Solar Panels for Container Homes

Solar panels for container home

Most customized container houses have flat roofs.  That makes them ideal for solar panels for container homes. For efficient solar conversion, special racks tilted at an optimal angle toward the sun will be necessary (further north or south from the equator, the smaller the angle). However, to fully optimize panels’ efficiency, you may need sun-tracking racks that automatically adjust the position of each panel (rotation and tilt) to maximize exposure and by that amount of generated energy per day. Unfortunately, such systems will add substantial costs to the already expensive project.

Solar pannels container Tiny-House

As can be seen, all roof-mounted solar panels are permanently tilted towards the sun. Source: Living Big in a Tiny House

       The main problem of solar-powered container houses is the limited space on the roof. Usually, roof-mounted solar panels will provide enough energy for lights, TV, electronics (computer, phone, stereo, etc..), energy-efficient fridges, and even microwaves (the latter uses high peak power, but only over a very short time, so energy-wise it can be handled by the batteries).

However, the amount of energy generated by roof-mounted panels may be insufficient for power-hungry appliances like washing & drying machine, dishwasher, water heater, and stoves, not even mention an AC unit or space heater. For that to happen a local “solar farm” may be needed, but not necessarily will be a practical solution, and certainly an expensive one.

solar panels-PV off grid

Often the roof is too small for the “solar farm”. In this example the large, large property with “mostly” exposed to the sun area allowed to build a sizable solar farm. Source: Life Uncontained – “Building the Rooms in Our Off-Grid Home!”

To give you some perspective, the following table shows how many solar panels (250W each) are necessary to generate specified energy:

Average-daily-production-of-energy-by-PV-Solar-Panels

Average daily production of energy by PV Solar Panels for a specific installed power (in kW). Note that these numbers represent theoretical values determined by the manufacturer’s ratings. In reality, generated energy will be always lower. Source: EnergySage (modified table from yearly to daily values).

It may be worth mentioning that modern solar panels are able to convert to electricity only about 20% of the solar energy they are exposed to. Specified as PV panel efficiency, it is widely used to compare the effectiveness of solar panels and PV technology. While the currently available PV efficiencies may look very modest (compared to our “appetites”), they truly represent huge technological progress because not that long ago, PV efficiencies in the order of 10% to 15% were common.

To make it clear – 20% efficiency reflects the fact, that the 250W-rated panel will have to be exposed to at least 1,250W of equivalent solar energy in order to generate its rated power, and if this exposure will continuously last for one hour, it will generate 250Wh (Watt-hour) of energy.

Potential Legal Issues

These days, solar panels are a widely accepted solution for the generation of clean, renewable energy. As long as they are installed on your roof, they will not cause any legal problems including these of aesthetical nature. In fact, they are already part of the “cityscape” even in residential areas.

Heat-Absorbing Solar Systems

In its simplest and least expensive form, it’s a network of black tubes continuously circulating the water (note that black surface absorbs the sun’s radiation, while the white one reflects it). For better efficiency, absorbing elements are usually covered or glazed to minimize instant heat losses to the ambient. The heat-absorbing elements (known as Heat Collectors) are connected by pipes to the “Storage of Thermal Energy” – usually an indoor, insulated water tank.

Most such systems (commonly known as Solar Heaters), are built as closed systems, which means that heat-absorbing tubes do not circulate the user’s water but rather the special liquid (antifreeze).

When tubes are exposed to the sun, the warmer liquid starts circulating through the system due to the “convection” effect (it’s the same effect as with hot air). In practice, however, Solar Heaters will use small electrical pumps to force the circulation of the liquid (water). This improves the efficiency of the system, prevents overheating of absorbers but also allows to the installation of heat-collecting panels on the roof (note that in Solar Heaters using natural convection, heat collectors must be at the lowest point of the circulating system). Given the fact that roof-mounted heat collectors will be the highest point of the system, the natural “convection” won’t work and so the forced circulation system is needed. However, thanks to such a location, heat collectors will have the best, unobstructed exposure to the sun using “free” (otherwise useless) space.

The heat carried by circulating glycol is then exchanged in a water tank supplying warm water to the user.
Despite higher complexity and cost, Solar Heaters working in closed systems have significant advantages over open ones.

  • a) By circulating antifreeze (glycol), they can be used in moderate climate zones, where temperatures may fall below freezing point.
    Note that all water-containing elements like the heat exchanger, water tank and all plumbing will be inside of the insulated home, so they won’t be exposed to outdoor weather.
  • b) User’s water usually contains several minerals (especially calcium). When the water reaches higher temperatures, calcium solidifies and adheres to the tube’s walls (the effect can be seen in every teapot). Calcium’s coating accumulated over the time on interior walls of the heat absorber and the heat exchanger creates the barrier, preventing the effective transfer of the heat (firstly from the absorber’s exterior walls into circulating liquid and then from the liquid into the user’s water).

