In the following two articles, we look at how the grid of the future will need to change to accommodate more renewable energy:

• Firstly, Professor Peter Crossley and Agnes Beviz of the Joule Centre for Energy Research explain exactly what the Smart Grid concept could mean for renewable energy;
• And Brian Patterson of EMerge Alliance Standard, looks at whether DC microgrids in buildings could facilitate renewable energy integration.

Smart Grids: Low-Carbon Electricity for the Future

By Professor Peter Crossley and Agnes Beviz Joule Centre for Energy Research

To incorporate intermittent energy resources, a category which renewable energy falls into, electricity networks will have to become ‘smarter grids’, with integrated communication systems and real time balancing between supply, demand, and storage.

Many countries have put in place ambitious targets that require them to achieve significant contribution from renewables. One prominent example is the EU, where by 2050 the targets effectively dictate that all electricity will be produced by zero carbon energy sources (both nuclear and renewables), and that coal or gas will only be used with carbon capture and storage. In addition, most forms of land transport will be powered by electricity, hydrogen or biofuels and thermal heating will be based on zero carbon electricity, solar thermal, biomass or heat pumps.

And even in the U.S., it looks increasingly likely that a Federal Renewable Electricity Standard (RES) will require a specific amount of renewable electricity to be generated. This adds to the many Renewable Portfolio Standards (RPS) already existing in many individual States - which have a similar aim.

To ensure security of supply, these shifts in electricity generation patterns will need to be matched with responsive energy use from consumers, and a smart electricity grid to balance supply and demand. For example, if wind farms become a dominant source of electrical energy, how do we cope with rapid changes in wind speed or extended periods of low wind, particularly when this affects large geographical areas during a winter anti-cyclone?

What is a ‘Smart Grid’ and How Would it Operate?

A ‘Smart Grid’ means different things to different people, but at a simplistic level it is a method of delivering electricity from suppliers to consumers using information technology and communication systems. An intelligent communications system between suppliers, consumers, storage systems, and the components of the electricity grid would save energy, reduce cost and maximize the use of national, local and domestic sources of low-carbon energy. When we consider the electricity supplied to a town or city over a year, the energy delivered will vary based on time of day, climatic conditions, season, working/holiday day, television schedules, and special events.

At present, in most distribution networks, particularly those in the developed world, consumers can have as much electrical energy as they require whenever it is needed; generators provide the flexibility. For example, if an important football game is being shown on TV, the electrical demand in those States where a team is supported will be low, but during commercial breaks the demand will suddenly rise as the community switches their kettles and cookers on.

The national power frequency will start to reduce, the steam valves on the generator turbines will open, the generator output power will increase and the frequency will return to normal. Currently, nuclear stations and less-expensive coal or combined cycle gas turbines are used for base load, while coal and gas fuelled generators and pumped storage plants are used for balancing during peak demand (see figure 1). Intermittent renewable generation, such as wind, is normally only a small percentage of the total and consequently is always allowed to generate, with a negligible role in balancing.

In a low-carbon future, we will have to find a way of balancing supply and demand without resorting to coal and gas fuelled generators. The term ‘Smart Grid’ refers to a system that would enable this integration of renewables and shift from reliance on fossil fuels, while maintaining a balance between supply and demand.

Key components of smart grids therefore include:

Storage Technology

In order to fully utilize intermittent renewable energy resources, excess generation will need to be stored when supply exceeds demand, in combination with exporting energy between countries through interconnectors.

The stored electricity can then be fed back to the grid at times of peak demand. This storage can be centralized within the grid or distributed storage in individual homes or communities.

Demand Side Management

Even with additional storage, systems will need to be in place to ensure that energy use is sensitive to the supply available and enhance the reliability of the network. If for example, renewable generation remains low for extended periods of time, in an unmanaged system all the stored energy could be used up leading to electricity supply problems.

To avoid such scenarios, consumers could have ‘smart home’ systems which receive pricing signals informing smart appliances that local energy costs are high and ideally that they should not operate.

For example, a consumer could program their washing machine to wash clothes within a time period of 24 hours, when the energy costs are low. This would reduce the magnitude of the peak demand by automatically shifting use to off-peak periods when the energy costs are lower.

