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Posted (edited)

We’re building a house in Canberra and I was hoping to get some advice on how to plan for a solar system if I could please.

 

It’s a ~190m2 (internal living), 4-bedroom, 1 open-plan living, media room and small study home. We’re a family of 2 adults (that work from home maybe 30% of the time) and 2 kids. We’re out of the house most weekdays for work/school, as you’d expect.

 

The planned house uses solar passive design (exposed slab, 3 to 5 air-changes/hour) and has a projected NatHERs rating of 8.2, so energy usage should be rather low. It will be all electric with induction cooktop/oven, water heat pump and one Daikin US7 RCAC (5kW I think but not specified yet). We’d like to get an electric vehicle in future too.

 

According to our energy bills, we currently use 30kWh per day average over winter and 26kWh per day over summer. The house is like a glorified tent though so energy requirements would be lower in the new place.

 

I was targeting a 10kW system (EV needs at least that doesn't it?) but could be convinced to install less (just what’s required) or to cover the roof, if that’s the best way to go. I requested 3 quotes from solarquotes last week but I haven’t received any feedback yet. Budget is around $15K, maybe a bit more.

 

The roof is somewhat puzzling. The block faces north on the longest dimension, yet the architect has specified a skillion roof that slopes 5 degrees south (the below image is from the rear/west of the house so north is left). It does look nice though so I’ve accepted it for now.

West-eleation.jpg.a3115d998a00595949060b3f7dbe039b.jpg

 

Below is from north-west:

 Perspective-views.jpg.b9e6eecfd5540e4f6164521e9b65a582.jpg

 

When I raised my concerns about its effects on solar (~28% decreased efficiency), the architect added a (6.5m x 4.3m) hip roof section at the rear of the house that tilts down to the north (which is straight up on the below aerial view).

Roof-plan.jpg.a34943a050611af749b740a2149a1631.jpg

 

 

It seems to me that we’ll need panels on both north and south facing roofs to get to 10kW. As north will outperform south we’d require micro-inverters, wouldn’t we? So, add 30% to the cost. Wouldn’t it be better to just add more panels to the south and make the roof south facing the whole way?

 

I have asked the architect about the costs associated with the hip roof at the rear but he hasn’t got back to me yet. I can’t see it being cheaper than skillion all along though.

 

I have mild concerns about the effects of the 5-degree pitch on panel self-cleaning but one solar installer told me that 5 degrees was the absolute minimum. If the roof is going to face south, I think I’ll wear it and get up there and clean them once in a while.

 

Any advice would be greatly appreciated.

 

 

Edited by br0d0
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Obviously roof angled toward the North will give best solar results but I have noticed a reluctance to slope a roof downward toward the 'front', or road.

 

New houses across the road here (Gungahlin area) all have single plane tilted roofs with panels, they are side on to the road with the roof facing East.  Simplely having the roof angle North would be better for efficiency, but maybe 'they' don't like the look.

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Posted (edited)

Not the best roof for a PV system.

 

10° is about the minimum for self cleaning and you'd still have to hose the lower edges from time to time as dust will build up there.

 

The ideal panel angle for Canberra is 30° and that's for North facing panels.

 

Edited by ArthurDent
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2 hours ago, br0d0 said:

I have mild concerns about the effects of the 5-degree pitch on panel self-cleaning but one solar installer told me that 5 degrees was the absolute minimum. If the roof is going to face south, I think I’ll wear it and get up there and clean them once in a while.

around my place, I just see those panels that are setup on brackets so they are made sure to be angled optimally eg see below...

 

eg below, but this may not be what want to achieve aesthetically ? 

 

rsz_14_flat-roof-1.jpg

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1 hour ago, eman said:

Obviously roof angled toward the North will give best solar results but I have noticed a reluctance to slope a roof downward toward the 'front', or road.

 

New houses across the road here (Gungahlin area) all have single plane tilted roofs with panels, they are side on to the road with the roof facing East.  Simplely having the roof angle North would be better for efficiency, but maybe 'they' don't like the look.

It does seem to be all about aesthetics. I'm still getting my head around a solar-passive build having a roof sloping down to the south myself.

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21 minutes ago, ArthurDent said:

Not the best roof for a PV system.

 

10° is about the minimum for self cleaning and you'd still have to hose the lower edges from time to time as dust will build up there.

 

The ideal panel angle for Canberra is 30° and that's for North facing panels.

