Energy Matters Forums

[Cherokee Solar]

Hi Gordon,

Yep, it's been cloudy here too and for a couple of days last week the wood heater was even kicked off.

Today and yesterday have been cloudless and warmish. Today, I picked up a cheapie second hand 8000L water tank to give a little bit more buffer over the increasingly dry summers here. Driving it back on the trailer was a fun experience as the thing is huge (a diameter of 2.5m which was the legal road limit).

Do you reckon there will be much change in the virtual tracker since summer?

I've had four days now since the start of the year when the system hasn't hit float.

Chris

[Gordon-Loomberah]

I know what you mean about the tanks Chris, I've brought 9, 10.5 and 13.5kl tanks home from the monthly auction in town on the trailer- and with the larger 2, I couldn't get the old Hilux over 60km/hr- its like towing a huge parachute!

I think the N facing panel will show a bit more of a peak around the equinoxes, since the sun will be face-on at solar noon with the panel tilted to face the celestial equator. The VT panels should increase in output a little faster in the mornings and stay a bit higher in the afternoons, as they will be more face-on in the morning and evening. Shorter days will mean less total energy though.

[Cherokee Solar]

I couldn't get the old Hilux over 60km/hr- its like towing a huge parachute!

Yeah, the thing only weighs about 150kg, but it was exactly like you said - a big parachute! The poor Suzuki was struggling down the road in 3rd and 4th for most of the trip... Thankfully being a Friday the back roads were quiet. The centre of gravity was a bit high on the trailer too.

The VT panels should increase in output a little faster in the mornings and stay a bit higher in the afternoons

Sounds about right. You'll be getting the maximum available sunshine, so it will be really interesting to see how it goes over the depths of winter.

PS: I got the wind turbine in the mail yesterday and although it was listed as a new item, it is clearly a second hand item. It is a bit of a nuisance...

[Tracker]

... do you reckon there will be much change in the virtual tracker since summer?
I've had four days now since the start of the year when the system hasn't hit float.....

The only perspective comment, is that east and west or east or west, is known to give 12% less power than true north and all being optimum.
Thus if you seek maximum CHARGE for the batteries, then clearly NORTH is the best option.
The advantage with E/W VIRTUAL TRACKING, is when you are trying to keep a consistent and useable supply rather than a optimum peak supply...

As previously mentioned, OVERSIZE, has been doing it for years, reducing his Peak and producing a more constant production..
Clearly best used when on no FIT, OR LOW FIT...

Off grid, it would be beneficial, for when you most always hit float at midday , and then go down hill again..
If you have lots of pv and and not enough hours...
If E/W could mean that you are held at float for all the day...
..
.

[Gordon-Loomberah]

The only perspective comment, is that east and west or east or west, is known to give 12% less power than true north and all being optimum.

That misses the point of VT- you can use essentially double the number of panels and get more power from your panels, without overheating your controller/inverter.

Thus if you seek maximum CHARGE for the batteries, then clearly NORTH is the best option.

Only if using the maximum number of panels the inverter will take and facing them all north. Face more of them, split E and W, tilted at 60deg, and you will get much more output from your system, without midday clipping and heat stress on your electronics.

The advantage with E/W VIRTUAL TRACKING, is when you are trying to keep a consistent and useable supply rather than a optimum peak supply...

You can have peak output all day with no clipping with Virtual Tracker- something not acheivable with all N-facing.

As previously mentioned, OVERSIZE, has been doing it for years, reducing his Peak and producing a more constant production..

Umm... no, he has been pointing them all North, except for a few recent ones when he ran out of space, and suffering lots of clipping, especially in summer. That is not Virtual Tracking, it's overdriving.

I get the impression that you dont quite understand the advantages of my Virtual Tracker idea

[Tracker]

.

I get the impression that you dont quite understand the advantages of my Virtual Tracker idea

I would think that I have it.. pretty well.. we have been discussing it for years.. you, thankfully quantified the results.

You can either go for minimum number of panels, east and west, and get a constant power throughout the day to cover background consumption, or you can max out both east and west and have a constant max all day, as distinct from a Nth. Setting.

I'm setting up for an absolute maximum of 1kW. All day....

That difference would be where you live and what restrictions on feed in you have, or the maximum power you can feed in

My assumption, which was not stated, was that when you have the SAME number of panels..
Surely you would not be saying that the same number E/W AND N, would give the same result..
kWH/kW/day just have to be higher for north. . 12% higher... if the theory is correct

Now if the wallet is cashed up then you can stack on those panels, to something like 200% at least of the DP...
PROBABLY, more like 300%, depending on the inverter... ie. 6kW into a 2kW inverter ..
Would that be your assumption...?

The issues vary wildly across Australia with retailers getting toey about just how much you can feed in to the grid, and in NSW under GFIT, technically, you can't add ANY panels. BIG BROTHER does not want to pay for ANY more kWh, than they do now.
So there is more to consider than the concept of of splitting directions..

Off grid you can do anything you like ... on grid.. there are real issues...!

So, bottom line.... what do we want to achieve. ?..... maximum power production kWH/day, or best solar supply throughout the day... ie minimum battery involvement.. constant kW/hour
...
..

[Gordon-Loomberah]

Surely you would not be saying that the same number E/W AND N, would give the same result.. kWH/kW/day just have to be higher for north. . 12% higher... if the theory is correct

I never said that - the difference is entirely dependent on the angle of the panels, both for north facing, and E & W facing, and the time of year, and no doubt the amount and distribution throughout the day of cloud, and the daily temperature profile as well. I chose clear, equally hot days, and one particular arrangement that I calculated will give the most even production throughout the day, in order to remove other variables.
The test I posted with the VT arrangement and N-facing panels tilted at my latitude shows 13% less for the same number of panels, for mid summer.

What anyone decides to do with their system will of course depend on the particular rules they have to abide by, but as I said earlier, when grid-connected the aim now is to match production with consumption when you are getting zero to a pittance per kWh. In NSW the rules are such that you can add a net-metered system if you already have a gross-metered system, and not be penalised, so you would aim to use a net system to match your usage and keep the gross system for income. All panels facing north to get the absolute maximum output from those panels is really only suited to gross-metered systems, now PV costs are so low and Net metering rules, Virtual Tracker panel arrangement makes sense if you can do it.
Off-grid you can do as you please

[jimbo]

Gordon did you ever use this system with your Lead acid batteries? I was just wondering how the charging differed with less of a peak? With a slower charge do you generally have less absorb time?

[Poundy]

I think Gordon was only advocating this for grid-connect scenarios where you need to cancel out your background usage rather than export and earn nothing from it. I think with charging batteries you still want to maximise that across the day, which would imply N facing.

[Gordon-Loomberah]

No, never done with Lead-acid batteries, only the tests in January with the LiFePO4s. The panels are normally tracked across the sky.

North-facing panels have slower charge up until the time the curves cross in the original graph, but that is tied to exactly how many panels are in use. When Absorb is started and ended will be related to overnight DOD%, battery capacity and size and arrangement of PV array. So many variables means it isn't possible to say anything about Absorb time without specifying a number of things.