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diy solar

is the optimum year round angle what you really think it is?

Jamie.sanders

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Dec 1, 2019
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stay with me, I'm just throwing out my thoughts but.
I was playing with the solar calculator looking at the best angle for year round, my results were:

Summer, 70 degrees
Winter, 40 degrees
best year round angle 55 degrees.

I understand 55 is half way between 70 and 40, I get that, splitting the difference to work as well as possible during both seasons, basically
robbing the same amount of performance from both winter and summer. (both are 15 degrees from the perfect angle) but...

if you factor in that in the summer here in Arkansas the number of hours of full sunlight available to generate electricity is 5.29 in the summer
and 3.88 in the winter, so in the summer you have 1.4 more hours of good sun. so...
wound it not be better to angle the panels more toward the winter angle to get optimum sun in the winter since you get more hours
of sun in the summer which would help compensate for not as good of an angle? or am I missing something?
I understand 55 degrees basically robs a bit of performance equally from the winter and summer angles, but would it
be better to rob more from summer since you get more sun hours in the summer? so angle the panels something like 50 degrees?
 
I am in Arkansas as well. I agree with your line of thinking but, it would also depend on what season you need more kw’s. If you burn wood say and need lots of a/c. I have a homemade single axis ground mount with 6.1 kw on it. I have them at 15 deg from horizontal in mid summer. Currently 60 deg from horizontal. I keep them with in 10 deg of ideal. It takes me about 5 or 10 minutes to adjust them. I have played with it and I can’t see any appreciable difference with in 10 deg.
 
You angle panels based on what production is more important to you. For maximal annual production it will generally be a tilt close to your latitude. If you want superb Summer performance then lie them flatter, if Winter is key to you then have them steeper. It all depends on what's most important to you - overall output or when the power is produced.

Then you need to work out azimuth and whether maximal peak production from a south facing array is more important than evening out production across the day with split azimuth facing east and west, or whether morning or afternoon production is more important. In some locations weather patterns might often see morning fogs or afternoon storms and so sometimes greater overall output is attained by an azimuth a little away from south (or north if you are in stern hemisphere).

For roof top array you kind of just put panels on the roof and the decision is made for you.
 
It also depends on your usage and net-metering agreement. For example, if the net-metering agreement isn't great and you use most of your power in summer, it might be better to optimize for summer.

I suggest using SAM. It'll include the other important factor: your typical weather. For example, I technically get the greatest amount of solar energy during summer. But it's also when it's the stormiest so it's not realized. SAM lets you play with the tilt and see the annual or monthly energy totals.
 
Without knowing you peak usage time, hard to tell. For me in Florida - it's summer - so 85 degree :p (almost flat)

We need 3x in the summer what we need in the winter. (A/C)
I understand 55 degrees basically robs a bit of performance equally from the winter and summer angles, but would it
be better to rob more from summer since you get more sun hours in the summer? so angle the panels something like 50 degrees?

how much space do you got? I have panels are different angles and different orientations.

So you basically build 3 panel arrays (half circle) - one south-east facing, one south one south-west. This allows maximum sun catching for the money. Not space efficient - but cost effective. The morning and afternoon arrays are steeper then noon array.
 
Also depends on what your system is used for (grid vs. off grid). I have a house in the Houston TX area and one in NE OK. I'm doing off grid backup systems for both. So here's the point... the primary season for power outages in Houston is the summer, during tropical storm season, while the primary issue in NE OK is the winter time... during snow and ice storms. So in situations where you have season-specific needs, that can also be taken into account. I'll probably set up the panels in OK to favor the winter angle.
 
I live in Houston too. My panels are installed on a roof surface that is 180° azimuth (South). I have a 4/12 roof pitch on that surface (about 19°). A fixed panel angle, that is optimal for Houston, is about 26°, but going through the heroics to mount panels on that angle would only result in a 0.5% increase in yearly production. There is not much justification for trying to adjust the angle of the array with fixed racking. Making the angle steeper will increase the production in the winter months, but any gain in winter production will be totally offset by losses during the long summer days.

