The typical solar PV power installation requires access to a private roof and a big budget. However, wouldn't it be possible to get around these obstacles by installing small solar panels on window sills and balconies, connected to a low-voltage direct current (DC) distribution network? To put this theory to the test, I decided to power Low-tech Magazine's home office in Spain with solar energy, and write my articles off the grid.
In today's solar photovoltaic systems, direct current power coming from solar panels is converted to alternating current power, making it compatible with a building's electrical distribution.
Because many modern devices operate internally on direct current (DC), alternating current (AC) electricity is then converted back to DC electricity by the adapter of each device.
This double energy conversion, which generates up to 30% of energy losses, can be eliminated if the building's electrical distribution is converted to DC. Directly coupling DC power sources with DC loads can result in a significantly cheaper and more sustainable solar system. However, some important conditions need to be met in order to achieve this goal.
We are being told to eat local and seasonal food, either because other crops have been tranported over long distances, or because they are grown in energy-intensive greenhouses. But it wasn't always like that. From the sixteenth to the twentieth century, urban farmers grew Mediterranean fruits and vegetables as far north as England and the Netherlands, using only renewable energy.
These crops were grown surrounded by massive "fruit walls", which stored the heat from the sun and released it at night, creating a microclimate that could increase the temperature by more than 10°C (18°F). Later, greenhouses built against the fruit walls further improved yields from solar energy alone.
It was only at the very end of the nineteenth century that the greenhouse turned into a fully glazed and artificially heated building where heat is lost almost instantaneously -- the complete opposite of the technology it evolved from.
The modern glass greenhouse requires massive inputs of energy to grow crops out of season. That's because each square metre of glass, even if it's triple glazed, loses ten times as much heat as a wall.
However, growing fruits and vegetables out of season can also happen in a sustainable way, using the energy from the sun. Contrary to its fully glazed counterpart, a passive solar greenhouse is designed to retain as much warmth as possible.
Research shows that it's possible to grow warmth-loving crops all year round with solar energy alone, even if it's freezing outside. The solar greenhouse is especially successful in China, where many thousands of these structures have been built during the last decades.
Combining the old local heating practices with modern radiant and conductive heating systems could lower energy consumption, improve health, and increase thermal comfort. This is especially true for uninsulated buildings, where air heating is particularly disadvantageous. Local heating sources can be applied on their own, but can also be used in combination with air heating. This may mean, however, that thermal comfort standards need to be redefined.
The steadfast rotating fan has been employed to keep people cool since the eighteenth century, and it remains highly effective, requiring much less energy and providing more comfort than air-conditioning. Cooling people by increasing local airflow is at least ten times more energy efficient than refrigerating the air in a given space, and it also adds the benefit of a personally controlled thermal environment.
If used in combination with air-conditioning, fans could lower energy use by 30-70%, even in incredibly hot climates or during heat waves. Circulating fans, which have become very energy efficient in their design, can be readily and cheaply applied in both new and existing buildings. Recent changes in international comfort standards have paved the way for their comeback.
While modern cooking stoves are convenient, when it comes to energy use they leave a lot to be desired. As we have seen in the previous article, the thermal efficiency of an electric hob does not exceed that of a conventional open fire. In both cases almost 90% of the primary energy is lost during the cooking process.
Cooking food could be achieved in a far more energy efficient way, especially if the cooking pot itself is insulated. This is the principle behind the fireless cooker, a well-insulated box that keeps food simmering with only the heat of the cooking pot itself. A fireless cooker doubles the efficiency of any type of cooking device because it shortens the time on the fire and limits heat transfer losses.
In the early twentieth century, fireless cookers were common additions to western kitchens, similar to the refrigerator or cooking stove. Some models even integrated fireless cookers with gas or electric hobs. These functioned by lowering an insulated hood over the cooking pot once the heat had been switched off.
You don't need electricity to send or receive power quickly. In the second half of the nineteenth century, we commonly used fast-moving ropes. These wire rope transmissions were more efficient than electricity for distances up to 5 kilometres. Even today, a nineteenth-century rope drive would be more efficient than electricity over relatively short distances. If we used modern materials for making ropes and pulleys, we could further improve this forgotten method.
How to downsize a transport network: the Chinese wheelbarrow For being such a seemingly ordinary vehicle, the wheelbarrow has a surprisingly exciting history. This is especially true in the East, where it became a universal means of transportation for both passengers and goods, even over long distances.
Firewood in the Fuel Tank: Wood Gas Vehicles Wood gas cars are a not-so-elegant but surprisingly efficient and ecological alternative to their petrol (gasoline) cousins, whilst their range is comparable to that of electric cars.
How to make everything ourselves: open modular hardware Consumer products based on an open modular system can foster rapid innovation, without the drawback of wasting energy and materials. The parts of an obsolete generation of products can be used to design the next generation, or something completely different.
Power from the Tap
Power from the Tap: Water Motors Just before the arrival of electricity at the end of the 19th century, miniature water turbines were connected to the tap and could power any machine that is now driven by electricity.