All-Electric Motor Home Goes Solar

Dethleffs covers nearly every inch of the e.home in solar panels, helping to keep the electric battery powered up. (Credit: Dethleffs)

Dethleffs chose the Iveco Daily Electric chassis that has several battery options and offers a range of up to 174 mi (280 km). However, Dethleffs suggests the e.home range might be closer to 103 miles (167 km).

The e.home uses solar panels to charge FIAMM sodium nickel chloride batteries that have a capacity of 3 × 76 Ah at 400 V. These can be recharged up to 1,500 times, which would cover a distance of about 250,000 km. Battery performance is improved by supercapacitors that provide faster recharge and delivery of the electrical energy. This increases the performance of the vehicle as well as the battery lifecycle. The batteries supply power to a liquid-cooled three-phase 107 hp, 80kW AC drive motor as well as other motor home electrical loads.

These batteries have sodium and nickel as active materials and a solid ceramic electrolyte, and all cells are contained in a sealed steel sheet. Typical failure modes, such as an internal short, do not cause a violent energy release; instead batteries remain in operation with slight loss of performance. An integrated battery management system (BMS) provides diagnostics alerts on anomalies and disconnects the battery in case of serious failure. In the event of BMS failure, an independent supplementary circuit protects the battery.

Battery Features

• Constant performance at -20° to +60°C
• 58V per cell
• 140 Wh/kg specific density
• No cooling required >2000 cycles at 80% DoD
• 100% maintenance free operation
• Allows remote monitoring
• Integrated low voltage disconnect (LVD)
• Integrated battery monitoring system (BMS) provides monitoring, diagnostics and data logging.
• Specific energy 70% lighter and 30% smaller than conventional batteries
• Long shelf live
• Capacity to store energy indefinitely when not connected
• No outgassing and zero ambient emission

A battery “fuel gauge,” time-to-go indicator, is part of the e.home system. The fuel gauge shows the remaining battery capacity, which depends on the ampere-hours consumed, discharge current, temperature, and the age of the battery. Complex software algorithms take all these variables into account. Next to the basic display options, such as voltage, current, and ampere-hours consumed, the Victron BMV-700 series also displays state of charge, time to go, and power consumption (Fig. 2). Another “gauge,” the BMV-702, features an additional input that you can program to measure the voltage (of a second battery), battery temperature or midpoint voltage.

A “fuel gauge” displays state of charge, time to go, and power consumption.

Solar Power

Dethleffs' e.home has 31 square meters of optimized thin-film solar cells, which provide about 3,000 watts of peak power to keep the 228-Ah sodium-nickel-chloride battery array charged.

Its key components include:

1. Solar charge controllers to harvest solar energy.
2. A combined inverter/charger for onboard ac electricity and charging of the lithium domestic power storage batteries.
3. Required ancillaries, which include battery safety protection, system monitoring and the e.home heating power supply.
4. A dc-dc converter ensures that all 12V, USB accessories, tablets, smartphones etc., can be supplied and charged.

Victron’s  SmartSolar Maximum Power Point Tracking (MPPT) system supports the solar panels. For a cloudy sky or partial shading, light intensity changes continuously, so an ultra-fast MPPT controller improves energy harvest.  An algorithm maximizes energy harvest by locking to the optimum MPP. Among its features are:

• Fully programmable charge algorithm and eight pre-programmed algorithms, selectable with a rotary switch.
• Over-temperature protection and power derating when temperature is high.
• PV short circuit and PV reverse polarity protection.
• PV reverse current protection.
• Internal temperature sensor compensates absorption and float charge voltage for temperature.

The SmartSolar Charge Controller.

Heating, Cooking, and Refrigeration

Heating is often the most intensive use of energy in a motor home. When changing to an electric heating system, Dethleffs’ developers had to find a new, even unconventional solution to generate a pleasant warm feeling with as little energy use as possible.

To achieve this, several latent heat accumulator plates made of phase change material (PCM) were installed in several places. These heat accumulators absorb energy at temperatures over 26°C and deliver it when the temperature goes down in the evening hours. Additionally, heating elements are also mounted in the floor, sidewalls and furniture that heat the interior via infrared warmth sources, but only the objects they reach—not the air. This is efficient yet still creates a cozy warm feeling, although the general room temperature is at 2 to 3 degrees lower than with traditional heating systems. Infrared warmth is available without any pre-heating time.

The e.home also includes a ceramic stove with three cooking stations as well as an energy-efficient compressor refrigerator.

Quality of life features include a special foil technology that you can use as a mirror, when switched on it spreads a bright, planar light. Another interesting feature is the electric window blind. This is a foil, that is set between the window panes of the insulated windows, which can be electrically dimmed as a protection from the sun and intense heat, as well as also being able to serve as a privacy screen.