We have a shed!
We’ve affectionately dubbed it the obelisk – yeah we know an obelisk is supposed to be pyramid shaped but hey! The unusual shape serves a very specific purpose. The roof angle is 22.5 degrees facing north, can you guess why?
Answer – 48 square metres of solar panels! We’ll do a post later on designing a house for autumn/winter solar gain, but suffice to say adding solar panels to a roof sloping south is expensive, inefficient, vulnerable to high winds and just bloody ugly. So we decided to make the shed a dual purpose installation. Well actually a triple purpose, because once we are up and running, it will be a commercial kitchen in one half, a small workshop in the other and a great big power station on top!
This is enough room for 8Kw of panels, which should see us through the year with only very small amounts generator use. In the background you can see what the locals call “Mt Buggery” (we are not game to ask why), but it causes us some problems in autumn with morning sun. Not so much in Winter as the Sun rises closer to north and misses the peak. This is why we needed a very efficient set up, that said we actually shouldn’t need a generator ever, but like all operational systems, not everything works as well in practice as on paper and we are only getting one shot at this.
The optimal all round compromise angles for panels for Melbourne is about 38 degrees to optimise year round capture. However, at 8Kw, most of the year our output will be many times what we’ll use. Winter is often solar setups most problematic time and 22.5 degrees just happens to be the steepest angle you can have on a skillion roof in an off the shelf shed – steeper would have been better but everything ends up a compromise. If you want to get an idea of sun angles (we’ll cover this in a future post on solar thermal design) then first click this link to find the longitude and latitude of your location. Once you know this then navigate to the AusDesign Page (brilliant site btw) and enter your data. You’ll get a table for any day of the year which will give a very good idea of sun angles for a set of time intervals. This will give you some idea of what angles the Sun will traverse your location and panel direction. Panels will output the greatest when sunlight is falling at 90 Deg in both planes to the surface of the panel. In other words straight at the panel surface, but it’s surprising how little you actually lose from non-optimal panel tilt. You can download this table from the Clean Energy Council which details efficiency vs panel tilt and direction by major city. Obviously this may not be exactly where you are, but it will give you a pretty good idea. For us, efficiency losses of opting for a 22.5 deg tilt, even in the middle of winter or summer, will be less than 2% – negligible really.
Just a few notes if you choose to do this. Let your shed designer know you plan on mounting solar panels on it so they can increase the structural load capacity of the roof and frame. It will add a small amount of cost but it’s necessary. You don’t want the thing falling down in high winds – don’t laugh a farm just up the road from Langi Billin had exactly this happen last year. There’s no other safety net, council don’t require building permissions for panels on sheds and the design you build might be fine on it’s own, but outside it’s safety envelope with a tonne of panels on the roof. So be careful! We had our shed professionally built because even though we are building much of the house ourselves, we are probably both beyond the days of swinging around 6 metres in the air placing steel beams without breaking our necks!
Some people have asked us why we didn’t just build a bigger shed with a gable roof instead. There are two answers: one is cost, we are doing this on a limited budget – bigger shed = larger cost. As it was, this one was a little over $20K complete, and the other answer is footprint. We are only working with 4 acres, every square metre we give up to buildings is another one we cant use as productive land. Plus we kinda think the obelisk is funky! We’ll add a lean-to out the front and a mezzanine inside for storage in time.
We had a little Mothers Day picnic in our new shed to celebrate.
Footnote – tonight after a fruitless drive to buy some pine poles that turned out to be rubbish (Facebook marketplace sucks) we decided to visit Langi Billin after dark. Now we’ve noted our resident – Wariin the wombat – has been quietly expanding his apartment complex. Until tonight we’d never seen him, but as we drove toward the west gate there was Wariin wombling along – he’s pretty cute. It was too dark for photos – maybe next time.