# Forum Home Renovation Solar Electrical Systems  It works !

## Wombat2

After being told the justification for a 2.5Kw inverter with 3.0Kw of PV panels was because system losses would account for so much loss I could never expect more than 2400 watts out into the grid I now feel vindicated for sticking to my guns and getting them to change to a 3000 watt inverter  :2thumbsup:    
This is yesterdays output before the clouds came over at lunch time. Figures at the top are today's at the time I did the dump.

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## watson

Well done for sticking it to 'em. The figures look good.
I hope you sent the suppliers a copy.  :2thumbsup:

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## Wombat2

> I hope you sent the suppliers a copy.

  
Sure did - with the the power reading saying 3003 watts  :Sneaktongue:

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## Bloss

Remember though that suppliers do the numbers on averages over a year not peaks - which will be a low percentage of total output (the aggregate output of between 2500-3000 over the year vs the total output - your graphic shows how small that is). Although it might well produce a peak and regularly mostly it will not be for long so when sizing inverter this is taken into account in making recommendations. Inverters are a costly part of the system too - many people would look at the revenue from the occasional additional output (ie: the extra bit) vs the additional cost and say nah, not worth it. Remember there is no reason for the installer to quote low - they make more money by selling you a larger inverter (that's blurred a bit right now because there are inverter supply shortage problems still so they might offering you simply what they know they can source and deliver!), but good design will generally have a good match between system components. But it's your money & your choice though.

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## Smurf

In terms of total annual energy output, missing a few peaks won't make a huge difference. 
My system is 1.02kW panels with 1.1kW inverter. Highest output I've seen is 1.1kW, and that was due to the inverter self limiting its output. 
But according to calculations, if I increased the panels to 1.36kW then I'd still only be losing 2% of total output over the year due to the limited capacity of the inverter. Financially, it just wouldn't be worth upgrading the inverter unless I was going to install a lot more panels - which I can't fit on the north-facing roof anyway. 
It really depends on what you want. For me, it is a purely financial decision and the 1.1kW inverter plus 1.02kW panels (6 x 170W) cost me zero after the $8k rebate. The only real expansion options I have are either another panel or facing North, or an entire new system facing East which would ideally use a separate inverter anyway. I'm just waiting to see what happens with the feed-in tariff here in Tas before making any decisions on that one.

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## SilentButDeadly

Nicely done.  As Watson said....well done for sticking to your guns.  An extra half a kilowatt per hour for three hours might not sound like a lot but it all adds up as the days get longer...

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## Wombat2

Ya gotta laugh !!   

> Thank you for the screen dump, that is indeed an excellent result, roughly 20 to 25% above our expectations for your size  system. This is great feedback on the quality of our Suntech panels.

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## jago

> Nicely done.  As Watson said....well done for sticking to your guns.  An extra half a kilowatt per hour for three hours might not sound like a lot but it all adds up as the days get longer...

  In NSW it would be 99c a day or an average of $352 pa  
Wombat I will PM you about your system as I have just had a $1300 bill with no  pool or real lights attached!!!

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## Wombat2

How many fridges?

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## jago

> How many fridges?

  one fridge 305litres no leaks and set correctly if that question is to me but that will increase to 3 one food one beer one wine

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## Wombat2

> one fridge 305litres no leaks and set correctly if that question is to me but that will increase to 3 one food one beer one wine

  Fridges are one of the biggest consumers of power after things like pool pumps and hot water heaters. Sounds like you need to install a power consumption meter and find out where it is all going.

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## jago

> Fridges are one of the biggest consumers of power after things like pool pumps and hot water heaters. Sounds like you need to install a power consumption meter and find out where it is all going.

  Thats the thing I have a consumption meter and had no lights only 3 lamps no electric cooking a plasma (380w) one fridge an office but seriously average consumption is 20kw a day ... It cant all be the hot water, I'm thinking the electricity company are making the bloody figures up. :Doh:

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## tony2096

modern ridges use surprisingly little power... http://forums.whirlpool.net.au/forum....cfm?t=1539574

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## Bloss

> modern ridges use surprisingly little power... http://forums.whirlpool.net.au/forum....cfm?t=1539574

  "Some" fridges - not all and we are way, way behind Californian standards on efficient fridges.

