Designing a new build roof for best Solar capture « Alternative Technology Assn Forums

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Designing a new build roof for best Solar capture

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Started 3 years ago by FenceFurniture
Latest reply from Profence

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FenceFurniture
Member

I'm doing plans for a house we would like to build, and of course I want plenty of Solar panels up there for Hydronic heating, HWS, and an electricity hungry woodworking shed.

Designing the roof is now a whole new ball game! And it's not so simple either.

I'm pretty new to this so if I have some misconceptions then feel free to correct. I have an understanding of the following:
- Solar PV work better in colder temps
- It's best to overclock the inverter by about 30%, so a 5kW inverter gets about 6.5kW of panels
- Batteries will be much more economically viable in the next 2-4 years
- panels are usually erected at an angle off the horizontal the is the same as the latitude (and it's this in particular that I want to discuss)
- it usually makes sense to have the roof at the same angle as the panels to avoid extra costs and difficulties

Some of the givens:
- we are in a colder climate here in Katoomba at elevation 1017m
- latitude is 34°
- therefore Equinox zenith is 34°
- Summer solstice zenith is 10°
- Winter solstice zenith is 57°
- there is always at least one person here during the day (one works at home, the other is a mix)
- we would like to install Hydronic in-slab heating with a heat pump, which will be a big elec draw
- we will definitely have heat pump hot water service
- undecided on putting in a couple of heads for Air-con (say a couple of splits running off on external unit). Summers are generally not that hot here, but the last one was, and future ones maybe.....
- considering using 300mm thick Hempcrete walls for insulation (sound and heat/cool). May also use Hempcrete to insulate the ceiling.
- will insulate the slab
- will be putting in a slow combustion wood fire in the living area (would love to make use of a wet-back on that somehow)

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So, coming back to the roof design. Conventional wisdom would be to pitch the roof at 34° which is seen as the best overall compromise. That means that the roof is optimised for the two Equinoxes in the year, in March and September. However, these are in fact periods where no heating or cooling may be necessary, or it could be some of each (we've had a fireplace going Xmas Day). Certainly it is unlikely that either system would be run extensively around the equinox - it is probably the most energy light part of the year.

That gets me to thinking that perhaps there should be two angles of panels set up, particularly as we might put up around 50 panels (pending advice). That would then cater for optimising for 4 periods of the year in which there would be higher demands for heating and cooling, than at the Equinoxes. Does this sound good?

It makes designing the roof somewhat.....ah.....tricky, to say the least. Particularly when you have to take in the aspect of the land, the desired design, location of other houses, trees, Council requirements. You get the idea....

Those two angles would be halfway between the Equinox and Solstice zeniths, so close as dammit to 45° for the cooler months and 22° for the warmer months. They would also provide better solar capture for the Solstice periods (and therefore maximum and sustained heat/cool draw), rather than the 34° compromise.

Following on from that, and given that there would be a lot of panels to play with, does it also makes sense to devote some of those panels to east and west facing to maximise early and late collection?

The 50 panels might be split like:
- 8 facing east, 8 facing west (or perhaps northeast and northwest to again skew it towards winter). Maybe on a 34° roof?
- 20 on the 45° roof (because there are a great many heating days)
- 14 on the 22° roof (because there are too many air-con days)

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So am I on the right track, or in serious danger of becoming lost?

Cheers
FF

Posted Wednesday 13 Sep 2017 @ 12:42:05 am from IP #
Bushwalker
Member

Given the altitude and the majority of heating requirement, I'd put all the panels facing north and at 45°

http://www.weatherzone.com.au/climate/station.jsp?lt=site&lc=63039

Panels facing east or west will give a boost when facing the sun, but the daily kWh will be significantly reduced compared to north facing panels.

In a cool climate, with exposed area to wind, I personally would head into Passivehaus (PH) territory for the house. We are in the Adelaide Hills in a high wind area. Before we sealed the house to PH level, the heating was basically vented through the gaps in the vents, the poor sealing of the original windows and doors. High pressure on the windward side, and low pressure on the other side sucked the heated air out of the house. The same occurred in summer. Be aware that a well sealed house needs effective ventilation, and ours has a Zehnder ventilation unit that exchanges the heat into the incoming air with a minor electrical consumption.

