Propane Generator Grid Tie

[Dr_Doggy]

Lately I have been looking at getting a propane generator that i want to tie to the hydro grid, but all the grid tie inverts i find are for 24v(solar), and all the generators i find are 120/240v, someone mentioned that i was looking for a synchronous generator, but i cant find one small enough that runs on the propane, what is best way to acheive this? Preferably, I want existing product, since I want this to be legal and SAFE!.

I plan for a max of 8-10kw feeding the grid, based on cost effectiveness and eligibility, I have idea to maybe use 3 3500watt generators keeping the budget close to under 2k$ , not including the tie system.

any ideas how i can achieve it?

 

[alec_t]

If the grid is owned by a utility company, won't you need their approval; and why would you want to give them your energy?

 

[Dr_Doggy]

ya, i need a whole isolated feed system from them, the approval comes when i have a safe configuration, intent is to sell using microFIT(FET), Problem is finding what "components" i need to do it, alot of the vendors i can find use huge systems, way out of my budget, i need smaller system, all hydro provides is the meter & wires to road.

 

[Reloadron]

Lately I have been looking at getting a propane generator that i want to tie to the hydro grid, but all the grid tie inverts i find are for 24v(solar), and all the generators i find are 120/240v, someone mentioned that i was looking for a synchronous generator, but i cant find one small enough that runs on the propane, what is best way to acheive this? Preferably, I want existing product, since I want this to be legal and SAFE!.

I plan for a max of 8-10kw feeding the grid, based on cost effectiveness and eligibility, I have idea to maybe use 3 3500watt generators keeping the budget close to under 2k$ , not including the tie system.

any ideas how i can achieve it?

I can tell you where you will face major problems. I have a home emergency generator system which works quite well, my generator is an 18KW unit and fueled by Natural Gas or Propane Gas easily selected. I use Natural Gas. The generator output is 240 VAC split phase 60 Hz power, typical US power. The mains frequency is a function of the generator rotational speed, and this is where it gets tricky. Solar Panel systems and wind turbines generate DC which is fed to an inverter resulting in AC. Since we start with DC and convert to AC using an inverter it becomes easy to grid tie synching the AC we generate to the mains AC. While the generator has a governor to control speed and thus frequency it is far from ideal. When for example a heavy load comes online like my air conditioning the generator senses the load as it slows briefly then returns to speed (actually 3600 RPM for 60 Hz). Looks like this:

Present-day generators consist of an engine directly connected to an alternator to produce electricity. One of the most common ways of changing the output frequency of a generator is to change the rotation speed of the engine.
The two factors are related as per the following formula –
Generator Frequency (f) = Number of revolutions per minute of the engine (N) * Number of magnetic poles (P) / 120
Conversely, P = 120*f/N
As per the above formulae, a 2-pole generator producing an output frequency of 60 Hz has an engine speed of 3,600 rpm. To change the output frequency to 60 Hz for the same generator configuration, the engine speed needs to be reduced to 3,000 rpm. Similarly, for a 4-pole generator, an engine speed of 1,800 rpm produces output of 60 Hz. Reducing the engine speed to 1,500 rpm yields an output of 50 Hz.

While my frequency is 60 Hertz in reality depending on loads in and out I may see 58 to 62 Hz varying making a synch to my AC mains pretty much impossible. Not easily done anyway. When my mains fail within about 10 seconds the generator automatically starts and switches over. When mains power returns the generator notes it and waits about a min. to make sure mains is stable and then switches back and shuts down following an unloaded cooldown period.

If you use 3 EA of 3.5 KW units I seriously doubt you will even get them in sync with each other. The only way this works is if each AC generator output is converted to DC and run through a large inverter to convert back to an AC true sine wave. Very expensive, inefficient and cumberson.