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## GraemeCook

> "Some" fridges - not all and we are way, way behind Californian standards on efficient fridges.

  
Yep,  there is a big variation. 
We replaced our fridge three months ago and I did the calculations on *** versus ***** fridges.   A three-star fridge uses about $1 per week oor $50 per year more electricity than a five star one.   Thus with a five-star on we will save oer $500 in ten years, and it did not cost $500 more than the three-star one. 
An unexpected bonus is that the motor runs less frequently so it is quieter than the old'n. 
Cheers 
Graeme

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## Abren

Double check that *hot water heater* if its an electric one!!!!!!!! I lived in a share house and our bill went up $400 in one quarter from $800 to $1200. I looked into it and could hear a *tinny* sound from the heater even though no water was going,,, turns out it had a tinny little leak/release vale had stuck open a little and was constantly having to heat water. This would account for your bill.  
Really its the only thing that would account for your bill unless you have a inside garden you didn't mention  :Wink:

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## Johning

> Remember though that suppliers do the numbers on averages over a year not peaks - which will be a low percentage of total output (the aggregate output of between 2500-3000 over the year vs the total output - your graphic shows how small that is). Although it might well produce a peak and regularly mostly it will not be for long so when sizing inverter this is taken into account in making recommendations. Inverters are a costly part of the system too - many people would look at the revenue from the occasional additional output (ie: the extra bit) vs the additional cost and say nah, not worth it. Remember there is no reason for the installer to quote low - they make more money by selling you a larger inverter (that's blurred a bit right now because there are inverter supply shortage problems still so they might offering you simply what they know they can source and deliver!), but good design will generally have a good match between system components. But it's your money & your choice though.

  Bloss
I have been getting quotes for a solar electrical system and some suppliers have quoted me systems with inverters rated at below the peak output of the solar panels. I was wondering how the inverter handles the condition when the potential power output from the panels is greater than the power rating of the inverter. Does it just open circuit the panels which would stop them producing any energy or does it pulse modulate the input to effectively just "lop" off the over voltage or is there some other method of control? 
To put it more simply. When the inverter is potentially over loaded, do you lose all the potential energy generation or just the potential excess?  Does my question make sense? 
John

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## Bloss

> Bloss
> I have been getting quotes for a solar electrical system and some suppliers have quoted me systems with inverters rated at below the peak output of the solar panels. I was wondering how the inverter handles the condition when the potential power output from the panels is greater than the power rating of the inverter. Does it just open circuit the panels which would stop them producing any energy or does it pulse modulate the input to effectively just "lop" off the over voltage or is there some other method of control? 
> To put it more simply. When the inverter is potentially over loaded, do you lose all the potential energy generation or just the potential excess?  Does my question make sense? John