Posted Wednesday 13 Sep 2017 @ 2:40:36 am from IP #
Benny
Member

Great that you're thinking of this in detail before building FF but with the low cost of solar panels these days I think perhaps you're over-thinking it. As BW says if your biggest load is to be in winter then I think it best to optimise for winter production - esp given that your house will likely require very little cooling. You can model your production on sites like PVWatts. Changing from N to E or W orientation only loses about 20% of the generation - depending on tilt angle - but you can compensate for this by installing 20% more panels. I would concentrate on the passive aspects of the house first - big flat N facing roof and wall of windows with some significant roof areas to E and W as well. With increased roof pitch to normal as you suggest so you don't need tilt frames. Once you've designed the house as passive as possible, get the energy requirements modelled so you can match to PV requirements. - as well as your workshop power needs of course.

Posted Friday 15 Sep 2017 @ 12:03:34 am from IP #
FenceFurniture
Member

Cheers Benny

Benny said:
..... I think perhaps you're over-thinking it. .

I seem to recall hearing that all my life.....

Posted Friday 15 Sep 2017 @ 12:55:31 am from IP #
Catopsilia
Member

Thinking about "over-thinking", Fence:

"Batteries will be much more economically viable in the next 2-4 years." That depends on the economic health of China.Are you optimistic about that?

"Summers are generally not that hot here..." Yes, and I doubt that global warming will make them noticeably hotter in a lifetime - perhaps half a degree. Katoomba is also cloudy in summer, and that MAY get worse, reducing the sun power for the house.

"...equinoxes...are in fact periods where no heating or cooling may be necessary..." Furthermore, the sun does not linger at the equinoxes, but races through. Perfect alignment at those dates gives little benefit. Bushwalker's suggestion of the steeper angle of 45 degrees is about right, I think.

Posted Friday 15 Sep 2017 @ 1:53:03 am from IP #
arttt
Member

If you are to have 50 panels then either you will be selling a lot to the grid or you need to work on reducing power use. If you need a 10kW array to power the house it would be best to revisit the size and thermal envelope of the house.

Good thing about an oversized array of panels and an efficient house is when you decide to install batteries you would only need a small set as even on cloudy days the panels will still produce quite a bit.

So since you are selling lots to the grid the main consideration re alignment is probably maximising what the panels will earn in feed in tariff. Remember that over the life of the system there will be all sorts of changes to the feed in tariff structure.... a few guesses to be made.

Posted Friday 15 Sep 2017 @ 4:18:06 am from IP #
FenceFurniture
Member

Yeah, I understand that 50 panels is well above average. The woodworking machinery is likely to consume quite a bit though. There are many machines that are 2-3-4 hp (1500-3000w), and some 3 phase jobbies that will run off VFDs on circuits that could be quite large like 32A.

Now these machines don't necessarily run continuously, but a 4hp dust extractor can (or at least should) be on for a goodly part of the day. Getting rid of fine dust (i.e. the invisible dust which is the most dangerous of all) is quite a power hungry job. Then there are the air scrubbers which are about 1hp each from memory, and I'll probably need at least 2 of them running more or less continuously. We're supposed to run this stuff for 2-3 hours after dust -making activities have stopped.

With FITs as there are right now I'd have to sell back to the grid about 2.5 times what I would use after the sun is no go for lecky production. That will no doubt be a different equation by the time I get to it, and I would select the best supplier for FITs (with some other considerations). Usually the best FIT is accompanied by horrific grid prices.

Another consideration, which I am yet to properly research (aka over-think ) is that I'm coming to the conclusion that Hydronic slab heating is hell expensive to install, but not too bad to run. I will have to get a more accurate quote, but I think I'm looking at something like $25-30k to install it.