My Thinking On It....
Ron

 

[Dr_Doggy]

yes exactly Ron, you see my problem.
you have the very kind of system i want to tie in to grid, instead of using for backup and still a little large for me. (BTW i hear these machines are too noisy to be used in the city 24/7, is that true??) but i will be feeding grid exclusively, so fluctuation wont happen often (unless the grid system feeds back loads)(I think?). Also when gird goes down, i wont be running bkup system. I may get fluctuation when a generator does go down, but thats it , which is why i hear its better to have 2(so i have continous flow) and run them at 50% each most of the time. Would that be simplified enough to address the original sync issue? I was thinking about your plan B, but came to the same conclusion about inefficient and cumbersome.

How would industry go about a system like this when designing their systems, when i first heard about synchronous generator, i though it would be ideal for my application, but again i also have problem finding a small(er) one of these?

(>10kw microFET gets more expensive from hydro)

also:
If you use 3 EA of 3.5 KW units I seriously doubt you will even get them in sync with each other.
what do you mean by this? would this problem correct with larger models?

 

[nsaspook]

If you use 3 EA of 3.5 KW units I seriously doubt you will even get them in sync with each other.
what do you mean by this? would this problem correct with larger models?

You will need the generators to be synchronous with the grid phase and have droop control to adjust the power feed to the grid. There is no easy or cheap way to get a normal emergency type generator designed primarily for a voltage source and turn it into a current source to the grid unless you convert the power to DC so the power generation source is asynchronous to the supplied power into the grid from the inverter. This is a dangerous idea that I think you have little understanding of.
http://en.wikipedia.org/wiki/Droop_speed_control
**broken link removed**

Without precise generator control you will have a burning pile of junk if the breakers don't trip the second you switch on to the grid.

 

[Reloadron]

yes exactly Ron, you see my problem.
you have the very kind of system i want to tie in to grid, instead of using for backup and still a little large for me. (BTW i hear these machines are too noisy to be used in the city 24/7, is that true??) but i will be feeding grid exclusively, so fluctuation wont happen often (unless the grid system feeds back loads)(I think?). Also when gird goes down, i wont be running bkup system. I may get fluctuation when a generator does go down, but thats it , which is why i hear its better to have 2(so i have continous flow) and run them at 50% each most of the time. Would that be simplified enough to address the original sync issue? I was thinking about your plan B, but came to the same conclusion about inefficient and cumbersome.

How would industry go about a system like this when designing their systems, when i first heard about synchronous generator, i though it would be ideal for my application, but again i also have problem finding a small(er) one of these?

(>10kw microFET gets more expensive from hydro)

also:
If you use 3 EA of 3.5 KW units I seriously doubt you will even get them in sync with each other.
what do you mean by this? would this problem correct with larger models?

Before you worry about tying into the grid something you want to consider right off the top is how much is your cost to generate 1.0 KW of electricity? Think about it. Here in the US the cost of electricity varies greatly from state to state. What it comes down to is states that are afforded for example Hydro Electric Power have relatively cheap or inexpensive power, states like Hawaii need to import all their fossil fuel to produce electric power making Hawaii the most expensive power in the US. Here in Ohio where I live my cost for electric power for comparison purposes is about 6.39 cents per KWH or $0.0639 per KWH. I can't begin to produce my own electric that cheap or inexpensive. Therefore I only rely on my generator during a grid failure. The generator is programmed to run once a week about 30 min as an exercise routine. People selling power back to the grid around here have large wind turbines which are DC Generators (usually higher voltage DC around 400 to 500 VDC). They drive large inverters which are easy to synch to line mains frequency, as I mentioned earlier and others have mentioned.

The unit I have is **broken link removed** but the unit that predated it. Note in the link the rounded corners, mine has square corners and when I bought it the new design had just come out so I got a great price on a store floor model. Our typical use or demand never exceeds 4.0 KW but during an outage I help my neighbors. My unit and the ones like it are very quiet. The noisy units are the smaller units which have small mufflers and are generally gasoline powered. I have an older one like that.

Unfortunately, there is no way you will ever manage to get 3 EA small units in synch with each other let alone with mains power. The only way would be converting each output to DC and then back to AC using a large inverter. It simply will not work easily. This is why I would suggest just having a emergency backup generator so you have power during any emergency. Forget grid tie inverters unless you plan on a really big wind turbine or solar panel array.

