Can electric utilities buy electricity from custormers?

[matlab2008]

Hi All,

This may sounds a basic question, but I would appreciate any feedback.

With distributed generation becoming more viable (especially solar systems on the roof of customers' buildings), customers might produce energy more than their demand. In this case can they sell it to electric utilities and get money (cash)?! I'm talking here about normal residential customers in normal cities. I know that they can sell energy to utilities but utilities deals with incoming energy?

Thanks in advance
AG

 

[Marmite]

It depends on the regulatory framework and the tariff structure. Some jurisdictions have introduced generous feed in tariffs to encourage the uptake of renewables,only to frantically backpedal when the money ran out. You usually get paid a per unit rate for export but obviously much less than the per unit rate for import. Of course you need an import/export meter to measure it.
Regards
Marmite

 

[matlab2008]

Thank Marmite for your input. So, this means I could get a negative bill if I produce energy more than my demand and export the excess to my utility? I would be grateful if you could explain more your sentence "only to frantically backpedal when the money ran out"

Thanks and regards,
AG

 

[Marmite]

Have a look here:-

http://en.wikipedia.org/wiki/Feed-in_tariff

This will tell you all you need to know about feed in tariffs around the World. These are essentially subsidies from the government to encourage renewable generation. In the UK and Australia the subsidy money ran out due to the popularity of the scheme.
Regards
Marmite

 

[cranky108]

Some utilities use a net metering as a way to entice customers to sell renewable energy as a method of acheving some renewable energy goal, without the expence of the solar panels. However in our case we also have a close relationship with the zoneing people, and the electrical inspectors, so we have a little more control on the quality of the installation.

Now with the advent of solar farms, you can purchase solar panels (a share of a farm) and be credited with the energy on your bill, without the need to have them installed on your house. The same goes for wind farms. The issue is we do limit the size of solar farms, and roof top solar to a capacity, above which the installation of additional capacity will be born by the energy supplyer (solar customer).

We also add limits on the amount solar capacity can be on a feeder to limit operational issues. With solar farms they will pay extra for the additional feeder capacity, where most roof top customers won't.

Solar energy may seem free, but there is an expence, maintenance, and life of the equipment, which if you calculate out is about where they start to break even. There are exceptions for remote locations where there is no current electric service, where they will pay back much quicker. But that is mainly because of the cost of the distribution lines.

 

[Overvoltage]

What, may I ask is the mandated limit on the size of a solar farm in your area? A bill about them is being pushed by our regional legislative body and I'm curious how the proposed limits compare to some that are already in place.

 

[cranky108]

We are have been authrised to allow up to 500 kW solar farms, and because we have a good number of sun days, it seems to work. We are also in an urban area, so we are not expecting much interest in larger solar farms. However one military base did install a 5 MW solar farm, which they did pay to interconnect, and they use to offset there bill for energy. The larger customers are normally served off the higher voltages, so there are fewer limits, but the cost is higher for service, but not in per MW capacity.

The ultimate issue is how the power inflow effects how the protection of the feeder works. Most distribution feeders were designed for a one way flow, but as it happens a limited amount of inflow from customer generation is in the area of few problems with the protection. Hence the limit of 10% of generation allowed for the feeder loading.

With the limits of 10% generation, and net metering, it makes since for us connect customer generation. But the devel is in the details, and if you look into most inverter manufactures they can perform to the requirments we need with a few external additions like generation metering, and a lockable disconnect switch. We also have built up billing and maping to support this, so there is a little back ground.

 

[Overvoltage]

Those are the exact concerns we have, although our sunny days are more intermittent. Because of that reason we're suggesting a 100kW limit to avoid voltage fluctuations and protection problems. The bill does not address total limits per feeder, but because of the layout of our territory (mostly urban) I would expect they would be dispersed pretty well. Larger units could, of course, connect but would require more study and may require more protection and other mitigation. The bill addresses units that we "must serve", hence the low limit. Thoughts?

 

[cranky108]

100 kW is bigger than most homes, but is about the right size for a small business, so no problems there. Because you are urban the feeders should not be very long so your voltage regulators should take care of most of the voltage changes (This may not be so with large wind inputs).
The concerns are that the inverters must shut off when power source is lost, and before you reclose. You might rethink the instantious reclose however. Because most inverters are electronic they should drop off very quickly for small power, so a 2 or 3 secong reclose should work (It even worked with engine driven generation at my old company).
I would consiter a 10 or 20% limit per feeder to be sure to not create an island, or if one forms it will die quickly.

Larger farms should only be connected to higher voltage where protective relays come into play, and not distribution reclosers, and fuses.

 

[bacon4life]

The proposed rules for Washington will require utilities to automatically allow connection of generators up to to 500 kW if the cumulative generation on all distribution components upstream are less than 15% of the peak loading on each component. If the generation is more than 15% of load and also for larger generators, the utility would be allowed to require an interconnection study to examine voltage rise issues.

 

[cranky108]

Does automatically allow connection include following some interconnection rules such as automatic disconnection for a source disruption, safety switch, and generation metering? Most such proposed rules do allow several safety concerns to be addressed, which most customers won't read that part. And as I sad they won't read that part and they will become angry when you inform them of the safety requirments.

If the bill dosen't allow any safety requirments, then your lobbyest should be fired.

Yes you can reclose onto customer generation just to make a point, which will probally be missed by the customer.

I love sarcasm, because it helps to describe things that you know are likely to happen. Like to guy that wanted to sell us power, but could not understand that we can't take DC power, and he thought the conversion was our problem.

 

[bacon4life]

By automatic, I meant that the utility must allow all generation connections that passes a very simple checklist approach and cannot require detail studies for loads under 500 kW unless they don't pass the checklist. The utility may charge no more than $100 for a 25 kW application or $500 of a 500 kW application and must approve/deny the application in a very short time line.

The other basic items on the checklist include:
Can't overload the service transformer
Must use either UL listed inverters or other similar IEEE 1547 protection for non inverter based generation
Can't over duty the utility's protective devices
Connection at 120V cannot unbalance a 120/240 v connection by more than 5 kw
uses and external accessible safety switch if required by the utility

 

[cranky108]

That sounds reasonable.

 

[Sn00ze]

http://www.enmax.com/Energy/Res/Greenmax/Technology/AlternativeEnergyTechnologies.htm

This is for my city. It doesnt say but i believe the maximum allowable capacity is 10 KW you can get.