Enhanced Grid Communications Systems

To balance the supply, demand, and storage, electricity grids will need an intelligent communication system. Such an information system would provide ‘real time’ electricity pricing to smart meters in homes and inte-grate all elements connected to the electrical grid. In a smart grid the above components are linked in to an intelligent network infrastructure, adapted to incorporate distributed generation. Such a network would have remote management and fault monitoring, and respond in real time to external factors such as changes in weather patterns and therefore electricity generation.

What is the Key Challenges Associated with Smart Grids?

As smart grids are essentially a way to adapt the grid to incorporate low-carbon intermittent electricity generation, there are several challenges involved in their development, and maintaining a secure and reliable energy supply system.

In addition to intermittent and variable energy supplies, the electricity grid of the future will need to cope with increased demand. While we currently use fossil fuels for transport and heating (in the UK), these are likely to become electrified in the future as we shift to low-carbon energy resources. This adds a significant additional load to the supply network. Even if the thermal efficiency of buildings is improved, together with the use of more energy efficient vehicles, electrification of heating and transport is still likely to quadruple electrical demand by ~2040.

In addition to meeting a larger average demand, the future electricity grid system will need the capacity to cope with (or be able to shift) an increase in peak demand due to electric vehicle charging. In order to meet these challenges, we will need to develop and deploy energy storage technologies and communication infrastructure to manage an increasingly complex energy supply mix. A key challenge is designing a communication system that can securely and reliably process a large volume of data, and identifying precisely what data needs to be transferred and where to.

As well as a diverse energy mix, Smart Grids will also have to deal with increased distributed generation, and the associated voltage and fault current control issues. Distribution Network Operators (DNOs) will need to understand the effect on the distribution network of widespread deployment of dispersed generation at both the high voltage level (e.g. 11 kV in the UK) or at the low voltage level (400 V 3-phase or 230 V 1-phase).

Some of the technologies that might be connected either directly or via power electronic converters include solar photovoltaic (PV), ground and air source heat pumps, domestic or community combined heat and power (CHP) systems or DNO-connected wind generators. The DNO also needs to be aware of the effect on their network of electricity storage technologies, electric vehicles and dynamic or price controlled loads (i.e. smart consumers).

What does a Smart Grid Mean for the Consumer?

One of the greatest challenges for future electricity grids lies in demand side response and creating a system that can shift peak demand, at the same time as being socially acceptable. This is a key issue as major behavioral changes are necessary to change energy use patterns and the current demand curve, likely to be facilitated by suitable user-friendly technology platforms. There are also key questions surrounding how this will be implemented, as a price-based incentive system is likely to push those on low income further in to fuel poverty.

On the electricity market where generators sell their electricity, prices fluctuate depending on the time of day and continuity of supply. These price fluctuations are not currently reflected in the electricity bills of the average consumer; most contracts have a flat price per kWh for electricity use. In the future it is likely that these will not be fixed, but will vary significantly at different times of the day or at different periods in the year, dependant on weather conditions and national, regional and even local behavior. In this context a ‘smart’ consumer would need to change their energy use pattern to minimize the cost of their electricity demand, and this behavior would add to the supply-demand balancing of the grid as a whole.

A ‘smart’ domestic consumer would have a domestic energy computer to maximize the demand when the electricity price is low i.e. charge the car; activate smart-appliances; maximize heat in the hot water and thermal storage systems. It should be possible to take a large proportion (up to ~60%) of the daily demand during low cost periods, reducing the electricity use when the price is high.

Engagement with all consumers and encouragement of behavior changes will probably be the most difficult challenges for the wide spread dissemination of Smart Grids and hopefully will be one of the important issues considered by demonstrators. As Smart Grids represent the adaptation of our electricity grid to incorporate renewable energy, they carry all the challenges of maintaining energy security and reliably while meeting future CO₂ emissions targets.

Could DC Microgrids in Buildings Facilitate Renewable Energy Integration?

By Brian Patterson, EMerge Alliance Standard

The growing quest for net-zero energy buildings is likely to change the way we approach the design and construction of buildings in the future. From the use of a broadened integration team and the heightened use of Building Information Modeling (BIM) tools in early planning – to the consideration of a diverse pallet of energy efficient building solutions and site-based renewable power generation and storage – the idea of deploying incremental improvements based on older technologies may not meet the challenge.