You can tell from the attached map of "Peak Sunlight hours", that solar production is not as easy as thinking it is "all about latitude". If that was the case, you would see nice horizontal bands across the map. Peak sun hours differ from" hours of daylight". Peak sun hour actually describes the intensity of sunlight in a specific area, defined as an hour of sunlight that reaches an average of 1,000 watts of power per square meter . By measuring all of the varying sunlight for the year and dividing that number by 1000 W/m² (peak sunlight value) the daily peak sunlight hours can be derived. Example: IF a measurement system, in your location, (tracking the sun) measured a total of 365 kW per m² of solar insolation for the whole year, then the peak daily sunlight hours for that location would be 1 hour. With a one square meter 20% efficient panel, one could then expect 73 kW (365kW x .2) of yearly production for each sq. meter of panel area (with a tracking system). Tracking systems can add ~30% to the production. (see attached image)

You can see that my same array, in parts of North Dakota, will have the same production as I have in Houston! This is largely because the Peak Sunlight Hours Map, takes into account atmospheric conditions. Houston will have more intense sun than North Dakota , but because of the moisture from the Gulf of Mexico. Cumulus clouds start to form near noon in the summer. Noon is when the best production is expected (solar noon), but now the clouds intermittently block the sunlight as they roll by and thus have a substantial effect on production. While the sunlight intensity in North Dakota is lower, that area is not plagued by as many clouds. As you move out West from Houston, there is less moisture in the air and those areas have almost unobstructed sunlight. You can see from the map that production is much better toward the desert area where cloudy days are less frequent.

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I don't find annualized maps to be all that useful, but then I live in that little green area in the upper left hand corner. My batteries don't operate on an annual cycle, it's the amount of sun I get in a week that matters to me. In the summer we have months of sunny days with no clouds at all, and even this far north get about 6 hours per day effective sun. In the winter we get 1-2, and have weeks with less than 1 per day. If I sized my arrays based on annual numbers, my batteries would be dead half the year. There are good calculators that do monthly charts based on local weather that are handy for planning.
 
I don't find annualized maps to be all that useful, but then I live in that little green area in the upper left hand corner. My batteries don't operate on an annual cycle, it's the amount of sun I get in a week that matters to me. In the summer we have months of sunny days with no clouds at all, and even this far north get about 6 hours per day effective sun. In the winter we get 1-2, and have weeks with less than 1 per day. If I sized my arrays based on annual numbers, my batteries would be dead half the year. There are good calculators that do monthly charts based on local weather that are handy for planning.
I opted for a "grid tied" system because we had decent "net metering" plans here in Houston and the grid has become my unlimited storage for excessive power.

Adding a battery would not be cost effective , especially since I was able to install my 12.58 kW system for only $.47 a Watt!

I commissioned my system in June of 2021, and I now have built up a reserve of nearly 6 MegaWatts (I have a bill credit of $773 @ $.129 per kiloWatt) which can be used during the lower production months. With the grid being like an unlimited battery, yearly production estimates are useful .
 
In the summer we have months of sunny days with no clouds at all, and even this far north get about 6 hours per day effective sun. In the winter we get 1-2, and have weeks with less than 1 per day. If I sized my arrays based on annual numbers, my batteries would be dead half the year.

I pretty much have the same situation. I actually just wrote about that on my blog. What I did was go for optimal angle for spring/autumn, ignore winter (no sun), and put as much panels as possible/feasible/needed. This works pretty much perfectly, with optimal power generation in the most difficult periods, and more power than what I know what to do with in summer.
 
I pretty much have the same situation. I actually just wrote about that on my blog. What I did was go for optimal angle for spring/autumn, ignore winter (no sun), and put as much panels as possible/feasible/needed. This works pretty much perfectly, with optimal power generation in the most difficult periods, and more power than what I know what to do with in summer.
With Enphase Enlighten , you can play around with the orientation of each array and instantly see the monthly and yearly production estimates. I entered in different "tilt" angles to see how the monthly and yearly production outputs changed. 26° tilt was the optimum for my latitude and with a fixed array, but that only would gain me 0.5% of yearly production.

I then pretended that my array orientation was 0° azimuth (NORTH) and that would have reduced my yearly production by only 20%.

