Can i do this - and can i pay someone to build it ?

craigcurtin

Senior Member
Guys,

I am in the process of setting up a Diesel Generator that is running on Waste Veggie Oil (WVO).

The sweet spot for output of this unit is 4KW. - Single Phase - 240V - 50hz.

I have just ordered a grid tie Solar system that will output 2Kw to the grid (we get Gross metering in NSW at 60c KWh) - the solar inverter is capable of having two strings of input to it to a maximum of 600v DC. The inverter is based on MPPT and runs the panels in series to produce power at its sweet spot of 280v

What i would like to do is have someone build me a "black box" to do the following

1) Hall effect sensor to measure the total load being placed on the generator - this would feed into a Picaxe - preferably a 40x1
2) Variable output rectifier - take in the 240v output from the generator, rectify it to 280vDC and allow a variable amount of current through (upto a maximum of 10amps) - controlled by the picaxe - based on the parameters i would set for load shedding. Essentially i would be using the Grid to load shed on the generator to keep it in its sweet spot.

I would like this as a "black box" in that it will have something along the lines of a piggy back 240v lead for the hall effect (much the same as the Australian Kill a Watt meters), and an anderson style connector for the DC output - no bare wires.

Obviously the PIcaxe would be powered through a regulated power supply as part of this, which could be fed by the mains/UPS for stability


Before anyone asks

1) Yes i do have an electrician involved to do all the wiring
2) yes i can grid feed from the generator in this fashion and count it as Green power as long as it goes through a certified Grid Tie inverter.

Do the brains trust think this is a doable thing with a picaxe controlling it ?

I know all the high level bits but am not at the level of being able to source and build something such as this.

regards

Craig
 

manuka

Senior Member
Craig: An interesting one - but some pictures would help visualise things! What is your actual Oz. location ? Budget ? Time frame ?

Aside from PICAXE issues, perhaps first clarify (especially for for snow bound northern readers), just why this particular WVO slant. For those unaware NSW= Australian state New South Wales, & given your abundant solar resource, WVO seems a tad tedious ! Associated gene noise & maintenance also arises, as do numerous hassles, the least of which is a reliable ongoing WVO supply. Guess you've factored in time, effort & energy needed to collect,store & purify it too ? Unless refined, free fatty acids in WVO can have a detrimental effect on metals, & diesel injectors only need to get zonked for $$$($) repair bills to arise. There's a great account of Thai experiences here- their CVO (= crook vege oil) powered genes gave only 300-500 running hours before failure.

I've a relative in rural California who flagged WVO away after finding he was spending more time & money on his "free" setup than it was saving. He concluded WVO best suits a community setup where a uniform & refined product can be utilised. FWIW-with 2009's global down turn causing a flagging in PV demand, quality solar PVs can be picked up now for ~US$5 a Watt. Double that for storage batteries & I'd say an Aust$10k capital outlay would set you up for the next 10-20 years Stan.
 
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Dippy

Moderator
It's probably doable Craig, but people are going to have trouble doing design work when remote from the kit. There may be oddities that can only be checked/tested on-site.

I think, as you know the desired product inside-out, it would be better doing it yourself.
You'd have to provide a pictorial design spec too and, without looking at it, I would guess that the designer will have to part with a reasonable amount of cash - and devote quite a lot of time.

I'm sure some people will volunteer via PM, but make sure that the experience level is satisfactory as some hefty component specs will be needed. The inexperienced may get a shock trying to prototype a design for this.
I reckon this should keep you busy over Christmas :)
 

Andrew Cowan

Senior Member
The inexperienced may get a shock trying to prototype a design for this.
Precisely - it's high voltage stuff. Make sure whoever does it has enough experience with high voltage at these currents - making a reliable, efficient design will require quite a lot of effort.

A
 

westaust55

Moderator
Precisely - it's high voltage stuff. Make sure whoever does it has enough experience with high voltage at these currents - making a reliable, efficient design will require quite a lot of effort.
A
Be cautious about terminology used - and working with voltage not trained to work with.