Although 2030 or 2050 may seem like a long way off to some, the building industry does not move at breakneck speed when it comes to change. Traditionally, the industry has held a very remote generation-centric view of electrical power. But the current strain on the public utility system has resulted in an ever increasing number of disturbances, disruptions and assorted other supply mishaps. Collectively, these problems cost the US economy alone more than US$150 billion dollars a year, according to the US Department of Energy (DoE).

Although utilities are working hard to address the underlying problems, an effort heavily aided by the US Government’s Smart Grid Initiative, nobody predicts this will solve all the current problems or the underlying and growing shortage of basic and clean electrical energy supply, and the consequential economic pressure this puts on energy cost.

There is a growing realization that there needs to be more than a smarter power distribution grid. Simply put, we need to be ‘smarter’ about how we use energy in buildings and we need to find ways to make it practical to supplement the current means of electrical generation with alternate, preferably renewable, clean sources.

Replacing incandescent or T12 fluorescent lighting and adding controls (dimmers; variable speed controls; automatic thermostats etc.) will help. But energy consumption, like population, is growing faster than conservation alone can satisfy. Without new clean energy sources that can be effectively employed at the user level, the remaining gap in the supply-demand relationship will end up being handled by using ‘smart’ power rationing, such as demand response, premium price-signaling, or legislated load shedding.

Creating a ‘User-Centered’ View

Many now advocate a more responsible ‘user’-centered view of the issue. And it is a view that could lead to some fundamentally new conclusions, namely a power system that will:

• Grow, shrink, rearrange and otherwise change dynamically, and includes an easy means of incrementally adding clean, preferably renewable, generation capability, and on-site energy storage;
• Self-organize as a network, as well as reconfigure or respond to individual user needs and complement the needs of the existing grid structure, including the ability to ‘island’ individual sub-networks, i.e. individual buildings or campuses; and
• Most of all, one that avoids the negative dynamic that dominates the current macro, unidirectional grid based power system, albeit having acquired new brains.

Sound familiar? It should. Our society just built a system like this and it is called the Internet. Now what we need to build is a power exchange network equivalent of the data exchange Internet. We could call it the Energy Net or Enernet. Much like the result achieved by the Internet, we are likely to find that besides solving the current economic and environmental problems with power, it will unleash a whole new era of innovation in both the creation and use of electricity.

Sound impossible? It shouldn’t be. Given the lessons from the Internet experience, it should be remarkably easier to accomplish. Who would have thought we could essentially tie every computer in the world, from mainframe to personal, into one interconnected network, with dozens of languages, more than a zettabyte of information being stored and exchanged, and an operating time domain that is 24/7/365…AND get it all right? But we did, and in less than 30 years.

How Do We Create Such a Vision for Energy?

Starting out, we need to recognize that our current 100-year-old electrical power system is full of mismatches. Most new, distributed and renewable technologies for power generation and storage are natively direct-current (DC), while the legacy utility infrastructure is almost entirely alternating current (AC). In today’s digital world, that means that most power is being converted one or more times from AC to DC or DC to AC.

If storage is a factor, it also means multiple conversions of the same original power. Each conversion can dissipate anywhere from 5% to 40% of the power, and with native DC generating renewables, the power loss averages around 10%.

One inconvenient truth about most renewable generation is that power generated tends to be out of sync with the timing of electricity demand in buildings. Solar PV generation is fairly well timed during the work week, but is less useful on weekends.

Wind generation has peaks and valleys which are most often mistimed to the demand both during the week and weekends. This means that the most effective applications of their use need to include a storage capability to buffer their asynchronous behavior. And among the best storage options are those that rely on electricity in the DC form.

Despite the constant references to DC electricity in this discussion, no one is proposing that we relive the Edison-Westinghouse battle of the currents, but isn’t it time to think in terms of a hybrid system that focuses on mini conversion loss and improving overall reliability at the user level?

In short, we need a solution to the problem of the growing mismatches in our power systems.

A Mounting Case for Near-Load Site Based DC Microgrids

Microgrids in general have attracted industry interest during the last few years. Much of that discussion has taken place in the context of the use of renewable energy sources. Simply described, a microgrid is a part of power systems that can operate connected to the AC grid or in an autonomous ‘islanded’ mode – using power supplied from locally networked resources.

In particular, when low-voltage DC microgrids use native DC supply power to feed native DC loads, they yield the benefit of lower losses due to fewer power conversion steps.

