Unlike the extent of reduction that has been presented to teams in the previous few years, the 2011 ballasting formula has the potential to give a notable advantage to a well set up non-electronics car.
This advantage will vary depending on the sun intensity where a greater advantage can be obtained be in lower sunlight conditions (modelling has shown the advantage may be in the order of 2-3 seconds at 20% sun).
The reason why this has been done is to encourage teams to operate without electronics (or at least investigate going without) and thus increase their knowledge and understanding of the interactions between the solar panel, motor and chosen gear ratios.
Because going without electronics is however a lot more difficult and basically impossible to get right in highly variable weather conditions, it is advised that all teams (whether beginner or experienced) first set up their car to run with electronics so they have something to fall back on.
To run without electronics, it is suggested that teams then set up their panel to allow its configuration to be easily switched between series and series parallel arrangements as well as give themselves the choice of several different gear ratios. Changing gear ratio alone will not allow a car's performance to be optimised in all conditions.
Although the optimal car configuration for a given set of conditions can be approximated theoretically to some extent, fine tuning will ultimately require on-track testing.
The reason why the configuration of the panel needs to be made changeable when going without electronics is to reduce the maximum power voltage of the panel at lower sunlights (panel Vmp on most cars using an electronics unit will be around 15V at 100% sun).
Without this, the Faulhaber 2232 6V motor that is almost universally used by all teams these days would need to be geared to spin at a high rpm in order to load the panel for max power. While there is nothing necessarily wrong with this from a panel loading perspective and a car may still run, the frictional/windage losses of the motor at high rpm (increase with shaft speed) will tend to reduce its efficiency at lower sun intensities. As a result, a better option would be to drop the panel voltage and increase the current (resistive losses in lower sunlights are significantly reduced due to being proportional to the square of the motor current).
Another way of looking at it is that the motors require a certain amount of current to overcome running losses (no load losses). For the Faulhaber 2232 this is around 25-30mA at 6V or 7100rpm (datasheet states 35mA although it tends to drop after the motor has been run in a little). These no load losses will increase with motor speed and at say 15 or 16V (ie 17000 - 19000rpm) this current will climb to around perhaps 60 or 70mA (determined experimentally).
So for a 16V (Vmp) panel @ 450mA in full sun (ie approx. an 8 module engelec panel), this panel would produce just (10/100)*450mA = 45mA at 10% sun. This is less than what is needed to even just run the motor on its own at the max power voltage and so there are going to be losses all round.
If the panel is instead switched to series-parallel and produces 8V @ 900mA in full sun (voltage is halved and current doubled) then it would produce 90mA at 10% sun. Since the max power voltage is now much lower such high motor speeds are no longer required and the frictional losses will therefore also be much lower (maybe 40mA). This would then leave a spare 50mA to drive the car.
The other good thing about switching panel configurations is that you won't need as many gear ratios for all the different sunlight levels since you will be able to use some of them twice (once for each panel configuration). The drive wheel setup also doesn't need to be made to cater for such a large range of gear ratios.
So the question now becomes how does one set up a panel to easily switch between the different configurations? Simple, through the use of a particular type of switch and some basic wiring.
Although the solution is quite simple, teams often have problems with it or trouble working out the best way to do it. As a result, an example of how a panel might be set up is presented below:
Here, a three position double-pole-double-throw toggle switch with a centre-off position is used to switch between all-series and series-parallel configurations although a 2 position version could alternatively be used if a standard switch for turning the car on and off is also included.
The above diagram is probably most relatable to a panel using Engelec modules although the wiring is essentially the same for Scorpio and other panels as well (boat panels too).
This setup allows the electronics unit to simply be unplugged and removed and then the switch connected straight to the motor (taking a matter of seconds to do).
When using this setup just be sure to carefully mark which side of the switch is all-series and which is series-parallel so you don't mix up the two. If you switch to the wrong configuration then it will slow the car down and if an electronics unit is being used then it will probably not even run if the panel is switched to the series-parallel arrangement (due to there not being enough voltage).
If you don't want any chance of accidentally switching to the parallel configuration with a maximiser in place and don't think that it likely that you'll race without it, you would probably then just be best off taking out the three position double pole double throw switch (make it so that it's easily removable) and replace it with a standard a standard on/off switch that you would normally go with. Then follow the very bottom left arrangement in the above diagram to change the panel to all series (this still gives the option of going back to running without electronics without having to get out the soldering iron).
Using this system the two configurations will then still be readily interchangeable (just involves changing a few more things over).
Finally, note that the 2 plugs coming off the panel in the diagram are arranged so that the panel is symmetrical (ie male pins on both plugs are +ve). This is done to eliminate the chance of any error being made (ie mixing up the plugs) when connecting the panel to the switch. Alternatively, a single 4 wire plug could be used between the array and switch.
Marc