  As so often the answer is 'depends' - in this case on the brand and even model of inverter. But the simple question is the right one - although the inverters are never 'overloaded', just operating at rated capacity. And that's the bottom line - the output from the inverter is what goes to the meter & then the grid and what you get paid for. This is generally a pricing balance - a design says what range of inverter rating is suitable and inverters also have a 'sweet spot' of optimal operation. Over-speccing often costs more than any income from additional peaks might put into the grid, but of course under-speccing will be worse as you will get reduced output close to the normal operational range not just peaks and that just cost you money. The designer of the system should simply be giving the optimal set-up for your site and the size of your array - end of story. 
That's why you follow some simple rules (and not much different to any major expense item or reno etc): use local businesses if you can and those that can show they have been in business for a few years at least (in this newish industry) get at least a couple of quotes - and ones where they visit your site not simply use google earthefficiency of panels and other techo stuff is largely irrelevant  - what counts is simply how much energy your system will produce on average over the years in your location because whether you are getting a gross or net feed-in tariff or simply selling your power that's what you'll get paid for. Good companies will give you a print-out from one or other bits of software that will show this - and they are pretty accurate (giving a range most often) if it sounds too good to be true it is - be especially careful of 'no upfront charges' offers - they are often simply finance contracts and you _will_ pay more than paying cash (they are a loan with interest whatever the blurb says - no money is 'free'!). Look closely at claimed 'discounts' - off what you need to ask? The only cost that matters is what you pay - so the quotes are what to compare.  never pay anything more than a 10% deposit and do not pay the final amount until you have a certificate or letter from the utility (not the installer or company you bought it from) saying you are connected to the grid Before signing up be sure that your meter box is able to accept the new meter - if the installer offers to upgrade it that's fine, but get a quite form another sparky for just the upgrade and compare. Often worth doing full upgrade to RCDs etc at the same time, but that adds cost - sometimes considerable. Make sure the quote is itemised, all inclusive and fixed price - with any inspections needed and fees identified too. It is not unusual to see mark-ups on govt or utility inspection charges that if you call and book will cost a standard published rate (check on the net). Go and visit a couple of clients of the installers who have had their system done recently - talk to them and have a look at the system to see how they feel. 
A good rule to compare is also simple - just divide the total cost be the average energy they claim to produce and that'll give you the cost per kWh for the 1st year - do the same for all quotes. Note again it's the overall energy produced that counts - you can get that by a few high output panels or by a greater number of lower output panels (if you have the space) - the total system install cost versus the output of energy you get is the really valuable comparison (assuming here that the component & install quality are the same). 
Note - the marketplace generally wants you to compare by system size - not a  useful measure for the system owner for the reasons I have given. 
That's what I reckon anyway .

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## chrisp

> It cant all be the hot water, I'm thinking the electricity company are making the bloody figures up.

   

> Double check that *hot water heater* if its an electric one!!!!!!!! I lived in a share house and our bill went up $400 in one quarter from $800 to $1200. I looked into it and could hear a *tinny* sound from the heater even though no water was going,,, turns out it had a tinny little leak/release vale had stuck open a little and was constantly having to heat water. This would account for your bill.

  Actually, it could be the hot water.  Water is one of the hardest substances to heat (i.e. it has one of the highest _specific heat capacities_) known.  See Heat capacity - Wikipedia, the free encyclopedia  
For example, If you are heating and using 100 litres (kilograms) of water from cold (say 15 degrees) to hot (say 80 degrees), you use: 4181.3 J/degree/kg x (80 - 15 degree) x 100 kg = 27.2 MJ = 7.55 kWh.Heating water takes a lot of energy.

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## jago

> Actually, it could be the hot water.  Water is one of the hardest substances to heat (i.e. it has one of the highest _specific heat capacities_) known.  See Heat capacity - Wikipedia, the free encyclopedia  
> For example, If you are heating and using 100 litres (kilograms) of water from cold (say 15 degrees) to hot (say 80 degrees), you use: 4181.3 J/degree/kg x (80 - 15 degree) x 100 kg = 27.2 MJ = 7.55 kWh.Heating water takes a lot of energy.

  
Cheers Chrisp 
I have the hotwater on its own metre and it contributed $229 of the total bill, still expensive, but I have the HW tank inside and with a jacket on it so that it doesn't have to constantly reheat from a low temp. Being from a cold country sometimes pays in knowledge.

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## Johning

> Cheers Chrisp 
> I have the hotwater on its own metre and it contributed $229 of the total bill, still expensive, but I have the HW tank inside and with a jacket on it so that it doesn't have to constantly reheat from a low temp. Being from a cold country sometimes pays in knowledge.