240Vac and thereabouts is not High Voltage (albeit still lethal).

Typical classifications by IEC standards and Australia Standards are:

Extra Low Voltage is <50Vac or 110Vdc (ripple free)
Low Voltage is > ELV and < 1000Vac

anything > 1000Vac or 1500Vdc is nominally deemed high voltage.

In Europe, switchgear manufacturers often use the term Medium Voltage for voltages from 1000Vac to around 33kV.

Then there is Extra High Voltage for systems above 230kV.

- - - - - -
Is can be all a bit relative to what voltage one is working with. In the electric power transmission engineering field, high voltage is typically considered any voltage over approximately 33kV.
 

Andrew Cowan

Senior Member
It's all relative. I call 5v normal, over 50v highish voltage, and over 200v very high voltage. While power station stuff may be several hundred times higherthan what I've delt with, I've never had to deal with it, so my scale only goes up to (rectified) mains voltage.

A
 

Dippy

Moderator
I'm a great supporter of standards and definitions, but in this hobbyist Forum maybe we shouldn't get too tied up with (comonly unconnected) semantics as this can lead us astray - possibley dangerously.

We really need to separate Electrical and Electronic, hobbyist and professional.

If I were to spout on about 240V being 'Low Voltage' on this Forum this could lead to many people inferring that is was safe and having a nasty surprise.
I think we should forget Electrical Enginering definitions for this Forum in the main.

After all, National Semiconductor supply an HV (60V) version of their LM2574 Switcher.
And "HV" stands for ...... ? Yup, you've guessed it...
Maybe someone would like to email Nat Sem and tell they've got it all wrong ;)
 

westaust55

Moderator
electronics can also be into the 10's of thousands of volts as well.

Some better known examples include CRT TV's & PC displays and X-Ray machines.

However, do not disagree that voltages above 50V can be lethal
 
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Dippy

Moderator
Oh absolutely, but there are all those other things like HT and EHT.
The list goes on forever... ending up in FB.

Let's just agree that one person's Hgh Voltage may disagree with someone else's.
One of the problems of definitions, pub experts and 'gut feelings'.

So, after this great and interesting tangent, can we agree that Craig's voltages are quite high and could easily take the taste buds off your tongue :) So, maybe not a project for a novice.

Craig, do it yourself ;)
It'll be quicker , design by committe is a nightmare and when it blows up there is only one person to blame.... Mr Muggins.
Happy Christmas.
 

craigcurtin

Senior Member
Thanks for the replies and taking the time guys

Craig: An interesting one - but some pictures would help visualise things! What is your actual Oz. location ? Budget ? Time frame ?

Aside from PICAXE issues, perhaps first clarify (especially for for snow bound northern readers), just why this particular WVO slant. For those unaware NSW= Australian state New South Wales, & given your abundant solar resource, WVO seems a tad tedious ! Associated gene noise & maintenance also arises, as do numerous hassles, the least of which is a reliable ongoing WVO supply. Guess you've factored in time, effort & energy needed to collect,store & purify it too ? Unless refined, free fatty acids in WVO can have a detrimental effect on metals, & diesel injectors only need to get zonked for $$$($) repair bills to arise. There's a great account of Thai experiences here- their CVO (= crook vege oil) powered genes gave only 300-500 running hours before failure.

I've a relative in rural California who flagged WVO away after finding he was spending more time & money on his "free" setup than it was saving. He concluded WVO best suits a community setup where a uniform & refined product can be utilised. FWIW-with 2009's global down turn causing a flagging in PV demand, quality solar PVs can be picked up now for ~US$5 a Watt. Double that for storage batteries & I'd say an Aust$10k capital outlay would set you up for the next 10-20 years Stan.

Stan, Yep i have been on the whole WVO thing now for about 2 years and have a good and stable setup for collecting, filtering, storing and using WVO. I currently run my car on WVO and have done so for the last 18 months.

My system is refined to the point where it takes no more than 30 minutes each week to process around 200 litres of oil. I currently have a stockpile of WVO of just under 4000 litres and can with the supply stream i have now easily collect 500 litres per month.

