Aiming at the sun (best fixed angle)

icarus

Re: Aiming at the sun (best fixed angle)

Don't we wish we could all be at solar noon all day? LOL.

Personally, I would take 10am/2pm angle over a noon all else being equal,,at the equinox if I had a fixed array.

Gloves

Re: Aiming at the sun (best fixed angle)

According to this, I think that Fremont, CA is a good candidate to keep the median angle as a start.




Fremont, CA climate is mild during summer when temperatures tend to be in the 60's and cool during winter when temperatures tend to be in the 50's.

The warmest month of the year is August with an average maximum temperature of 78.60 degrees Fahrenheit, while the coldest month of the year is December with an average minimum temperature of 41.70 degrees Fahrenheit.

Temperature variations between night and day tend to be moderate during summer with a difference that can reach 20 degrees Fahrenheit, and fairly limited during winter with an average difference of 16 degrees Fahrenheit.

The annual average precipitation at Fremont is 14.85 Inches. Rainfall in is fairly evenly distributed throughout the year. The wettest month of the year is January with an average rainfall of 2.97 Inches.

Looking forward to a dry weekend so I can finish the setup. I got it all planned out. And yes, it will be easily adjustable.

niel

Re: Aiming at the sun (best fixed angle)

do not confuse weather conditions with the optimal solar angle as the sunlight approaches your location at a specific angle no matter what. now if the mornings are say foggy then one may want to concentrate in reaping that energy that impedes you location from a different direction that is geared more to the west, but the solar angles do remain the same as it arcs across the sky and if aiming anywhere except in a southerly direction this will impact the elevation angles for the pvs to be increased as that will see the sun below the solar noon angle. if one would aim a pv at sunrise or sunset one would need a pv at around 80-90 degrees. this is independent of weather conditions at the time and i only illustrate that if an off angle has more unimpeded sunlight then you aim for it, but the arc that light hits your location from sunrise to sunset does remain unchanged except when the seasonal adjustments are necessary due to the earth's position around the sun.
i am probably being a bit confusing here in trying to convey what i mean in such a way as to make you understand what i'm saying so i will stop for now.

dwh

Re: Aiming at the sun (best fixed angle)

I think what niel is trying to say is that 37 is just right when the sun is at noon, but the sun is only at that spot for a short while.

So standing the panel up a bit more will get more of the "before noon" and "after noon" - both of which last a lot longer than "exactly noon" so in the end you get more harvest.

Gloves

Re: Aiming at the sun (best fixed angle)

I hear you guys on the 37°...
But I'm having the hardest time visualizing the non-noon sun not at 37°

At Equinox:
This sun goes across the sky at a consistent 37° from E to W. It doesn't go N to S
(thus needing to adjust the angle from 37°) For people who have a sun-tracking
system, I imagine the system only tilts E to W not up/down.

The sun stays stationary, and the Earth only rotates steadily on it's axis...

I'm imagining that during winter and during summer you can adjust the solar panels
but not by the full ° of the Earth's tilt because then the panel would only be getting
full exposure at exactly noon.

I might need a visual of some sort to better understand your theory.

BB.

Re: Aiming at the sun (best fixed angle)

Here is a website (University of Oregon) that will give you various charts about the sun arc across the sky...

You can generate many types of charts, and it will output a PDF file for you to review/print.

-Bill

Gloves

Re: Aiming at the sun (best fixed angle)

I've never taken an astronomy class in my life... This make no sense to me but, I'm going to roll with it.

Color sun path curves: Green
Color hour curves: Blue
Color chart label: Magenta

My Solar Path Chart

According to this chart, I should keep my solar panel pointed at ~50° ???

I guess this is why I posted in the beginner forum.
I'm going to need help deciphering this chart for my optimal angle.


P.S. Thanks for the link.

icarus

Re: Aiming at the sun (best fixed angle)

Go outside at the equinox (or in your imagination) the sun will rise directly east, and set directly west, and the time from sun rise to sun set will be exactly 12 hours. (hence the equinox)!
The height at solar noon is directly related to the number of degrees north or south latitude your installation is.

Now picture the summer solstice (or winter inverse) The sun rises north of due east, and sets north of due west, how far is related to how far north your are until you get to just near the arctic circle, where the sun rises just east of north, and sets just west of north. Cross the arctic circle, and of course the sun never sets at the solstice.

