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Old 09-02-21, 05:26 PM   #1
FrederikSchack
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Hi,

Im new to solar, but Ive done some research and more or less figured out how I think its best to configure a new solar system for our home.

But I would need some constructive critique of my ideas

We live in Uruguay and were a blessed with a lot of sun and a lot of incompetent professionals So I might end up doing it myself, even though I would prefer a professional installer.

I also had to wire the house myself, after talking with some of these "professionals".

The primary reasons for installing solar system is unreliable power from the grid. The power is usually out for 15 minutes and sometimes for a few hours, a couple of days ago we were without power for about 5 hours. There may also be fluctuations in the voltage. So the system needs to work sort of like power stabilizer and UPS.

The secondary reason is to be able to "survive", without grid-power for extended periods of time. Which means keeping the combinede freezer/fridge running, heating a bit of water, having a bit of light, washing clothes. We have a big solar oven and a wood fired oven.

We expect to get most of the consumed energy from the solar system, but would like the convenience of having the grid as a backup.

We dont expect the solar system to be able to pay for itself, but probably everything besides the batteries. We pay about 0.2 USD/kWh.

We would like to keep maintenance low, keep the batteries inside the house (close to the inverter) and as mentioned it should work like an UPS.

So far I think this points in the direction of deep cycle AGM or lithium and a suitable hybrid inverter.

We have very limited options in regards to what we can buy here in Uruguay, but I can get a GroWatt 5000W hybrid inverter, that delivers 5000W and can receive maximum 8000W of solar power.

We have sun most days, most of the year, usually cloud free or very few clouds. According to WeatherSpark.com, the darkest day of the year has 2.5 kWh per squaremeter a day and 7.8 kWh/sqm/day at the day with the most light, but WeatherSpark.com significantly overexaggerate the amout of clouds we have.

The highest point of the sun in the summertime is about 85 degrees and about 35 degrees in the winter time. We live in the southern hemisphere, so the sun is coming from the north. I figure we would get more stable output from the panels by angling them more towards the winter sun, so maybe 45 degrees? Or alternatively have a system for adjusting the angling manually once a month. I figure that if we angel 1 squaremeter of panels at 45 degrees and the sun is coming in at 35 degrees, youll catch sun for about 1.72 squaremeters of ground in the wintertime and in the summertime 0.77. So, factoring in an efficiency of the panels of 20% we would have 7.8 kWh/sqm/day * 0.77 * 0.2 = 1.2 kWh/day and in the wintertime 1.77 * 2.5 * 0.2 = 0.9 KWh/day per squaremeter of solar panel.

We need about 400 kWh in the winter months and about 300 kWh in the summer months.

I roughly estimate that we would need 5-6 kW of solar panels, taking into consideration non-optimal angling during the early, later part of the day and some loss in the system.

We would like to mount the solar panels on the roof of the porch, which is about 28 m2 and is facing north (slightly titlted). Possibly extended to the roof of an office just besides the porch (additional 8 m2).

We would like the system to discharge max 50% and then switch to grid power, but have the ability to discharge further in case of brown outs. We would like the emergency discharge to be able to cover a couple of hours without sun, I consider to have a rated battery capacity for half a days consumption, about 150 AH at 48v.

If we buy deep cycle AGM, then we have to consider that they are not as good at deep discharging, so we would have to buy more battery capacity to compensate for that. Further AGM has almost half the lifespan of lithium. Lithium Ion is a bit more than double the price of AGM. All in all I think they economically end up somwhere in the same ballpark. So that makes me look at other factors.

Lithium Ion has a higher roundtrip efficiency, can better utilize the stored energy at various loads and can charge/discharge faster, which should translate into better utilization of the collected energy and a better user experience. So this tips me in favour of lithium ion.

We already have 3x6mm2 cable (about 4 meter long) that goes to the porch, that could be repurposed for transporting energy from the solar panels to the inverter. Theres also an empty tube where I could pull another cable if necessary. I figure that if the panels are configured to deliver 48 volts, it should be a fine cable (voltage drop of about 0.7%).

We have laws in Uruguay, I dont think a lot of people use them for anything, so I feel free to do whatever I want ;-D

We do very rarely get golf-ball sized hail, but would probably figure it out in advance. They caused 3 half cm deep dents on the roof of my Hilux.

Any thoughts, corrections and suggestions are very much appreciated.

Best regards,
Frederik

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Old 09-14-21, 07:43 PM   #2
jeff5may
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Welcome to the forums!

I put Jose Pedro varela into the solar irradiance calculator and it said:

42 degrees optimum winter angle
57 degrees best overall angle
72 degrees optimum summer angle

With the overall angle, it looks like you get about 6kwh per day per square meter in December and January, dropping to about half that in June and July. Fiddling with panels can boost June and July to around 3.6 or so, depending on mother nature. Here's the link:
http://www.solarelectricityhandbook....rradiance.html

Main thing I can tell you about solar is if you're serious about it, do it right the first time and enjoy your power source. Plan the whole thing out before you go shopping for materials. Consult with suppliers and a local engineer and spec out the drawing. Figure out details with the power utility and local government. This homework will pay you back in longevity and reliability for a long time. Not doing the homework ahead of time and just eyeballing and rigging things will definitely come back to haunt you.

Last edited by jeff5may; 09-14-21 at 07:55 PM.. Reason: Info
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Old 09-14-21, 09:08 PM   #3
FrederikSchack
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Hi Jeff,

Thanks!

i found the calculator and its probably giving a very good angle. Im close to Nueva Palmira and it returns 41 degrees for optimal winter sun.

I find it curious that they calculate the angle relative to a vertical surface, is that the norm? So 41 degrees vertical would be 49 degrees relative to horizontal.

There is a lot of factors and preferences to take into account. I made my own calculations based on kWh data from WeatherSpark and sun angle from suncalc.org. And its hard to say where the optimal point is. I guess thats very individual depending on preferences. It gets even more complex if we have to take preference whether we want more energy early/late or at mid day into consideration

49 degrees relative to horizontal is definitely not a bad angle for winter sun.

Ill definitely get myself an adjustable mount, so I have the option of changing my mind

I would have liked to post some graphs from the calculations I made, but I cant post pictures yet.
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Old 09-14-21, 11:28 PM   #4
jeff5may
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The reference angle is "lean back from vertical" where zero points the panel at the horizon. An increasing angle points the face of the panel higher in the sky. If you look around in the mentioned site, they have more calculator pages that can tell you exactly where the sun comes and goes in the sky and such. Plus the sizing and output estimate and such.

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