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Keef's new off-grid solar breaks all the rules...and it's BRILLIANT!

(76 posts) (14 voices)

Started 6 years ago by Keef
Latest reply from Morbo

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Keef
Member

I've just put in a complete new system.
48 Volt AGM batteries at 280 AH.
MPPT Regulator
2 Kw sine wave inverter.

Here's the brilliant part.
I ignored the industry advice to tilt my panels at 30 Degrees.
(I'm located on mid coast NSW)
My roof has a slope of less than 10 Degrees.

Rather than waste money on hideous tilt stands I spent the money on extra panels.
Cosine error is much less than most people imagine.
Panels that are almost flat collect more energy on cloudy days.

I have 2500 Watts of Trina Honey panels.

I also ignored the rules on battery requirements.
Rather than spend a lot of money on batteries to give me 3 days autonomy I put in only enough for my overnight requirements.

Even on the most miserable cloudy day I am collecting enough energy to fill up my batteries by mid morning.
I even have an electric hot water system (with a 1 Kw element) to soak up the surplus.

The rules of the game have been changed!
Now that the cost of panels has come down it is no longer necessary to tilt the panels so that they produce maximum energy at midday on the winter solstice!
That is a silly idea (imho)

I'm as happy as a pig in plop

Posted Wednesday 29 Jul 2015 @ 4:20:47 am from IP #
darrynm
Member

Sounds great - I'd definitely be happy to lose some efficiency for a low profile installation. Approx how much did the system cost?

Posted Wednesday 29 Jul 2015 @ 4:37:26 am from IP #
Keef
Member

Batteries about $2500
Regulator about $1000
Inverter about $2000
Panels,racking, cabling about $3000

Total about $8500

I'm hoping it will last me until senility sets in.
(Don't be rude)

Posted Wednesday 29 Jul 2015 @ 4:49:47 am from IP #
dlvb19
Member

Nice one!

I tried to get a thread going on similar lines:

http://www.ata.org.au/forums/topic/6725

Perhaps one for the EM forums.
Mobile electrons to you good sir!

Posted Wednesday 29 Jul 2015 @ 5:04:19 am from IP #
Keef
Member

I run a nice new Samsung electric fridge (big saving on the old gas fridge)
I have a TV computer, electric kettle, toaster, coffee maker, kitchen gadgets.
Finally I can have a normal electric household with nice bright lighting and all the mod cons.
My regulator has online capability (naturally) so I might post the data online at PVOUTPUT to prove I'm not bullsheeting

Posted Wednesday 29 Jul 2015 @ 7:01:53 am from IP #
Benny
Member

So thats about 13kWh battery capacity ? Are batteries lead acid, so real capacity is more like 7kWh or lithium ?
I guess if you're bringing them back up to full charge by mid morning with 2.5kW panels (10kWh/day) you're only using 2-3kWh overnight ?

Thats a good price !

Posted Wednesday 29 Jul 2015 @ 8:38:56 am from IP #
Keef
Member

Quite correct.
I'm budgeting about 2 Kw-hours overnight, never need to dram down more than 20% of capacity.
The traditional solar model is to spend much more money on batteries and less on panels and have about 3 days reserve.
Problem with that is that you have a large investment in batteries and leaving them in a low state for several days is not good for their health.
My idea (and you are welcome to tell me that I'm wrong) is to have enough panels so that even under cloudy skies the batteries will be brought up to full charge by early morning.
I get 500 watts as soon as the sun comes up and even on a cloudy day I collect more than 2 Kw-hours.

Posted Wednesday 29 Jul 2015 @ 9:38:38 am from IP #
Keef
Member

I chose these ones

"Trina Honey 260W Panels

The Trina ‘Honey’ Modules deliver high efficiency of up to 15.9% – one of the highest from a standard crystalline panel.

This, combined with its high performance under low light conditions allows for consistently high output and the ability to maximise the financial return"

Seems to be working for me

Posted Wednesday 29 Jul 2015 @ 9:56:30 am from IP #
johnmath
Member

What industry advice did you ignore? Advice is (or should be) centred around achieving a particular goal. For example, I export more electricity than I use, so I was advised to aim for the greatest net export over 12 months. The best angle for this is about 12 degrees, so that is the angle of my panels. This isn't a 'new' idea, my panels have paid back their installation cost twice over in net exported power over the past 6 or so years.

Posted Wednesday 29 Jul 2015 @ 1:38:16 pm from IP #
Keef
Member

I don't claim that it is a new idea but there is a widespread misconception that it is essential to mount panels at latitude tilt.
In my local area I see many installations that have tilt stands going in which look ugly and cost extra money. Very often these tilt stands are fitted on roofs which have a North facing slope at a moderate angle.
They have been told by installers that this is the optimum angle or have blindly followed the example of the other installations in the area.

