In 2007, the company I work for was the first to propose 48V DC as the voltage of choice in a local DC system, when we introduced DC-ready LED lighting. France’s Schneider and General Electric (GE) did the same in 2013 and 2014.
DC will be the on-site electricity distribution option. More and more technology-driven companies are recognizing this and as a result there is now agreement that 48V DC is the voltage of choice, for now, for local battery systems and DC distribution.
However, this is still based on lead acid technology being cheaper in 12 volt increments and the low voltage directive. With LifePO battery systems that have 3 volts per cell and with no cost penalty for odd voltages, actual local system voltages can go from 48 volts (24 cell lead acid based) to 66 volt (22 cell) systems. LifePO based) and the DC power equipment will have to tolerate input voltages from 40 to 75 Vdc.
More and more devices in the home and workplace are native DC devices that will benefit from direct DC feeds. Such devices include most of the essentials of modern home and office life, such as solid-state LED lighting, solid-state refrigeration, heating and air conditioning, computers, telephones and networks, access control, entertainment systems , water treatment and pumps. Even production machinery can be converted to DC devices at a reasonably higher cost.
A DC infrastructure with a battery storage system lends itself to direct power from an alternative energy source, such as solar or wind. Generating and using power yourself has a significant impact on the effectiveness of alternatively generated power. For example, when the generation feeds into the grid and takes power from the grid, it has a minimum loss of the entire process of 30%.
Losses in alternating current (AC) systems (other than heating) typically range from 15-30%, this is typical for a laptop or PC power supply, oven power supply, microwave or LED lighting power supply. If those devices can be equipped with a DC-to-DC power supply with efficiencies ranging from 90 to 95%, additional savings will be achieved.
The effect of NOT feeding the grid and using DC to DC power supplies is that almost all of the locally generated power can be used instead of throwing half into a system that uses the grid instead of battery storage.
Multiple factors from recent technological advancements make DC more viable now than in the past:
- When Edison made batteries up until a few years ago, the technology was not very durable and represented the highest cost in a local DC system. Batteries lost capacity rapidly, were heavy and difficult to maintain, lasting around 1-3 years depending on how deep the cycles were. New battery technologies are now commercially available at reasonable prices that promise a 10-year lifespan and 85% of its original capacity at end-of-life cycled daily.
- Solar panel prices are at an all-time low.
- Semiconductor power device technology has gotten so good that system losses to charge or discharge batteries are in the range of 1% to 2% for systems with a load greater than 5 kW.
- Most of the devices are internal DC devices.
- Lighting will transition entirely to LED, which is a DC-driven semiconductor technology.
Back in 2007 I have been accurately predicting that LED technology will replace any and all lights and now it is clear that it will.
DC Systems will enter the home and office space in the future because they are the most efficient way to use local alternatively generated power in the most efficient way and in doing so provide a strong backup and disaster strategy.
Another advantage of DC systems that use the grid as backup is that they can significantly reduce the demand on the grid. For businesses that pay for both demand and energy used, this can also result in a significant reduction in your energy bill.
