Doing my own solar survey? Where to get inst?

Gooserider · June 2009

I want to evaluate our house for solar potential, and especially evaluate which (if any) trees need to come down, and what impact various potential other shading obstructions might have on a potential setup.

Since I want to do both PV and thermal, I'd like to do a bunch of surveys from different spots to see what various points on our roof have to offer. I'm not sure I can get a solar install outfit to do the kind of survey that I have in mind, and leave me the full results so that I can persue DIY or competetive options. I figure that doing my own survey gives me a bit more control over the data.

There is an article on the "Build it Solar" home brew website on how to do this with a home made setup, but it seemed to need a pretty good stable surface to work on... My understanding is that you really need to do the evaluation at the potential install site so that you can see what the panels will actually "see" - and I don't see a way to realistically setup the rig that Build it Solar describes on our 12/12 pitch roof, and follow his instructions from a ladder...

The other option appears to be one of those "solar dome" type units that has a mirror to reflect the obstructions onto a chart, which appears like it would be far easier to setup and use in an awkward / hard to get at location like our roof.

However I haven't been able to locate a source for the instrument, probably in part because I'm not 100% sure what it's called

Anyone have a pointer to where I could rent or purchase one (second hand would be OK, and perhaps preferred since I want to save $$$)

(I did a search before posting this, didn't find anything - if this has already been covered, a pointer to the relevant thread would be helpful...)

Thanks
Gooserider

icarus · June 2009

Re: Doing my own solar survey? Where to get inst?

Far and away the most important aspect of PV solar,, is that any potential site (roof/wall/area) needs to be free from shadows. Obviously direct shade reduces PV solar to zero,,, but even the shadow from leafy trees,, a telephone wire,, utility pole or chimney can have a huge negative effect on PV output. While you can work around shading to some extent by parallell/series array, multiple inverters etc,, the best situation is one that has no potential shading during the expected sun part of the day, over the course of a year. In my parallel array,, as a test, I put a broom stick over one panel,, my output dropped in that case by about 25%,,, almost the entire output of that panel was lost due to that simple shading. If I had that panel in series with other panels,, the loss would have been even greater.

Thermal solar on the other hand is much more tolerant of partial shading,, even shading a collector 50% will still let it run at 50% output,, unlike a Pv array that would put out close to 0 with 50% of it shaded. A small shadow from a phone line or chimney would have almost no effect on a solar water heater collector for example.

I would pay attention to your surfaces,, especially now that we are nearing the solstice. You can photograph your surface at various times of the day,, and then do some extrapolation to see what happens to the surface as we near the equinox(s) and the other solstice,,, using some simple line drawings with know angles,, both of the roof structure for example,, but also the sun angle and potential blocking/shading by seasonal obstructions.

Good luck,

Tony

Roderick · June 2009

Re: Doing my own solar survey? Where to get inst?

That dome thing is called a solar pathfinder, and I've seen them on eBay. If you Google the name, you'll see a lot of places selling it.

When I got bids for a solar array, the installers had no objection to me walking the roof with them to watch - in fact, they seemed to be proud to explain what they were doing. I think it's fair game to get a free quote, if there is the remotest possibility you might take it. I was amazed at how cheap an installation is nowadays, and if I had a quote like that 3 years ago, I would have taken it. My neighbor got 4 kW put in for $20k, BEFORE all rebates and incentives. Final net price about $12k. I could not have achieved that price via DIY.

Might be hard to tag along with the installer on your steep roof, though.

Cariboocoot · June 2009

Re: Doing my own solar survey? Where to get inst?

Get a digital camera, go outside every hour and take a picture of your roof. That will show you where the sun or shadows fall at which times of day. To be really accurate, you have to do this at four different times of year (at least), although the closer to the equator the less trouble from that. Here at 51 Lat the sun's arc swings wildly between summer and winter!

Gooserider · June 2009

Re: Doing my own solar survey? Where to get inst?

Thanks for the pointer - looks like there is pretty much just the one company making the units, with several people reselling them (all at about the same price)

They also have a neat looking software package to help with the data analysis, but unfortuneately it doesn't appear to run on a safe operating system, they only mention it running under various forms of :puke: Windows.

(Though I have asked if it will run under WINE at least...)

Gooserider

anotherfarmer · June 2009

Re: Doing my own solar survey? Where to get inst?