Under clear skies the latitude tilt advise would provide the highest peak output but even a 30 Degree error causes only a 15% reduction in output (Cosine error).
Under cloudy conditions it is much better to have the panels looking at the whole sky rather than being pointed at only the Northern portion of the sky.

The benefit of having reliable power even under cloudy conditions is a big plus.

Posted Wednesday 29 Jul 2015 @ 10:16:43 pm from IP #
Lance
Key Master

It's not a misconception, it was perfectly valid for off-grid systems when panels were $10/watt, but now they are so cheap, tilt frames can cost more than panels, so it is just something that has changed over time. I do agree that many installers are probably behind the times in their thinking on this.

Panels shouldn't me mounted at too shallow an angle as they need a reasonable tilt (some say 5 degrees, some say 10 degrees) in order for dust etc to wash off properly rather than pool at the edges of the frame, covering parts of the cells at the panels' lower edges.

Posted Thursday 30 Jul 2015 @ 12:15:24 am from IP #
Keef
Member

johnmath said:
What industry advice did you ignore? Advice is (or should be) centred around achieving a particular goal. For example, I export more electricity than I use, so I was advised to aim for the greatest net export over 12 months. The best angle for this is about 12 degrees, so that is the angle of my panels. This isn't a 'new' idea, my panels have paid back their installation cost twice over in net exported power over the past 6 or so years.

I'm not offering any advice for grid connected systems.
(except to say that tilt frames look ugly and are probably not cost effective)

Since putting in my new off-grid system I've never needed to run a generator even after a week of cloudy weather.
My neighbors with much more expensive systems (most of the money was spent on batteries) have to run their generators very frequently.

Posted Thursday 30 Jul 2015 @ 12:26:58 am from IP #
wlb
Member

I came to the same conclusion a few years ago during winter after watching the performance difference between the main 1400W north-facing array angled for winter sun, and a 700W 2nd array temporarily installed on the battery shed roof, pitched 7 degrees off horizontal. The 2nd array considerably out performed the main array on overcast days. This led to me move the 2nd array to the house roof (also 7 degree pitch) when I increased its size to 1750W about 3 years ago.

The next move is to add another 350W to the main array and relocate both arrays to the east-facing side of an out-building which has a gable roof with a 45 degree pitch (ridge runs north-south), and add 2 more arrays totalling 3300W to the west-facing side.

What you say about the current relevance of sizing the battery bank for 3 days without sun is certainly true. You should size them according to your expected overnight demand, plus a safety margin.

Posted Thursday 30 Jul 2015 @ 3:21:03 am from IP #
Keef
Member

" You should size them according to your expected overnight demand, plus a safety margin"

My safety margin is that I'm not expecting a prolonged solar eclipse or nuclear winter.
I am totally confident my batteries will be topped up every morning no matter how bad the weather is.

That makes me a very happy camper

Posted Thursday 30 Jul 2015 @ 8:02:15 am from IP #
Natimuk Solar
Member

so.... on the same day you post this.

I've just installed a 12.88kw PV system.
2 x 5kwSunny boy, and a 5kwSunny Island.
batteries: 660ah @ 48volt.
autostart generator.

When an professional installs a system. It is designed to be run without any input form the customer. They just use their power.

Does the CEC deisng spec protect the customer or make the system prohibitively expensive?

Posted Thursday 30 Jul 2015 @ 9:42:33 am from IP #
Natimuk Solar
Member

Natimuk Solar said:
so.... on the same day you post this.

I've just installed a 12.88kw PV system.
2 x 5kwSunny boy, and a 5kwSunny Island.
batteries: 660ah @ 48volt.
autostart generator.

When an professional installs a system. It is designed to be run without any input form the customer. They just use their power.

Does the CEC design spec protect the customer or make the system prohibitively expensive?

Posted Thursday 30 Jul 2015 @ 9:49:36 am from IP #
Keef
Member

"Does the CEC deisng spec protect the customer or make the system prohibitively expensive?

My system was an upgrade.
I didn't get any subsidies.
Therefore I spent my own money very carefully.

What was the actual cost of your system (not including any subsidies)?

Posted Thursday 30 Jul 2015 @ 9:51:14 am from IP #
wlb
Member

Keef said:
" You should size them according to your expected overnight demand, plus a safety margin"

My safety margin is that I'm not expecting a prolonged solar eclipse or nuclear winter.
I am totally confident my batteries will be topped up every morning no matter how bad the weather is.

That makes me a very happy camper

Sorry - wrong choice of words. What I meant was ... plus a margin for error.

Posted Thursday 30 Jul 2015 @ 10:43:41 am from IP #
tom rickard
Member

I don't know of any "typical" households that could cope with a 2kw max load. In a typical household people don't check if the dishwasher is on before they use the microwave

I do agree that there are many different ways of achieving your off-grid goals.

