Solar array alignment

System · November 2007

My ongoing project of rehabbing my RE system continues!

The collective advise from the folks here has been most helpful!!

I've rewired my solar array using a Midnite solar combiner and ugraded the wiring to drop my voltage drop from 19% to 3.5 %. YIKES!!!

I've cleaned up the DC wiring in the power system and installed a nice beefy class T fuse and DC disconnects.

Nice ventilated battery box is now housing the heavy stuff.

I built a small Kubota powered, DC charger with a programmable Balmar Controller to cover the shortfalls in solar insolation. I burn about a gallon a week to keep things topped off.

Now, to the point! My house (and solar array) is aligned about 23 degrees off true N/S so the array faces SSW. My solar colection really only gets going at about 11 a.m in the summer (and a good deal later in the winter) because of the large trees and steep terrrain at my homesite. Cutting the trees is not really an option. My array is centered in the best and highest location on the house to maximize total insolation. I could build a rack on the 5 in 12 pitch roof to align the panels due south (not easy, but doable).

Is it worth the trouble? As it stands, I actually have a slight bias to the later afternoon sun in all seasons. Any thoughts as to how I might calculate the difference?

Thanks

Mike

westbranch · November 2007

Re: Solar array alignment

Mike, as I see it, without knowing where you reside, I think you have it right at this time as to averaging/maximizing your year long insolation, this being due to the trees shading your panels until 11:00 or later.
I have seen a graph but can not locate it right now that shows the reduction in pv ouput relative to a due South alignment... however your site limitations negate the early daytime incidence. Stay with what you have or go to a tracking setup. In summer you will get more output than in winter if you are in the north where the sun sets earlier in winter... I'm sure the experts here can give you lots of calculations to do to fine tune your alignment but, as you say, "not easy but doable"..
Cheers
Eric

icarus · November 2007

Re: Solar array alignment

I'm confused. You say that the panels are aligned for best insolation, but the you mention moving them. (I guess you must mean the best insolation in thier current location)

You haven't mentioned how many or how big they are. The question is how much more sun will they get in the new location relative to thier present one? If you are not getting full sun until near noon especially in the winter you should be able to get a good idea of the added insolation on the roof and do a rough calc. It may be simpler and cheaper to add another panel instead of moving them. On the other hand maximizing your output is allways the goal.

My problem is the opposite, mine loose their sun by 2:30 pm winter and summer, but they get full sun from sunrise at all times of the year.

Icarus

BB. · November 2007

Re: Solar array alignment

Somebody might have a better link... But this solar power calculator/sizer seemed to be pretty accurate for my location.

It allows you to adjust roof angle and compass direction, based on the solar irradiation data for your area. It is not perfect, and you kind of have click around to get the power data (it is intended to estimate power savings and cost to install grid tied systems--but because it includes sighting and roof pitch, I find it worth the trouble). Use IE to get everything to work (It works somewhat in FireFox--but not all functions work).

Mine faces SSE, and with my system (grid tie, time of use metering, and sometimes morning clouds, even a tall redwood blocking, for now, winter sun in the AM) it would be better if it faced south or SSW--but I was surprised how little it really mattered (according to these predictions).

Given you have shading until 11am or later--pointing it due south might be a mistake... Generally, anything that points within 10 degrees of where you want it is pretty close to dead-on (COS 10d = 98.5% or 1.5% loss, COS 20d = 94% or 6% loss)...

-Bill

System2 · November 2007

Re: Solar array alignment

"You say that the panels are aligned for best insolation"

Under the circumstances! The entire array aligns on a bearing of about 202 degrees. My reference to "best insolation" was, out of the shadows the maximum amount possible. I have only 440 watts of panels at this point, so doubling the panel array is in the plans.

My thoughts on moving the array was only to re-align to due south but, otherwise, staying in basically the same location on the roof.

The 6% loss for off angle siting is plenty livable given I've reduced my DC line loss by over 16%. Actually the line loss is only 2.3% now.

Based on the discussion. I'm inclined to add the new panels on lo profile Uni Racs to take advantage of the increase in efficiency gained from changing panel elevation for the season.

Thought about a tracker, but with the minimal morning sun, it may not be a good return on investment.

I might take some trees out in the the SW quadrant since the garden plot needs some earlier sun

Excellent thoughts compadres.

thanks

Mike

BB. · November 2007

Re: Solar array alignment

Make sure that you have a good $$$$ estimate on how much everything costs and how much (extra) power you will generate...

My installation is on a two story roof, and 30-40 years ago, I probably would not have thought of setting up a latter and walking on the roof... Now, I was surprised how I have changed (fear of falling).

