The conventional electrical system in place today sees our electrical devices powered by AC mains. But as renewable technologies such as solar photovoltaics and wind power become more prevalent at a household level, DC microgrids could be a cheaper and more efficient alternative.

Take lighting and ‘gadgets’ for example. Lighting is widely considered to account for around 20% of global electricity consumption, and a recent report from the International Energy Agency estimates that up to 15% of domestic energy is consumed through ‘gadgets’ - i.e. computers and consumer electronics.

LEDs are emerging as a preferred option for high efficiency lighting, and they run on DC power. Similarly, most gadgets operate on DC power, so these two sectors alone add significant and increasing global consumption of electricity by DC devices. But these are presently powered by AC mains via multitudinous individual transformers.

Could DC micro grids be more feasible today?

Fuel cells and many small scale renewables natively generate low voltage DC power. Most of these generators supply power to AC mains networks and require costly and inefficient power invertors; even where the power may ultimately be delivered to a DC device.

A possible solution is to install a DC network linking DC devices to DC power supplies. Such networks have not yet emerged because of the higher electrical losses associated with transmitting a fixed amount of power as low voltage DC, rather than higher voltage AC. But with the proliferation of low power electronic devices, bringing the potential for LEDs to reduce lighting loads by a up to a factor of 10 and the potential for efficient distributed power generation, localised DC networks – or DC microgrids - may finally be practical.

Aside from reducing resource and financial costs, a key advantage of DC microgrids is that the low risk of dangerous electric shocks from low voltage DC makes plug-and-play grids a possibility. This greatly reduces the installation cost of micro-generation, and could empower end users to take responsibility for understanding and controlling their individual energy consumption.

Adding intelligence and internet connectivity to DC micro-grid controllers further enables consumer engagement with AC mains devices - through smart metering and ultimately with dynamic demand management. And this could reduce costs associated with periods of high and low power consumption.

What next for DC microgrids?

However, despite some compelling reasons for their adoption, widespread take up depends on the engagement of end-users, not to mention key enabling professionals outside the green-tech sector. “LED lighting technology is evolving rapidly, and desirable LED solutions are now available for most applications”, says Architect David Kohn: “Clients are increasingly interested in low-carbon technologies both for their own and for legislative reasons”.

Steve Appleton, director of Electrical Services at UK engineering company Ramboll UK, added, “it is standard practice when building or refurbishing to install multiple cable networks to carry lighting, ring mains, internet, intercom, telephone, and television. Thus adding a secondary DC electrical network is perfectly feasible, particularly if this network is in fact simply an extension of the lighting ring. In existing buildings, the conversion of the existing lighting circuit to a DC system and extension to provide DC sockets may be realised at modest cost.”

What DC microgrid products are available today?

In June 2009 the Low Carbon and Fuel Cell Knowledge Transfer Network brought together pioneers of DC microgrid component technologies to discuss near-term applications and sense-check the concept in the current technical, legislative and economic climate.

All of the components are in existence today and, if not already, will be available in plug-and-play form within 2 years:

• Moixa Energy is developing a ‘Home Energy Server’ to provide DC microgrid control as well as consumer engagement and monitoring of AC mains devices. First field trials are scheduled for late in 2009 with further trials in early 2010, and full roll-out possible from the end of 2010;
• Horizon Fuel Cell provides off-the-shelf fuel cell stacks from 12W-5kW. Whilst these stacks are not yet plug-and-play, Horizon have produced over a million fuel cell devices for consumer markets and are partnering with several OEMs to develop small fuel cell generators.
• BOC, a member of the Linde Group, has been supplying hydrogen for decades and is currently field trialling a new consumer friendly mini-cylinder suitable for microgrid applications along with a plug-and-play hydrogen fuel cell generator. The first target market is off-grid offices i.e. on construction sites.
• Sun Microsystems has for several years been selling a 4-watt virtual client computer which is ideally suited to DC microgrid applications in offices and educational settings;
• Philips has embraced LED for a very wide range of applications including internal residential and commercial, as well as external lighting.

Further information: what is a DC Microgrid?

A DC microgrid comprises:

• DC power generation (i.e. fuel cell, solar PV panels, or micro wind turbines);
• DC electrical storage (i.e. battery or super capacitor);
• DC power distribution (i.e. wiring and control);
• DC gadgets (i.e. laptops, telephones, satellite TV controllers);
• DC lighting (i.e. LEDs).

Whilst homes generally require an AC supply for inherently “high” power devices such as washing machines, kettles and hairdryers, there are a surprising number of environments, such as site offices and outdoor events, where these devices are not used.

In such cases a DC microgrid could be the sole power provider. The elimination of invertor cost, simplified installation and reduced fuel costs yielded by a DC microgrid system potentially make it cost effective to operate independently of the electricity grid and conventional mains-power generators.