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