So, make sure that, if you have an adjustable rack, this is something that you will want to change pitch on 2-4 times per year for the next 20-30 years.

And, check how much power extra power that will give you (such as here).

If, you have grid tied power (vs battery/off grid), maximizing your overall power generation is a good thing. Biasing a system towards, for example, winter production may make good sense for off-grid system where you have only a few days of storage.

If you have Grid Tie (in California, you can have 1 year net metering), your storage capacity is essentially 1 year. And, for my home, my summer months generate ~530 kWhrs / month, but dead of winter I generate as low as 135 kWhrs / month (cloudy/wet month).

I can try to double my winter power (not likely--tilting to +15 degrees would get me ~6% more power in December) and get an extra 135 kWhr/month... Or, I can get 25% extra power in the summer and get about 133 kWhrs/month extra and not worry about how in the heck I can adjust my panels for seasonal conditions...

-Bill

mike95490 · November 2007

Re: Solar array alignment

Get a chainsaw, get lots more panels, or buy a lot of gas for the gennie.

2 or 3 hours of sunlight per day is not much.

icarus · November 2007

Re: Solar array alignment

I'm sure you have thought about all this already, but just in case,,,

Is there any possiblity that you can move the entire array to a better spot on the property? In front of trees, pole mount etc. Even if you are consderable distance from the load(s) you could increase the voltage, even inverting at the array and send the higher voltage to the loads with much less loss. Another option, (although perhaps not a good one), would be to move some of the panels to take advantage of the earlier sun, and leave some to take advantage of the afternoon bias. For example if you use specific loads in the morning (or afternoon) it MIGHT maximize your charging. You could do soe simple calcs to find out. I don't know how far north (or south) you are, and therefore don't have a clue about you winter/summer sunrise and set times. Where we are the sun is off my panels by 2:30 12 months, but is in full sun from sun rise. Right now the sun sets about 4 pm so I not losing much, and it rises just after 8. Summer rises at 3:30, set about 10, so I lose porpotionaly more.

Good luck

Icarus

System2 · November 2007

Re: Solar array alignment

A little more data on me. I am a off the grid and I use about 2 kw/hrs a day. I have all CFL
lights but am transitioning to LEDs. NO electric appliances of note except this Mac and satellite internet.

39 degrees north latitude in California. Peak insolation is alittle over 6 in the summer and substantially less in the winter of course.

My total fuel costs are about 2 gallons of diesel a week for my little charger set (about 6 hours of operation).

I have 700 AH of storage right now. but am looking at a larger bank (maybe 24 volts for the efficiency) to reduce the depth of discharge. I run my shop on a 3 phase, 8 KW Cummins/Onan diesel. (Mostly for the CNC router).

I have considered a tower mounted array (40 foot windmill tower) and a remote power station. Wind is not a great problem here. But calculating the wind load is beyond my current capabilities (working on that though!).

Right now my needs are well met! Just looking at ways to fine tune things.

I got THREE chainsaws (miserable little bastages!!) HA!!

Life is good! I have modest needs and endless curiosity.

Later

Mike

westbranch · November 2007

Re: Solar array alignment

Another option is to do a 'manual tracking' when you are around, if the panels are pole mounted. Works best in summer when there is lots of light ot intercept, not a lot to gain in winter.

IFF you do not want to remove some trees, I would think more panels are first for you, then more storage. If you only get 6 hrs max insolation in the summer, say 5 for simplicity then you probably are gettting your 2 Kw plus a bit more, in summer, but winter is you problem time... without the spec of your panels it is hard to determine but I am guessing that you are near the minimum recommeded amperage value (3 %) for PV recharging. with your 2Kw usage you probably want to be above 5%.

cheers
Eric

System2 · November 2007

Re: Solar array alignment

Yes, I have 4 SM-110 shell panels right now and it looks like about 4% available charging current..... max! Of course "max" is few and far between in the real world. Likely less, most of the time.

I'm thinking of four 130 watt Kyoceras as my next move and in several months two more panels and new battery bank in the 1000AH class, like a 6-85-13 or 6-85-17 folk lift battery.

This would give me something on the high side of 60 amps of pv output. My goal is not to run more stuff, but to reduce the non solar power inputs.

I kinda make the upgrades based on what I can save in a few months, then make the investment in workable chunks. I have spent a surprising amount of money on just copper it seems!!

I scored several ballscrew jacktuators that might work nicely to raise and lower the PV array for seasonal changes. My guess is, I could optimize collection by monitoring a TriMetric and peak it out.

Thanks

Mike

Solar array alignment

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