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Forum Index : Electronics : Question on Grid Connect Invertor
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marcwolf Senior Member  Joined: 08/06/2009 Location: AustraliaPosts: 119 |
I now have a 2kw Solar system with a Invertor connected to the grid. However if the grid goes down I have no power as the invertor also shuts down. And that also mean's no water!! In case of an emergency (and I mean fire season, no power, and there is a fire running through one's backyard) I was wondering the following. 1. Isolation switch to isolate the house from the grid 2. 12v Battery with small 240v invertor that can then fool the Grid Invertor that it is on grid and so connnect and produce power. I cannot see any reason for this not to work.. Many thanks for any advice Dave p.s. As mentioned this is an emergency thought for when mains does go out!!! Coding Coding Coding.. Keep those keyboards coding.. RAW CODE!!!!! |
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graynomad Senior Member Joined: 21/07/2010 Location: AustraliaPosts: 122 |
I don't know if it will work or not, sort of sounds like it should. But what will you do with it, you'll have no real grunt to drive pumps or anything. ______ Rob Rob Gray, AKA the Graynomad, www.robgray.com |
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Don B Senior Member Joined: 27/09/2008 Location: AustraliaPosts: 190 |
Hi Dave, A few comments that might help to answer your query. Grid tie inverters are designed to shut down when the grid goes off for safety reasons (ie to avoid electrocuting power supply workers trying to fix the fault). They also lack the capability to feed the neighbourhood on their own, which is what they would be trying to do if they did not shut down. In any event, an inverter can only transform energy from one type (say, the solar panel DC output) to another (say, the grid AC). If there is no energy available from your solar panels (as there would not be at night), then an inverter could not power your pump anyway. You could set up batteries, a battery charger, and a dedicated inverter to run your pump, but this would be an expensive, complicated, and relatively maintenance intensive option. In your situation, the least expensive and most versatile option would be to get a petrol or Diesel driven generator that is big enough to start your pump (it will then be amply big enough to easily run it). Such a generator would also be useful to then start and run run other essential household appliances when the power is off (like your beer fridge). Regards Don B |
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| Don B Senior Member Joined: 27/09/2008 Location: AustraliaPosts: 190 |
Hi again Dave, One other option that might solve your pump problem is to change to a DC pump, and feed it from a 12V (or 24V?) battery which is maintained by a multi-stage mains operated charger. You will still need to keep an eye on your battery, and it will not last forever, but you should comfortably be able to get, say, 5 years out of it. With a slightly larger capacity battery, you could also run that other essential appliance, the (DC) beer fridge. Regards Don B |
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| marcwolf Senior Member Joined: 08/06/2009 Location: AustraliaPosts: 119 |
Hi all and many thanks for your advice but what I was really asking (before we got onto 12v pumps etc) Is whether an Grid Invertor can be tricked into starting by isolating the house from the mains and then applying the output from a 240v invertor to simulated an attached grid. This way from a small 180W 12v to 240v invertor one can then get the full usage of that the solar system is putting out. Dave Coding Coding Coding.. Keep those keyboards coding.. RAW CODE!!!!! |
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| Don B Senior Member Joined: 27/09/2008 Location: AustraliaPosts: 190 |
Sorry Dave, I misunderstood your question. As Rob has said, maybe tricking your grid inverter into thinking that you still have a 240V AC supply by using a small inverter might work in some circumstances. Don't forget though that an inverter can only transform energy from one form to another, not manufacture it. If you have no solar energy available for it to transform into AC then it will not work. Regards Don B |
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Downwind Guru  Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
The short answer to your question is "Yes" but a bigger picture also needs to be viewed. Depending on the small 12/240v inverter and if it will back feed to the battery when the GTI is punching out more power than the smaller inverter is able to support. The small inverter could end up exceeding its capacity in reverse. So yes it will work and to prove it one needs to take a leap of faith, BUT depending on the components used in the system it is possible something might upset the other and it fail. These types of systems are used in commercial products, as in SMA systems, as i have a 24v Sunny Island inverter for off grid supply, and a Sonny Boy GTI inverter connected to it. The Sonny Boy has been reprogrammed for off grid use. The sonny boy has the solar connected to it and supplies the house direct, and any extra power the house dont require backfeeds to the batteries via the sonny island inverter. Once the batteries are charged and the solar makes more power than house consumption requires the sonny island inverter adjusts the frequency from 50hz to 52hz, and the sonny boy sees this change in frequency and backs off the power to suit. All transformer based inverters with a H-bridge driving them will back feed to the batteries if the current exceeds output demand. Now most small 180w x 12v inverters will be transformerless, and i have no idea what might happen in that case, it might still work and it might let the magic smoke out of one or the other. Pete. Sometimes it just works |
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| marcwolf Senior Member Joined: 08/06/2009 Location: AustraliaPosts: 119 |
HI any many thanks for the answer. This is what I was looking fore. seeing we are only a couple of days away from the end of the world it's nice to know that I might have some backup when the power goes off. Don - I fully undertsna that - thats why I have a 12v car battery to run the 12V invertor. But as mentioned this in only for emergency consideration. Dave Coding Coding Coding.. Keep those keyboards coding.. RAW CODE!!!!! |