Stated better than I could:

The annual change in the relative position of the Earth's axis in relationship to the Sun causes the height of the Sun or solar altitude to vary in our skies. Solar altitude is normally measured from either the southern or northern point along the horizon and begins at zero degrees. Maximum solar altitude occurs when the Sun is directly overhead and has a value of 90°. The total variation in maximum solar altitude for any location on the Earth over a one-year period is 47° (Earth’s tilt 23.5° x 2 = 47°). This variation is due to the annual changes in the relative position of the Earth to the Sun. At 50 degrees North, maximum solar altitude varies from 63.5 degrees on the June solstice to 16.5 degrees on the December solstice. Maximum solar height at the equator goes from 66.5 degrees above the northern end of the horizon during the June solstice, to directly overhead on the September equinox, and then down to 66.5 degrees above the southern end of the horizon during the December solstice

(http://www.physicalgeography.net/fundamentals/6h.html)

So assuming you are living where I live ~50 degrees north,the highest the sun gets ever, during the summer solstice is 63.5 degrees above the horizon, the lowest being only 16.5.


Point is, any fixed array is a series of compromises over the day, and over the course of the year. The further north (or south) you are from the equator the funkier the problems become. Given your location in Cal. the problems, are less of a problem.

The next clear day, go out with a protractor and sight the sun angles over the course of the day to fix in your head what you know intuitively.

Gloves

Re: Aiming at the sun (best fixed angle)

It's installed and working!

120W of solar goodness.
It has already taken my batteries from 11.7V to 12.8V during the first 3 days.

I think I figured the best way to install; I used a 2x4 with door hings for the front base.

On the back I used 2, 2x4 blocks with 2 slotted-angle poles for support and easy adjusting.


I took this picture today, notice how flexed the wind generator blades are



So the the roof doesn't leak from all the screws I slathered the bottom of the 2x4s with Henry.

icarus

Re: Aiming at the sun (best fixed angle)

I would be worried about your batteries if they were at 11.7 vdc for very long!

http://www.batteryfaq.org/

http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

11.7 is ~ 30% State of Charge. Batteries left below ~ 90 of SOC will sulphate very quickly and die a very premature death.

Tony

Gloves

Re: Aiming at the sun (best fixed angle)

after reading through a few of those links...
it seems I'm not to let my batteries go below 12V and full is about 12.75?

My charge controllers cut off at 13V.

BB.

Re: Aiming at the sun (best fixed angle)

It is a bit more complex than that...

~15.0-15.5 volts equalization (flooded cell only)
~14.2-14.5 charging (AGM towards 14.2 volt range)
~13.7 volts "float" (hold battery at charge/no power usage)
~12.7 volts fully charged resting voltage (~2-3+ hours)
~12.0 volts ~50% discharged resting voltage

So, that 12.7 volts--That was after several hours of no load around 77F?

What do you mean by:

My charge controllers cut off at 13V.

For automotive type chargers--is is rare for them to get in the 14.5 volt range... For cars, they tend to max out around 14.2 volts (if it is decently regulated charger). At 14.5-15+ volts, some "12 volt devices" (12 volt laptop computer adapters, etc.) actually can be damaged.

Not taking your battery below 12.0 volts--is the resting voltage--If you have significant discharge current, your battery voltage may depress below 12 VDC and yet not be 50% discharged.

The fundimental recommendation is to keep the batteries, roughly, > 75% state of charge and if they go below 75% state of charge, try to get them recharged the next day and not let them sit around for days/weeks/months below 75% SOC or they will sulfate (and die).

People recommend not taking a battery below 50% state of charge very often as the batteries do not cycle as many times the deeper the discharge. However, for weekend cabins and RVs--the batteries will probably "age out" before they "wear out". But--in any case, you should get them recharged ASAP (next morning with solar or backup genset).

Some other recommendations--Don't let the battery go below 20% state as one or more cells may actually reverse charge and die.

And don't overcharge the batteries either... Equalize only when needed (if flooded cell)--When the cells are unbalanced (spread in specific gravity of 0.030 or greater between high and low cell). Only equalize until the SG stops rising (check every 30-60 minutes).

-Bill

icarus

Re: Aiming at the sun (best fixed angle)

In addition, any battery testing needs to be done with no load and no charge current, difficult to with a battery on a PV system.

A battery measured under load or under charge will give very false information.

Gloves

Re: Aiming at the sun (best fixed angle)

I'll have to double-check my charge controllers to see where they turn off. I thought that my turbine switches off after batteries are at 13.0 V and i don;t remember when my Solar shuts off, i'll know in a couple days.

So full can be up to 14.5V?
I'm sure a 750W Black & Decker inverter can easily take 14.5V. Especially since I don't use more than 250W at a time. It's only been powering 2 laptops.

To recap best practices for my 2 T-105 flooded batteries:

• 12V (absolute lowest it should ever be)
• 13.25V (about 50% should let it charge some before using more)
• 14.5V (absolute fullest it should be)

BB.