In my system I have gone for minimal PV, as with the LFP's it is more economical to charge with a generator (if you already have the generator).

Posted Thursday 30 Jul 2015 @ 10:50:53 am from IP #
wlb
Member

Keef said:
My system was an upgrade.
I didn't get any subsidies.
Therefore I spent my own money very carefully.

Me too. Subsidies would have been nice. When we bought the place 17 years ago it had a modest but, in those days, expensive 450W array charging a large capacity but, in those days, inexpensive second-hand set of ex-Telecom flooded cells. The system had been built about 10 years earlier. We were eligible for a RAPS subsidy for an upgrade but 3 days before our application was to be submitted, the rules changed and the subsidy was dropped to $2.50 per watt and only for new systems, not upgrades. It was no longer worth the trouble. We've increased the system without any subsidies ever since.

Posted Thursday 30 Jul 2015 @ 10:54:41 am from IP #
David
Member

Natimuk Solar said:
When an professional installs a system. It is designed to be run without any input form the customer. They just use their power.

Does the CEC deisng spec protect the customer or make the system prohibitively expensive?

??? CEC has little do with good quality design of an off-grid system. The Australian Standards do, along with first hand experience, mind you having/living with a system sure does help.

After all how one designs an off-grid system has changed considerably in the last few years in particular. AC coupled systems off-grid/RAPS/SPS did not exist when AS4509 was written, MPPT DC charge controllers were pretty new, PV costs were many dollars per watt, framing systems were crude compared to what's available now.

As you are obviously aware it's quite common to install a lot more PV and have much less than the recommended original 5 days of autonomy in battery storage using boring DC solar charge controllers. This is a much better choice, lead batteries certainly thank us for this as they generally get to fully charged virtually every day of the year. LiFePO4 don't care about fully charged but there are more electronic controls required to protect them from mistreatment of over/under voltage, something they really don't like.

The only thing the CEC do is regurgitate essentially what is already in the Australian Standards anyway.

Posted Thursday 30 Jul 2015 @ 12:59:15 pm from IP #
David
Member

Keef said:
Quite correct.
I'm budgeting about 2 Kw-hours overnight, never need to dram down more than 20% of capacity.

Try 10kWh's overnight, see how that works out, my system provides this nearly every night. As will a system I'm about to install next month.

Posted Thursday 30 Jul 2015 @ 1:12:34 pm from IP #
Keef
Member

2 Kw-hours overnight is plenty for my requirements.
I used to get by on way less than that with my old 12 Volt system but it was not very enjoyable.
Fridge uses no more than 0.5 Kw-hours overnight.
TV lights and computer use the remainder.

There are just the two of us, it would be different if we had teenage children.
Certainly you can scale up your own system to suit higher demand.

Just to restate the bleeding obvious.
Tilt stands are ugly, have high wind loading and can only provide a 15 % improvement in peak power at best. (Cosine 30 Degrees = 0.866)
Tilt panels take up a lot of roof area, you can fit way more panels if you don't have them.

Battery degradation is a function of depth of discharge and the time that the battery is left discharged.
You do need enough capacity so that you only draw about 10% to 20% but using the traditional design criteria you would have a very large and expensive battery bank that was left in low state of charge for several days and then you had to fire up the generator.

With modern panels mounted at a shallow angle and using an MPPT controller you will always get about 20% plus of nameplate rating even when it is extremely cloudy.

I really do question why designers and installers are fitting tilt stands on roofs that already have adequate slope.

Posted Thursday 30 Jul 2015 @ 10:51:03 pm from IP #
David
Member

Keef said:
I really do question why designers and installers are fitting tilt stands on roofs that already have adequate slope.

There are reasons for installing tilts, peak winter bias (yes I know what you said), if the roof is extremely flat, in some cases to actually fit more on rather than less, believe it or not. I've used tilts to increase the number installed and improve the winter bias as well as making them properly self cleaning, 5 degrees really doesn't cut it for staying clean.

Posted Friday 31 Jul 2015 @ 8:39:41 am from IP #
Keef
Member

"Winter bias" ?

I'm more concerned with "cloudy weather" bias
Sorry, but I just can't see how you can fit more panels on a given area by tilting them.

Posted Friday 31 Jul 2015 @ 8:45:59 pm from IP #
Keef
Member

tom rickard said:
I don't know of any "typical" households that could cope with a 2kw max load. In a typical household people don't check if the dishwasher is on before they use the microwave

I do agree that there are many different ways of achieving your off-grid goals.

In my system I have gone for minimal PV, as with the LFP's it is more economical to charge with a generator (if you already have the generator).

I'm not a typical household because I've been off-grid for many years and have learned to be an energy miser.
A larger inverter, say 5 Kw would have been nice but would have blown the budget.
My inverter has some overhead in case I accidentally turn on the toaster and the kettle at the same time.
If it proves to be necessary I can add a slave inverter on later.