  Jago 
I am from a cold country too and my hot water tank is inside my house with extra insulation. Old habits die hard :Annoyed: . By having your HW tank in your house you may reduce the heat loss from your tank (depends on climate) but this is usually a very small proportion of the energy needed to heat the water in the first place. As an added bonus, when it is cold, any any heat loss from the HW tank helps to heat the house so it is not lost at all :Biggrin: . 
You say that your hot water system is supplied by its own meter. This would suggest that it is an off-peak meter and would reduce the price you pay for the energy you use. (different parts of Australia use different methods for metering electricity). 
If we take Crisps figures for the energy needed to heat 100 litres of water by 65 degrees as 7.55 kWh and assume that the price you are paying for electricity is 12 c /kWh (price in SA) and you use 300 litre per day we get:= 
3 X 7.55 X 0.12 X 90 days = $244  
This is quite close to your actual bill. 
It does not explain your total overall bill. 
John

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## Johning

Bloss 
Wow! 
Thanks for the time and effort you are willing to expend when replying to my questions. You have added to my knowledge base considerably and your post will help me become a "smarter" buyer.
Thanks again 
John

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## woodbe

> A good rule to compare is also simple - just divide the total cost be the average energy they claim to produce and that'll give you the cost per kWh for the 1st year - do the same for all quotes. Note again it's the overall energy produced that counts - you can get that by a few high output panels or by a greater number of lower output panels (if you have the space) - the total system install cost versus the output of energy you get is the really valuable comparison (assuming here that the component & install quality are the same). 
> Note - the marketplace generally wants you to compare by system size - not a  useful measure for the system owner for the reasons I have given. 
> That's what I reckon anyway .

  Yep, I agree with this. In my own case, I decided that what the various companies claimed the panels would produce introduced variables into the mix, as did the REC price quoted. Even for the same sized systems, the various software used by the quoters spits out different numbers. So, in the end I did a simple calculation based on this:  *Gross Quote Price (excluding RECS)/Total Watts of Install* 
My reasoning is similar. XkW of one brand of panel should produce pretty much the same as XkW of another brand of panel in the same location, I took out the output claim variables and just compared what was being delivered against the cost before RECS. 
As far as RECS are concerned, the price has pretty much crashed at the moment, so a quote showing a fixed high RECS value brings extra merit, but should be considered separately to the price you pay for panels/inverter/installation. Bear in mind that the RECS price wil change in the new year as the rules are changing again... 
In the end, I paid under $5.00/watt of install gross of RECS and have the RECS on the quote at $40. Happy with that. 
If your quotes are for panels in different orientations between one quote and the next, then Bloss'  method would probably be better as it should capture that variable better. 
woodbe.

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## Bloss

Yep - that's OK too - nice & simple and for the most part the difference of panel/ array output at any location won't be all that much.  :2thumbsup:

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## Smurf

> Jago 
> I am from a cold country too and my hot water tank is inside my house with extra insulation. Old habits die hard. By having your HW tank in your house you may reduce the heat loss from your tank (depends on climate) but this is usually a very small proportion of the energy needed to heat the water in the first place. As an added bonus, when it is cold, any any heat loss from the HW tank helps to heat the house so it is not lost at all.

  The HWS in the house I grew up in was in a cupboard in the corner of the laundry. Only trouble was, we had to be very careful when opening the laundry door so as to avoid squashing the cat sleeping in front of the HWS in the corner. 
I couldn't feel any heat coming from it, but the cat was convinced that it was a desirable place to sleep despite being occasionaly squashed by an opening door. So I'd take it from this that there was at least enough heat loss for the cat to have noticed. 
The other cat we had liked it somewhat warmer and slept around 10cm from the roaring pot belly fire in the dining room. More than once I burnt my hand not on the pot belly, but on the cat. How it tolerated the heat I'll never know, but it didn't seem to do any harm and the cat lived to be 20 (very old for a cat).

