Passive versus Active energy systems while Trekking

A Passive Solar Energy Device

When trekking we take advantage of both active and passive temperature control and other systems. Of course simple conservation is the best passive system to use, in my opinion. By practicing this hot water and energy requirements are reduced. Judicious approaches to cooking also reduce energy requirements, even if propane or other fuels are used. Solar power has a significant advantage over other energy sources if plentiful sunlight is available. This is particularly true for those planning on spending long periods in the camper or RV with a preference not to be "plugged in". However, solar power is not "free." The solar energy collection and storage systems had to be built, have to be maintained and they do have a finite lifespan. There is a cost for that and while it is possible that some of the systems will have a 10 year lifetime or even longer, some approaches will not. In other words, all solar and battery systems are not equal.

The sun sail in the photo above is an example of a "passive" solar system. It doesn't use energy nor does it rely upon mechanical devices. The awning on the side of the vehicle can shield most of that side from the heat of the sun. Reflectix reflective bubble pack in windows is another. The screen on the rear door is a third example of passive temperature control. These things, when used together can assist in regulating the interior temperature.  By orienting the vehicle to the sun and using these techniques, the interior temperature can be improved in both hot and cold weather.

Of course, many of our homes also use passive systems such as insulation, south facing windows for winter solar heat and so on.

Other passive approaches used when RVing include simple orientation of the vehicle to the sun's solar radiation (infrared energy). In the summer this includes parking the vehicle in the shade to reduce interior temperatures. In the winter, parking it in the sun and allowing entry of sunlight through windows is a method to increase interior temperatures. This is effective because the infrared energy from the sun is converted to heat on striking an object. Certain colors absorb more infrared than others. Black, for example is an excellent energy absorber while white or highly reflective surfaces absorb less energy. Infrared which is reflected is not converted to heat, so to maximize heating we attempt to reflect as little sunlight as possible. For minimum heating we do just the opposite and reflect as much sunlight as possible.

Active systems include the use of electrical energy from a variety of sources. These include the 50A or 30A, 120VAC shore power connectors on RVs and the solar panels many come equipped with and the battery systems. The solar panels, controllers, batteries and inverters are active systems because they collect and store that solar energy, and then later convert it for use in heating, cooling, cooking and so on.

An Active Solar Energy Device

Solar on Full Sun

Of course, if the vehicle is equipped with roof top solar panels, then it may be a necessity to park in the sun to take maximum advantage of the solar energy which is available and to avoid depleting the batteries. So, there are trade-offs with such active systems. Some get around that with smaller portable solar panels which can be set up 10 or more feet from the vehicle and oriented as desired. This approach has the advantage of allowing the vehicle to be parked in the shade for cooling, while energy is collected and stored by the solar panel(s) which are in the sun. Of course, portable solar panels can't collect energy while stored in the vehicle and rooftop collectors can. So there are trade-offs to all approaches. Of course, one can use both rooftop and portable solar collectors and get the best of both worlds.

Further passive temperature control in the vehicle can be accomplished by opening widows or door(s). With the vehicle in the shade, the windows and/or doors open and good airflow, the interior temperature will be the lowest possible and will approach the outside temperature. If in the sun, with a sun sail properly positioned and the awning extended the interior temperature will be lower than it would otherwise be in full sun.  Vehicle color also plays a part. Certain colors such as black generally absorb more infrared energy while white reflects more energy.

Cooking is another opportunity for use of passive systems. Simply cooking outdoors will lower the interior temperature of the vehicle. It will also lower the relative humidity. Boiling liquids creates steam and that may lead to discomfiture and even water on cooler surfaces. There are also a variety of solar cookers on the market. If the desire is to reduce consumption of energy in the vehicle, then cooking over a wooden fire is always an option, assuming suitable firewood is available. People have been making "solar tea" forever; all it takes is a glass jar and a tea bag. If the vehicle has sufficient batteries and solar collectors, then an inductive cooktop can be used inside or outside the vehicle.

Even active system benefits can be improved and extended by use. For example, most vehicles which have coach batteries include an inverter. The inverter may also be used to control the charging of the batteries while the vehicle is on shore power (120VAC) or the vehicle engine or generator are running. However, the primary purpose of the inverter is to convert 12VDC from the batteries to 120VAC at 60 hertz (Hz). Unfortunately, using an inverter will more rapidly deplete the stored energy of the batteries because inverters are not 100% efficient. During the inversion, some DC is used, or lost, primarily as heat. That heat may also be transferred to the interior of the vehicle. So, to maximize battery power available, it is best to use 12VDC devices and avoid the inverter all together. Many plug-in devices such as laptops, or cellphones and other electronic devices can run or be charged on 12VDC. For additional interior "cooling" there are 12VDC fans available, and even for refrigerator compartment cooling a 12VDC fan is frequently used.

Using passive systems may require a shift in one's thinking and approach to some activities. It may require a change in awareness, and an inquiry into "what am I hoping to accomplish here and how can I reduce the energy required?" However, a lot of this becomes habit after a while. For example, on cool mornings we generally cook indoors and use that heat to increase the interior temperature. Later, when the outdoor temperatures are at their peak, we may cook outside to maintain interior comfort levels. This approach is necessary for other tasks such as water consumption. True, there are passive water sterilization techniques and ground campers and backpackers use them all the time. However, there is a limited capacity to the grey and black water tanks. One needs to determine just how much of a "camping" experience their trekking is to be. Many of us want it to be less camping and more like home. Simultaneously we prefer to minimize the use of shore power, generators and extend the time until the grey and black tanks are full. If so, that desire becomes a driving force for better and more flexible energy sources in our trekking vehicles. It also provides a motivation to be better trekkers.