New Offgrid, DC or AC Coupled, and components

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Re: New Offgrid, DC or AC Coupled, and components

Postby australsolarier » Thu Jun 14, 2018 10:11 am

dakiller,
i have no links. it is my observation. if you do not believe it, just try a very easy experiment:
tilt a panel around in overcast and see what direction it generates the most power.

basically the sun hits the clouds and disperses the filtered light in all directions down to the ground. besides data will not do you any good. there are different intensities of overcasts. in indirect sunlight however horizontally oriented panels will most definitively bring the most. like i mentioned before, those panels are mainly for overcast weather. for, in sunny weather i would not need them for my usual needs.
as a matter of fact in overcast a 30 degree inclined panel towards the equator will generate the same amount as a 30 degree inclined panel towards the pole. the same for east west orientation. in the afternoon a eastern oriented panel will generate the same like a west oriented panel and vice versa.(in cloudy weather)
there is however the 20 degree inclined panels (towards equator) that are a very good compromise between generation in sunny and overcast weather.
get as many panels up as you have room and or funds. if not design the system for easy add on panels for a later time. you cannot have too many panels.
7 degree inclined panels towards the pole will generate the same annually as towards the equator in Germany.
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Re: New Offgrid, DC or AC Coupled, and components

Postby Warpspeed » Thu Jun 14, 2018 11:38 am

I will second this.
On those awful grey twilight days, every sky direction looks the same. Absolutely no visible sun at all.
Any direction will work pretty much the same, but straight up usually works the best.

Basically the more sky area the panel can "see" from horizon to horizon in all directions, the better the results, although output will still be pretty miserable.

I have four separate groups of panels.
An east/west virtual tracker looking 60 degrees above the horizon in both directions.
A north facing array also looking sixty degrees above the horizon.
And some panels mounted direct onto a flat roof looking almost straight up.

On horrible winter days with total 100% cloud cover, the up panels are always producing the most, pitiful though that may be.
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Re: New Offgrid, DC or AC Coupled, and components

Postby Gordon-Loomberah » Thu Jun 14, 2018 11:52 am

There is no doubt about it, dakiller, straight up is best in heavy overcast. My trackers which operated by pointing at the brightest part of the sky always ended up pointing near straight up, as that is where the sky is brightest (for a uniform cloud cover), as you are receiving solar radiation through the least thickness of cloud when looking vertically. It isn't always that obvious visually though, the sky appearing fairly uniformly grey, but a decent spot light meter shows it well.
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Re: New Offgrid, DC or AC Coupled, and components

Postby australsolarier » Thu Jun 14, 2018 11:54 am

rule of fist for those "awful days" is 10x more panels than what is required for an equivalent sunny day. there is naturally different darkness of clouds. during thunder storms it can go down to zero. luckily they only last an hour or so.
it would be interesting to look into the cost of over powering the solar panels as compared to the cost of a generator and fuel. personally i prefer the over powering.
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Re: New Offgrid, DC or AC Coupled, and components

Postby australsolarier » Thu Jun 14, 2018 12:00 pm

Gordon,
i used to have an active tracker for a couple of years. even after the sun settled and the tracker moved the panel to the resting position, horizontally, pointing in the sky on a clear sky produced some minimal power, so 80w if i remember correctly. this must have been a bit of a reflection of the stratosphere or atmosphere or something. as the sun was behind the horizon. (sometimes my tracker system thought it is morning again and did another move east)

i removed the tracker as the winds kept me worrying too much. i just added a few more panels in lieu. mind you at the time the panel still cost a mint.
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Re: New Offgrid, DC or AC Coupled, and components