 

It's not a great roof for solar hey. Tilting south means the generation is only going to get worse above 5 degrees, obviously, so the best solution is a hip roof with half of it pitched 30 degrees north. I'm not sure if it means enough to me yet to demand a hip roof though.

 

PVWatts calculator shows that a 10kW system on the 5 degrees south roof will generate 13,276 kWh per year (470 in June) while the optimal 30o north roof will generate 15,531 kWh/yr (834 in June). 

 

Solarquotes payback calculator gives this for 5o south so it still seems worth it:

178004735_solarquotescalc10kw5osouth.JPG.d88186f9baa635107e5d208770a300b1.JPG

 

For a 20 kW system @ 5o south, PVWatts gives 26,553 kWh/yr (939 in June or 31.3 kWh/day).

769111017_solarquotescalc20kw5osouth.JPG.a635591cbc3b5731be126dad7f1434ab.JPG

 

The 10kW system gives the best IRR for systems 10kW to 20kW according to solarquotes, assuming $1000 per kW install cost, 11c feed-in, etc.

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57 minutes ago, betty boop said:

around my place, I just see those panels that are setup on brackets so they are made sure to be angled optimally eg see below...

 

eg below, but this may not be what want to achieve aesthetically ? 

 

rsz_14_flat-roof-1.jpg

I have thought about those but they're at least $50 a pop apparently. So ~$1,600 extra. Might be worth it. Will keep it in mind.

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44 minutes ago, br0d0 said:

PVWatts calculator shows that a 10kW system on the 5 degrees south roof will generate 13,276 kWh per year (470 in June) while the optimal 30o north roof will generate 15,531 kWh/yr (834 in June).

Take any of these projected generation figures and payback periods with the proverbial grain of salt.

 

The usually provided solution for less than ideal panel direction and angle is to simply add more panels.

 

But unless you can use that extra output you're unlikely to get the extra cost involved back via FIT.

 

How many panels can you get on the North facing and sloping the right way roof?

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why do you want 10 kW?

 

do you have a long-term contract from someone who is going to buy your output?

or do you just want to be a PV generator, irrespective of the financial return?

or do you propose to convert the vast majority of your output into batteries for your own use?

 

if you are going down the battery route, have you worked out how expensive the battery will be and what the savings might be? 

Have you worked out how much battery you will need for your in-house use to avoid expensive prices? (electricity isn't always expensive, if you have chosen a TOU plan).

Or, do you just want to be self-sufficient no matter the cost?

 

If your main aim is to sue the solar in-house, and are less worried about being a PV generator (and are concerned about the risk of investing in panels that will only ever export,with the expectation that PV export prices willfall, or go negative at times) then think about how much PV you need for in-house use.

 

If you are using 24 kWh a day, over a 24 hour period that means an average load of 1 kW.  Your actual demand will be higher at breakfast, and in the late afternoon/evening but it won't average much more than 2 or 3 kW, and is unlikely to get much above 1 kW during the day when the sun is shining.

 

Don't get me wrong, solar is excellent, but I just don't see why having a large system on a house makes financial sense.

A 3 kW system, or perhaps a 5 kW system would be good.

Something with northerly or north-westerly aspect is good.

Southerly aspect - you are wasting your time.

 

Benje

 

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1 hour ago, ArthurDent said:

Take any of these projected generation figures and payback periods with the proverbial grain of salt.

 

The usually provided solution for less than ideal panel direction and angle is to simply add more panels.

 

But unless you can use that extra output you're unlikely to get the extra cost involved back via FIT.

 

How many panels can you get on the North facing and sloping the right way roof?

A guy with a quote rang me before and I think he said 3kW would fit on the north roof. 

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2 minutes ago, br0d0 said:

A guy with a quote rang me before and I think he said 3kW would fit on the north roof. 

That 3kw would vary depending on what panels he based in on.

 

What are the dimensions of that bit of roof?

 

 

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14 minutes ago, ArthurDent said:

That 3kw would vary depending on what panels he based in on.

 

What are the dimensions of that bit of roof?

 

 

6.3 x 4.8m

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3 minutes ago, br0d0 said:

6.3 x 4.8m

In landscape that would fit 12 panels with a nice 1.2m gap at the east end to avoid shading.

 

12 LG Neon 2's at 335 w each is 4kw total.

 

Or you could squeeze an additional 2 panels portrait on the end.

 

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Posted (edited)
1 hour ago, Benje said:

why do you want 10 kW?

 

do you have a long-term contract from someone who is going to buy your output?

or do you just want to be a PV generator, irrespective of the financial return?

or do you propose to convert the vast majority of your output into batteries for your own use?

