Grid connect or not, for new system?

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Grid connect or not, for new system?

Postby PVnoob » Thu Apr 03, 2014 5:17 pm

Hi all,

I'm a French guy, and recently settled in NSW with my Aussie girlfriend.
We're considering installaling PV panels on our roof, but don't know much about how this thing works.

According to what I read on the Internet, there are different ways to perform PV, and we're looking for the better solution. Shall we have our installation connected to the grid or not ? If so, how much savings on our energy bill coud we expect for a 3kW installation (monthly) ?

It seems that we hear one thing and its opposite on the Internet...
Thanks in advance for your help !
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Re: Grid connect or not, for new system?

Postby Gordon-Loomberah » Thu Apr 03, 2014 5:38 pm

Welcome to the Energy Matters Forums :)

How much you can save depends on a lot of factors, paticularly how much energy you use per day, and how the usage is spread throughout the day, plus the charges per kWh you have to pay, along with the standing charges.


Going off-grid is something quite a few people are aiming for as the cost of grid power and connection continues to rise, and a few forum members already are off-grid. Off-grid does cost a lot more to set up, but when done properly, is a lot more reliable than many grid power supplies, plus you will never have to pay another electricity bill or deal with the power companies :!:

Have a good look around the forums, there are plenty of topics discussing on and off-grid systems.
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Re: Grid connect or not, for new system?

Postby Tracker » Thu Apr 03, 2014 8:05 pm

.
More information needed...

Are you building cold Turkey, Taking on an existing home or what

The next question is who will be home during the day..

The point. Is that if you generate pv power and if you can't use it then it is a real waste, as it grid feeds with NO VALUE for you..
..
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Re: Grid connect or not, for new system?

Postby Smurf1976 » Thu Apr 03, 2014 8:48 pm

PVnoob wrote:I'm a French guy, and recently settled in NSW with my Aussie girlfriend.
We're considering installaling PV panels on our roof, but don't know much about how this thing works.

In short, here's how grid connect works.

In a grid (any grid - Australia, France, wherever) there are numerous generating units (eg at power stations) feeding into that grid and a huge number of loads (houses, factories, offices, electric trains, etc) drawing power from it.

Any individual generator is just pushing power into that grid and that applies whether it's a great big 660 MW (660,000,000 Watts) generator at a major coal power station in NSW or whether it's a small 3kW (3,000 Watts) solar inverter at home. Either way, it's just putting out power which then "disappears" into the grid and is ultimately consumed by the connected loads - everything from big factories with huge consumption down to your mobile phone charger at home.

So your grid-connect solar just operates in parallel with all other generators in the grid - coal, gas, hydro, other solar systems and so on.

Metering is where it gets a bit more complicated. A home with no solar will just have standard metering which records power flow in one direction only. It records how much you use, and the electricity supplier then sends you a bill based on that consumption. Historically, meters just recorded total consumption and that was it. These days, there's a move toward "smart" meters which record not only how much was used, but WHEN it was used and in some cases different pricing will apply at different times - eg cheap overnight, more expensive during the day when demand is higher.

With solar grid-connect, power flows in BOTH directions into and out of your home. As such, the meter has separate registers to record this. One register will be going up when you're drawing power from the grid, and the other will be counting up when you are exporting power to the grid ("feed-in").

The complex bit is that you will be paid different rates for feed-in (under what is known as a feed-in tariff - FIT) to what you draw from the grid. And for new installations the FIT rate is a lot lower (generally around 8 cents / kWh) than what you pay for power from the grid (typically somewhere around 25 cents / kWh).

If you solar is generating 2kW and you are using 1kW in the house, then you'll be feeding the other 1kW into the grid and that's all the meter "sees". It doesn't "see" your consumption and doesn't record it, it just sees that you're exporting 1kW and records that. And you'll be paid the FIT rate for that power.

But if your solar is producing, say, 0.5kW late in the afternoon and you are using 2kW in the house, then the meter will "see" that as 1.5kW being drawn from the grid and record it as such. It won't "see" your solar at all, it just sees the net 1.5kW being drawn from the grid in this situation.

Exporting power - you get paid the FIT rate.

Using your own power at home - you are saving the cost of otherwise buying that power from the electricity supplier. So you're saving around 25 cents / kWh typically (your electricity supplier could tell you exactly what they charge).