If you need to charge your batteries with a generator then it's not really a solar system is it

Posted Friday 31 Jul 2015 @ 8:54:12 pm from IP #
David
Member

Keef said:
I just can't see how you can fit more panels on a given area by tilting them.

Double height portrait framing system can allow roughly 50% more PV to be installed on the roof than without it, such as on an American style barn split level roof. That equates to more power for the off-grid system.

On one of my own rooves about 100% more PV than would have otherwise fitted (custom designed framing system) 4 high portrait framing system. 54sq metres of PV on a 36sq metre roof, once you take into account minimum clearances and setbacks for regular mounting systems it would have been about half what it is.

Likewise another one I did not long ago with double height portrait framing, would have been 1/2 what it is now for the extra array installed which are all micro inverters as well due to shading issues, all on a hybrid system with a custom power management controller so that the micros can stay online without causing overcharging issues for the batteries.

Posted Saturday 1 Aug 2015 @ 9:34:55 am from IP #
Keef
Member

Double height portrait framing?
That's going to look delightful!

I think that would be a special case perhaps a long narrow roof where you are taking advantage of the "air space"

On the threads which discuss grid-connect systems there are many folks saying that if you don't have a North facing roof it is OK to fit panels East, West or even on both E & W in which case you can "overclock" the regulator and get full power from the East in the morning and from the West in the afternoon.

Because most grid connect systems are in urban areas it is not common nowadays to see tilt frames, they are usually fitted flush with the roof on whichever face has the best sun exposure.

For off-gridders the situation is different.
Owners are either following (outdated?) advice that tilt stands facing North are essential or are simply copying their neighbour's design.
The result is often unattractive, a stylish new house with solar panels up on stilts!

The Desert Knowledge Solar Centre has a "solar compass" array with panels facing North South East and West. I think they are all at the same tilt.
Even the panel that faces the wrong way (S) is only down about 50% over the year

I understand the argument that in the short days of winter you need all the output that you can get and following the conventional wisdom to have latitude tilt Northwards will certainly give the highest peak output at midday on the winter solstice BUT that is only true of direct sunlight. To take advantage of diffuse sunlight (cloudy conditions) you really can't go past (almost) flat panels.

This has been my experience from having a flat panel on the roof of my camper, it worked well even during winter in the Snowy mountains and in rainy Tasmania.
That was the reason that I fitted my new system flush with my roof which has a 10 Degree slope.
Cloudy day performance is excellent.

Posted Saturday 1 Aug 2015 @ 10:06:17 pm from IP #
Greg C
Member

13.4kW of battery for $2,500 is pretty good. But I am on grid, so need a hybrid system. Those same batteries and a Selectronic SP Pro for an AC coupled system.

http://www.rpc.com.au/pricelists/pricelist-retail.pdf

Batteries $2,500, and there are some from Rainbow Power for about the same
Selectronic SP Pro $9,000 for a 7.5kW/48V model. If you go Lithium you probably need the 120V model and that is $10k. I would need a 7.5kW model as we have electric boosted solar HWS with a 4.8kW booster and electric cooking. Also an electric car might be part of the mix in a few years.
A disconnect relay and installation $700-1,000?

So still a little over $10k which is my benchmark for affordability. A lot better than the all in one units at $30k. Maybe you can get them cheaper than from Rainbow?

Posted Sunday 2 Aug 2015 @ 1:40:28 am from IP #
David
Member

Greg C said:
Selectronic SP Pro $9,000 for a 7.5kW/48V model.

I sell them for less than that

Greg C said:
If you go Lithium you probably need the 120V model and that is $10k.

Why? and in relation to the price again.

I have installed LiFePO4 more than once for both hybrid and off-grid systems using Selectronic SP-Pro and AC-coupled it's perfectly viable to use them (LiFePO4) with either of the 7.5kW inverters assuming that's the size that's really needed, which is really a matter of what you really need to deliver power and why.

Greg C said:
I would need a 7.5kW model as we have electric boosted solar HWS with a 4.8kW booster and electric cooking. Also an electric car might be part of the mix in a few years.

Greg C said:
A disconnect relay and installation $700-1,000?

You need a proper BMS and cell voltage monitoring which is more than simply a disconnect relay for LiPO's.

Don't be fooled while LiPO's great and I really like them and I like installing them you really need good monitoring of them to get the fine tuning required for it to get humming along that can take some messing around. I normally do fine tuning remotely because it's not a five minute job to get it right.

Although I prefer to setup some sort of remote access where possible so I can support a system that goes for both hybrid or off-grid, particularly with LiFePO4 it's almost essential.

Posted Monday 3 Aug 2015 @ 11:40:39 am from IP #

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