Project- Portable Solar Generator for emergency use, (advice needed)

Re: Project- Portable Solar Generator for emergency use, (advice needed)

TeeKay wrote: »

I've been a silent reader of the forum for some time now. I'd like to thank all those that so graciously give their time and experience to aid others.

Welcome to the Forum TeeKay!

What I found in the box was a 200 watt Infomon panel spec'd at:
Max power: 200 watt
Max power voltage: 37.95
Max power current 5.27amp
Open Circuit Voltage: 45.53
Short Circuit Current: 5.69

I had planned (already ordered) to use a Prostar 30 charge controller, allowing for an additional panel. It's my understanding that the voltage output from the panel I was sent will not work with the Prostar 30.

My questions at this point are,
Was this panel worth $300 shipped?
Is it comparable in output to what I thought i was purchasing?
Can I change over to a Morningstar SunSaver 15 Amp MPPT Solar Charge Controller and still be able to proceed forward with the project?

I don't know anything about the brand--But you got a pretty good deal including shipping (shipping can be a killer). Assuming it got to your place without getting shattered or the back covering getting pierced. More or less, almost all panels >100 Watts (except for a very few) are going to have Vmp>>17.5 volts. So--It was not unexpected that you received this panel.

Your two, low cost/good quality choices for MPPT Charge Controllers. The Morning Star 15 amp MPPT charge controller is very good. You should get the Remote Battery Temperature Sensor--The internal sensor tends to read hot which can slow down the charging of the battery bank. If you do not plan on adding panels, then the 15 amp controller is enough.

If you plan on adding one (or possibly two) more panels--Then you should look at the Rogue 30 amp 12/24 volt MPPT charge controller (and run all panels in parallel). The Rogue does include a digital meter as part of the base price (as far as I know).

And, if you do add panels, you will need to make sure there Vmp matches (within ~10% or better) for best power production (i.e., don't let them ship you the panel you thought you were buying).

For the Rogue, roughly, the maximum wattage of panels I would suggest for 12 volt system:

• 30 amps * 14.5 volt batt charge * 1/0.77 panel+controller derating = 564 Watts or so

You could round up to 600+ watts--During the middle of cool sunny days, the controller will max out at ~30 amps and you will loose a bit of harvest during this time (the controller will be just fine--MPPT controllers are designed to limit their maximum output current).

Have you decided what you want to power? Battery Bank Size, inverter, etc.? I would also suggest a Battery Monitor would be nice. If AC power, you can get a Kill-a-Watt meter (or similar) pretty cheaply too.

-Bill

Re: Project- Portable Solar Generator for emergency use, (advice needed)

Tony,

It is very difficult to estimate battery capacity/usage with just a precision voltmeter (which, if I understand correctly, the Midnite unit is--Just a quick guess). I would suggest a nice DC Current Clamp Meter instead... This one is Cheap (always important around here) and has the normal other DMM type function for ~$60.

If you go with flooded cell battery(ies), you can always use a good Hydrometer for accurate state of charge measurements. If you go with sealed/AGM type--A Battery Monitor is much better deal (but is hard to justify for a smaller system). You could also go with a straight Amp*Hour/Watt*Hour meter too (those models are uni-directional, do not totalize Amp*Hours charging/discharging).

Regarding battery capacity--A good starting point is 5% to 13% rate of charge. Assuming ~77% efficiency for solar panels+charge controller:

• 200 watts * 1/14.5 volts * 0.77 derating * 1/0.05 rate of charge = 212 AH @ 12 volts
• 200 watts * 1/14.5 volts * 0.77 derating * 1/0.10 rate of charge = 106 AH @ 12 volts
• 200 watts * 1/14.5 volts * 0.77 derating * 1/0.13 rate of charge = 82 AH @ 12 volts

For a system that cycles daily--I would suggest around 10% rate of charge--Quickly recharging the battery bank after use.

If you need a larger battery bank (emergency, heavy/short loads), then you could go to the 5% rate of charge. AGM's are more efficient than flooded cell and have lower levels of self discharge--So might be better for larger capacity battery bank (note AGM are ~2x the cost of flooded cell).

Part of the discussion also needs to include your power needs. Flooded Cell batteries are good for about C/8 maximum continuous discharge. And can supply C/2.5 current for starting surges, etc...