One of the beauties of using a stationary engine is that it can provide a lot of possiblities for Combined heat and power production - in my case i intend to use some of the waste exhaust heat to help process solidified fats. In Australia most people who use Vegoil tend to stay away from the solidified fats (lard and other variations) because of the complexities this introduces into the design of a vehicle system.

Recently on one of the forums that i am regularly on someone at Coffs harbour (about 5 hours drive) made available 3000 litres of solid Fat (FRYTOL), i intend to make a few trips over the next 6 months to collect this - as i plan on running my engine for 15+ hours per day, i will have a lot of excess heat that can be used to liquify and ultimately process this oil/fat. The engine will use approximately 250ml of oil per kw hour of electricity produced -so at its sweet spot of 4KW around 1 litre of oil per hour. based on a projected runtime of 100 hours per week - i am therefore up for 100 litres of oil per week.

The engine i will be using is a clone of an old english design and is known as a Listeroid, these are slow turning (in my case 800rpm) workhorses that reliably run for months at a time - the maintenance and running issues with these workhorses are well known - a complete engine landed in Australia from India is in the region of $1500 - the raft of spares i have purchased with it are another $500. An injection pump costs all of $55 AUD and an Injector $9 AUD !!.

I am well underway to constructing the shed for this unit which due to the location of my block will lend itself very well to allowing this unit to run without annoying neighbours (search on YOUTUBE for Listeroid) and you will get some idea of the level of noise these units make (they are not the 3600 RPM screamers you typically think of)

Whilst i know what i want and need to achieve with the system i am building and can nominate the parts at a high level i do not have the construction skills (or time) to learn how to do this from scratch.

I have done this type of outsourced collabarative design arrangement with a US based person previously for a home heating and control project and that worked very well to achieve what i wanted in terms of finalised boards delivered to me - which i was then able to program etc.

Due to the different electricity standards etc in Australia i though it would be easier this time around to get someone OZ based (preferably) or NZ or UK.

Both my wife and i run business's from home that revolve around the provision of computing services to customers - as such we have a number of machines that have a continuous current draw of about 1.5KW - this equates to a base load in our house of some 36KW hours per day - our total house draw based on our last bill is in the region of 60KW hours per day - it is not feasible or economical to provision this from solar and batteries.

The type of setup i am purchasing for solar now provides approximately 2KW of solar panels and grid tie inverter for approximately $6K after Govt rebates for Solar RECS are applied. To get enough solar to run the house (based on an optimistic 6 hours of sun per day on average) would set us back about $40K - before buying any batteries and all the associated maintenance hassles with those.

Our latest electricity bill ran us to $1200 (this is with a 5% overhead for purchasing so called green power), recent news articles have highlighted that legislation is going through in NSW that will see electricity price rises in the order of 60% over the next 3 years.

The biggest consumable with my setup will be the electrical generator itself - these are Chinese ST gen heads that cost approximately $1000 AUD - once they are bedded in and settled down they will require a rebuild twice a year for the projected hours of runtime i am looking at.

Based on our usage patterns and moving some of the more flexible loads around (things like dishwasher, hot water heater, clothes washing etc) i am projecting that i will achieve a 90% reduction in our costs of usage from the grid by running the generator for 15 hours per day - if these pan out during the first year of operation we will then asses whether we buy a 2nd system (smaller) for overnight usage or look to slowly investing in a large battery bank that can feed UPS's/Inverters to run the off peak loads.

In terms of your other questions

We are based in Castle Cove in Sydney (north shore near chatswood)
Timeframe for the finished design would realistically be the end of March.
Budget - i have allowed $1000 for this side of the project - the outcome of which will be a total of two "systems" - one for live production and one for testing/ongoing development

In terms of the electronics side i see that i have the following needs

1) A method to monitor the load being placed on the system in terms of electrical current - from previous questions asked and research it appears that the easiest/safest/most accurate way is with a hall effect sensor that can monitor the single phase output of the generator and interface to a picaxe through an ADC port this single phase output will come to a sub board from my main switch board, this sub board will be electronically isolated from the main board through electrical interlocks whilst the generator is operational.