When AC to DC conversions are necessary, they are more effectively aggregated, rather than taking place at each and every power source or load. This makes the use of native DC generated directly from renewable sources significantly more efficient.

In addition to improving electrical efficiency, DC microgrids can reduce waste heat generation that would otherwise need to be cooled, further lowering operational cost. Operating in the DC mode also makes the whole system more controllable via electronic means, improves power quality and provides the opportunity for bi-directional power flow.

Connection of site-based renewable DC generation and energy storage is also easier to accomplish in such a system. This topology is preferably used together with on-site energy storage. The side effects of incorporating DC microgrids, which some users may well consider the main benefits to this approach, are increased user safety, low cost plug-and-play reconfiguration flexibility, and increased equipment reliability.

The Path Forward

To realize this enormous potential, we must first set standards for such hybrid systems. Those standards need to define critical interconnection interfaces between device, microgrid and grid layers. New standards also need to include appropriate call-out of communication protocols so that control and information needs can transcend interoperation difficulties of layer-to-layer coordination.

And most importantly, just as it takes an industry to build a building, it is likely to take a good portion of it to create, or at least adapt, our existing industry eco-system to one that can support those new standards.

To take on this considerable challenge, a group of industry leaders have created an open industry, nonprofit organization called the EMerge Alliance. Founded by companies like Johnson Controls, OSRAM-SYLVANIA and Armstrong World Industries, its membership ranks already include more than 65 organizations willing to move forward.

Its collective vision is to begin by creating new, open standards for room and building level DC microgrids in commercial buildings that include the occupied space, data and telecommunication centres, building services and utilities, and outdoor power facilities. The standards are targeted to complement the existing AC infrastructure with a hybrid DC power layer at the local building and campus level.

At the user interface, one of the first released standards defines safe, low DC voltages and limited current potential to enable plug-and-play device flexibility. At deeper layers of electrical distribution, higher DC voltages are included to keep transmission efficiencies high. In every case, the Emerge Alliance standards are targeted to yield energy savings by avoiding unnecessary power conversions and maximizing the opportunity for highly-articulated digital control.

Perhaps most importantly, they are designed to allow direct integration of site-based renewable energy sources and storage devices without the use of costly and inefficient power inverters. This, in turn, should make the integration of site-based renewable energy generation in all forms easier and more cost effective to implement. Further, it simplifies the integration of electrical power storage devices, upon which the most efficient use of polychromic renewable sources depends.

The Seeds Have Been Planted

The Alliance has already begun deployment of small-scale beta and demonstration installations across the U.S., all of which are prototyping much larger full floor, entire building or campus-wide applications. Many of them are already integrating on-site power generation and a few are planning to add new local power storage means as those technologies mature.

On average, the efficiency of an on-site solar power system increases from approximately 89% to 99% by eliminating DC to AC inversion with a direct connection to a DC power distribution system. Currently, there are two EMerge demonstration sites in the USA, integrating on-site renewable energy generation. An installation at Optima Engineering, a professional engineering design firm in Charlotte, North Carolina, further enhances the energy efficiency and sustainability of the company’s Platinum LEED headquarters by incorporating new acoustical ceilings as a part of an EMergebased system for the direct distribution and use of DC power.

The system includes an AC-DC power supply module that accepts direct DC inputs from a solar PV array (Nextek Power Systems); a DC-powered ceiling grid and acoustical tiles (Armstrong Ceiling Systems); low-voltage structured cabling and interconnects (Tyco Electronics); DC-driven LED recessed and track lighting fixtures (Lithonia Lighting); and lighting controls, including photocells, occupancy sensors, and dimming (Sensor Switch).

A similar retrofit project at the University of California – San Diego’s Sustainability Resource Center, a mixed use facility on the school campus, focuses on a DC to DC lighting system that integrates solar PV panels on the generation side and lighting controls and LEDs on the device side, as well as day lighting and photo luminescent exit lighting. The sophisticated direct DC microgrid energy system generates more than 80% of the building’s energy needs.

While nobody can yet make the claim that this is a tried and true platform, early results indicate it is clearly headed in that direction. After all, it is designed to be a simpler system at almost every level.

This article first appeared in Renewable Energy Focus U.S., Issue 2, September/October 2010.