The alternative is something like this electric slab heating:
http://www.floorheatingsydney.com.au/comparison-with-hydronic-systems/

As I say, I have to research it more, but it looks like around maybe $10k to install, but with higher (probably much higher) running costs - which would be defrayed by all those panels to a fairly large extent. Run the slab heating during the day and then a bit of wood-fire in the evening.

It just depends on whether the draw on the inverter/batteries is enough to run the electric heating. Maybe it's too high a draw.

Posted Friday 15 Sep 2017 @ 4:57:39 am from IP #
arttt
Member

That is a fair sized wood work set up to have at home. At least you are going to be using all that gear during the day when the sun is out. I will leave that to you to work out how much solar you need for that.

FiTs are changing. There is a 17c offer by origin i think it was in canberra. the rest of the rates were not too bad either. Im sure other states will get better ones in time.

If you build the house right you should have very minimal heating needs. Put $20K extra into insulation and windows and getting the solar design right and you will get away with a $5000 heating system and have $5000 spare to run it for the next few years.

This is much better then $30k into a heating system + stuffing around when they install it wrong (look at all the threads here about complex systems not working quite right) + big running costs + huge solar array to try and cover the heating system needs + maintenance.

Posted Friday 15 Sep 2017 @ 5:11:52 am from IP #
FenceFurniture
Member

That brings up a good point. If we go with something like hempcrete, with good solar design, good insulation, as you say we may not need all that much auxiliary heating. I would feel like a right dick if I'd spent 25-30k on a heating system that wasn't needed much. Spending around $10k on something more expensive to run, but not having to run it that much.....maybe I'll still feel like a dick, but this would be a case where size really does matter!

Posted Friday 15 Sep 2017 @ 5:35:25 am from IP #
Catopsilia
Member

Fence, you are planning to heat the slab.

I know nothing about heating a slab with electric current or water, but I do heat my slab by conduction from brick and tile surfaces that are in the sun.

It is clear that heat moves in and out of the slab VERY, VERY SLOWLY. It takes days, weeks or months. In discussions of artificial slab heating that I have read or heard, it seems that no-one understands this. Everyone wants to rush. They let the house get cold, come home from work and turn on the device to heat the slab. Nothing seems to happen, so they give up the system as a failed investment.
Slab heating should be turned on, manually, or by a thermostat INSIDE the slab, before the slab gets cold. Then the system will use only the power required to make up for losses. That is, very little if the house insulation is adequate.
No-one will ever feel "toasty" warm. They will simply never feel cold.
Since I have not tried this, I may be wrong.

Posted Friday 15 Sep 2017 @ 6:47:20 am from IP #
arttt
Member

Dont heat slab except with the sun.
Look at what Catopsilia did with his house and many others on this forum.
Get passive solar right and avoid most of the cost and complexity of fancy heating systems.

My house is nothing special, a 1950s govvie in canberra with a well thought out extension and improvements. Its a comfortable temp year round and my total heating need this year was 3 wheelbarow loads of old fence pailings in the fire and maybe 100kWh for some extra spot heating in bathrooms etc. That is for the whole of winter. The rest of my heating was free from the sun.
The point is a new house should be able to do as well as that no problem.... if done right.

Posted Friday 15 Sep 2017 @ 7:32:58 am from IP #
FenceFurniture
Member

arttt said:
If you build the house right you should have very minimal heating needs. Put $20K extra into insulation and windows and getting the solar design right and you will get away with a $5000 heating system and have $5000 spare to run it for the next few years.

Yes, double glazing is where we are headed. Probably with the slim venetians inside them, which eliminates the need for curtains which are just damned dust collectors. No doubt expensive, but so are curtains, rails and labour....and washing, dusting, replacing.

arttt said:
This is much better then $30k into a heating system + stuffing around when they install it wrong (look at all the threads here about complex systems not working quite right) + big running costs + huge solar array to try and cover the heating system needs + maintenance.

Yep, totally agreed.

Catopsilia said:
It is clear that heat moves in and out of the slab VERY, VERY SLOWLY. It takes days, weeks or months.

