Interpretation of rules 4
Note 1 from the Technical Committee, August 2013
The organisation of the DONG Energy Solar Challenge 2014 (DSC) has received a
request from a number of teams to revise the technical regulations with respect to the
allowed battery capacity.
The allowed battery capacity is defined in a way similar to the World Solar Challenge in
Australia. The nominally allowed capacity is 1 kWh.
Since the measurement of the real battery capacity is not easy for the large amount of
participating teams the capacity has been translated to an equivalent mass of the battery.
This is based on an estimated energy density (Wh/kg) of the specific battery types. This
ruling has served its purposes but also has potential flaws.
One of the flaws is that it allows participants to look for better batteries within the
specific classes. Since battery technology is a rapidly developing field of technology, the
energy density develops as well. Especially the energy density of lithium-based batteries
has gone up over the last couple of years. In the World Solar Challenge this has been
acknowledged and the estimated energy densities have been corrected to industry
standards. The new technical regulations for the DSC have followed this approach for the
2014 race. Effectively this means that the allowed masses for lithium-based batteries
have been corrected to lower values.
As a consequence lithium-based batteries purchased for the 2012 race cannot be used
again in the 2014 race. Since these batteries represent a considerable investment some
teams have expressed their concerns about the financial viability of their participation for
the 2014 race. Next to that some teams have expressed their concerns on the use of
batteries with the capacity of 1 kWh in the newly introduced sprint competition. They
fear an unacceptable high electric load on the battery during sprints.
The organisation has considered these arguments. On the one hand we acknowledge the
fact that an advanced battery is a considerable investment. Next to that we understand
that to perform best in the sprint competition a higher battery capacity is preferred. On
the other hand the race is about racing on solar energy, not a race for electrically powered
boats where battery capacity is the main design driver. Furthermore, the race also wants
to promote innovation. Re-use of equipment used in previous races does not stimulate
Based on the arguments given above the organisation decided to change the ruling for the
batteries for the 2014 race. Therefore, rule 7.1 will be changed into the following: The vessels may be fitted with a battery pack with a maximum capacity of 1.50 kWh. All
further references to the battery pack will refer to the ‘main battery’. To be able to judge
this requirement, all batteries will have to undergo a capacity test. This capacity test will
be a constant current, full discharge test. The current applied during the test is
determined by the nominal voltage of the battery and given by the following expression:
Vnom = nominal voltage of the battery in V
For lead-based batteries the test current is the test current given by the expression divided by 8 unless the Peukert coefficient of the battery is supplied by the participant. The starting point of the test is a fully charged battery. Fully charged is defined as the point where the individual cells have reached their maximum voltage and the battery pack as a whole is balanced. The maximum cell voltages are: Lithium-ion:
A lead-based battery is considered fully charged when the voltage is 14.4 V for a 12 V nominal battery voltage and current through the battery has declined to less than 2% of the nominal capacity of the battery in Amp-hours (e.g. 2 Amps for a 100 Ah battery). The end of the test is when the battery is fully discharged. Fully discharged is defined as the point where the discharge is stopped by the Battery Management System. This must be the point where all individual cells have reached a voltage below the value given: Lithium-ion:
A lead-based battery with a nominal voltage of 12 V is considered fully discharged when the voltage is 10.5 V. In order not to damage the battery during discharge the discharge will continue until the voltage reaches 11.7 V. At that time a depth of discharge of 70% is considered to have been reached. The full capacity will be calculated on the basis of that. Discharge tests will be performed after charging and a consecutive rest of at least 8 hrs. Testing will be performed at a room temperature of 20°C ± 2°C. Non-lead based battery packs must be designed such that the individual cell voltages can be measured. This may be done via an electronic interface which then must be supplied during testing. Only one battery pack per team can be offered for testing. The battery pack offered must be balanced and have been fully cycled for at least 5 times. The organisation does not take responsibility for incorrect functioning Battery Management Systems, unbalanced battery cells, and other kinds of failures of the battery pack that may appear during testing. These will also form no grounds for seeking redress.
Batteries with a too large capacity will result in the issuing of a time penalty. This time penalty will be ten minutes for every stage for each percentage point of the allowed maximum battery capacity. (e.g.: installing a battery with an overcapacity of 6% will yield a time penalty of 6 x 10 minutes = 60 minutes for all stages). An equivalent rule applies for non-battery energy storage devices. If a participant decides to install a different means of energy storage, which is not a battery, the total storage capacity is limited to 1.50 kWh (=5.4 MJ). For the use of other types of batteries not mentioned in the overview the participant is required to contact the organisation to have determined the maximum allowable mass.
As a consequence of the change of rule 7.1, rule 5.23, fifth bullet will change into: Replacement or recharging of batteries will result in the issuing of a time penalty of five hours for the next stage. Stages that have already been started will be counted as complete stages (e.g.: installing a new battery or recharging an already installed battery during or after the second stage will yield a time penalty of five hours for the third stage). An equivalent rule applies for non-battery energy storage devices.
The consequence of this new ruling is that the allowed battery capacity is now more or less equal to that used in the Solar Splash regulations for their Sprint Event. In the Solar Splash teams may use two different sizes batteries, one for the Solar Endurance Events and one for the Sprint and Solar Slalom Events. After the DSC in 2014 the organisation will evaluate the newly introduced sprint competition. As a consequence of that we may want to revise the battery regulations for the 2016 race. Therefore investments made in batteries for the 2014 and earlier races cannot be guaranteed for the 2016 race. Furthermore, the new ruling requires testing of all batteries. This is not doable within the time frame of the technical inspections. The teams will thus be required to make their batteries available well before the race. Details of this will be announced later but be aware that this may be as early as two months before the start of the race.
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