The core of the energy supply is an array of six solar panels of 285 nominal watts each at a nominal 24V DC.  The panels are connected in parallel in two banks totaling about 1700 nominal watts or about 70 amps in perfect conditions.   The voltage is chosen to match the compressor voltage, but could be 36 or 48 volts when compressors of that voltage are available.   The panels could be 36 volts nominal or connected in pairs in series series to make a 48 volt array.  
In future versions we may use thin-film panels bonded to the freezer roof to save weight.
The panels are riveted to aluminum mounting bars which are bolted to the truck roof's structural joists.    In the future we will have 4'X4' custom panels for these 8' roofs to optimize the use of space.

An off-grid solar system needs to have batteries, to cater for variations in available sunlight and to allow for after-dark operation.  Van de Soleil has two battery banks, mounted in cradles under the truck bed, which slide down for maintenance.  The batteries are wired in serial to create nominally 24 volt banks.    We use lead-acid deep-cycle batteries.   In the case of the predecessor Man the Van, we used sealed AGM deep cycle batteries, because they had to be mounted inside the van cargo area, to avoid hazardous hydrogen emissions.  
The total 450 AH of batteries in Van de Soleil is probably over-engineered.  Measurements suggest that 300AH would have been sufficient.   The battery banks allow for 24-hour operation in Van de Soleil. 
In the future we plan to upgrade to Lithium Ion or other advanced battery chemistry, to cut down weight and maintenance.
Although the panels are rated at 24V, they actually produce higher voltages.   In order to protect the batteries, these Renogy Tracer solar controllers convert the voltage to match the actual battery voltage, and provide various electrical protections to the batteries.    We have two of these, each of which handles one side of the solar panel bank, because of capacity limitations on the controllers, which are 1,000 watts each. 
For shore power, which may be needed for long-term parking, vehicle storage in a building or adverse energy conditions, we provide this pair of Iota 24 volt chargers.    Although Van de Soleil is designed to be able to operate 24/7 on solar power alone, we view shore power as an essential backup.   In real-life situations, for one-person operation, 110V AC shore power will be available wherever the operator sleeps, so, as the system takes less than 2000 watts (about 20 cents worth) of shore power we view this as cheap insurance to enable the operator to get a good night's sleep.
24 Volt alternators are readily available, as used in earth moving equipment and boats.   They are well-understood technology.   For certain applications, such as 'custom critical', where the truck is double-crewed and runs to its destination as fast as possible, stopping only for fuel, and where 100% reliability is required remote from home base, an optional 24V alternator can be fitted.   Alternators are demand driven, so, when switched out of the circuit, they use little or no fuel.   A mechanical clutch can be included to reduce fuel usage to zero when not deployed. 
We have avoided using an alternator in our prototypes, because we want to test the solar performance.   Based on our experience, we estimate that the alternator would be deployed less than 1% of the time and ot significantly increase fuel usage overall.