Ron

 

[JimB]

At first sight the economics of this do not make sense to me.

You are going to buy propane, to run a generator, to feed into the grid, to get paid for the electricity produced.

Is propane so cheap that you can use it to generate electricity to feed the grid and make a profit?

JimB

 

[ClydeCrashKop]

I suggest you listen to a 3600RPM generator before buying one. I find them obnoxious.

 

[KeepItSimpleStupid]

A: https://www.wholesalesolar.com/products.folder/inverter-folder/xantrexxw4548.html
B: **broken link removed**

C=A+B

You pretty much have to create DC and have an inverter sync to the power line. The xantrex system can let you run off-grid too. One of your largest loads is the Air Conditioning (AC) system, Your critical loads running at the "same time" basically become the smallest system. Load shedding might not be worth it, but it is done with the AC system. Th elderly or those with respiratory issues may want AC during a period of an outage.

Using an inverter has an interesting benefit to a utility. It capable of local (surrounding area) power factor correction.

 

[crutschow]

The whole scheme sounds un-doable.
The economics make no sense.
It's difficult to synchronize a small engine powered generator to the mains.
It not only has to be at the same frequency, it also has to be at the same phase.

By the way, all small power generators are synchronous (i.e. the output frequency is directly proportional to the shaft speed).

 

[Nigel Goodwin]

By the way, all small power generators are synchronous (i.e. the output frequency is directly proportional to the shaft speed).

Actually, that's not been true for a long time - many now use inverters to create accurate frequency AC independent of engine speed, and have for a number of years.

Energy efficient
The output is produced through Honda’s unique and pioneering Inverter technology. It works with the load-sensing device; which instantly reacts to any fluctuations in load, no matter how heavy, to deliver a stable wave of clean power (above left). This makes these generators ideal for hospitality units, emergency work, sensitive electronic products and lighting.

 

[nsaspook]

Actually, that's not been true for a long time - many now use inverters to create accurate frequency AC independent of engine speed, and have for a number of years.

I'm not saying the OP should do this but the Honda generators can be made to grid-tie or more properly used to power up grid-tie solar panel systems when isolated from the grid because they use inverters. It's still tricky as you need a smart panel to detect reverse power and a dump load to maintain stability.

 

[Nigel Goodwin]

I'm not saying the OP should do this but the Honda generators can be made to grid-tie or more properly used to power up grid-tie solar panel systems when isolated from the grid because they use inverters. It's still tricky as you need a smart panel to detect reverse power and a dump load to maintain stability.

Not just Honda's of course, many (if not most?) modern generators are inverter models.

 

[Nigel Goodwin]

Not particularly relevant to this thread, but the other year following a catastrophic explosion at a large sub-station a considerable area round here was fed from a goodly number of container sized generators placed around the area. This went on for a good few weeks, as they even had to demolish and rebuilt one of the buildings at the sub-station.

It was never explained what happened, but apparently a week or two before the explosion someone tried to break in and steal cabling - makes you wonder if they tried again and were vaporised

 

[Reloadron]

For the truly curious at heart:
Generators, Inverters, Inverter Generators: What’s the Difference… and Which is Better?

For the most part the majority of inverter type generators I have seen are quiet and as mentioned built around quiet. However, for the most part are also low power output. They are lightweight, handy, easy to carry and move but again low power. While the link mentions 1.0 KW to 4.0 KW most I have seen are 1.0 KW or less. My older 4.0 KW Gasoline fueled unit is quite noisy but a brute, I am not sure how well the inverter flavors handle overloads?

Ron

 

[KeepItSimpleStupid]

We have a guy nearby that has a "shave ice business." run out of a custom trailer. He uses a Honda, about 3 KW, generator to intermittently run a motor for a few minutes a customer. The generator detects the load and increases it's RPM. It's very quiet.