Re: Aiming at the sun (best fixed angle)

Gloves wrote: »

To recap best practices for my 2 T-105 flooded batteries:

• 12V (absolute lowest it should ever be)
• 13.25V (about 50% should let it charge some before using more)
• 14.5V (absolute fullest it should be)

Not really... There are resting voltages... That is the battery after it has sat for a few hours at a stable 77F (standard conditions. From this Battery FAQ:

Deep Cycle Battery FAQ

12.70 volts 100% state of charge
12.37 volts 75% state of charge
12.06 volts 50% state of charge
11.58 volts 20% state of charge
10.50 volts 00% state of charge

Those are really the only accurate way to gauge a battery state of charge (other than using a hydrometer for flooded cell batteries).

If you have a load on the battery when measuring the voltage, you will probably read somewhat lower voltages.

For charging:

Bulk Charge - The first stage of 3-stage battery charging. Current is sent to batteries at the maximum safe rate they will accept until voltage rises to near (80-90%) full charge level. Voltages at this stage typically range from 10.5 volts to 15 volts. There is no "correct" voltage for bulk charging, but there may be limits on the maximum current that the battery and/or wiring can take.

Absorption Charge: The 2nd stage of 3-stage battery charging. Voltage remains constant and current gradually tapers off as internal resistance increases during charging. It is during this stage that the charger puts out maximum voltage. Voltages at this stage are typically around 14.2 to 15.5 volts.

Float Charge: The 3rd stage of 3-stage battery charging. After batteries reach full charge, charging voltage is reduced to a lower level (typically 12.8 to 13.2) to reduce gassing and prolong battery life. This is often referred to as a maintenance or trickle charge, since it's main purpose is to keep an already charged battery from discharging. PWM, or "pulse width modulation" accomplishes the same thing. In PWM, the controller or charger senses tiny voltage drops in the battery and sends very short charging cycles (pulses) to the battery. This may occur several hundred times per minute. It is called "pulse width" because the width of the pulses may vary from a few microseconds to several seconds. Note that for long term float service, such as backup power systems that are seldom discharged, the float voltage should be around 13.02 to 13.20 volts.

When charging, the battery voltage is a combination of its present state of charge and how much current you are pushing into the battery bank.

To know when a battery is fully charged, at the "absorb" voltage, the current will reduce from the maximum output of the charger to just a few percent of the output current as the battery reaches equilibrium and converts most of the charging energy to out-gassing (generating hydrogen and water). Depending on the output voltage/current of the charger, size of battery bank, and such--this make take 1-4 hours or so...

If you where monitoring with a hydrometer, you would see that the cells reach their maximum specific gravity and stop going any higher--At this point you should stop charging and/or reduce the voltage to "float" voltage (maintain charge).

In theory, you want to operate your battery roughly around the 80-90+% state of charge... You don't want to take it to 100%+ (equalization--heavy/overcharging) every day--that can be very hard on a battery bank. Equalization should only be done when needed (roughly more than 0.030 s.g. between the high and low cells--if flooded cell battery). That should not normally be more than ~1 time per month or so...

And, you don't want to let the battery sit for days/weeks/months below 75% state of charge. The longer it sits below 75% state of charge, the more the sulfates "harden" (crystallize) and recharging cannot recover that lost capacity...

I sort of sumerize it as you should charge the next day or so if you are below 75% state of charge. If you are below 50% state of charge you should recharge back to ~80-90% early the next morning with a genset (if there is not enough sun).

If the batteries are near 20% state of charge--You should cut the loads immediately and/or fire up the genset / AC charger and recharge the bank.

You can let the solar panels finish of the last portion of the charging the rest of the day.

Just rough rules of thumb... Day to day "damage" is small, but cumulative. Taking a battery below ~20% state of charge runs the risk of "reverse biasing or reverse charging" one or more cells. That can kill a cell/battery immediately (or the battery may limp along for a few days/weeks then die).

The reason we use 20% is there can be as much as 20% capacity variance between cells (cell capacity does not always match 100%)--While some batteries may be at 20% state of charge, one or a few cells may be approaching 0% state of charge.

Again, the above is just a rough set of guidelines. Not everyone will agree with me--And I have probably taken some liberties to simplify them down to the above.

Also note that it is not always easy to measure specific gravity... AGM, Gel, and other sealed batteries cannot be measured with a simply hydrometer.

And battery meters (which I highly recommend--especially for sealed batteries) have their own issues with inaccuracies and how the determine when a battery is full (plus battery capacity reduction as they near end of life).

Read through the battery faq above, and the one below, and you can get more of the details and underlying information.

www.batteryfaq.org

-Bill

Gloves

Re: Aiming at the sun (best fixed angle)

BB, you have convinced me to look into getting a 2nd panel.

