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How home solar arrays can help to stabilize the grid, Part 1 of 2

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Editor’s Note: Scientific American’s George Musser will be chronicling his experiences installing solar panels in Solar at Home (formerly 60-Second Solar). Read his introduction here and see all posts here.

Solar arrays can do more than feed energy into the power grid. They might also be able to help the grid cope with a problem many people aren’t aware of: the fact that electrical appliances not only consume energy, but also momentarily store and release it. The worst culprits are motors and transformers, whose internal magnetic fields represent a significant cache of energy, giving these devices a type of electrical inertia that causes them to get out of sync with the grid. To describe the problem and a possible solution, I’ve invited a two-part guest blog from Arnold Mckinley of Xslent Energy Technologies. Here’s part one.

We all know that solar power curtails carbon emissions, decentralizes the electrical system, and reduces the nation’s reliance on foreign oil resources, but did you know that solar can now help to stabilize the grid? The grid is highly temperamental. It requires careful monitoring to maintain frequency and voltage within very limited ranges to ensure that motors don’t burn out, that power surges don’t zap computers, and so on. In the U.S. we take quality electricity for granted, but our good fortune comes with a huge infrastructure behind it to make sure it stays that way.

When the grid does get destabilized, the results can be nasty. Blackouts on the West Coast in 1982 and 1996 forced six million people to eat by candlelight. The infamous 1977 New York blackout left deep scars on the city. The 2003 U.S.-Canadian blackout affected 60 million people. In 2004 a joint U.S.-Canadian Task Force compared these events and found that the principal factor common to all was that the demand for reactive power exceeded the supply.

Few people have even heard of "reactive power." So what is it, who needs it, why wasn’t it such a problem before, and how might solar help prevent future blackouts?

We homeowners pay our utility bills based on "active power." It is also known as "real" power, partly because of a mathematical technicality and partly because it carries the kilowatt-hour energy that does the work of lighting our homes, compressing the fluids in our air-conditioners, and pumping water into our swimming pools.

But simultaneously, alongside the active power, flows reactive power. It performs an ancillary service that ensures fluorescent lights actually do light, that computer power supplies actually do work, and compressor and pump motors actually do turn. Modern electronic wizardry, from LCD TVs to electric cars, worsens the reactive-power demand on the transmission lines — so much so that the European Union and the U.S. government are beginning to force manufacturers to reduce significantly the reactive power draw of these devices.

Reactive power flows whenever the load on the grid cause the voltage and current, which oscillate at a very constant 60 hertz, to get out of sync. In the graph at left, the current lags the voltage slightly.

Multiplying the voltage and the current together gives you the power. It is the sum of two components: the active power, which averages to a positive number and therefore represents the energy delivered to the load, and the reactive power, which averages to zero over a full cycle and represents energy that moves back and forth between the grid and the load. That is, the reactive energy flows in one direction toward the load, then turns around and flows in the other direction toward the generator, repeating every cycle.

The total power is measured in kilo-volt-amps (kVA), the active power in kilowatts (kW), and the reactive power in kilo-volt-amps-reactive (kVAr). The ratio of kW to kVA is called the power factor (pf). If pf equals 1, all of the kVA power is active power; if it equals 0, all of the kVA power is reactive power. Home energy monitors such as the TED 5000 display this quantity.

Reactive power causes instabilities for two reasons:

  1. It impedes the flow of the useful traffic on the transmission lines. In essence, the fluctuating energy takes up room on the transmission lines that could be used for active power.
  2. Excessive reactive power can cause sharp drops in voltage. If, for example, drawing a certain amount of active power causes the voltage to drop from 118 volts to 117 volts, drawing the same amount of reactive power will cause it to drop from 118 volts to 108 volts. That is, by definition, a brownout.

In the next article, I will explain how a new solar technology, called microinverters, can help control the reactive power on the grid and help stabilize our electrical system.

Photo and diagrams courtesy of Arnold Mckinley

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  1. 1. jtdwyer 3:19 pm 05/24/2010

    Accepting the argument at face value, wouldn’t it then make financial sense for public utilities to provide funding for the acquisition of home solar arrays, especially if it could defer enormous capital requirements for grid investments?