Postby Gordon-Loomberah » Thu Jun 14, 2018 12:19 pm

Even after the sun has set locally, the atmosphere above you is illuminated for some time, and any dust, water droplets etc reflect some light towards the ground. This can generate a little bit of power with a decent array size, but not for very long. Cloud in the east could be significantly brighter than the overhead sky while the sun was on it after local sunset, so could cause a tracker looking for the bightest part of the sky to move to the east.
Both the trackers I have up at the moment have withstood a 76km/hr gust (measures on my weather station close by), so I'm not concerned about damage due to wind. However, given the cost of panels (especially 2nd hand ones) any more panels I add will be mounted as virtual trackers or near to vertical pointing (actually a bit to the NE due to the large trees and hill just to the SW of them)

If the sky is clear, you can see the Earth's shadow rising opposite the sun for a while after sunset. Once the sun is 18 degrees below the horizon, no part of the atmosphere you can see is illuminated, that is the end of astronomical twilight. It is typically about 90 mins after sunset for much of populated Australia, but longer in Tasmanian summertime, where twilight is much extended.
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Re: New Offgrid, DC or AC Coupled, and components

Postby australsolarier » Thu Jun 14, 2018 12:32 pm

here is my latest video:
https://www.youtube.com/watch?v=-8IVJjdZMGc&t=8s

there are two more videos in the channels
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Re: New Offgrid, DC or AC Coupled, and components

Postby Warpspeed » Thu Jun 14, 2018 12:34 pm

There is a lot of light scattering in the atmosphere even in a cloudless sky.
The fact that it does not go instantly totally pitch dark (in seconds) when the sun sets, is a pretty good demonstration of that.
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Re: New Offgrid, DC or AC Coupled, and components

Postby Davo Yarra » Tue Jul 24, 2018 12:22 pm

TsaTsa2CV wrote:The maximum we have ever drawn was 18kwh in 24h. After sunset we rarely use more than 3-4kwh with lighting and TV and hydronic circulation pump on.

We ablsoluly love the off grid life and the only difference is scheduling power consumption to an appropriate time. I feel confident that you will get away with a much smaller system!


Hi TsaTSA2CV,

Your post on this topic really caught my eye. My wife and I are currently in the detail design phase of a very well insulted new home we are going to build in the Yarra Valley. Its not going to be a 100% Passive solar house, as we really wanted verandas all around, however it will incorporate as many of the other passive type designs as possible eg orientation, insulation, sealing, glazing, window to floor ratios etc. The house will be approx 28 Squares and we are hoping to have hydronic heating in a slab; and cooling primarily using good cross flow ventilation principles and some type of air conditioning (?? not sure whats best) to be used only on the hottest, most uncomfortable of days.

Due to a 350m distance to the nearest service pit (2 Phases) and the expensive pioneer clause cost (cica 15K) just to get into the pit, I'm very very interested in the possibilities of going off-grid and your post did give me some heart. Especially your discussion of the heat pumps (cica 3kWh/day) and overall max that you have seen to date of 18kWh. I guess I just naturally though that heating water for domestic and hydronic use couldn't be done when off-grid i the middle of our winters. Does your sanden heat pump provide both of those functions or do you require a separate one for each?

Given that you have most probably jumped through all the hoops and felt the nervousness I am at the moment, any help or pointers you might be able to give us (or anyone on the forum) which can help us steer our design direction for on or off-grid - would be greatly appreciated.

Thanks and regards,

Iain and Mackenzie
Last edited by Gordon-Loomberah on Tue Jul 24, 2018 7:34 pm, edited 1 time in total.
Reason: fixed up quoting
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Re: New Offgrid, DC or AC Coupled, and components

Postby australsolarier » Wed Jul 25, 2018 9:15 am

TsaTsa,

everything can be done off grid.
as for cooling the house in summer: when off grid you will have heaps of surplus electricity in the summer. the off grid system should be designed for the winter days. which has reduced solar input. so having a heatpump you can cool your house down to 18 degrees no worries.

as for hydronic heating, you will need a heatpump air to water. or solar hot water with tanks that store some of that heat. but again in the summer you will not heat the house and have tons of unneeded hotwater. the solar hot water heating is very costly to install. you might be better to invest the money in more solar panel.
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