Hello resilient friends, I would like to introduce to you Low-Tech Magazine: Doubts On Progress and Technology, one of the most resourceful (stuffed with resources, in fact :=) free online magazines out there.
Here is today's email delivery: an intriguing article on the return of DC power and it's potential. An extract and the link below.

On a bit of a ZZ Top roll today :=)

http://www.lowtechmagazine.com/2016/04/slow-electricity-the-return-of-lo...

Slow Electricity: The Return of DC Power?

Early power station
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.

Picture: Brighton Electric Light Station, 1887. Stationary steam engines drive DC generators by means of leather belts. Source.

Electricity can be produced and distributed using alternating current or direct current. In the case of AC electricity, the current changes direction periodically, while the voltage reverses along with the current. In the case of DC electricity, the current flows in one direction and voltage remains constant. When electrical power transmission was introduced in the last quarter of the nineteenth century, AC and DC were competing to become the standard power distribution system -- a period in history known as the "war of currents".

AC won, mainly because of its higher efficiency when transported over long distances. Electric power (expressed in watt) equals current (expressed in ampère) multiplied by voltage (expressed in volt). Consequently, a given amount of power can be produced by a low voltage with a higher current or by a high voltage with a lower current. However, power loss due to resistance is proportional to the square of the current. Therefore, high voltages are the key to energy efficient power transmission over longer distances. [1]

The invention of the AC transformer in the late 1800s made it possible to easily step up the voltage in order to carry power over long distances, and then step it back down again for local use. DC electricity, on the other hand, couldn't be converted efficiently to high voltages until the 1960s. Consequently, it was impossible to transmit power effectively over long distances (> 1-2 km).

Brush_central_power_station_dynamos_New_York_1881Illustration: Brush Electric Company's central power plant dynamos powered arc lamps for public lighting in New York. Beginning operation in December 1880 at 133 West Twenty-Fifth Street, it powered a 2-mile (3.2 km) long circuit. Source: Wikipedia Commons.

A DC power network implied the installation of relatively small power plants in every neighbourhood. This was not ideal because the efficiency of the steam engines that powered the dynamos depended on their size -- the larger a steam engine, the more efficient it becomes. Furthermore, steam engines were noisy and produced air pollution, while the low transport efficiency of DC power excluded the use of more distant, clean hydro power sources.

More than a hundred years later, AC still constitutes the basis of our power infrastructure. Although high-voltage DC has been gaining ground for long-distance transportation, all electrical distribution in buildings is based on alternating current, either at 110V or 220V. Low voltage DC systems have survived in cars, trucks, motorhomes, caravans and boats, as well as in telecommunication offices, remote scientific stations, and emergency shelters. In most of these examples, devices are powered by batteries that operate on 12V, 24V or 48V DC.

Renewed Interest in DC Power
Recently, two converging factors have renewed interest in DC power distribution. First, we now have better alternatives for decentralized power generation, the most significant of these being solar PV panels. They don't produce pollution and their efficiency is independent of their size. Because solar panels can be located right where energy demand is, long distance power transmission isn't a requirement. Furthermore, solar panels "naturally" produce DC power, and so do chemical batteries, which are the most practical storage technology for PV systems.

Solar PV panels naturally produce DC power, and a growing share of our electric appliances operate internally on direct current

Secondly, a growing share of our electrical appliances operate internally on DC power. This is true for computers and all other electronic gadgets, as well as for solid state lighting (LEDs), flat screen televisions, stereo equipment, microwave ovens, and an increasing amount of devices operated on DC motors with variable speed operation (fans, pumps, compressors, and traction systems). Within the next 20 years, we could see as much as 50% of the total loads in households being made up of DC consumption. [2]

DC Power plant of the Hippodrome in Paris. A steam engine runs multiple dynamos that power arc lamps. Source unknown.
In a building that generates solar PV power but distributes it indoors over an AC electrical system, a double energy conversion is required. First, the DC power from the solar panel is converted to AC power using an inverter. Then, AC power is converted back to DC power by the adapters of DC-internal appliances like computers, LEDs and microwaves. These energy conversions imply power losses, which could be avoided if a solar powered building would be equipped with DC distribution. In other words, a DC electrical system could make a solar PV system more energy efficient. Continued at site - link above.

It's a fascinating read and I enjoy receiving Low-Tech Magazine's articles via email - http://www.lowtechmagazine.com.
I would love to hear your thoughts about and experiences of DC Power. Both at home in a RE system and in local power grids of neighbourhood size.

I have some stuff in my mac's gizzards somewhere on local power grids and a book about it. I'll hopefully get to writing something about it for us.

Peace be with us, if we liberate our homes and neighbourhoods form the national grid,
gerrit