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## Smurf

> Bloss
> I have been getting quotes for a solar electrical system and some suppliers have quoted me systems with inverters rated at below the peak output of the solar panels. I was wondering how the inverter handles the condition when the potential power output from the panels is greater than the power rating of the inverter. Does it just open circuit the panels which would stop them producing any energy or does it pulse modulate the input to effectively just "lop" off the over voltage or is there some other method of control? 
> To put it more simply. When the inverter is potentially over loaded, do you lose all the potential energy generation or just the potential excess? Does my question make sense? 
> John

  It depends on the inverter in question. 
Looking at my own situation, I've calculated (using the manufacturer's software) that the losses from connecting 1360 W of panels to my 1100 W inverter will be just 0.2% of potential energy production. Clearly that's not a problem and not enough to worry about. 
Some inverter manufacturers actually recommend under-sizing the inverter for largely financial reasons. Using the above example, there's just no real point in having a larger inverter. 
For the SMA (Sunny Boy) inverters, they simply have a "hard" limit above which they just will not go. Connect up however many panels you like (within the inverter's voltage limit!!!) and it will simply limit power output to the inverter's maximum rating with no harm done to anything.  
So if you connected something ridiculous like 5000 W of panels to my inverter, it would just sit there all day producing 1100 W. 
In a practical sense, the inverter is simply not drawing full potential current from the solar panels such that the "unusued" power is in fact not produced at all. Just like connecting a small bulb to a car battery is placing only a very small load on the battery compared to what it is actually capable of supplying. 
That said, make very sure that any solar array (string) is within the voltage limits of the inverter. And remember to use the maximum (open circuit) voltage of the panels when doing the sums. 
And be aware that there are some inverters that don't like being over-powered at all and there are some that will cease operation completely if input power exceeds the inverter's limit. Check the manufacturer's technical data if in any doubt. 
Personally, I'd be more than happy to buy a system using a quality inverter that is moderately over-powered. It will keep the cost down with virtually no loss in output, indeed the inverter will actually operate more efficiently under cloud etc. 
As for cheap inverters, well I wouldn't buy one of those at all. Cheap panels yes, I'd be willing to take the risk there since failure rates are low, but I wouldn't buy a cheap inverter that will harm the performance of the overall system and/or will wear out rather quickly due to being poor quality.  :Smilie:

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## Bloss

All great stuff for those with a technical bent, but IMO for a regular buyer best just to rely on selecting a couple or three good companies getting quotes and relying on them as described in my earlier post. 
The sums are simple - for each system I am quoted on how much will I actually be paying and how much can I expect to get back over time. All the tech stuff might be interesting, but is simply not relevant for most buyers.  :Cool:

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## Wombat2

Got my first full quarter account - $143 CR - happy with that

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## jago

> Got my first full quarter account - $143 CR - happy with that

  
If you deduct the investment for that period how does it read?

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## Wombat2

> If you deduct the investment for that period how does it read?

  I don't care - my power bills were $350- $500 a quarter - I'm now in credit and I'll  pay the system off in 4 years ( OK so I'm doubling my monthly instalments) and from then on I'm laughing.

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## Smurf

Calculating the financial value of installing solar is somewhat difficult since it would be virtually impossible to predict the extent of increases in electricity costs over the coming years given all the goings on in the industry at the moment. 
But... 
I could afford the total cost of about $1350 for solar power (cost after the planned expansion) that will presently save me $390 a year. 
And I could afford the extra $1650 for a heat pump water heater that's saving me $285 a year. Plus it came with a 10 year warranty on the tank versus the more common 5 year warranty on a HWS. I needed a new HWS anyway since the old one had sprung a leak. 
Worst case I've blown $3000 if electricity becomes literally free tomorrow. More likely I've made an investment that is presently returning 22.66% per annum tax free and that return will increase in July next year to 24.66%, and to 26.8% in 2012 with planned electricity price increases. For a passive investment that is rather safe (everything is covered by insurance and presently under warranty) that's a pretty decent return. 
OK, I haven't factored depreciation into that figure, but not many people actually live for 20+ years in the same house these days so the odds are that eventual replacement won't be my problem and I will recoup at least some of the expenditure if I do sell the house (it must surely add something to the value, even if not the full amount that I spent on it). 
But the main benefit for me is risk management. I could afford the $3K now but there's no guarantee that I'll be able to afford to keep paying power bills in the future. If the worst happens and I become unemployed etc then at least I've cut my essential living expenses, noting that it is difficult to predict how much these expenses otherwise might be such that keeping cash in the bank "just in case" is an imperfect alternative. In that sense, solar is essentially an insurance policy from my perspective - if it ends up making a profit then that's just a bonus,

