motor you want to use and the Sun level you want it start running and dictate the panel required.

As an example the motors on the Boat kit we are currently playing with have a typical no load running current varying from 0.18 amps to 0.22 amps when just out of the box, after a few hours running in this can drop to about 0.12 amps. So, taking the worst case of 0.22 amps, this motor when coupled to the No. 4 panel with a current output of 0.9 amps at full Sun will see the motor start to run at about 20% Sun. We must also consider the orientation of the panel, if it is facing the Sun it will produce more current than if laying it flat on the ground.


After choosing the motor and panel combination that seems to be the best it is a good idea to test the results.

My students design and construct a solar power model. In previous years we have had solar powered: garage doors, lifts, merry-go-rounds, spinning wheels and discos! In the past I’ve used the MOT12 motors (1.5 – 4.5 watts) with the No. 8 and No 4. solar panels. What size solar panels I should get to power a 6 watt motor?

While your question seems very simple it is in fact quite complex. We will try to explain simply but will start with some basics about motors and solar panels.

Firstly:

Power in a DC circuit in Watts = Voltage multiplied by Current.

For this type of permanent magnet DC motor RPM (Revolutions per minute) varies directly with voltage. Double the voltage and the motor RPM will double. Torque varies directly with current. Double the current and the motor torque will double. The current that the motor requires depends on the load it is required to drive. Increase the load on the shaft and the current required goes up.

Mechanical power is calculated by multiplying torque by RPM for a solar panel.

At the solar panel maximum power point, voltage per cell is about 0.5 volts so if you have 10 cells in series you have 5.0 volts. Current produced varies directly with light intensity. Double the light intensity and double the current is available. Current also varies directly with cell area. Double the area and twice the current is available.
A low ohm (resistance) load will pull take all the current available at the prevailing light level and pull the panel voltage down to near zero. i.e. power to the motor is now near zero. It is critical not to overload the panel.

Unfortunately, all of the above interact to control the performance of any motor connected to a solar panel. It is really a very complex system highly dependent on load on the motor, solar panel size and light level.

As for what size panel is required to run a 6 watt motor. If we assume you want 6 watts out of the motor, you need to input about 12 watts to the motor as they are only about 50% efficient. If you want 6 watts at low sun levels you need a panel with a much larger surface area than required for 6 watts at full sun. 

This is a simplified explanation but I hope it gives you some insight into the operation of motors connected to solar panels.

Why do the Solar panels crack?

Over the past few years it has become apparent that some types of solar panels have a far greater tendency to cell cracking than others.

Cell cracking does not always result in a drop in power output, but often will. The wicked part is power drop due to cracking can be intermittent depending on how slight movements within the panel position the crack edges. Consequently, the power output of a cracked panel often varies in a random way. We have seen panel power of 8.5 watts drop to 6.75 watts due to cracking. A crack in a critical location can reduce power to zero.

What causes this problem? In the panels typically used in model solar applications there are two major causes, one being straight out mechanical stress due to deflection (bending) of the panel and the other being thermal stress created by the differential expansion of the materials used in panel construction.

Mechanical stresses can be managed by careful handling, but thermal stress is another matter. In order to produce power, the panel must be exposed to sunlight and consequently will heat up causing thermal stress. The practice of cooling panels with ice can increase the thermal stress.

What type of panel is most at risk of thermally induced cracking? From our observations any panel with hard front cell encapsulation is likely to be at risk. Modules that have a soft front encapsulation do not display any of these crack due to thermal stress.

They have been tested them by cycling them from a freezer to full Sun many times without inducing any cracking. However, just by exposing panels with hard front encapsulation to the Sun moderate levels of cracking have been observed. Testing from the freezer to sunlight produces significant levels of cracking. 

The fibreglass encapsulated car and boat panels from Scorpio Technology while having a hard front encapsulation do not suffer from thermally induced cracking due to the fact that the front and rear encapsulation are both fibreglass which has similar thermal expansion rates to the silicon solar cells so there is little or no differential expansion occurring to cause thermal stress and crack the cells.

We would like to make our own solar panels to drive small projects (low voltage motors). Would you be able to supply us with the cells we require?

QUESTIONS:

Have you ever made solar Panels before?

Are you aware of what is involved, and what all the requirements are?

WHY?

Scorpio Technology used to make our own solar panels in house (here, on the premises). That was discontinued some years ago, and we now have our panels made overseas by companies who specialise. The reasons for discontinuing were:

  • all the careful work that was required, and still only about 50% of panels worked as expected
  • the need for proper ventilation (when using resin) and dust extraction (when cutting)
  • the level of soldering skill and experience required
  • high failure rate (and hence the cost)

MAKING SOLAR PANELS

Making solar panels requires a lot of care and experience, as well as special items and tools:

  • the cells are very thin and fragile. They require a lot of care and delicacy, or the result is a box of broken bits
  • special silver solder (3%?) is required, or it will not adhere to the tracks
  • a special conductive strip is needed
  • either fibreglass or a special resin is used to coat the completed cells. If using resin for encapsulation (would you use hard or soft encapsulation?) a backboard is needed. Care is also needed to avoid air bubbles or other problems.
  • care when cutting - very fine saws (preferably diamond) are needed.
  • Otherwise, lasers can also work for cutting.
  • care and experience / good soldering skills are essential
  • you require a way to test completed panels (usually a light box and test equipment)

Thus, as you can understand, making your own solar panels is not an easy job, nor is it recommended. We spoke to two people who have experience in this field. Neither recommended tackling it.