All that makes it very difficult to say exactly how much any given size of solar system will save you financially. It's fairly easy to calculate total output, a 3kW system should be around 4,000 - 4,500 kWh per annum depending on location. But how much of that gets fed in (paid at around 8c) and how much you use within the house (saving 25c or thereabouts) depends on your consumption pattern. So it's a hard question to answer.

The key point to understand is that one does not offset the other. Eg you export to the grid 1000 kWh during the day over a given period and you also draw 1000 kWh from the grid at night over the same period. They will be treated completely separate - you'll be paid FIT for the export, and will pay a different (higher) rate for the power drawn from the grid. Even though it's the same physical volume of electricity, they don't "cancel each other out" so far as billing is concerned - they're treated separately.

Off-grid? To go fully off-grid means that you need to produce ALL your own power, since you'll no longer be connected to the electricity grid at all - the physical cable from your house to the power lines in the street will be removed or at least disconnected.

Going off-grid thus requires that you have batteries to store the power in, and enough solar to produce all that you consume. If you don't have enough then the lights will quite literally go out - you no longer have any access to the grid.

An alternative is a partial off-grid system. Eg you remain connected to the grid, but install a separate off-grid system to supply some of the electrical circuits in your home. So, for example, you might have the lights and power points on your off-grid system, whilst still running the oven, hot water and air-conditioning from the grid. In that case they are completely separate systems - your oven etc will only ever use grid power, it can't access the solar, and your lights etc will always run from batteries charged by solar (never from the grid). This is a fairly common step for those seeking to go off-grid later but who don't have sufficient $ to install everything straight away.

So that's the basics of it, there's heaps of info on these forums about all of it in much more detail.

It's also worth considering specific appliances. Eg a solar hot water system which uses solar to directly heat water rather than producing electricity. Or other options like gas which, in most parts of Australia, is considerably cheaper than grid electricity.

What's best overall comes down to what you want to achieve? Saving money is a perfectly legitimate goal and will point toward one set of solutions.

Others may be considering solar for other reasons, for example because the grid is unreliable (as it is in some parts of Australia outside the cities, largely due to the low population density and the natural hazards which cause damage to the power lines from time to time).

Others will do it for environmental reasons. In Australia, about 75% of all electricity is produced from coal, the rest being mostly gas, hydro and wind. On a state by state basis, coal dominates in Qld, NSW, ACT and Vic. Gas is the largest source in NT, SA and WA. Tasmania, with its' elaborate hydro-electric schemes and significant wind power, is the only state where supply to the main grid is from predominantly renewable sources (SA is in second place with around 30% from wind).
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Re: Grid connect or not, for new system?

Postby davidg » Thu Apr 03, 2014 9:56 pm

Smurf1976 wrote:An alternative is a partial off-grid system. Eg you remain connected to the grid, but install a separate off-grid system to supply some of the electrical circuits in your home. So, for example, you might have the lights and power points on your off-grid system

What happened to a hybrid-grid system which is a mix of the Grid and batteries runs in sync with the grid, exactly what I have and have installed for other people on a number occasions as well. Allows all sorts of options including not drawing power from the grid unless the batteries are low and then based on configuration that maybe a limited amount in from both batteries and the grid simultaneously (load sharing) for instance.
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Re: Grid connect or not, for new system?

Postby crazyk » Sun Jun 29, 2014 8:55 am

Great thread and some fantastic info in there Smurf. Answered a few questions I had.

I'm going to follow this thread closely.
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Re: Grid connect or not, for new system?

Postby Tracker » Sun Jun 29, 2014 10:17 am

..
Whatever happened to the OP.. :roll:
..
.
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Re: Grid connect or not, for new system?

Postby bpratt » Sun Jun 29, 2014 10:42 am

Tracker wrote:..
Whatever happened to the OP.. :roll:
..
.


Last visited about 4 hours after his post. :(
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Re: Grid connect or not, for new system?

Postby Tracker » Sun Jun 29, 2014 7:12 pm

..
:cry:
..
..
Makes one wonder.. :idea:
..
Commiserations. Smurf, after your classic effort..
..
.
Retired Engineer and keen PV experimenter - Always ready to learn and share.
2 x CMS2000 (fan cooled) GCI and SE 170W panels
1.7kW First Solar/Outback Island circuit - Peak Replacement Power
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Re: Grid connect or not, for new system?

Postby crazyk » Sun Jun 29, 2014 8:03 pm

I enjoyed Smurfs effort. Loved his post
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