Renewables&TheGrid
ancillary services can help fix this, but the technology to use Changing the grid to support S-Dist means changing the
one wind farm to support another for ancillary services, like relaying and the protective devices installed in the grid to
voltage support or frequency management, is not allowpowertoflowbackwards(onthegrid).Todaythegridis
commercially available yet. The global industry has worked designedtoallowpowertoflowoneway,fromthehighvoltage
very hard to manage power quality, and that has allowed network to the customer: As S-Dist is installed and operated
homeowners to have computers and other digital devices in attached to the grid, power has to be able to flow in both
theirhomesandbusinesses.Ifthenetworkpowerqualityfalls directions. In a typical grid, there is a protective device for
enough,utilitieswillhavetoeitherturntousinghighvoltage every 100 to 200 customers. Changing these devices is a
DC transmission networks and labour-intensive process that can
converting the power closer to the
...asmoreandmore
interrupt the power to all customers
customerintoACpower,orindividual
generationbecomesV-Cent,the
downstream of that device. The next
customers will have to return to using
motor-generator sets or solid state
abilityoftheoperatortoprevent
issue is how to pay the generation
owner for the power they generate.
power electronics to manage power ablackoutwilldecrease Whenautility‘islands’thecustomerit
quality. These costs have not been is easy – they simply pay them for
factored into any of the RPSs or other plans that push for a removing their load from the grid and not for the kilowatt
high fraction of variable sources. These barriers are not hours of power generated. As we integrate S-Dist, we need to
insurmountable but they do need to be honestly addressed createameasurementsystemandchangethetariffstosupport
withresearchandengineering. thepaymenttocustomerswhogeneratepower.
Inthefuture,asmoreandmoregenerationbecomesV-Cent, S-Dist has a further problem. Most of these generators use
the ability of the operator to prevent a blackout will decrease electronicinverterstotaketheDCoutputofthegeneratorand
and more of the grid may be at risk. The most common turnitintoACpoweronthegrid.Becauseofthesmallsizeof
generationsourcesinthiscategoryarewindandphotovoltaic the generator, it is too expensive to create three-phase power,
farms,twoofthefastestgrowingsourcesintheworld. so instead they generate a single-phase of power. This means
that power flows out of the generator onto a single-phase of
S-Dist thegrid.Ifthisgeneratorisinstalledontherightphase,itcan
SchedulabledistributedgenerationdiffersfromV-Distinthat be very useful in balancing the load between phases.
it is done on a more ‘human’ scale, typically in less than 1 Unfortunately you have a better chance of winning in Las
megawattsizes.Thismeansthatitisnotconnectedtothehigh Vegasthanyoudoingettingallthegeneratorsinstalledonthe
voltage network, but rather to the low voltage or distribution right phase, since the owner of the generation has control of
network. Because it can be scheduled, it offers the ability to their device and not the utility. This can lead to very large
provide highly distributed power, close to where customers phaseimbalancesandbigdifferencesinvoltageonaphaseto
consumeitonthegrid.Thishasanumberofbeneficialimpacts phasebasis.Phaseimbalancenormallyleadstowastedpower,
– if the S-Dist is built to a plan that supports the needs of the in some extreme cases as much or more than the distributed
gridanditisplannedintothedistributiongrid.Unfortunately, generatorcreates.
this is seldom the case: Homeowners and business owners Furthermore, the inverters have another issue that is yet to
decide they want to install generation and they do so. Today, betackled.Theycreateharmonicsthatcanbeharmfultothe
themostcommonsourcesarenotrenewableatall,butrather operation of the grid as well as appliances and computer
gasoline and diesel-fired internal combustion engines. In the systems installed on that grid. These harmonics can shorten
futurethesemaybepoweredbybiodieselandethanol,making the life of these appliances. Today, harmonics in the low
them (technically) renewable sources. There are literally voltage network are normally ignored since the cost to solve
thousandsofinternalcombustiongeneratorsinthedistribution the problems outweighs the value of fixing them. As large
grid today. Companies like EnerNoc were formed to install screenTVmonitorandothernewsolidstateelectronicdevices
controlsandscheduletheiroperationonthegrid.Thisresource areinstalledandaddtheirharmonicstothegrid,theirimpact
hasbeenignoredinthepastbecausethedistributiongridisnot isincreasing.Sinceharmonicshaveanegativeimpactonthe
ready to handle two way power flows, when in fact, in many life of consumer devices this can mean that the average
cases,thewaytheyareusedistodisconnectthecustomerfrom lifespanofmanyofthesedevicesisdecreasing.Eventually,the
thegridandletthemrunasastand-aloneisland. industrywillhavetotackletheharmonicsissues.Mostutilities
142 worldPower2009
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