Some AGMs can supply upwards of C*4 worth of current (such as a computer UPS which can supply power for ~15 minutes).

So, for example 106 AH @ 12 volt flooded cell battery running an AC load:

• 106 AH * 12 volts * 0.85 inverter eff * 1/8 discharge rate = 135 watt continuous AC load
• 106 AH * 12 volts * 0.85 inverter eff * 1/2.5 discharge rate = 432 watt starting AC load

-Bill

Re: Project- Portable Solar Generator for emergency use, (advice needed)

Also, want to add a warning--PV Panels are thin (~1/8") tempered glass. Pulling around on a trailer and setting up in the sun on a windy day can put your panel(s) at risk of damage/falling... some sort of covering/drive in anchor may be helpful for your situation.

And how much power can you gather? From PV Watts for Detroit Mich... Fix array tilted to latitude of ~43 degrees from horizontal:

Month    Solar Radiation (kWh/m 2/day)
1      2.90     
2      3.59     
3      4.13     
4      4.84     
5      5.52     
6      5.58     
7      5.42     
8      5.48     
9      5.18     
10      3.96     
11      2.59     
12      2.15     
Year      4.28      

For example, February is 3.59 hours of sun per day. Your system woudl generate (on average in good weather):

• 3.59 hours of sun * 200 watts * 0.52 end to end efficiency = 373 WH per day in February

If you were to move the panel to track the sun, you can get more power--For example, the same setup but two axis tracking (you will not do that well manually):

Month    Solar Radiation (kWh/m 2/day)
1      3.50     
2      4.29     
3      5.04     
4      6.20     
5      7.74     
6      7.99     
7      7.66     
8      7.52     
9      6.49     
10      4.74     
11      3.01     
12      2.49     
Year      5.56      

So, for being so far north--You can get more power if you baby sit the system (move every 30-60 minutes) and track the sun.

-Bill

Re: Project- Portable Solar Generator for emergency use, (advice needed)

TeeKay wrote: »

Bill,
I have to admit, I'm confused about some of which you just told me.
How will a DC clamp meter be used in such a way as to give me a more accurate idea of charge state versus a voltmeter like the Midnight? And Watts Up or Dr. Watson?

To estimate the state of charge of a battery bank, you need to measure the resting voltage of the battery. No load/charging for 3 or more hours. It is very difficult to accurately estimate the battery bank's state of charge while under charge or load.

With a DC Clamp Meter, you can measure the current into or out of the battery and estimate how much charge you will use... A 100 AH battery discharged at 10 amps will, roughly, discharge the battery 10% per hour.

A Watts Up or Doc Watson will measure the actual Amp*Hours you are drawing out of the battery (amps*hours--1h*10amps + 2h*5amps = 20 AH drawn down).

A battery monitor will count up or down depending on the direction of current flow (in Amp*Hour, percent state of charge, etc.).

I plan to install the panels permanent on the barn roof and then just move the battery bank via a wagon/garden cart. Not the way I'd plan for long term usage, but fine for an emergency backup device. Given the panel will be mounted, I'll reduce risk of breaking it, but loose the ability to track. Are adjacent reflective surfaces ever used to increase PV?

Sounds reasonable... Use a DC (or other non standard-120 VAC) plug to allow quick disconnects from the wagon.

People have seen significant power increases from white sand or reflections off of snow. The problem with adding mirrors include, tracking issues, and possible excessive heat (most solar panels will void their warranties if you use reflectors).

So the MS 300 Watt TSW inverter would need to be fused 85a.
Using your math I'd need 210a fusing for the 1500 watt inverter, and that's without allowance for surge, correct? Can you recommend a model/brand/type for me?

The manuals for the inverters will list the exact values... You only need to fuse for continuous loads, not for very short (few seconds) of loading. There are issues of voltage drop--Short/heavy cables for inverters (and for charge controller to battery connection too) to minimize voltage drop (12 volt systems especially need low voltage drop as you have about 1 volt to work with).

I have read a few times where advise is given to those on limited budget to use a small, good quality pure sine inverter backed up with a higher power/lower quality modified sine for the bigger work. Do you agree with this advise?