The image below is what the Enphase array builder looks like (accessed by clicking the little gear in Enlighten on the PC application)

enphase setup.png
 
Can you trust that unregulated grid in Texas? Look what happened last winter.
I lived in Texas for 43 years now. There are over 50 power providers in my area to choose from (only about 10 offer solar buyback), but most people fall for the plans with gimmicks. The best non-solar plans offer Energy at 5.8 cent a kW (plus the Centerpoint delivery charge of 4.6 cents a kW) . This will result in a 11 cents per kW delivered!

Last year, during the crisis in February, power was down for only 3 hours in my area. When I look at the yearly power outages in 2021, it probably amounted to a total of 6 hours. Many of the minor outages are because of trees falling on power lines. If I was really worried about the grid, it would be more economical to install a natural gas generator than a battery.

I am eyeing a Ford F-150 EV in 2024. With the 100 kW battery, it can power a home for 3 days. I can't see buying a battery wall ,which is rarely used, when I can buy an EV and get the best of both worlds.

I keep an old AC powered alarm clock in one of my bedrooms. Whenever the grid goes down, it stops and when the grid is restored, I can tell exactly how long the grid was down by calculating how far behind it is compared to the real time. This is helpful when power goes down when I am sleeping or not home.
 
Winter is pointless since there is no sun, and in summer I have too much no matter what the angle is.
I’m not as latitude challenged as Finland but that’s why vertical worked out for me (although I did it to keep snow off, summer was more than enough).
This chart is an interesting point:
Having panels facing two or three compass directions has the effect of a solar-tracking mount in that you get the max of each sub-array spread over the day. For example, 400W SE, 400W S, and 400W WSW ‘can’ act like 500W or if you’re lucky 600W tracking the sun in practice (even the SE panels will have minuscule amps to contribute in the afternoon on a full-sun day, and the overlapping panels will contribute more than a single facing 400W array as the sun moves and there’s no wear-items cuz nothing moves)

There are smarter-than-me people who say that all panels pointed south will acquire more wattage in a day. And considering they’re smart they are probably right. However, in practice my daily harvest experiment did two beneficial things according to the daily KWh summary on my charge controller: my sum daily watts harvested went up - not dramatically but substantially iirc like 20% but that comparison got obscured for relevance by lengthening days and partly cloudy weather. But I did get to play games with musical panels for 7 or 8 days. Second thing- and my reasoning for the experiment- I both achieved full charge earlier in the day (basically “running 100% on solar” midday) and I maintained fully charged several hours closer to sunset.

So if you’re like me and don’t/didn’t want to adjust panels periodically (assuming that’s why you want an optimal annual tilt) you can experiment and perhaps find a compromise arrangement and overpanel just enough to mask the compromise.

While the optimum year-round angle to the sun angle is different based on locale, the compromise of creatively over paneling may lend itself to your benefit as well.
Just some thoughts to consider- I don’t think what you’re doing is a totally bad idea; it works here in Vermont for me.
 
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I’m not as latitude challenged as Finland but that’s why vertical worked out for me (although I did it to keep snow off, summer was more than enough).
This chart is an interesting point:

Having panels facing two or three compass directions has the effect of a solar-tracking mount in that you get the max of each sub-array spread over the day. For example, 400W SE, 400W S, and 400W WSW ‘can’ act like 500W or if you’re lucky 600W tracking the sun in practice (even the SE panels will have minuscule amps to contribute in the afternoon on a full-sun day, and the overlapping panels will contribute more than a single facing 400W array as the sun moves and there’s no wear-items cuz nothing moves)

There are smarter-than-me people who say that all panels pointed south will acquire more wattage in a day. And considering they’re smart they are probably right. However, in practice my daily harvest experiment did two beneficial things according to the daily KWh summary on my charge controller: my sum daily watts harvested went up - not dramatically but substantially iirc like 20% but that comparison got obscured for relevance by lengthening days and partly cloudy weather. But I did get to play games with musical panels for 7 or 8 days. Second thing- and my reasoning for the experiment- I both achieved full charge earlier in the day (basically “running 100% on solar” midday) and I maintained fully charged several hours closer to sunset.

So if you’re like me and don’t/didn’t want to adjust panels periodically (assuming that’s why you want an optimal annual tilt) you can experiment and perhaps find a compromise arrangement and overpanel just enough to mask the compromise.