2) The ability to activate relays to have various loads come on or off based on the data gathered above - i am comfortable with doing this as i have had a few years experience doing this with Picaxe with my home hydronic heating system - the ultimate system design will decide whether this is better done on a single board (should be doable with a 40x) or if we go to a discrete 2nd board with some form of interboard comms in the form of i2c or HSI or some such

3) One of loads to be activated would be a "dump" load of rectified DC power that could be fed to the inputs of the MPPT Inverter - this is the part where i am a little lost - i think i understand the whole rectified DC thing from AC but do not know how to control the current flow so that i can feed a varying amount of 280v DC to the inverter - based on the load i want to shed and the maximum input the inverter can accept - this also leads to the need for me to monitor the other DC input (from the solar panels) for voltage and current to make sure i am not feeding the inverter more than it can handle.

4) The board as designed would also need the usual peripherals such as Serial in/out to a PC, LCD output, DS1307 for RTC and some form of local storage through i2c memory modules - again all of this i have done with my previous boards and have ongoing experience with.

regards

Craig
 
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papaof2

Senior Member
3) One of loads to be activated would be a "dump" load of rectified DC power that could be fed to the inputs of the MPPT Inverter - this is the part where i am a little lost - i think i understand the whole rectified DC thing from AC but do not know how to control the current flow so that i can feed a varying amount of 280v DC to the inverter - based on the load i want to shed and the maximum input the inverter can accept - this also leads to the need for me to monitor the other DC input (from the solar panels) for voltage and current to make sure i am not feeding the inverter more than it can handle.
Other than some input current variation with changes in the input DC voltage, the current the inverter takes from the (rectified) generator output depends on the load on the inverter; which *should* have internal limiting on the amount of power it attempts to provide to the grid.

John
 

manuka

Senior Member
Craig: Thanks for that electrifying background, which I'm sure others "up top" will appreciate. Those engines certainly look just what the Dr. ordered- Indian technology can be very reliable indeed. I'm wary about arms length PICAXE application to such a setup however.

FWIW, even with your PC base load, I'm staggered at this (presumed monthly) electricity bill of yours! Is it correct? 60 units x 30 days = 1800 units, which doesn't make sense when related to that Aust $1200. Is it two monthly hence? What sort of home PC setup demands 36 units daily- most of our swag (largely laptops) draw only 20-50 Watts (~1 unit each daily) ? I've just measured an always on HP thin client here & find it's drawing ~10 Watts (screen off). During NZ winters (mild- even frosts are rare), our own 4 kid all electric family home energy bill is only a mere fraction of this! We've a heat pump, wood fire, extensive double glazing & passive solar slanted house - nothing off grid beyond a backyard solar shower & a few PV shed lights. Mains powered lights & PCs blaze away all hours & with sporty kids hot showers are seemingly in continual use.

All manner of NZ tariffs can apply,& we Kiwis are also continually reminded about price hikes, but local energy is billed at ~NZ 20 cents a kWh unit (~10p or US/Aust ~15c). Our own typical mid winter domestic usage is around 25 units daily, falling to ~7 units mid summer -high humidity here in coastal Wellington is thankfully rarely bad enough to need summer air con. I've never experienced down under domestic monthly power bills at your level - are you up with NegaWatt approaches ? Stan.
 
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craigcurtin

Senior Member
I should have said that bill was quarterly - sorry

Craig: Thanks for that electrifying background, which I'm sure others "up top" will appreciate. Those engines certainly look just what the Dr. ordered- Indian technology can be very reliable indeed. I'm wary about arms length PICAXE application to such a setup however.