Slab heating should be turned on, manually, or by a thermostat INSIDE the slab, before the slab gets cold.
No-one will ever feel "toasty" warm.

Yes, I certainly understand the principle of the massive inertia and momentum of slab temps. O'course some small part will depend on what time of year the build is finished (in terms of insulation), as to the status of the slab temp at that point. This is where the electric slab heating may (only "may") come into its own - perhaps spend, I dunno, $100 or so heating the slab up and then just maintain it, with some passive design supplemented with a bit of (mostly) free electricity.

I don't in fact want to be toasty warm. My partner may disagree, but she ain't designing this sucker, or paying the bills.........and nor does she know about this forum.

arttt said:My house is nothing special, a 1950s govvie in canberra with a well thought out extension and improvements.

This is the battle, and what is promoting the over-thinking.....errr....slow and deliberate consideration. My design needs are different to most, and of course it will be largely controlled by the aspect that the block of (as yet unpurchased) land has, its exposure to noise, neighbours etc etc etc.

Posted Friday 15 Sep 2017 @ 9:26:54 am from IP #
FenceFurniture
Member

arttt said:Its a comfortable temp year round and my total heating need this year was 3 wheelbarrow loads of old fence palings in the fire

Oh my Gawd, I have to take exception to this.

Note my forum name. In fact the same forum name (and avatar) I use everywhere, which started with a woodworking forum).

Palings are for making decks, boxes, tables, wardrobes, and so on. Palings are NOT for firewood! There is a zone just under all that grey, and before the new timber where the character of timber exposed to the sun for 15-30 years lies. "The prize lies beneath - hidden in full view". Put those old boys through a thicknesser (electric planer....around 3-4hp) to take off the grey ½mm at a time, and you'll be staggered at the beauty and character of the timber revealed. Blondes, Reds, Browns, Fiddleback, Curly, Quartersawn and everything else.

People look at the small back deck here and think the timber is gorgeous, and "where did you get THAT from?" and I point to the remaining grey fence just 3 metres away. They can't believe it.

Anyway, I'm just joshin' yer - I burn plenty of palings because they are not all good. Some are very fragile or rotted and only deserve one treatment apart from becoming landfill.

Only yesterday I happened to drive down my street the opposite way to usual, and there was what used to be a short fence (until yesterday morning) put out the front. Spray painted with "Free firewood" in fluorescent orange. Went about my business, came back 10 minutes later to find cars with trailers circling the prey. As luck would have it I arrived before them, taking the prime parking spot of course, and got on with it - sussing out the strong palings from the firewood. On my way back from business I had already stopped and noted that this was a fence worth my attention.

The lady and guy (separate parties) were busy chatting with the owner. "Good" I thought, "keep talking while I load up."

And so they did.

And so I did!

She drove off with nowt (too much competition?), and Trailer Guy (who was a very nice chap) and I came to an agreement that I would take solid (not rotted, fragile, split) stuff and he could have everything else, which seemed to be about a 50/50 split. He only wanted it for sacrilegious heating purposes anyway, so it all ended well.

Posted Friday 15 Sep 2017 @ 9:30:34 am from IP #
FenceFurniture
Member

"Palings are for making decks"

That might seem a bit weird, but after they are put though the thicknesser (both sides) they can be glued and clamped together to make a board that is 20-25mm thick. These are immensely strong, especially if the growth rings are set opposite to each other.

I was sitting in my (now deceased) father's back yard about 4-5 years ago, in Coffs Harbour. This is right in the middle of "Norf Coast Hardwood" country, which is where all NSW hardwood fence palings have come from for millennia.

So I'm smoking my cigarette (no longer though), and eyeballing the fence, and damn me if the whole fence isn't comprised of fiddleback timber! This is the curly 3D stuff that they make the backs of violins....and Fiddles, from. It used to be regarded as the rubbish because it can be quite difficult to deal with, but is exceptionally rewarding.