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## jago

Wombat thats  good news I was asking as I need to consider Solar as my bills are growing..... 
Smurf thanks for the detailed response it helps, ulike the corrupt wankers  of NSW government selling our power...my last bill $762  plus the  quater before of $1300  ....$2k for 6 months in a country with so much natural light !!!!!!!!!!!!!!!! Just shows they're not politicians but thieves. :2thumbsup:

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## Wombat2

I'll explain my thinking a bit more : as stated my electricity bills were $350-$500 a quarter. We installed a 3Kw system (really should have been 4.5Kw to meet our consumption fully- but the extra cost was disproportional to the return) We qualified for a 'Solar Loan' in a deal with the Sunshine Coast Council, Ingenero and the Maleny Credit Union ( aiming to install 50,000 homes on the Coast) 
The unit cost $13000 after RECs ( I see them cheaper now) and the loan is 10 years - no establishment fee, no ongoing fees and can be paid out early with no penalty. Loan payments are $200 a month but I am paying $400 so will pay it off in under 4 years (provided interest doesn't go too high) My rational is my base payment is near enough to the same as the electricity payment so not out of pocket cash flow wise - the credit is a bonus and helps make up the difference , the extra I'm paying is a hedge against the future so the day will arrive sooner when I don't have to worry about funding an essential utility. 
I calculate with the current difference in tariffs we need to average 8KwH a day to break even financially. So far we are averaging just over 10KwH

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## jago

Thanks David, the glass house mountains beautiful area.

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## Bros

> OK, I haven't factored depreciation into that figure, but not many people actually live for 20+ years in the same house these days so the odds are that eventual replacement won't be my problem and I will recoup at least some of the expenditure if I do sell the house (it must surely add something to the value, even if not the full amount that I spent on it).

  What happens if you move can you apply again or is it a once off?

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## Bloss

> What happens if you move can you apply again or is it a once off?

  Depends what you are asking and in what State or Territory. 
With the Commonwealth subsidy (RECs) the rules change from 1 January 2011 see here: http://www.climatechange.gov.au/medi...r-credits.aspx, but in any case the simple answer stays the same even after then - if you move to new premises and put a _new_ solar PV system on the roof then you will be entitled to a new subsidy. If you removed the old ones and re-installed on the new premises then you would not get any RECs because they were already used on the initial purchase (and in any case the economics make that highly unlikely). That's the Commonwealth government subsidy. Note that the multiple of 5xREcs for the first 1.5kW capacity of any PV system will reduce to 4xRECs from 1 July 2011 - that will be a reduction of about $1200 (from $6200 to $5000). Minister for Climate Change and Energy Efficiency :@Media releases@2010  
If you State & Territory has a feed-in tariff scheme for paying for the energy generated from a renewable energy generator (in this case a PV system) then the original contract is for the original premises (and in most cases can be claimed only by the occupier - this varies check your location). So if you sell then whoever signs up for the new electricity account at your old premises gets the feed-in tariff (at the same rate as the original contract and pro rata for the remaining period). 
Again the contracts are with a retailer and although they are made under authorising legislation you will need to discuss the implications with the retailer and with the purchaser of your house - you have an asset on the roof which produces a guaranteed revenue stream (less some expected minor maintenance costs) for 25-30 years. You need to come to an agreement with the purchaser on setting a value for that in the sale contract. 
So in case of the State or Territory feed-in tariff if you install a new system at new premises then you can get the tariff again and for the full period - but it will be at the rate applicable on the date of grid connection of the PV system on any new contract.

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## Bros

Thanks that answers my question.

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