FWIW, even with your PC base load, I'm staggered at this (presumed monthly) electricity bill of yours! Is it correct? 60 units x 30 days = 1800 units, which doesn't make sense when related to that Aust $1200. Is it two monthly hence? What sort of home PC setup demands 36 units daily- most of our swag (largely laptops) draw only 20-50 Watts (~1 unit each daily) ? I've just measured an always on HP thin client here & find it's drawing ~10 Watts (screen off). During NZ winters (mild- even frosts are rare), our own 4 kid all electric family home energy bill is only a mere fraction of this! We've a heat pump, wood fire, extensive double glazing & passive solar slanted house - nothing off grid beyond a backyard solar shower & a few PV shed lights. Mains powered lights & PCs blaze away all hours & with sporty kids hot showers are seemingly in continual use.

All manner of NZ tariffs can apply,& we Kiwis are also continually reminded about price hikes, but local energy is billed at ~NZ 20 cents a kWh unit (~10p or US/Aust ~15c). Our own typical mid winter domestic usage is around 25 units daily, falling to ~7 units mid summer -high humidity here in coastal Wellington is thankfully rarely bad enough to need summer air con. I've never experienced down under domestic monthly power bills at your level - are you up with NegaWatt approaches ? Stan.

Stan, That bill was quarterly not monthly sorry - on our smart meters here we have 3 time of day billing bands , peak, shoulder and off-peak,

Off-peak runs at about 9c/kwh, shoulder 17c/kwh and peak 38c/kwh

My wife runs a bookeeping business for a number of clients - as such we have server class machines here - one of them which runs 7 virtual machines of varying descriptions and functions pulls 800w continuous. Another one pulls around 400w.

We also have the standard home PCs, laptops and the like that do draw the types of current you mention.

yes i am aware of the whole negawatts thing. !!

regards

Craig
 

premelec

Senior Member
Interesting project - one thing you likely need to know more about is what sort of "DC" the inverter can deal with - just rectified AC likely will be too extreme in pulsing at the AC frequency - so you'd need some sort of filtering - or run your generator as a DC unit in the first place. No doubt a grid intertie PV inverter can stand a certain amount of input variation considering clouds and such - however it's not likely to work well on zero DC 100 times a second - I could be wrong...:) There are capacitors on my 2KW 12VDC inverter input.

It would seem you want to offset your power most at high price times so that implies a real time clock in the project too. Balancing all the variables and taking lags into account could come out a bit complicated in the control function - otherwise some oscillation could occur if you try feed the inverter from PV & oil. Maybe a separate line tied inverter for each power source is deserved.

Measuring the oil/gen into the inverter power is not so complicated but what you do with that to keep it pretty stable seems like there might be troubles - flywheels help :)

Perhaps you could make up a tighter specifications and block diagram of all the units involved and their characteristics and capabilities... That would make it clearer for me just what needs to happen - the little box with the PICAXE inside is one small part - continue!
 

westaust55

Moderator
Hi Craig,

Things are really going full circle with fuels.

Dr Rudolf Diesel's first "Diesel" engines were designed to run on vegetable oils (such as peanut oil) and even butter fat.


In Dr Diesels own words from 1912:
" The use of vegetable oils for engine fuels may seem insignificant today. But such oils may become in course of time as important as petroleum and the coal tar products of the present time. "

An engine like this, installed in 1907 at a Tantalum mine about 125km south of Port Hedland in WA, was still standing out in the bush on a hillside when I last went there in 1994. (I spend some time wandering around the country side in that region around that time frame and came across a number of ancient engines of assorted makes from past mining ventures).



There is truth in what premelec says about the need for filtering.
Thinking about VSD/VVVF drives for variable sipped control of motors, the larger kW rated units have around 50% of their volume occupied with capacitors and inductors/reactors to filter out the AC ripple from DC. The Inverter section then works from the DC bus to recreate AC at the desired frequency.

How does your grid tied inverter handle reactive power?
Many do not, so the typically home installed PV systems only generate kW's (real power) and all required reactive power (kVAr's) is drawn from the grid.
 

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moxhamj

New Member
I'm not an expert by any means but it seems to me there might be a couple of ways to do this:

1) Run one or more standard car/truck alternators off your engine. Match the speed etc. Charge up a 12/24/48V battery. Run this into your inverter and hence to the mains. Advantage is that inverters already exist that do this, and they don't really know or care if the power going in is from solar or from an alternator. The batteries don't need to be very big as they are just there as a small buffer - as soon as the power goes in, it goes out again, and indeed, the inverter should be able to handle matching the power. If you can get a 4Kw one...

