What options do I have - upgrade

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Re: What options do I have - upgrade

Postby Warpspeed » Thu Sep 14, 2017 6:03 pm

It sounds like you have made a pretty sharp deal.
Great stuff !!!
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Re: What options do I have - upgrade

Postby Newt » Thu Sep 14, 2017 6:08 pm

Now I think about it, the east/west panels will likely be of little use in winter due to the low sun angle. My north panels I can tilt, but the roof panels will be fixed....any way of getting around this? I guess the upside is far reduced energy consumption in winter.

The house faces north/south, so really only N,E and W roof surfaces.
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Re: What options do I have - upgrade

Postby Warpspeed » Thu Sep 14, 2017 6:32 pm

East west still works in mid winter, maybe not as well as spring/autumn equinox in a clear blue sky.

But on those horrible grey totally cloudy days in mid winter, the light is totally diffused pretty much equally in every direction, east west, or even south pointing panels will work as well as north facing panels.

With 100% solid grey cloud cover, total exposed panel area is what counts, and the direction makes very little difference.

So my own personal experience is that a mix of north, east, west, and "straight up" facing panels will give pretty much an optimum all round solution under a very wide range of conditions.
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Re: What options do I have - upgrade

Postby Newt » Thu Sep 14, 2017 6:45 pm

Okay, thanks warpspeed...certainly right about even diffused light on a 100% overcast day and its amazing the panels still produce power, but they do.

Another question. I have a 3200watt max MPPT controller for these panels. With east/west what would be the max number of panels I could install...max power? I'll install all 2.6kW on the east side....what size array could I add on the west without going over 3.2kW midday?
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Re: What options do I have - upgrade

Postby Gordon-Loomberah » Thu Sep 14, 2017 7:36 pm

Newt wrote:...With east/west what would be the max number of panels I could install... without going over 3.2kW midday?


Entirely dependent on the mounting angle. What angle will they be?
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Re: What options do I have - upgrade

Postby Newt » Thu Sep 14, 2017 7:57 pm

Gordon-Loomberah wrote:
Entirely dependent on the mounting angle. What angle will they be?


I had a feeling you'd ask that...I only eyeballed it today and guessed about 30- 35 degs
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Re: What options do I have - upgrade

Postby Warpspeed » Thu Sep 14, 2017 10:34 pm

That is a geometrical problem that you can solve yourself with a scale drawing.

Imagine you are the sun looking down on a solar panel. How many square metres can you actually see ?
If looking straight down on a panel from directly in front, you will "see" the whole actual area.

Completely edge on, you will see nothing, just a thin non working edge.

Viewed at some angle, the panel surface might appear to you as a thinned down rectangle narrower in one dimension than it actually is. If you make a scale drawing its possible to make a reasonable estimate of how much the power drops off, think of it as a decreasing aperture as the sun angle becomes less effective.

I am sure this is not completely accurate, but its probably close enough.

If you work this out for two panels propped up to form an equilateral triangle with three sixty degree angles, you will find the area the sun "sees" hardly changes at all throughout the day, and you can get an almost flat power curve equal to the full rated power of one panel, or half the total combined rated panel capacity. That is probably the optimum mounting angle for a virtual tracker if you can do it that way.

A typical roof might be more like forty to forty five degrees, so there will be a mid day power hump, and power will fall off at both sunrise and sunset. Not optimum, but still pretty useful.
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Re: What options do I have - upgrade

Postby australsolarier » Fri Sep 15, 2017 7:22 am

warpspeed,
excellent explanation.

a note to over powering, the midnite classic 150 solar charger seems to handle this over powering perfectly. on my 12v system i have twice the recommended solar panels. (although different orientations) the midnite just limits the current and the pv voltage goes up. midnite does not officially recommend this, but the technicians at midnite have no problem with it.
so, the morale of the story is, get a high quality product. with good customer support. and there are not that many choices left. (remember, the biggest outlay is the batteries, and you want the charger to be reliable and not cook them)

and if you have time, there are a lot of youtubes were people try out the cheap chinese electronics. i just don't think the chinese are there yet. maybe in 20 years.
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Re: What options do I have - upgrade

Postby Warpspeed » Fri Sep 15, 2017 7:59 am

Any half decent solar controller should (?) have an internal current limit. I design and build all my own electronic equipment here, so I am completely unfamiliar with commercially available controllers.

In that case, you can safely overpower the controller and still get the maximum output the controller is capable of, even in less than optimum solar conditions. That has the obvious advantage of giving you more in poor solar conditions without letting the smoke out on exceptionally good days.
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Re: What options do I have - upgrade

Postby Newt » Mon Sep 18, 2017 7:28 pm

I have picked up the 14 panels....with racking, they look good. I can only add a max 4 in series to keep within the MPPT controller max volts of 140V. I guess 2 panels in series is too low a voltage, so I could input 7 strings.

Otherwise 3 stings of 4 panels, so I would have 2 left over. I can only put a max of 8 panels on the east facing roof which is adjacent to the battery shed. Maybe 2 strings of 4 there for now and look at the west side later.

I will be asking how to wire these....where junction boxes go etc...diodes and so on.

Cheers
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