So I did.

120W (installed)
130W (on it's way)

Total: 250W

Tell me if this is about right. (i'm doing some rounding here)

Given 4 solid hours of light a day... (can i expect better than that?)
I should be generating 1KWh

I use 15KWh (fairly consistently) so I'm generating ~6% of energy
consumption with said setup.

BB.

Re: Aiming at the sun (best fixed angle)

From Post #11 in this thread, based on SFO airport (you are in a sunnier area) hours of sun by month:

1, 3.09
2, 3.99
3, 4.68
4, 5.81
5, 6.20
6, 6.24
7, 6.76
8, 6.21
9, 5.97
10, 4.72
11, 3.35
12, 2.82
"Year", 4.99

So, roughly 3-6+ hours per day depending on season.

Also, there are significant losses with batteries (flooded cell 0.08 eff) and AC inverters (0.85 eff). So, from solar panel to charge controller to battery to AC inverter, you are looking at:

• 3 hours * 250 Watts * 0.52 sys eff = ~750 Watt*Hours per day in winter
• 6 hours * 250 Watts * 0.52 sys eff = ~1,500+ Watt*Hours per day in summer

That is useful AC power per day by season... The reality is that you will have a difficult time using 100% of that amount every day.

For an off grid home--you would probably plan on a base load of 50-75% of your "available power" and plan on using a bit more on Wash Day and such...

-Bill

icarus

Re: Aiming at the sun (best fixed angle)

Using my 50%*4 rule of thumb,

250/2*4=500 watt hours on average of harvest.

Even the 50% rule is a bit optimistic in my experience since as the controller ramps down as the battery comes close to full you end up leaving more potential energy "on the table".

You can mitigate that some what by time shifting your loads so that you use power when the sun shines, leading to a more efficient harvest.

As I think I have said before in this thread, we have 400 watts of PV, and on an "perfect" day we can generate 1-1.5 kwhs. On average, 12 months, we use ~6-800 wh, and generate just about that much.

Tony

Gloves

Re: Aiming at the sun (best fixed angle)

icarus wrote: »

Using my 50%*4 rule of thumb,

250/2*4=500 watt hours on average of harvest.

Even the 50% rule is a bit optimistic in my experience since as the controller ramps down as the battery comes close to full you end up leaving more potential energy "on the table"

TONY! ...

FIFTY-PERCENT!!! OUCH! Capturing energy is SO difficult!
How does the power company do it?

- - - - - - -

Couple of things, I was talking with a guy who said that T-105s are ok, but I should look into getting batteries that are called, "Sweet 16s" any idea what he's talking about?

icarus

Re: Aiming at the sun (best fixed angle)

I'm sure he is talking about L-16 batteries. I would not recommend getting any at this point. Consider your current batteries as your "starter set". L-16s are much bigger, more expensive. Remember, batteries should be sized for the charge current of the PV and the load. To big batteries with two small a PV is a recipe for killing a battery bank!

As for the 50% rule. Remember you have loses everywhere. First, Pvs seldom put out 100% of rated, 80% is a much more realistic average. Couple that with basic battery chemistry that requires you to generate ~120 ah for every 100 ah of load. So right out of the gate, you are down ~40% from nameplate. Add in charge controller loses, wiring loses and inverter loses 50% is pretty optimistic.

A grid tie system comes closer to 90%. That is the penalty one pays for a battery based (off grid) system.

Tony

Cariboocoot

Re: Aiming at the sun (best fixed angle)

Gloves wrote: »

TONY! ...

FIFTY-PERCENT!!! OUCH! Capturing energy is SO difficult!
How does the power company do it?

Actually the utility companies suffer the same sort of massive losses between generation and point of use in some cases. Line loss is a problem for all power systems!

Couple of things, I was talking with a guy who said that T-105s are ok, but I should look into getting batteries that are called, "Sweet 16s" any idea what he's talking about?

Tony is 100% correct; for a first set, stay away from the "tall case" L16 batteries. Get some inexpensive "golf cart" type T105's. It is so easy to damage the first set of batteries you work with!

Gloves

Re: Aiming at the sun (best fixed angle)

icarus wrote: »

I'm sure he is talking about L-16 batteries. I would not recommend getting any at this point. Consider your current batteries as your "starter set". L-16s are much bigger, more expensive. Remember, batteries should be sized for the charge current of the PV and the load. To big batteries with two small a PV is a recipe for killing a battery bank!

Tony

Are u guys telling me this hobby is just getting started? :O

BTW - this is a glorious sun-shiny Thanksgiving day here in CA!

::Sent from BlackBerry