2) Consider a simple 3 phase motor. (I think this works for single phase too). A 3.6kw one is pretty small (I've got 5 of them running pumps) and only costs a few hundred dollars. Match the speed to your engine with belts. Imagine the motor is running at its rated speed (and you can specify that by specifying the poles on the motor). At no load it draws virtually no power from the grid. Load it and it draws amps. But try to run it faster than its rated speed and it puts amps into the grid. Now, consider your engine. It might have a speed control on it (with no speed control it would get faster and faster, like revving a car engine with no load). Say you start your engine and it gets the 3 phase motor running at very close to the speed you want. Then you connect it to the grid. Now if you disable the speed control on the engine, and change the throttle on the engine, you can adjust how much power goes into the grid (or even the other way with the grid driving the engine). The system will try to run at a constant speed, and you just need to match the motor and the engine with belts so they are both running at their designed speed.

The mechanicals are rather simple - belts, pulleys, a motor. The complicated part of the above 2) is how it handles, say, the grid suddenly dropping out. It would need to have a speed control on the engine that works within a certain range and gets it close to 3000rpm (or whatever depending on the poles), then does the handover to mains and then adjusts the throttle to keep it at 4kw.

From a practical perspective, I've built engine controllers using picaxes with speed control at 12hp. But I'm not sure I trust picaxes 100% - they tend to reset with mains power nearby, and they will reset sometimes with flouro lights nearby.

The algorithms for the controller are fairly simple though - probably simple enough for a few op-amps and 555 timers and they are more robust when it comes to interference.
 

westaust55

Moderator
The complicated part of the above 2) is how it handles, say, the grid suddenly dropping out.
Certainly in Western Australia and believe it applies in all states:
For these grid connected inverters, the inverter must shut down immediately in the even of the mains power being lost.

This is for safety reasons.
 

BeanieBots

Moderator
Certainly in Western Australia and believe it applies in all states:
For these grid connected inverters, the inverter must shut down immediately in the even of the mains power being lost.

This is for safety reasons.
Correct, which I find a real irony with grid-tied alternative energy.
If there's a grid power cut, you still lose your power even if though you can generate your own!

It's not just for safety, it requires the grid load and line frequency to actually work.
 

moxhamj

New Member
BB and Westy, good points. Sometimes with a project, making it work is the easy part. The harder part is asking how it fails.

Consider an engine where you suddenly remove the load (your car going up a hill and you put it into neutral but don't take your foot off the accellerator). What is the time constant for over-revving? Is the control gear fast enough to react?

Then you have different grid shutdown scenarios. If the grid has an overload, I think it retries 7 seconds later, and then I think it might try again once more. So, what do you do for a 7 second outage - keep the engine running but idling, or shut it down? What about a 3 minute outage, or 30 minutes?

In some ways having some sort of battery storage could solve some of these issues. Ok, not a huge battery bank, but at least storage of a few kWh. Normally you keep things balanced with power going in=power going out, and maybe you keep the batteries almost charged, but if the grid goes down, well power isn't going out any more (grid intertie inverters can handle that ok), but the batteries are charged up for a bit, until you might decide after 10 mins that it is time to shut down the engine.

Things end up being rather standard. The charging part can be standard alternators, or if there is AC, then just rectify it and use it to charge batteries. You can measure the current going into the batteries fairly easily. You can set the revs on the engine so it runs at x kw. Batteries slow down the time constants considerably - indeed it might be as simple as charge at x kw, which you set manually on a throttle setting, and if the batteries go above x volts, shut down the engine.

The batteries won't go above x volts normally because you set the grid intertie to send power to the grid at slightly less than x volts (but not if the batteries go under a certain voltage). That would be the same as running it off solar.

Even though solar won't power the house, with the rebates etc you might be able to get the government to pay for quite a bit of it.