 

[nsaspook]

The other cool thing about the small Honda (type) generators is the 12 volt DC tap and they are quiet. 60dB(A) for the 2000 Watt model at full load.

To the OP, even if you could get it working in principle there is no way you will ever get a permit for it without having some PE put his name on it as safe for a utility grade power interconnect without spending more than the equipment is worth.

 

[tcmtech]

I plan for a max of 8-10kw feeding the grid, based on cost effectiveness and eligibility, I have idea to maybe use 3 3500watt generators keeping the budget close to under 2k$ , not including the tie system.

any ideas how i can achieve it?

Do a simple operating cost Vs time analysis and you will see you go negative a the beginning and end up even further in the hole by the end.
-----------------
Here's just three reasons why.

1: Small spark ignition engines don't last very long. The best ones out there might make it through 4 - 6 months of run time before they are worn out. Most cheap ones might make it a few weeks before they are to the point they burn oil as fast as the do fuel.
The better engines have about 1000 - 2000 hour life expectancies the cheaper ones are maybe a few hundred before they are too worn out to be worth running or repairing. The only engines that would last in that type of work cycle are hugely expensive so figure between $500 - $1500+ per running kilowatt of shaft power capacity.

2: Factor in the realistic conversion efficiency of fuel energy to electrical energy including all the losses. Then compare cost of fuel burned to value of electricity produced.

3: On top of both of those also factor in the almost standard co gen permits costs and connection fees on top of everything else you are spending to keep the system going.

-------------------
Now as for doing pirate GTI well that's easy. Most any common single or three phase induction motor being spun faster than its normal slip speed (say a 1740 RPM motor) over its equivalent synchronous speed (1800 RPM Plus 60 RPM = 1860 RPM) does work very well as a grid tie generator plus has the safety bonus of being easy to do a direct online connect and disconnect with no synchronization needed plus if the power fails they will not work as a stand alone generator and backfeed into a dead line. They will simply unload themselves and free spin without the grid power to keep them excited.


As for a DIY system I would recomend using a small industrial engine (tractor, forklift, irrigation pump, military surplus other such application) and running it well below its capable ratings like for instance taking a normally 100 - 150 HP 3 - 4 liter inline four cylinder engine having the head milled for around 12 - 14:1 compression and using that to directly drive a 10 - 15 HP (~7.5 - 10 KW) 1740 RPM three phase motor at around 1860 RPM in a direct drive configuration.
From there use the waste heat from the cooling system and exhaust to heat your house or something useful and send the electrical power back to the utility.

A typical decent quality industrial engine running at lower RPM's and a very light relative load if maintained properly can have a service life equivalent to several years of continuous operation.

 

[Dr_Doggy]

I love it, lots of great feed back ,even if we have lots of challenges! all things i am thinking about, some im not totally in depth with yet but have considered,
To start I would like to ensure that if i do this i have no intent to diy it, i will pay for installation if requed, which I will also need to budget in.

Noise - seems to be my top issue, and the "Inverter Generators" mentioned catch my interest, for other reasons aswell, but i wonder if it is going to be quiet enough for 24/7 use in the city. I contacted bylaw but they told me its all discretion of the officer which is none too pleasing, so i may need to move to the country, something once mentioned was burying the generator, but i wonder if that will actually help(enough). or is a good idea, or maybe a better one out there.

Grid Tieing - grid tie works by hydro simply installing a second meter specific for return path, then counting the watts, as far as i know the only inspection hydro does is to make sure that their end can support it. Besides that, i think all i need is a electrical safety inspection, and maybe one for gas. If that is the case then all the legals are out of the way and all I need to find is what to plug in. TCM pls elaborate on point #3, is there balpark price?

Scope of Economics- I would like to come back to this later, but for now I do need to consider all things in expenses first. Including life cycle, which was a very good point.

A=B+C, this was how I initially thought i could work things, but i am wondering if there is a cheaper way to go, it is sounding like i should go with the low rpm machines, i guess i may need to raise the budget, so if i do get a good industrial generator, would that eliminate the worry of grid tie equipment and synch issues?