Distributed energy systems can range from the micro sized do it yourself systems being installed on rooftops and on hilltops to small scale systems ranging up to around 20MW (megawatts) of capacity, although it must be understood that this is a pretty fuzzy boundary. The defining characteristic of distributed energy systems is that they generate energy close to the point of use where that energy will be consumed; hence the admittedly fuzzy 20MW upper boundary for their size. If an energy generation facility becomes much larger than this it produces far too much power to be consumed locally (except in a few rare exceptional cases where large industrial consumers are nearby). The excess power must then be transmitted to distant markets and the energy system can no longer be described as being a distributed energy system.
Besides being relatively small scale distributed energy systems are usually understood to be powered by renewable energy sources such as solar or wind, but also biomass or other systems such as tidal, wave and geothermal and that to put it another way they do not rely on fossil energy supplies. Many however also include micro-turbines, fuel cells and the more traditional gas or diesel powered backup generators in this category by virtue of their small scale.
Some Advantages of Distributed Power Systems
Distributed electric energy systems offer many advantages over the current energy topology of a smal number of massive thermoelectric fossil fueled power producing plants that feed a vast grid with essentially a uni-directional flow of current through a whole series of transformer sub-stations that both step voltage up then step it down along the way to the consumer at the far end of the very long pipe.
- It is suited to regions currently lacking well developed and maintained grid infrastructures. This is the case in much of the less developed world, but also includes remote areas in the US and other industrialized nations.
- By off-loading demand from the grid it can reduce or avoid the necessity to build new transmission/distribution lines or upgrade existing ones.
- They can avoid the line loss associated with transmitting electricity over long distances and in the process of stepping voltage up and then down in transformers in order to put power onto these very high voltage transmission systems and to pull it down off from them before being able to use it.
- Because of its smaller scale it avoids the large increment problems faced by large scale utility sized plants of Gigawatt scale. In other words it can more smoothly fit actual current use patterns and can be installed in easy small increments as needed and does not tie up massive long term capital for a single project.
- Because it is easy to bring small scale distributed systems on and off line when compared to large thermoelectric plants they can function as backup and emergency power sources and help prevent blackouts and brownouts.
- Distributed systems (such as hydro, or biomass, but also micro-turbines, fuel cells etc.) can be configured to produce power during peak load times when the grid is under its greatest stress and energy is most costly.
- Distributed systems are well suited for and promote the diversification of power supplies, which makes them particularly suitable for renewable energy sources.
- By virtue of their smaller scale distributed energy systems are more suitable for co-generation. Co-generation uses the waste heat from a one process, such as power generation, to provide space heating for buildings. Small biomass, micro-turbine, fuel cell, or combined solar facilities are naturally suited to also being sources of co-generated heat. Heat that would otherwise need to be produced by some other means.
- Last, but not least, distributed electric energy systems can help to make our country more secure. Because they are widely dispersed and do not depend on a small number of central facilities they are much less vulnerable to disruption – either through accident or hostile action. Distributed electric energy systems are inherently more survivable than a centralized grid relying on a very small number of fixed facilities and key transmission nodes.
The System We Have
Our current electric energy infrastructure is characterized by massive thermoelectric plants, mostly fired by burning mountains of coal but also by the heat released through nuclear fission. These plants are typically massive driven by economies of scale to reach up into the Gigawatt capacity order of magnitude. Our entire grid system is characterized by this centralized power infrastructure. Of course it is true that a small amount of energy comes from renewable sources– around 6% of the total electric energy generation comes from (often massive) hydro-electric plants and currently a little less than 1% from wind power — but our energy infrastructure is mostly dominated by massive thermoelectric plants with coal burning plants comprising almost half of the nations electric energy generation capacity.
This has lead to a grid structure of correspondingly massive scale and of a similarly centralized nature. But will it always be so? Are we destined to continue down a path of massive power plants feeding a highly integrated grid with power that needs to stepped up to very high voltages for long distance transmission then transformed down in stages until it finally reaches the industrial facility, home, or commercial building where it is ultimately consumed. Is this way of doing things really suited to the nimble and diversified future that awaits us just around the corner of the curve of diminishing fossil energy reserves and spiking costs as increasingly marginal fossil energy supplies are developed to feed our future energy needs?
Recent Trends Seem to Indicate that Distributed Power is Finally Taking Off
Distributed power may finally be taking off, driven by the continued rapid drop in the cost of renewable energy sources, by the increasing incidence of brownouts and blackouts in an over-taxed grid, by the inability of the grid to adapt to future needs, by a desire amongst many to exert more control over their how they get their power and by a growing awareness of global warming.
Solar Energy Sector
A recent report by Pike Research that is focused on the growth in small scale distributed solar photovoltaic power systems predicts that the global market for these systems, which is currently at $30 billion per year (2008 figures) will grow to almost $60 billion by 2013. That is a compound annual growth rate of 22%. Of all the opportunities in PV, Pike Research finds that the most compelling growth potential lies in decentralized electricity generation, whether in small rooftop or large commercial installations. Solar PV has the advantage of being truly modular, which makes it particularly well suited for distributed energy systems.
In addition the modular small scale solar thermal systems suitable for distributed power systems are also taking off. For example Sterling Energy Systems a solar company based in Scottsdale, AZ has recently released an the production design of its SunCatcher system that is a solar thermal dish system that uses concentrated solar energy to run a high efficiency sterling engine. This system has been in development for ten years. Each dish unit can generate 25 kilowatts of energy and has been certified by Sandia National Laboratories as having the highest sun‐to‐grid energy conversion in the world; last year one of the original SunCatchers set a new solar-to-grid system conversion efficiency record by achieving a 31.25 percent net efficiency rate, toppling the old 1984 record of 29.4
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Stirling Energy Systems in partnership with Tessera Solar are building a 1.5MW field Peoria, Arizona. The modular nature of these types of systems makes it a good fit for smaller scale and more widely dispersed distributed solar generating systems, because they are easily scaled to fit current energy market conditions.
The Wind Energy Sector
According to a the Small Wind Global Market Study a study on the market for small wind turbines from The American Wind Energy Association (AWEA), the U.S. market for small wind turbines, which it defines as those with capacities between 20and 100 kilowatts (kW), grew by 78 percent in 2008. It must be said that the installed base is still very small – the total new capacity is a little over 17 megawatts (MW) – however the rate of growth is impressive if it can be sustained.
In the report manufacturers predict a 30-fold increase in the US market in as little as five years, even under current economic conditions. Primary drivers include the eight-year 30% federal investment tax credit enacted in October 2008, recent and potential private equity investment, and greater equipment manufacturing capabilities.
Distributed electric energy generation can help alleviate many of the critical problems facing our current over-taxed grid and avoid the need in many cases to lay down thousands of miles of new high voltage transmission lines. Distributed power as an idea seems sensible, especially in a post fossil world where power is gathered from low density and widely scattered variable sources, such as the wind or the sun. While there are some factors encouraging economies of scale – for example large turbines are more efficient than smaller ones – alternative energy seems well suited to a distributed energy topology typified by a large number of smaller scale facilities that are, in many cases, closely sited to consumers. In this manner power is delivered almost straight to the consumer and the grid becomes increasingly a kind of peer to peer power network re-distributing surplus power to regions of energy deficit – the grid as a more of a load balancer than a one way power pipeline from a few massive thermoelectric plants to the multitude of consumers.
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