Sun-Absorbing-Open_heating-system-EPA-01a
Solar Heat- Collector: here, an open system circulates the user’s water. Typically, it is a good and inexpensive solution for pools in moderate geographical zones where temperatures neither falls below freezing point, nor exposure to the sun can lead to boiling temperatures).
Source: US Environmental Protection Agency (EPA)

concentrating-solar-heat-collector-EPA-02a
Improved-efficiency Solar Heat Collector for colder geographical zones. The parabolic concentrator, acting like a mirror reflects sunlight and focuses (concentrates) it on the heat absorber. Source: US Environmental Protection Agency (EPA)

Compared to PV Solar Panels, Solar Heat Collectors have much higher efficiencies. Popular, inexpensive heat collectors can easily absorb up to 50% of the solar energy they are exposed to, while modern, technologically advanced models can have efficiencies in the range from 90% to 95%. Also, the wear & tear process of closed-system heat collectors is much smaller than that of PV panels, so their operational lifetime is significantly longer.
Having said that, we have to mention that both solar systems: PV-based and Heat-Absorption-based have similar limitations.

Their effectiveness depends on the length of the daylight, the angle of sun radiation (latitude, time of day, and season), and weather. Also, nothing is perfect, so black tubes are never perfectly black, and (what makes it worse) – at sunlight angles smaller than 90 degrees compared to the absorptive surface, a portion of the sun’s energy will be reflected (smaller the angle higher the amount of reflected energy). That’s why for good efficiency, Solar Heat Collectors must be oriented towards the sun and tilted at the optimum for a given geographical zone angle.

The water, (similar to any matter) has Thermal Inertia, so it can store the thermal energy for hours after sunset (provided that the water tank is well insulated). In other words, for thermal energy, the water plays the same role as the battery does for electrical energy, but at a much lower cost. On the negative side – even good insulation will NOT guarantee warm water for a long period of time, in fact significantly much shorter than the period over which batteries can store the electrical energy.

In colder climate zones, Heat-Absorbing Solar System may not be able to increase water’s temperature to the desired value. However, acting as the “Pre-Heating” system, it will save the electrical energy needed for the subsequent electrical heater.

solar-water-heating-illustration-EcoHome-01a
The typical application of the Solar Heater provides hot water for appliances, kitchen, and personal use (bath, shower, vanity sink…). Source: EcoHome.net

Heat-Absorbing Solar Systems can be also used for underfloor heating. Such application (known as Solar Hydronic Radiant System), does not require high temperatures for circulating liquid, they can act as the “pre-heater” and still make a noticeable impact. It’s because even a slight amount of heat uniformly distributed across the whole area of the floor makes a big change to our perception of comfort.

Riadiantec-hydronic-floor-heating-system-1a
Indirect Hydronic Solar Heating System uses two closed loops: an Exterior Loop consisting of a Solar Heat Collector and Heat Exchanger and an Interior Loop including a Tank storing Thermal Energy and an underfloor heat distribution network. Source: Radiantec (Lyndonville, VT, USA).

Indirect systems can store the thermal energy for some (limited) time extending the availability of heating for some time after sunset. Basically, this is what really counts, because the exterior loop is the most efficient at midday, while the need for heating starts late afternoon and culminates at early night. When needed, the backup electrical system may be used to heat the water in the storage tank, so even in cold, cloudy days, you will still be able to keep the interior at comfortable temperatures.

The direct system consists of a single loop where the underfloor Heat Distribution Network acts as a Heat Exchanger. The liquid in such systems circulates at higher speeds, so it never gets too hot which is beneficial for the floor (no overheating) and minimizes exterior losses along the pipes as the temperature gradient between the warm liquid and outdoor temperatures is small. The system however cannot store any noticeable thermal energy and with only one loop, partially exposed to outdoor temperatures, cannot use the electrical backup.

The amount of harvested solar energy (either electrical or thermal) depends on many factors, but the most important one is the amount of available raw solar energy (in more practical words – the intensity of sunlight and daily length presence). Moving further North from the equator (South in the southern hemisphere) decreases available solar energy and so makes any solar system less and less economically justifiable. That’s why also Heat Absorbing Solar Systems will be of little use in Arctic climates. It’s not only because locations at much higher latitudes receive much less of the sun’s energy, but also because all exterior components of the system (including the heat collector) will be permanently exposed to low ambient temperatures. Incurred heat losses to the ambient will bring the efficiency of the whole system to low digits.

There is also the opposite part of the story, on very hot and sunny days the antifreeze (when used instead of water) after longer exposure to high temperatures will break down to acidic (corrosive) components, impacting the durability of the whole system. Typically, it will happen to start at around 150 deg C (300 deg F). At first, it may sound unrealistic, but it can happen however in areas with prolonged exposure to intensive sunlight (especially when heat concentration is used).

Solar-Water-Heater-Viessmann-01a
Vitosol 200-FM flat plate roof-mounted heat collector and water tank from Viessmann. These heat collectors are equipped with special coating (filter) that at higher temperatures decreases heat’s absorption and by that stabilizes the temperature of glycol preventing its decomposition.
Source: Ecohome.

The common characteristic of all Solar Heat-Absorbing systems is the inherent thermal inertia of the circulating medium (be it glycol, or water…). Instead of expensive banks of batteries (needed in off-grid PV-solar systems), the well-insulated, adequate capacity tank will do the job. That’s why Absorptive Solar Heating systems are usually less expensive than PV-based ones.

Potential Legal Issues

Similarly like in the case of PV-solar panels, roof-installed Heat Collectors do not create any aesthetic or legal problems even in densely populated, residential areas..

Leave a Comment

Your email address will not be published. Required fields are marked *