Living off the grid...

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powerplay

Senior Member
I am being asked to prepare a "double switch" for feeding back into Hydro from someone preparing to live "off grid". She plans to use solar panels and the stream by her place to make power to live off, and asked me to prepare to incorporate a switch by the meter, that allows the owner to sell power back to hydro. I know little about this, and wonder if anyone has any info about what to I may need to prepare for.
 

charlie b

Moderator
Staff member
Location
Seattle, WA
Occupation
Electrical Engineer
Since your profile does not show your own location, and since you speak of selling power back to "hydro," I infer you (and your customer) are in Canada. The rules are likely to be different there, but it is likely that the local power company is not going to let a user sell power back to them without imposing a few restrictions. Relaying and protection schemes come to mind. So I would start by checking with them.

If you are in the US, then I think the US Army Corps of Engineers might have something to say about a homeowner using a local stream for the energy source to generate their own electricity. I imagine there would also be a Canadian agency with similar interests in the use of local streams. So I would suggest checking with them.

Finally, I don't think a "switch" is the component you need, in order to allow a two-way flow of power (i.e., depending on whether the homeowner is generating more or less power than they are using). But I have not dealt with such systems myself, so I really can't give you any useful information.
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
If this is a private stream with all water and mineral rights on a large plot of land she is probably ok. However we don't have enough info as to the whole project.
 

gar

Senior Member
110527-1213 EDT

From a technical perspective you do not use a switch but rather a grid-tied-inverter. The grid-tied system automatically distributes the energy from the inverter and the grid to the load, or into the grid.

Basically you have a voltage source with an internal impedance feeding the house (the grid) on the grid side of the KWH meter, and a current source with a maximum current (the inverter) also feeding the house on the house side of the KWH meter.

When the house load is greater than the inverter capability, then the house is supplied by both the grid and the inverter.

When the house load is less that the inverter capability, then the inverter supplies all of the house load, and feeds the balance of the inverter capability to the grid. The grid is the moderator of the load voltage even when energy is being fed to the grid.

This automatic balancing results from current levels, voltage levels and internal impedances,

In some other thread I tried to provide a simple explanation of how this works.

In the real world because of contracts, rules, regulations, and laws you many not be able to do legally what you can do technically.

.
 

tallgirl

Senior Member
When you spec inverters, just remember to spec battery backed ones. The Xantrex grid-interactive inverters are the most flexible (they can handle both grid and generator sources), but their communications protocol leaves much to be desired and they can be unreliable because of that. OutBack is more reliable, but their grid-interactive inverters don't play well with generators. SMA is spendy and a pain in my rear.

Also, since she's got a stream, you'll need dump loads and diversion controllers for when the stream is making more power than she's using.
 

kingpb

Senior Member
If they are wanting to get off the grid, that means there is no tie to the grid, and you will definitely need batteries to store energy when the PV or hydro cannot keep up with demand. I would suggest also adding a wind turbine, as these, like hydro can still work at night. Besides, wind is the cheapest of all.

You would still need an inverter to convert the generated DC to AC, or if you really want to go out there, convert the house to DC.

Tied to the grid you are doing a grid-tied system. If the utility lets you tie-in, then make sure you find out if they do Net-metering or wholesale metering. Net is the simplest because they pay you at the same rate that you are charged and only requires one meter. If not, and they only will do wholesale, then you will need two meters. With the inverter you need to match maximum generation with inverter capability. With a Grid-Tied system you do not need batteries.
 

jaggedben

Senior Member
Besides, wind is the cheapest of all.
That is rarely true at the residential scale. I would not suggest to anyone that they install wind without first setting up a weather station and recording a year's worth of data to find out how much wind resource they actually have. Wind resource can vary greatly over very small distances. It's not like solar, where you can often guess your resource accurately according to readings taken miles away.

Utility scale wind projects can be cheap per kWh because they are set up in places where the wind blows almost all the time and because large turbines reach higher off the ground where winds are faster.

I recently did a solar install for a customer who had set up a weather station for both sun and wind on his roof. He lived in what people think of as a pretty windy and foggy part of our area. He went with the solar, not the wind.
 
That is rarely true at the residential scale. I would not suggest to anyone that they install wind without first setting up a weather station and recording a year's worth of data to find out how much wind resource they actually have. Wind resource can vary greatly over very small distances. It's not like solar, where you can often guess your resource accurately according to readings taken miles away.

Utility scale wind projects can be cheap per kWh because they are set up in places where the wind blows almost all the time and because large turbines reach higher off the ground where winds are faster.

I recently did a solar install for a customer who had set up a weather station for both sun and wind on his roof. He lived in what people think of as a pretty windy and foggy part of our area. He went with the solar, not the wind.
You are right on. Actually a true wind survey requires a minimum of a year.

Most people don't know that wind turbines wont produce until the blade is spinning 100 rpm. That takes about a constant 12 mph wind. So, it may look like the turbine is producing when it is not.

PV is not so ambiguous. If it is getting direct sunlight at 90 degrees, it will produce 1000 watts per meter x the efficiency ratio (usually that works out to 140 watts per meter) On a sunny day with a single axis tracker, the max can be as much as 6 - 7 hours per day.

What I found very interesting was the fact the PV panels still produce on cloudy days, just at a lower rate. Compare that to wind that shuts down totally on slow days.
 

gar

Senior Member
110530-1505 EDT

powerplay:

Does your customer have reliable utility service and just want to reduce power plant fossil fuel consumption, or is the service so poor that there are daily power outages?

Off grid operation.

There is a long history of this type of operation. At Henry Ford's Fairlane Estate in Dearborn, Michigan, on the Rouge river, built in 1914-1915 there is dam on the Rouge River and a power plant. Almost certainly DC. There may have been AC in the home as well as DC. There was major flooding on the Rouge on the night of Mr. Ford's death, 7 April 1947, and the power plant was flooded so Mr. Ford died by candlelight as he had been born. The night of 6 April 1947 a classmate of mine and I drove around looking at the Rouge flood level. At Gulley Road over the Rouge the water level was up to the bottom side of the bridge. It has never been that high since. Our heavy rain this last week did not bring the level close to the 47 level.

At
http://www.thehenryford.org/rouge/historyofrouge.aspx
is a three part discussion of the history of the Ford Rouge Plant. In the 2nd section is brief mention of the Rouge power plant. This was large enough to supply the Rouge and more.

Also Ford had many small plants located on the Raisin, Huron, and Rouge rivers. Each of these had its own dam and generator for plant power. I believe all these would have been DC.
http://corporate.ford.com/about-ford/heritage/places/villageindustries/666-village-industries
http://www.detroit1701.org/Nankin Mills.html
http://www.milfordpowerhouse.com/1/165/how_it_works.asp


The Ford Highland Park Plant, this predated the Rouge, had it's own power plant. There were 9 very large DC generators. One is in the Henry Ford Museum. Per generator the rating was 4000 KW at 250 V, 6000 HP 80 RPM. The ammeter on the panel is 20,000 A. I estimate the flywheel is about 24 ft in diameter. Looks like about 89% efficiency from mechanical to electrical.

This site gives brief mention of Ford being Chief Engineer of Edison Illuminating Company in Detroit
http://www.history.com/this-day-in-history/henry-ford-leaves-edison-to-start-automobile-company

.
 
The company that invented window shades, The Stewart Hartshorn Curtain Roll Co., had it's own steam turbine generator powered by the scrap wood and sawdust generated from the factory. The turbine was long since shut down when I worked there in 1976, but the power house was used for scrap collection as all the scrap wood and sawdust was sucked into huge tubes and deposited in the power house.
 
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