While the optimum year-round angle to the sun angle is different based on locale, the compromise of creatively over paneling may lend itself to your benefit as well.
Just some thoughts to consider- I don’t think what you’re doing is a totally bad idea; it works here in Vermont for me.
I only have experience with my one installation which I designed and built myself. I am using microinverters and I think that microinverters treat each panel as "independent contractors". As such, there is no influence from adjacent panels (as in a string inverter) and I can tabulate each panel. I don't know the subtleties of a charge controller since I don't have any batteries.

All my 34 panels are on the South Plane of my roof. I used a Solar Irradiance calculator and just changed the azimuth to see the yearly irradiance for EAST, SOUTH , and West azimuth at the optimum tilt for Houston (about 26°). The yearly irradiance for each m² was 55.45 KWh for South, 44.32 kWh for West, and 44.35 kWh for East. This shows that mounting 3 panels on the South face would provide 15% more yearly output than mount 1 panel on sides East, South, and West.

I ran the numbers for Burlington Vermont where the optimum fixed tilt angle was 45°. The results were almost exactly the same, there was 15% more power per m² if all panels were mounted on the South face than if they were divided on the East South and West faces. There was also an additional 15% reduction of power of Vermont compared to Houston.

My friend in Austin has panels mounted on all roof faces because he has a hip roof with limited area on each face. His total system hourly graph looks like a gumdrop (parabola). If mounting panels on all roof planes would be like simulating a tracking system, then there would be more of a flat-topped graph.

Below are the results from the calculator. If there are no trees or shadow on any roof plane, the South plane (180° azimuth) can't be beat in any month.

WeChat Image_20220204105902.pngWeChat Image_20220204105855.pngWeChat Image_20220204105844.png
 
mounting panels on all roof planes would be like simulating a tracking system, then there would be more of a flat-topped graph.
That’s with the one big factor not considered, very pronounced in my case: I cannot use 100% of the available power except on certain cloudy days if facing one direction.
I produce a lot less power midday with two direction facings, but in summer or a good sunny winter’s day I’m fully charged by 8 or nine instead of 11am, and I’m exceeding my draw to ?? within 45 mins of sunset.

The math and calculators are limited to a static condition which is useful but doesn’t always reflect in-practice uses. Plus you entered E and W not SE and SW

Of course a true ‘tracking’ array gets 100% longer. And of course four sides of a hip roof will suffer. However, overpaneling directionally has pretty clear results on my controller interface’s graph of watts harvested. I never suggested that was a even-steven replacement for a tracker- I said:
you can experiment and perhaps find a compromise arrangement and overpanel just enough to mask the compromise

I do know 400W single direction was not enough almost 1/2 the days, and 400W split facing 200W + 200W 90* different was enough 27 days of a month. The later afternoon gain seemed to be the most useful.
 
That’s with the one big factor not considered, very pronounced in my case: I cannot use 100% of the available power except on certain cloudy days if facing one direction.
I produce a lot less power midday with two direction facings, but in summer or a good sunny winter’s day I’m fully charged by 8 or nine instead of 11am, and I’m exceeding my draw to ?? within 45 mins of sunset.

The math and calculators are limited to a static condition which is useful but doesn’t always reflect in-practice uses. Plus you entered E and W not SE and SW

Of course a true ‘tracking’ array gets 100% longer. And of course four sides of a hip roof will suffer. However, overpaneling directionally has pretty clear results on my controller interface’s graph of watts harvested. I never suggested that was a even-steven replacement for a tracker- I said:


I do know 400W single direction was not enough almost 1/2 the days, and 400W split facing 200W + 200W 90* different was enough 27 days of a month. The later afternoon gain seemed to be the most useful.

If you have empirical data for your location, then it is a good argument for your conclusion. If clouds seem to roll in during the middle of the day (this happens in Houston from the prevailing South winds injecting moisture from the Gulf of Mexico into the atmosphere) then a more East facing azimuth may have better production.

Do you have total year production data from the panels on the different azimuths? It would be interesting to see how annual production compares. My panels are all on the surface which I made a skylight/roof- door to access and has a 4/12 pitch. The other roof planes are 12/12 pitches and not walkable.

PV Panel East View.jpg
 
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