What I'm not sure about is whether those rebate schemes apply to solar=>grid directly with no batteries, or whether you can get the intertie inverters that run off batteries. One advantage of batteries is at least you don't get as many power outages, especially the 7 second ones that reset the alarm clock and you get to work half an hour late, like happened to me two days ago!

The vegie solutions sounds very attractive.

Wind also can be attractive, possibly more so than solar, though the rebates all seem to emphasise solar.

60kWh per day is quite a server farm! Any way of decreasing that on the demand side, eg laptops instead of desktops?
 

dougyy

New Member
But I'm not sure I trust picaxes 100% - they tend to reset with mains power nearby, and they will reset sometimes with flouro lights nearby.
.
Are there inexpensive ways of shielding the picaxe and/or circuit components that would prevent resets?
 

Dippy

Moderator
Unless the external 'event' is a destructive or excessive energy there is always a way to prevent resets - I was genuinely surprised Drac said that.

As to whether it is 'inexpensive' depends on the amount of protection/suppression required - and depends on your definition of 'inexpensive' ;)
In many cases it is cheap, but requires knowledge and experience and sometimes expensive test-gear. The designer will have to work out whether the situation is transmitted along power or signal lines and/or induced into the circuit.

So 'shielding' can range be from simple decoupling, through transient absorption (line and/or signal) and physical screening , active/passive protection and supply backup.
It's a big subject and also a bit of a black art.... as well as knowledge of correct component selection through calcualtion and reading data Sheets.
A good designer should be able to cater for all but the most painful events.
 

westaust55

Moderator
What I'm not sure about is whether those rebate schemes apply to solar=>grid directly with no batteries, or whether you can get the intertie inverters that run off batteries. One advantage of batteries is at least you don't get as many power outages, especially the 7 second ones that reset the alarm clock and you get to work half an hour late, like happened to me two days ago!
Yes they do. Most modern home PV grid interconnected systems have no batteries.

The Australian rebates vary vastly from state to state and are varying now.

In some cases, you effectively get a rebate only for the kWh transferred back into the grid.


Other states are at least now considering a gross kWh rebate which will cover every kWh produced whether you use it in your own home or sell it to the grid. Sometimes this gross rebate only applies until the cost of the PV system is recouped then drops to a much lower value.
 

BeanieBots

Moderator
Are there inexpensive ways of shielding the picaxe and/or circuit components that would prevent resets?
It's more about knowledge than expense. At the sort of power levels involved here with grid-tie etc, total reset prevention will be a major challenge.
 

craigcurtin

Senior Member
Some feedback on the responses so far

Guys,

OK thanks for all the time everyone if putting into this. A couple of points and clarification

1) NSW offers a Gross Feed in Tarrif of 60c KW/h effectively they provision an additional meter to show what is being exported to the grid

2) As noted the grid tie inverters are designed to disconnect from the mains in the event of a Grid failure

3) The 3 phase motor is not really on option as the Engine/Generator head is going to be generating primary power for a good portion of my house - as such it is not feasible to mess around with the speed of operation - otherwise this will throw out the power generation from the main unit.

4) The car alternator into a battery bank will not work either as the Grid Tie inverters are all MPPT - most their starting input voltages are in the 150V DC range and a good many of the larger units start in the 240v DC range - this is a conscious design decision to enable the use of cheaper runs of cable - with the assumption for most people that the panels will be located a reasonable distance from the mains where the inverter is.

From what i can see in the US most people go down the route of using a rectifier to convert directly to DC from their AC (in the USA they seem to try to use both legs of their power to they have 2 x 110v) and then some form of smoothing to ensure that the DC is seen as stable by the inverter - so i guess i come back to this way again and wonder if it can be done in Aus.