"Hey Dad", I yelled, "forget leaving me the hoose (if you were going to), I'll settle for all of the fences."

As it turned out, second wifey got the bleeding lot, and I didn't even get a bent nail or a single old tool, but you get that with second marriages. Oh well, luckily I have plenty of bent nails.

Posted Friday 15 Sep 2017 @ 9:48:35 am from IP #
arttt
Member

Dont worry. Im only burning offcuts from lining the underside of my northern eaves in fence palings.
Lots of work but looks amazing. I didnt thickness them just kept the weathered look.

Posted Friday 15 Sep 2017 @ 11:12:17 am from IP #
FenceFurniture
Member

Yes, that would look good.

So yesterday I did one of my large batch cook-ups, which was various BBQ meats. This means a lot of standing around with not much to do. That means an idle brain searching for entertainment, and so I got to thinking a little more about heating.

The requirements can be broken down into:

1. Living area (open plan Kitchen, dining, living) approx 14x6 metres. This area should be reasonably warm most of the time. Doesn't matter about overnight, but that would come with it, I imagine. As much as possible this area will be designed to catch north sun - pending land aspect.

2. My office and IT room, ~3.3x3m, immediately adjacent to the living area. I am in and out of it all the time, and can spend considerable periods there. Heating requirements as for Living area. Not really fussed about flooding with light, due to predominant IT screen usage, so no Solartube.

3.My partner's office and IT area, ~3.3x3m, next room down the hall. On the days she is at home she uses it as I do mine. Usually she is out at work 3 days per week, and the room need only be warm on the 3-4 days she is at home. However, there are long University breaks - mainly in Summer, when she will spend more time in there. Not really fussed about flooding with light, due to predominant IT screen usage, so no Solartube.

4. Guest Bedroom at the front (of the current design), 3.3x3.6m. Only needs to be warm on demand, when someone is staying with us. Once per month for 1-3 nights?

5. Bathroom/Laundry/Ensuite cluster. Each is 3x2m including toilets. Don't really care about the Laundry as virtually nil time spent in there. For the Bath/Ens it would be nice if our feet didn't freeze to the floor, and this can be at any old time, although silly to heat it for o'nite use (suck it up). The airspace can be temporarily heated with a blower heater if necessary as it is only for short periods. WAIT! What am I saying? My partner spends half her life in there! Absolutely hanging out for separate facilities....

6. The Wood Studio or Handtools room, ~6x4.5m. This room needs a temp of around 18-19° at the most, and only during the day, Evenings and o'nite don't matter much, although reasonably stable temps are better for the tools and timber.

7. The Machinery Room (actually the Garage). 6.5x6.5m and could be slightly larger. Tempting to say "similar to the wood studio" but could be kept a bit cooler, say around 15-16°. Just as long as the machines are not icy to the touch. Many of them have thick cast iron tables with similar cold holding capacities to concrete slabs. Dust extractors are vented externally so there is no warm air being supplied by them. In fact, these DE machines can move 2000-3000 cubic feet per minute (or 55-85m³ per minute). Not much point in heating up the air only to see it sucked outside at that sort of rate. Theoretically the entire room air volume of 100-120m³ is exchanged every 2-3 minutes while the DE is on.

EDIT: Forgot the Main Bedroom, so call it Area 4a. Not particularly fussed about heating this room as we are mostly asleep in it. Apparently sleeping in temps of 19° or less promotes brown fat rather than white fat, and it is therefore healthier fat.

Posted Friday 15 Sep 2017 @ 11:45:16 pm from IP #
FenceFurniture
Member

There may be an argument for doing the prep work for Hydronically heated room panels, without going the full distance until we see how the house performs. What I mean by that is that we could put in just the pipework required for the panels without connecting anything up until later on. Sure, this part may end up being wasted money, but surely it would only be $2-3k to put the pipes in? Certainly better than putting in a whole house of slab heating (either Hydronic or electric) at a cost of $10-30k only to find it unnecessary. It would mean that there would be a capped off pipe in the various locations, and a cluster of capped pipes at the termination end, but I doubt it would be much of an eyesore really. There may even be some way of keeping it buried within the Hempcrete wall, just under the surface, and plot the various locations - or use a metal detector. No chance of leakages within the walls because the pipes would only have air in them until they were implemented.