That works well for many people. Here is a bit more reading:

All About Inverters
Choosing an inverter for water pumping

MSW inverters can cause overheating with some devices--Wall mount transformers, some induction motors (like fridge), etc... But it is difficult to predict which will have problems... Old 80/20 rule, 80% will probably be OK and 10-20% have problems. Figuring out which is which is the problem.

-Bill

Re: Project- Portable Solar Generator for emergency use, (advice needed)

TeeKay wrote: »

Is there a chart or graph you could refer me to that would represent percentage of capacity by voltage?

A generic chart for Lead Acid at 77F is in the Deep Cycle Battery FAQ:



[TH="width: 132, bgcolor: #FFFFFF, align: center"]State of Charge[/TH]
[TH="width: 132, bgcolor: #FFFFFF, align: center"]12 Volt battery[/TH]
[TH="width: 132, bgcolor: #FFFFFF, align: center"]Volts per Cell[/TH]


100%
12.7
2.12


90%
12.5
2.08


80%
12.42
2.07


70%
12.32
2.05


60%
12.20
2.03


50%
12.06
2.01


40%
11.9
1.98


30%
11.75
1.96


20%
11.58
1.93


10%
11.31
1.89


0
10.5
1.75




Note that cell voltage can be modeled by this equation:

Specific gravity = single-cell open-circuit voltage - 0.845 (example: 2.13v – 0.845 = 1.285)
Or
Single-cell open circuit voltage = specific gravity + 0.845

And, note that different batteries (by type, model, mfg) have different maximum specific gravity. I ran across this page on why different types of batteries have different starting s.g. fills.

Specific Gravity vs Applications
1.285 Heavily cycled batteries such as for forklifts (traction).
1.260 Automotive (SLI)
1.250 UPS – Standby with high momentary discharge current requirement.
1.215 Geral applications such as power utility and telephone.

As mentioned earlier, the specific gravity (spgr.) of a fully charged industrial battery, or traction battery, is generally 1.285, depending on the manufacturer and type. Some manufacturers use specific gravities as high as 1.320 in an attempt to gain additional Ah capacity, but at the cost of a shorter cycle life.

...

Higher Gravity = vs Lower Gravity =
More capacity / Less capacity
Shorter life / Longer life
Higher momentary discharge rates / Lower momentary discharge rates
Less adaptable to "floating: operation / More adaptable to "floating" operation
More standing loss / Less standing loss

What does the "mps" refer to in 1h*10mps? Typo for amps? Lot's of acronyms in this field, so I gotta ask

You got me. Most of the time I am perfect--Ask my wife and kids. :roll: I will fix the original post.

Is the Doc Watson or similar programmable with the AmpHrs of the bank?

No, it is just a meter that counts Amp*Hours from zero and up. Intended to be a bench top meter (Radio Controlled cars/planes/etc.).

The problem with battery banks is that they are a bit like a gas tank in a car without the fuel gage. A true Battery Monitor is sort of like placing a fuel totalizer in the fuel line to the gas tank... And all draw down and fill ups occur through the fuel line. It is not perfect and the meters usually reset to "100%" full if they see (for example) >14.5 volts for 2 hours to keep the meters from drifting too far.

I realize that battery monitors are not cheap--And many people do manage their battery banks pretty successfully with just a good volt meter.

For people with expensive (large) battery banks, and especially those with sealed batteries (no specific gravity to read), I highly recommend Battery Monitors (Victron is another good brand). There are just so many ways to kill a battery bank either directly by user error, or by spouse/kids/guests that leave everything on in a small cabin/off grid home. It is so much easier to tell them to call you / turn off loads / start the generator if the State of Charge is less than 50% and turn off the genset once the meter reads ~80-90% state of charge.

But--for small systems--yea, it is difficult to justify the price of a "real" battery monitor.

-Bill

Re: Project- Portable Solar Generator for emergency use, (advice needed)

Yep, Vmp~38 volts for a 24 volt Lead Acid battery bank and standard MPPT/PWM controller is "close enough" for solar work.

And if you have cold batteries and hot weather, it will probably charge/equalize a bit better than a Vmp~35 volt panel...

Either you are looking at about an 8% loss using a PWM controller vs MPPT (35v/38v=0.92 "efficiency" difference) with this panel (not very much in the grand muddy that is solar estimating).

-Bill