Thoughts on this system

offgridcabin

I put this system together online today. I'd be interested in comments. Cabin is at 8,000 feet. 13 deg F lows in winter. Not accessible Dec to March. 2 Stories. Low Electrical needs currently. Will add over time.

The system: Trojan T105 6 V 225 AH x 8 OutBack VFX3648 3600 W 48V pure sine inverter OutBack FM60-150Vdc MPPT Charge Controller Solar World SW 320 Mono 320W Solar Panels x 3 Iron Ridge Top of Pole Mount (3 Panel)

All for just under $5K incl shipping.

Balanced? Makes Sense? What am I missing? Can it handle an efficient electric refrigerator/freezer. (my alternative is propane. expensive)

Thanks

Photowhit

I'd suggest your system is a bit under paneled, the Solar world 320 watt panels have a NOCT value of 244.5 watts (Normal Operating Cell Temperature) so roughly 750 watts peak on summer days so should produce about 15 amps or about 6.7 % of your battery bank (750/48) Should be fine for weekend use.

We it support a fridge depends on what other loads you will have, also local climate...

Mountain Don

It all depends on what you use.  That is very similar to our system; the number of batteries is the same but ours are in a 24 volt configuration. Even less PV capacity. But for us it has worked well for 6+ years. We are frugal consumers. Part time use for most of the year, heavier, more continual use in June thru August. Maximum draw down for us is 15%. Often less.

So we are either under paneled or over batteried.  I see it as being over batteried. Reason for that is winter. Cold reduces battery capacity big time. We snowshoe in for weekends and the system works for us.  We have pretty good sun most of the year; NM. 8800 feet. We also have a Honda gen just in case. 

We use a propane fridge. Possibly a DC Danfoss could work for us, but I would want more PV in that case.  At present we recharge and get into float each average day. I don't think regular use of an electric fridge would permit the same dependable full charge daily w/o more panel capacity. Or a tracker could do that too.

Thinking about it there is little doubt that if I was doing this all over today I would buy more panels to begin with. They are way cheaper today than 6+ years ago. 

offgridcabin

I currently have 8 indoor LED lights 9 W each 60 W equiv.  2 Ext LED lights 16 W & 100 w equiv.  LED TV 41 W SAT TV box 36 W. 
Some phone or other recharging as needed. 

Pretty low low needs so far. 

BB.

Yes, those loads are pretty small at this time... However, we also need to know the hours per day of usage. A Kill-a-Watt meter can make these measurements much easier:

http://www.solar-electric.com/kiacpomome.html

Knowing Watts is like knowing Miles per Hour... Without knowing the time, we really cannot estimate how much fuel (energy or Watt*Hours) you are using:

8x 9 Watt LEDs * 5 hours per night = 360 Watt*Hours per day
2x16 Watt LEDs * 12 hours per night = 384 WH per day
41 Watt TV * 5 hours = 205 WH per day
36 Watt Sat Box * 24 hours per day (if not turned off) = 864 WH per day
23 Watts * 24 hours per day (inverter just turned on) = 552 WH per day
===============================
2,365 Watt*Hours per day

My guesses above--But that is not a small amount of power for an off grid cabin (no refrigerator, no cell phone charging, no water pumping, etc.).

You have 3x 320 Watt solar panels (hopefully in series)--How many hours of sun per day for "break even":

• 2,365 WH per day * 1/0.52 typical off grid system eff * 1/960 Watt solar array = 2.5 hours per day of "sun"

Ok--From that point of view, assuming my numbers are anywhere near accurate (or over estimating power usage), you should have enough sun to keep up with the loads you have (except winter for most regions).

If you can let us know where your cabin is located (roughly, near what major city)--We can look at the sun for your location.

The other thing we like to do is size the solar array for the battery bank. Large battery banks need larger solar arrays for proper charging. 5% to 13% is what we start with. 5% can work OK for an off grid weekend/seasonal cabin. 10% or more is better for a full time off grid home.

• 225 AH battery bank * 59 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge =862 Watt array minimum
  
• 225 AH battery bank * 59 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 1,724 Watt array nominal
  
• 225 AH battery bank * 59 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 2,241 Watt "cost effective" maximum array

So--You are >5% minimum array (960 Watts for your system)--That looks OK for weekend/seasonal usage. At this point, a 48 volt system is pretty large for your needs--But if you plan on building out (adding a second string of batteries, more solar panels, more loads), you will have a very capable system (suggest ~3,300 Watt*Hours per day as an efficient off grid cabin/home with refrigerator, well pump, clothes washer as a starting point).

Your thoughts?

-Bill

offgridcabin

Cabin is near Zion National Park and Kolob Reservoir.  Solar Radiation kWh/m2/day annual avg 6.07.  Dec. low 3.81, June high 8.12.

I appreciate all of the knowledge that has gone in to the responses so far.  I will be reading and re-reading to make sure I understand it.
It sounds like another panel or 2 might be in order.  With this it seems I could run an electric refrigerator/freezer.  I'd rather put money into my solar system than into a propane refrigerator as there are more potential uses for the electricity than the propane. 

petertearai

Yep go electric fridge and more panels . 

BB.

In general, you will have to add the solar panels in "matched strings" based on your battery voltage and solar charge controller.

For example, many large format panels are Vmp~30 volts... You need the Vmp-array>=72 volts to charge a 48 volt battery bank reliably. So, 3x more panels in series would do it... There are panels that range from ~200 watts to larger panels with Vmp~30 volts--You just need to match the Vmp-string when putting in parallel with the other original panels (match Vmp-string within 10% or better). (matching panels in series, you need to match Imp within 10% or better).