With those above (previous post) requirements in mind, I wonder how the following might pan out.

Areas 1, 2, 3 (Living and offices) have pretty similar requirements - to always be around 20° except for overnite. The Living area will get some north exposure. These areas can only really cool down o'nite if they can be warmed up fairly quickly in the morning, so I guess they will be pretty much constantly warm, especially as my partner's day can begin at around 5am, and sometimes even earlier (rare). Maybe set the Kitchen Hydronic panels to switch on at about 4-5am if necessary, so that they are on for a while before arising.

Not too sure about this area - it's probably the trickiest of all due to the size and constant use. Possibly the strongest argument for electric in-slab to be laid in these rooms - but no connection until it is found to be necessary. In this case there would be no preparatory Hydronic pipes for panels in these rooms. To lay the electric cables is about $35/m², so at about 100m² it would be say $4000. That's not toooo bad as an insurance. Have to make provision for the controllers etc.

Area 4 (guest bed) could have a hydronic panel that is only switched on when someone is staying. Perhaps turn it on 24 hours beforehand. For an unscheduled stay the room could be blasted with a hot air blower or conventional radiator, and then the hydronic panel takes over.

Area 5 Bath/Ens. It has to be said that a panel in these rooms can be very useful for drying or warming towels. As long as there is a suitable wall space.

Area 6 Wood Studio. Maybe similar to the Living area - lay the electric cables at a cost of about $1000, and implement the system if it becomes necessary.

Area 7 Machinery room. Don't do anything, or perhaps provision for a couple of Hydronic panels but only if that provision is being made elsewhere.

Posted Saturday 16 Sep 2017 @ 1:11:27 am from IP #
Greg
Member

FenceFurniture, you might like to take a look at an app called ScantheSun. You stand where your panels will be (not always easy to do but anyway) and it works out the best orientation to maximise your yearly solar. Not sure that it takes regular weather into account or not but seems a great feedback tool.

"Yes, double glazing is where we are headed. Probably with the slim venetians inside them"
Venetians get just as dirty and I think they are less thermally efficient than honeycomb blinds.
pic of mine
http://i1199.photobucket.com/albums/aa471/KnowHowe/blind2_zpsaamz3kwd.jpg
http://i1199.photobucket.com/albums/aa471/KnowHowe/blind1_zpsowi3zcas.jpg

I'd still suggest checking price difference between insulated slab and just going for hydronics in an insulated screed.

All our heating, slab hydronics and radiators are from a wetback.

Planning a, design and research is important but execution is key as I found out when both architect and builder changed things without consultation.

Posted Sunday 17 Sep 2017 @ 12:16:29 am from IP #
FenceFurniture
Member

Thanks Greg, but Photobucket want a stupendous amount of money from you for those links to work.

Posted Sunday 17 Sep 2017 @ 1:15:16 am from IP #
Home Handyman
Member

totally agree with this statement...

If you build the house right you should have very minimal heating needs. Put $20K extra into insulation and windows and getting the solar design right and you will get away with a $5000 heating system and have $5000 spare to run it for the next few years.

Investing in insulation early in the building life cycle will save you many $$$ for years to come and heating / energy expenses are only going to increase over the years...

Posted Wednesday 20 Sep 2017 @ 12:01:32 am from IP #
Profence
Member

Home Handyman said:
If you build the house right you should have very minimal heating needs. Put $20K extra into insulation and windows and getting the solar design right and you will get away with a $5000 heating system and have $5000 spare to run it for the next few years.

Don't try to save money by doing you're insulation on the cheap, it will only cost you more money down the track.. a dollar spent today will save you 3- 4 dollars in five years time...

Posted Wednesday 20 Sep 2017 @ 1:48:45 am from IP #

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