 

if you are going down the battery route, have you worked out how expensive the battery will be and what the savings might be? 

Have you worked out how much battery you will need for your in-house use to avoid expensive prices? (electricity isn't always expensive, if you have chosen a TOU plan).

Or, do you just want to be self-sufficient no matter the cost?

 

If your main aim is to sue the solar in-house, and are less worried about being a PV generator (and are concerned about the risk of investing in panels that will only ever export,with the expectation that PV export prices willfall, or go negative at times) then think about how much PV you need for in-house use.

 

If you are using 24 kWh a day, over a 24 hour period that means an average load of 1 kW.  Your actual demand will be higher at breakfast, and in the late afternoon/evening but it won't average much more than 2 or 3 kW, and is unlikely to get much above 1 kW during the day when the sun is shining.

 

Don't get me wrong, solar is excellent, but I just don't see why having a large system on a house makes financial sense.

A 3 kW system, or perhaps a 5 kW system would be good.

Something with northerly or north-westerly aspect is good.

Southerly aspect - you are wasting your time.

 

Benje

 

The 10kW target came from wanting a battery and an EV. I'm sure I read that I'd want at least 9 or 10 kW for an EV (3 phase).

 

I want it for our our own use to offset electricity (and petrol) bills I guess. I wouldn't be getting the battery or the EV immediately. I see them as future upgrades when prices are more economical and when I can afford them.

 

I'm planning the install now as I have the impression that adding it during the build would make for a better install but I have heard that retro-fitting it isn't that difficult, so I could put the whole thing off. That way I can measure our energy use in the new house and get an accurate picture of what we need. Especially if the panel orientation is going to be far from ideal.

 

Edited by br0d0
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59 minutes ago, ArthurDent said:

In landscape that would fit 12 panels with a nice 1.2m gap at the east end to avoid shading.

 

12 LG Neon 2's at 335 w each is 4kw total.

 

Or you could squeeze an additional 2 panels portrait on the end.

 

That might be the go. Install as many panels as I can fit on the best orientation. It'll be smaller but we'll get good use out of it. Solarquotes gives an IRR of 27.92% which isn't bad (point taken about the salt though).

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Posted (edited)

There are more efficient and better panels than LG.  However I didn’t go for any of these as they  start to add to the cost dearly.   
Just remember like any technology it changes very quickly, what was a decade ago isn’t available now.... And visa versa.  A decade ago panels only managed to be around the 200-280W when I was looking at it, now we are pushing 400W plus, 1/2 panel technology, better warranty and some are even tougher stronger than the LG and have better warranty.    Even if you look at inverters, we now have microinverters and optimisers And nearly all are Wifi supported....   

I didn’t go for the best materials available. The quality of installation also determines reliability so tread carefully here....  

I didn’t chose LG panels or Enphase microinverters, or Fronius these are considered the best in the business....

To get around cost I had 20 330w Qcell 1/2 panels installed.  9 facing Nth, 11 facing west....  in the morning the Nth facing will be productive and after or around midday both sides will generate.   Both sides are dual tracked strings  with a basic SMA inverter.  With the Victorian government approval of $2225, less now and will continue to reduced further in the future, the fed gov’s  STC the entire system fully installed was just under $5500.   Day After installation on a sunny day in April I got 28.28kw/hr.... got be happy with that!  My go is against the grain and advise,  I’d carpet bomb the roof that’s going to be productive because production In winter sucks!  Worst recorded was 4.49kw/hr in June.   I only have an electric oven, and a microwave the rest is gas,  all light globes are now LED and most computers are Laptops so average usage is around 6kW/hr per day..

Again heat pumps and solar hot water systems are just way too expensive, if they come down on price it’s great but not to be.... when you consider a 135lt gas stainless steel tank by Aquamax that $1650 fully installed it’s a fraction on a heat pump or a system that diverts your solar production into heating water, any of these solar hot water solutions will go Nth of $5k and beyond, Not there’s any high tech in doing so!    Those Aquamax stainless steel tanks are maintenance free,  my brother and parents have had them trouble free for almost 20yrs....  can’t say the same for high tech that cost the earth!   I ripped my Solar hot water panels off the roof, way too unreliable and too many issues and I’m glad I did!  Replaced them with PV...   when I took them down the tip for metal recycling they were 10yrs old and they had corrosion showing,  not to mentioned all of those hot water panels have had issues and have been replaced!   If you’re going down this road ensure it’s a stainless steel tank,  any others forget it.

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