Craig
 

manuka

Senior Member
Craig- AFAIK that appealing NSW Govt. 60c/kWh Gross Feed in Tarrif (starting Jan. 1st 2010 !) applies only to solar & wind systems (& rated <10kW). I've been following the scheme's roll out from over here in the NZ "Shakey Isles" (where- sniff- we have no such scheme), & believe that it's essentially intended to encourage solar PV adoption,& thereby reduce the NSW carbon footprint. A similar scheme applies in Germany, and has been very successful in making them perhaps the most proliferate users of solar energy. Of course the Australian solar resource- even in a NSW winter- is near blisteringly superior to the feeble sunbeams most Europeans consider exploitable !

The spoilsports assessing your eligibility may decide WVO biofuel setups do not qualify. Best you check first...
 
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premelec

Senior Member
Filtering

To get some idea of what you are up against - say you require 200 volts at 20 amperes DC output from a full wave bridge at 50 Hz - and can allow a ripple of 5 volts - Q=CV=IT so C=IT/V or .01x20/5 = .04 Farad or 40,000 microfarads rated at about 300 volts DC as an approximation. As I said earlier you need to know more about the inverter's input ripple requirements - consult the manufacturer on that. Perhaps an auxilliary DC generator is in order to get away from large capacitors... :)

I should mention that if you have 3 phase AC with a 3 phase FW bridge the requirements are much reduced...
 
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dougyy

New Member
It's a big subject and also a bit of a black art.... as well as knowledge of correct component selection through calcualtion and reading data Sheets.
Sigh, there is just so much that needs to be learned. Was kind of hoping for a generic solution that would solve a general case without the design requirements. Back to the books for more info....
 

Dippy

Moderator
dougy, there are, for sure, generic solutions that will sort most mild inicidences.
And slight variations will sort out slightly worse ones.
Sorting out for fluorescent light issues is easy and that would also cover most low-level problems. But when the 'wick' gets turned up then more drastic measures will be needed.

I suppose we could have generic solutions in 'bands'. But some cases need special treatment. That's where test gear, knowledge, a calculator and Magic Wand are needed :)

But to 'promise' you a one-size-fits-all solution would be pushing it a bit far...
I guess this is why some people get paid a lot of money to design electronic circuits.
 

RexLan

Senior Member
But to 'promise' you a one-size-fits-all solution would be pushing it a bit far...
I guess this is why some people get paid a lot of money to design electronic circuits.
And for what OP wants I would suggest an opening price will be $10,000 US dollars or more. The liability alone makes it a bad project.
 

craigcurtin

Senior Member
I think i will summarise the points i am trying to address

1) I am purchasing a solar system that will be grid tie interactive - this will have an inverter of approx 3Kw capacity (on the AC side) - this is a certified system that will use a Fronius IG30 Inverter.

2) The system is designed as a standalone one and is being purchased to take advantage of the NSW Gross Feed In Tarrif for Green electricity

3) In parallel with this i am purchasing a diesel generator that will run on Waste Vegetable Oil - i have confirmed with the NSW Govt that it is acceptable to feed EXCESS power from this unit into the Grid through the same Grid Tie Inverter - as the system is running on a Waste Feedstock.

4) I do not at any time anticipate feeding more than 1.5Kw from the Generator into the Inverter

5) All of the Grid Tie inverters that are being offered under the current system (from a variety of suppliers) appear to be based on MPPT - they will kick in from 150VDC (and above)

6) I therefore need a way to generate 150VDC (or above) at a maximum of 10AMPs - preferably controllable in some fashion as to the exact amount that i feed out.

regards

Craig
 

BeanieBots

Moderator
An MPPT controller designed for a PV source will be expecting to see something approximating a constant current source. Driving a constant voltage generator at constant speed will not be compatible with such a controller.

Depending on the nominal generator output voltage, this could be done with a basic switcher design used to control output CURRENT but also keeping that stable while the MPPT tries to maximise it AND not to impose variable loads on the engine at the same time whilst simultaneously trying to maximise the generator load will be 'one hell of a battle' between conflicting design criteria.

Not impossible, but I'd be contacting the manufacturer of the inverter for their input on this. They can probably supply alternative firmware for the existing product. PV simulators can be purchased. You could supply one of these from the generator and use it to supply the PV MPPT grid-tie inverter.
 
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