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  2. 2. dwbd 8:42 pm 05/24/2010

    What utter nonsense. Almost all the reactive power on the grid comes from big electric motors – used widely in heavy industry. Industry pays for peak demand. That’s why they use power factor correction capacitors to save on peak demand and move their power factor close to unity.

    The biggest advantage of home power systems, is not the micro-inverter but a battery bank. A home battery bank can give the homeowner the security of a reliable emergency power supply and greatly reduce or eliminate peak demand of the household. Which of course is a big saving for the utility. And storage batteries need only cost $150 per kwh vs $600 per kwh for EV traction rated batteries. So V2G is a bad idea. And $150 per kwh for storage batteries beats the hell out of Smart Grid costing >$1k per home.

    As-a-matter-of-fact the home battery bank BLOWS AWAY THE SMART GRID as a method of improving the economics of Grid Management & Peak Power production. While giving the homeowner control, rather than the idiotic Smart Grid idea, of letting the Utility control our power consumption, or forcing us to pay extreme peak market prices for electricity, so the less wealthy of us, will have to cut back on electricity consumption, during peak demand periods or if NUTTY Wind Turbines aren’t delivering, as they commonly aren’t.

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  3. 3. Mark Pine 11:33 am 05/27/2010

    Does reactive power explain why my 4-ft. fluorescent bulbs sometimes flicker rather than light? The flickering doesn’t happen all the time, and for some reason it doesn’t happen much in the winter but it does happen frequently in the summer.

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  4. 4. jjas2264 3:00 pm 05/28/2010

    It would seem to me that unless EVERYONE made their own electricity EXCLUSIVELY for their own consumption; i.e. ELIMINATE the "grid" altogether, that the prospect of literally tens of thousands of small power sources (no matter what their type) connected to the grid would have the unintended consequence of essentially destabilizing that grid to the point of practical USELESSNESS. This is an exponentially rising tide of complexity giving rise to a Chaotic future of blackouts and brownouts whose causes will be, practically speaking, nearly untraceable and whose solutions will be almost impossible on the whole. Imagine trying to fend off a giant swarm of biting gnats with your hands – you may squash some of them but it’s NEVER going to be enough. We have NEVER really understood the behaviour of large electrical grids (like the one in N.America); even the people who run them are simply crossing their fingers and praying every day that some unexpected event doesn’t cause another mass failure.
    (p.s. Sorry ’bout the caps but its hard to emphasize anything otherwise.)

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  5. 5. jjas2264 3:12 pm 05/28/2010

    In case anyone points it out – yes, there is more than one electrical grid in N.America – but, increasingly, even the grids that are supposed to be "isolated" are becoming more and more interconnected and, consequently, interdependent.

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  6. 6. ArniMcK 12:22 pm 06/2/2010

    There is an interesting study done by authors from Oak Ridge National Labs, the Calif ISO, The Univ of Tenn, and PG&E, entitled "A Tariff for Reactive Power", written in 2008. The argument is the one you just gave and they suggest a tariff that utilities should be willing to pay for the production of reactive power by solar producers.

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  7. 7. ArniMcK 1:45 pm 06/2/2010

    jjas2264: FERC and recently the CAISO are aware of the potential risks you mention, as are the utilities, of course. CAISO is in the middle of setting standards for large solar producers (20MW) and more. (see on-line "Revised Draft Final Proposal for Participation of Non-Generator Resources" March 8, 2010). Destabilizing has always meant a lowered voltage due to too much reactive demand. Too much reactive supply raises the voltage too high and is as bad. So the issue here is the effect of allowing EVERYONE, as you put it, to produce reactive when it isn’t really needed. So power selection management is an important part of the CAISO recommendations.

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  8. 8. ArniMcK 1:53 pm 06/2/2010

    Mark, It could. Fluoresecent bulbs will flicker if the starter is bad, but then it flickers all the time or nearly so. They will also flicker if the voltage is too low, say 108 VAC instead of the more typical 117 V – 120 V. Too much reactive demand at your end of the utility pole will draw down the voltage, which could happen if you are way out on the line, or if it is hot day in mid-summer and lots of air-conditioning is on in the area.

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