If you get a full size energy star refrigerator (365 kWH per year = ~ 1 kWH = 1,000 WH per day.

Say you want 4,000 WH of AC power per day--Roughly batteries are designed to 1-3 days of storage and 50% maximum discharge (for Lead Acid Batteries). 2 days of storage is usually a good optimum:

• 4,000 WH per day * 1/0.85 inverter eff * 1/48 volts * 2 days storage * 1/0.50 maximum discharge = 392 AH @ 48 volt battery bank

So--If you where going to go with a 120 VAC refrigerator and some other loads, I would be suggesting adding a second string of batteries (other issues, mixing old/new batteries, paralleling batteries need to watch state of charge with a hydrometer, suggest a DC Current Clamp meter () to ensure batteries are sharing loads/charging current.

And add solar panels too...

Your existing bank would probably work well enough for you to test/measure out your system (real loads, new refrigerator, etc.).

-Bill

Mountain Don

Am I correct to assume the setup includes a Mate so the VFX can be programmed?

sridharTS

in off grid system, batteries and charger controller is used.
IF we choose inverter for off grid system, i have one question.
String inverter shall i use it for off grid?

BB.

String inverter--I guess I would call them "Micro Inverters" (a smaller 200-300 Watt Grid Tied inverter per panel connected to AC utility power).

Normally, I would not use them, however, it is possible--You get an Off Grid inverter designed to work with GT inverters "back feeding" the Off Grid inverter (yes, in many cases, you can push power "backwards" through an off grid inverter and actually recharge the battery bank).

This is not a "simple" setup. If you have the wrong type of off grid inverter, it is possible to overcharge the battery bank and cause the batteries to fail or even catch fire. You need some way to turn off the battery charging. You can put a dump controller on the battery bank (like used for a wind turbine). You can have a battery charge controller that turns off the AC power to the GT inverter strings. Or, you get an Off Grid inverter that can change its output frequency (50 Hz +/- 1.0 Hz or more)--then the battery is full, the OG inverter goes to 51/49 Hz which causes the GT inverter to shut down.

-Bill

sridharTS

Some maufactures says inverter/ charger.
It functions when the ac mains is there it recharges the battery.
What happened when ac mains is not there.
Is it takes only the power from inverter.

I want to know in off grid system no grid is there inverter should take power from battery not to recharge the battery. is inverter/ charger is used in this type of situation

BB.

Many inverters have the ability to connect both to the AC Mains (or backup AC Generator) and charge the battery bank--And their output will take energy from the AC input (if present) or energy from the DC Battery bank.

Many times, the AC inverter-charger is actually a pretty nice battery charger--Very configurable to meet your needs vs the (usually) low technology AC battery chargers that most people find.

Some of the modern Inverter-Chargers have some very complex operations/options. One of the neat things that some inverter-chargers do is "generator support". You can have a 3 kWatt AC generator running a 6 kWatt AC inverter--When your generator is running, it will charge the battery bank (if no loads). As the AC loads increase, the power is redirected from charging to supporting the AC loads. And, if the AC loads are larger than the AC generator's rating, the AC inverter starts taking battery energy to "support" the AC loads (makes the AC generator look like it is much larger).

-Bill

sridharTS

That,s ok .This is for grid tied with battery backup. For off grid, inverter takes power from battery alone. in this case which type of inverter is used.

sridharTS

let me clearly tell i don't have gnerator,grid.
I have designed to connected PV array to charger controller and to battery and to inverter and to ac loads.
I can use power inverters - dc from battery to AC
wt will happen if i use inverter/charger as in schiender electric XW+.

softdown

Propane prices are seasonal and based on the size of the sale. Prices are usually lowest around August. Ask the dealers what quantity is needed for the best prices.

Having said that....many modestly sized modern refrigerators are so energy efficient that they make a lot of sense. Especially when panels are so cheap.

sridharTS

in off grid system when no load is connected to inverter, pv power comes into the inverter will charge the battery,after getting fully charged what will happen to pv power generated.

vtmaps

sridharTS said:

in off grid system when no load is connected to inverter, pv power comes into the inverter will charge the battery,after getting fully charged what will happen to pv power generated.

Your question doesn't make sense... you're asking what will happen to the power generated, but there is no power generated.

When your battery is fully charged there will be no PV power generated.  The panels will warm up a bit because the solar energy that had been converted to electrical energy will be converted to heat in the panel.

--vtMaps

Photowhit

sridharTS said:

in off grid system when no load is connected to inverter, pv power comes into the inverter will charge the battery,after getting fully charged what will happen to pv power generated.

PV power in an off grid system does NOT come into an inverter! The pv is connected to a charge controller, then to the system. The charge controller regulates the charging of the batteries. Solar, unlike wind, can just shut down and not generate energy. In fact off grid system must generate more energy than it can use so that the batteries can be maintained.

sridharTS

Hi vtmaps,
             you told that panel get heated up. suppose when the load is not connected  to about 10 days.due to heating the panel get damaged ?

zoneblue

sridhar, can i make a couple of suggestions.
- post your questions in your own threads
- as english is possibly not your first language, try using google translate to more clearly phrase your questions. Better question = better answer.

vtmaps

sridharTS said:

Hi vtmaps,
             you told that panel get heated up. suppose when the load is not connected  to about 10 days.due to heating the panel get damaged ?

Silicon based solar panels will not be harmed in the sun when unloaded.  That is not true for some CdTe panels.

--vtMaps