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New solar system, need some feedback :)


FrederikSchack
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Hi,

I´m new to solar, but I´ve done some research and more or less figured out how I think it´s 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 we´re 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 don´t 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, you´ll 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. There´s 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 don´t 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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Hi Frederik,

it looks like you have done quite a bit of good research. I was in the same situation 2 years ago. I first opted for 9 panels (3S3P) with a total of max 3kW, 9.8kWh (200Ah) Li Fe Ph battery, and a 5kW hybrid inverter. My considerations are first: the life time of such battery goes trough as much as 3 AGM lives. It also eliminates the aggressive acid vapor from the lead battery.

Second: studies show that the more you tilt the panels the shorter is optimal exposure. Flater panel installation yields longer daily power. I got mine flat on the roof of approx 26°, we are about 34° south. Good panels accept quit some sun angle. Mine delivered up to 3.3kW in the afternoon, that is 10% more than specification despite the far from optimal exposure. My concern for you is the hail. Good panels are quit sturdy but I don't know if they would stand such hail. Perhaps you should install a protective glass over them, perhaps acrylic glass. 

In the mean time I have upgraded with 3 more panels, an additional inverter in parallel (electric cooking) and another 100Ah battery pack. We suffer from frequent scheduled load shedding of up to 2.5 hours up to 3 times a day. And I am afraid that it is going to the worse.

The consumption you indicate seams correct. But consider that it depends on the number of persons in the household. Also think of thermal heating panels for the water heater. The simplest would be to find a place for the panels lover than the heater. If the panels are higher than the heater it would require a pump with a control system.

Good luck!

 

 

Edited by Beat
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There are a lot of online tools available that work well for planning purposes. I do have links to a number of such tools in my thread on designing my system. You are welcome tom have a look.

A micro grid may be helpful but a bit more expensive and involved, see here.

 

All the best

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On 2021/09/07 at 9:03 AM, Beat said:

Hi Frederik,

it looks like you have done quite a bit of good research. I was in the same situation 2 years ago. I first opted for 9 panels (3S3P) with a total of max 3kW, 9.8kWh (200Ah) Li Fe Ph battery, and a 5kW hybrid inverter. My considerations are first: the life time of such battery goes trough as much as 3 AGM lives. It also eliminates the aggressive acid vapor from the lead battery.

Second: studies show that the more you tilt the panels the shorter is optimal exposure. Flater panel installation yields longer daily power. I got mine flat on the roof of approx 26°, we are about 34° south. Good panels accept quit some sun angle. Mine delivered up to 3.3kW in the afternoon, that is 10% more than specification despite the far from optimal exposure. My concern for you is the hail. Good panels are quit sturdy but I don't know if they would stand such hail. Perhaps you should install a protective glass over them, perhaps acrylic glass. 

In the mean time I have upgraded with 3 more panels, an additional inverter in parallel (electric cooking) and another 100Ah battery pack. We suffer from frequent scheduled load shedding of up to 2.5 hours up to 3 times a day. And I am afraid that it is going to the worse.

The consumption you indicate seams correct. But consider that it depends on the number of persons in the household. Also think of thermal heating panels for the water heater. The simplest would be to find a place for the panels lover than the heater. If the panels are higher than the heater it would require a pump with a control system.

Good luck!

 

 

Thanks for the feedback :)

You made me realize that I actually forgot to take the ambient light into consideration and focused mostly on direct sunlight. I don´t know exactly how to take that into consideration.

When that is said, the solar angle in the winter time is 35 degrees (at the highest point), so if I put the panels down 20 degrees I´ll cover about 1.4 m2 of the incoming direct sunlight hitting the ground with one m2 panel (sin(35)*sin(180-35-20)), if I put it at 45 degrees I´ll cover 1.7 m2 for each m2 of panel (sin(35)*sin(180-35-45)). After 45 degrees, there´s very little benefit in raising the panels further.

Also the angle might help so that the hail will hit the panels at a steeper angle, so less of a straight hit, in case that we don´t cover them in advance. We have it maybe once a year and will usually  know it in advance.

Yesterday I did another calculation in Excel based on the solar angel (at the highest point) and incoming solar energy for each month. I also compensate for the suboptimal horisontal positioning during the day, with a few tricks. I consider a 19% panel efficiency and 15% system loss. So then I end up with about 25 m2 of solar panels or about 5kW. Then I might need to compensate a little for dirt on the panels, higher consumption some days and other unforseen things. All in all 5-6kW still seems reasonable, maybe more towards 6kW.

image.thumb.png.62c643076b0b20243d85c086d71baa34.png

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6 minutes ago, FrederikSchack said:

When that is said, the solar angle in the winter time is 35 degrees (at the highest point),

Also consider the angle of the sun on the same day but say from 08:30 to16:30 or whatever time makes sense for your situation. With low sun angles early and late, you might be able to have longer effective total time with usable solar generation. You can look at this to see (scroll down to post of August 2nd) how much shadow at what time of day you will get. Its a good simulation if you use your location data to show how much energy you can potentially generate.

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2 hours ago, Sarel said:

Also consider the angle of the sun on the same day but say from 08:30 to16:30 or whatever time makes sense for your situation. With low sun angles early and late, you might be able to have longer effective total time with usable solar generation. You can look at this to see (scroll down to post of August 2nd) how much shadow at what time of day you will get. Its a good simulation if you use your location data to show how much energy you can potentially generate.

Thanks. Yes, there is indeed a lot of factors to take into consideration and then I might still be surprised 😄

What I tried to do is to calculate the production based on the vertical angle, then I wanted to subtract the benefit of having horizontal tracking (which should be the same as what I loose by not having horizontal tracking). I found a percentage improvement of 2-axis tracking relative to a fixed panel, then I subtracted the percentage improvement of vertical tracking. I multiplied the (100%-(2axis - 1axis)) with the production (which is already taking into account the vertical position), in this way I sort of have a good guestimate of how much I´ll produce. A bit tricky and not correct, but if I´m just landing in the right ballpark, I´m ok with it :)

Edited by FrederikSchack
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19 minutes ago, Sarel said:

There are lots of online tools to help with this type of calculations and a lot more other stuff besides. The link I shared shows a number of these tools, it removes the guesswork.

I tried to click that link, but it led me to a post with a micro-system. I tried some of those calculators, but didn´t find the right one yet :)

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4 hours ago, Sarel said:

That is the correct one, there are some pictures with green and lots of numbers.

Hi,

NREL probably made a good system for the US, but I´ve tried it and it doesn´t work for Uruguay.

I see that you are deeply into your stuff, much deeper than me :)

How is your experience with Canbus BMS?

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My system was designed and certified to work by the manufacturers, so it just works. Cannot comment on any others. I have build and used some RS485 systEms and they work well but have no experience with Canbus.

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