Tool for choosing the best panel location

westbranch · March 2008

I will have to move my small array to a new location

when we start construction of a new cabin,:D hopefully sometime in the next year.

I have been observing several potential locations and trying to assess which of the sub optimal spots I should use (shade from tree branches, short duration of light interception, etc) . Intent is to max out the input to 'keep the batt topped up' during the construction period. I do not expect any use to be made of the solar setup as the batt will be stored in a small outbuilding well away from the new site...

So I had a brain wave when I read SolarJohns way of monitoring his voltage on a small installation... use a voltage data logger! like this http://www.microdaq.com/lascar/usb/el-usb-3.php

My idea is: use a 12 v motorcycle battery, a cheap 5 w solar panel ($10 at Can Tire) mounted on a stake and the data logger to record voltage output every 5 minutes through the day(s). Then download the data to an Excel spread sheet for analysis, and compare the duration and peak outputs of each site. Pick the best site based on max input. The time stamp of the data would also give me the time period when interception occurs and thus fine tune the optimal bearing to align the panel to.. not many of the paths thru the trees get best exposure at or near noon...:roll:

Comments please

Cheers
Eric

Solar Guppy · March 2008

Re: Tool for choosing the best panel location

http://www.solarpathfinder.com/

No data loggers or panels or guessing needed

BB. · March 2008

Re: Tool for choosing the best panel location

Ignoring weather, a Solar Pathfinder (don't know price) is faster (won't take 1 year to evaluate site) and probably just about as accurate.

You might also try looking through the links on this site... Perhaps you can do the equivalent of the Solar Pathfinder by printing a chart out and plotting the horizon obstacles.

I have lived on or near the Pacific coast for most of my life, and with the marine layer and micro-climates--I have always thought throwing an active solar power monitor on a roof for a year would be very interesting. Issue is that when you look at the PDF solar data from this site, there is a very large variation from "average" over the 20+ years of their data... So how useful 1 year would be is anyone's guess.

Lastly, type typical silicon solar cell does not accurately reflect available energy from the sun by tracking open circuit voltage and I am not sure you can find a 10 watt MPPT solar charger...

So, your better bet would be to measure the panel's Isc (short circuit current--usually by measuring a small voltage drop across a shunt resistor)--which, as I understand, is much more linear with respect to solar energy.

-Bill

Dueling posts again... Maybe shorter/faster is better...

crewzer · March 2008

Re: Tool for choosing the best panel location

I'd think that you'd want to monitor current from the module rather than voltage.

You'll also have to consider seasonal variations (winter Sun track vs. summer Sun track), and perhaps even local weather patterns. For example, a location that experiences regular PM clouds and/or thunderstorms might be better off biasing a south-facing array a bit to the east, and a location that suffers from morning clouds (i.e., "June gloom" along the SoCal coast) might be better off biasing the array a bit to the west.

Just things to consider...

HTH,
Jim / crewzer

westbranch · March 2008

Re: Tool for choosing the best panel location

thanks Jim, I had figured that voltage might be a better indicator of 'shading', but I guess Amps would be affected similarly..?? Possibly both? more $ though to track both.

I forgot to include that these measurements would be taken while I was out there for a weekend or so and set up might be fro some of those odd (non standard) directions following the gaps in the tree cover.

Cheers
Eric

crewzer · March 2008

Re: Tool for choosing the best panel location

Eric,

I wouldn't expect for the voltage to change a lot. It would just range between nominal battery voltage (dark, or fully shaded module) and some nominally higher "surface charge" voltage when the module is exposed to the Sun and generating current, though not much.

Output current, OTOH, would range between 0% and ~100% of Imp spec -- assuming bulk mode, of course.

HTH,
Jim / crewzer

mike95490 · March 2008

Re: Tool for choosing the best panel location

westbranch wrote: »

I have been observing several potential locations and trying to assess which of the sub optimal spots I should use (shade from tree branches, short duration of light interception, etc) . Intent is to max out the input to 'keep the batt topped up' during the construction period. I do not expect any use to be made of the solar setup as the batt will be stored in a small outbuilding well away from the new site...

If all you need is 30 minutes of full sun a day to keep an idle battery full, I would not sweat it. Almost any spot should work for you, and if you can adjust the elevation twice a year, you should be fine.

Tool for choosing the best panel location

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