I am pretty sure Real Goods will rent a solar pathfinder. Call to find out.

A quick and dirty homebrew solar patfinder is the moon: a little research may be in order, but I am pretty sure the full moon nearest Summer Soltice (maybe tomorrow night) tracks very close to the lowest (Winter Solstice) winter sun. At our high latitude (near 45) the winter sun is surprisingly low in the sky, and really and all up here a wind turbine is needed for those dark months (if off the grid, anyway).

Jim Sluyter

icarus · June 2009

Re: Doing my own solar survey? Where to get inst?

Finding out how high the sun is in the sky at any latitude is pretty easy. http://solardat.uoregon.edu/SunChartProgram.php

Then you can buy a $15 Engineer's "P"level, or borrow a builder 'transit' level. With the builders level dialed in relative to the known sun angle,,you can swing the 'transit' through various angles,, finding any obstructions within any given sun angle date. You can do it for June 21, Dec 21, Mar 21, Sept. 21 or any other date and/or time and fnd out if and when you are GOING to be shaded.

Icarus

Gooserider · June 2009

Re: Doing my own solar survey? Where to get inst?

Good ideas for alternatives, but most of them seem to have one significant problem - I am expecting that I will want to be doing the survey at several points from the roof of the house and garage. The roof areas are all 12 / 12 pitch (45* slopes) which makes getting up there and moving around tricky at best - when we have had work done on our chimney, the sweep has needed THREE ladders to get to the chimney top, and was clearly far from thrilled about what he needed to do to get there...

Thus what I'm hoping to do is something with a "one shot" setup procedure, that does NOT require moving around to take the various measurements once I've managed to get myself and the survey gear to a given location on the roof. It seems like the solar pathfinder allows one to do this if doing either the "draw on the chart" approach, or the possibly easier "take a picture and process it on the ground later" method.

I am thinking that if I use two ladders, one to get up TO the roof, and the second with a roof-hook to give me footing to climb up the roof itself, I should be able to do 2-3 strips of survey locations, w/ 2-3 spots per strip - i.e. strips at each end of the house and in the middle, with stops near the lower edge, middle and peak on each strip. At each point, it should be possible to climb above the point, sit on the ladder while putting up the pathfinder below me (in order to get it to the south) and do the survey, then go to the next point...

The alternatives seem to all require that one either drag more equipment up onto the roof, or move around a lot more while taking measurements (i.e. the survey tools)...

Looks like renting a pathfinder is my best option - several places seem to be doing that.

(The other option seems to be seeing if there are any solar outfits that are inclined to build what *I* think is desirable, rather than apply one of their canned "solutions" that doesn't do what I'm wanting to accomplish....)

Gooserider

icarus · June 2009

Re: Doing my own solar survey? Where to get inst?

Scale models/scale drawings,, with requisite angles etc.

Tony

BB. · June 2009

Re: Doing my own solar survey? Where to get inst?

icarus wrote: »

Scale models/scale drawings,, with requisite angles etc.

Tony

Hmmm... I get an image in my mind of Gooserider in his living room with mashed potatoes and shaving cream building his scale model -- Just like Richard Dreyfuss in Close Encounters of the Third Kind. :roll:

-Bill

Cariboocoot · June 2009

Re: Doing my own solar survey? Where to get inst?

icarus wrote: »

Scale models/scale drawings,, with requisite angles etc.

Tony

To that end: Google SketchUp: http://sketchup.google.com/

It's not perfect, but it's better than mashed potatoes and shaving cream.

Unless you like playing with mashed potatoes and shaving cream.:p

icarus · June 2009

Re: Doing my own solar survey? Where to get inst?

"Daddy,, after we get done here,, can we throw dirt in my room?" "beep, beep, bing boong (sic)

Tony

peakbagger · June 2009

Re: Doing my own solar survey? Where to get inst?

There was an article awhile ago in home power on how to design a house model on a google sketch program and then import it into Google Earth and use a feature of google earth to model the sun angle at different time of the day.

So the model concept is fairly close although I am not sure how one made of mashed potatoes would up load to google;)

shastaron · June 2009

Re: Doing my own solar survey? Where to get inst?

Reel Goods does rent the pathfinder.

Doing my own solar survey? Where to get inst?

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