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| M Del Senior Member Joined: 09/04/2012 Location: AustraliaPosts: 155 |
Hi Guys Question for Pete. Instead of having your system back off the power to suit, why not divert it into a water heater or other like item? Seems a waste of otherwise hard gained energy. Might have to look into this type of system for myself, have nearly everything you listed. Was thinking about a seperate off grid as a trial, but this may be an option. Mark Mark |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
The reason the system backs off is to protect the sonny island, this is why the sonny boy has been remapped for off grid use, or it wont back off. It will work without remapping it, but if the sonny boy capacity exceeds the capacity of the sonny island then it may blowup the sonny island. I had considered putting the extra power into hot water, but the problem is the HW service has a 3600 watt element and is just too hungry to use the excess power, i dont like the idea of cycling the batteries so hard during the day, as they may be drawn down and not get a chance to fully recharge before night. The thought was to monitor the 240v frequency and when it went above 50hz then switch the HW heater on, but this would instantly drop the hz back to 50hz and start drawing heavy from the batteries as well. If it was a 400w element then all would work far better. I done some tests with a 600w bar heater and that was just manageable on a good sunny day without taxing the batteries too hard. The best solution would be bigger batteries and store more power and not dump it into HW. Pete. Sometimes it just works |
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| M Del Senior Member Joined: 09/04/2012 Location: AustraliaPosts: 155 |
Hi Pete, see what you mean, 3600 watts direct draw would put a hole in your battery storeage if it happened late in the day. Would need 4kw of panels just to run it, scratch off the water heater idea. Mm, thinking cap back on and more research to do. Mark |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
All is not completely lost and it can still be done, i just lost interest in doing it and have now been given some hot water solar panels i intend to add to the system. One option was to throttle back the 3600w element for dumping power. I recently came across this device that would allow some control over the wattage. http://www.ebay.com.au/itm/110723383030?ssPageName=STRK:MEWA X:IT&_trksid=p3984.m1438.l2649 Also had thought of adding a stepper motor to the pot so a micro could control the amount of power dumped to hot water.................. then it all got too hard and i lost interest in the project. In reality its only sunny days one has good amounts of excess power, and on good sunny days the solar HW should produce more than i need. What would be better and easier, is for the odd days in winter where excess power is avalible would be to run a small wall mounted bar heater in the lounge room to knock some chill from the air and save a little from the night time heating bill. Pete. Sometimes it just works |
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| graynomad Senior Member Joined: 21/07/2010 Location: AustraliaPosts: 122 |
Pity you don't have some micro-hydro, you could pump water back up to the reservoir. _____ Rob Rob Gray, AKA the Graynomad, www.robgray.com |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Now there is an idea, perhaps i can use a few 1000 leds and turn the power into light and shine it back into the sky, as im told what goes up must come back down, and when the light falls back down i can catch it with my solar panels and reuse it. Im sure there is a bug in the idea. Pete. (being foolish) Sometimes it just works |
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| graynomad Senior Member Joined: 21/07/2010 Location: AustraliaPosts: 122 |
Yep, the whole idea is to use the excess solar power, and you want to create more :) The basic issue is one of timing, if you could delay the light returning for a few hours I think you'd be onto something. BTW, is there a "quote" button, apart form typing in some text
how do you quote a small piece of text? _____ Rob Rob Gray, AKA the Graynomad, www.robgray.com |
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| graynomad Senior Member Joined: 21/07/2010 Location: AustraliaPosts: 122 |
Holy crap, I've broken the board, that was supposed to show quote tags but I put them inside a code tag thinking they wouldn't be parsed. Wrong. Rob Gray, AKA the Graynomad, www.robgray.com |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Use square brackets [ then "quote" then ] and the standard [/ "quote"] to finish the quote. Now i hope that dont get formated as a quote. Sometimes it just works |
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| graynomad Senior Member Joined: 21/07/2010 Location: AustraliaPosts: 122 |
That's what I normally do [ quote ] some stuff [ /quote ] But you have to type it in, why isn't there a "quote" button on the tool bar like every other forum? As for the above problem, I put the quote tags inside a code tag, anything inside a code tag should not be parsed but presented verbatim. That has to be a bug in the forum code. And now I can't edit the post, what crap forum software. Appologies to marcwolf for stuffing up the format of his post. _____ Rob Rob Gray, AKA the Graynomad, www.robgray.com |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
I sent Glenn an email to advise him of the problem. Quote tags is not common on all forums and is a personal grip of mine to with no quote tag short cut. The other option is to use the message quote button on the top of every post and delete whay you dont want in the quote. Glenn has a system that you can only edit or delete a post upto the point another post is submitted, then you are locked out. I do agree i dont like this new system, but it was due to members removing past information from the forum causing broken topics. But i still dont like it! Pete. Sometimes it just works |
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| MOBI Guru Joined: 02/12/2012 Location: AustraliaPosts: 819 |
Hi Rob, If you use "[quote=some_name]" then the heading will say "some_name" wrote...followed by the quote on the next line. I have a "copy paste" text file on the desktop that I use for bank passwords etc and now for the quote functions. A lot quicker than typing all the quote business as it is mouse only. david.m David M. |
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