…… another batch of solar questions

[parsonswife]

We now have
(4) 310Watt solar panels IMPP 8.03am / vmpp 37.02 72 cells
(3) Trojan L16 batteries and
MTTP Controller and 3000watt inverter

Forgive me if I am not asking the right questions but this is whats going through my head tonight.

So the question is how much power will we have (assuming sunny days). We plan on powering a pellet stove auger and fan that runs at 2.08 amps and (4.8 amp start up power but we an disconnect the igniter if we need to).

DH want to know if we will be able to use the laptop, and a few LED lights also at the same time as the stove. I know the frig and the freezer are not possible but would a mini fridge be possible?

If there is no sunny days can we recharge the batteries with our propane genny and in general how long the genny would have to run to charge them?

I am helpless with the math questions and understanding amps vs watt vs volts.

Input would be appreciated

 

[desert knight]

im not an expert, and only have a few years under my belt in the off grid solar world. but a quick check of the batteries you have are the 6 volt trojans. you need to have them in pairs so you can series them together to make a (12) volt battery, then if you had a 4th battery, you can then parallel them together to make (2) 12 volt batteries that have around 740 amp hrs of capacity. however, with flooded lead acid, it is not recommended to go below 50% of that capacity very often or the lifespan of the batteries will be reduced greatly. with normal continuous use, lead acid batteries last about 2-4 years, depending on how deep they are expended, how often, and how they are maintained.

the solar panels seem like they have plenty of wattage available to charge your batteries, depending on your location. a generator can be used to recharge if there are cloudy days, however, make sure you get the charging specs from the battery manufacturer. victron energy has a great 25 amp charger that can be modified to specific parameters via there bluetooth app, which makes charging much simpler and more precise.

im sure others here are much more knowledgeable on this, but as long as you don’t regularly go below 50% capacity, and you get (4) 6volt trojan L16 batteries, connect them up in a series/parallel configuration, you should have enough power to run the things you noted. if you can afford (3) more to make a total of 6 batteries, that would be better. the battery bank is the heart and soul of any off grid system.

 

[LoupGarou]

We now have
(4) 310Watt solar panels IMPP 8.03am / vmpp 37.02 72 cells
(3) Trojan L16 batteries and
MTTP Controller and 3000watt inverter
...

As Desert Knight has said, you need at least a 4th L16.

As far as quick notes on power capability and capacity: If the L16s are standard trojan L16s, then they are good for 6V @ 225AH each of nameplate capacity, so two in series for 12V still have 225AH of nameplate capacity. The trouble with batteries nameplate capacity is that it is a measure of total capacity in the cell, not what you want to try to pull from it. Some batteries, in order to have a long life, want no more than 20% used (80%SOC (State of Charge) off the top if you are using them daily, this means that if you actually want to pull what the nameplate capacity shows, that you need 5 times that much nameplate capacity to actually get that usable capacity out. In the case of L16s, like Desert Knight said, 50% SOC (State of Charge) is about max of what you want to use them down to. This means that if you had 4 batteries, instead of having 12V @ 450AH to play with (what the nameplate capacity of 4 L16s in 2S2P (2 in series to make a set, and 2 sets in parallel to make a battery bank)), you are actually looking at having 12V @ 225AH of usable capacity to work with. If you had 6 L16 batteries, 2S3P, then you would have 12V @ 337.50AH of usable capacity.

The solar panels are going to produce a MAX of 1240W of power in full sun through your MPPT charge controller. If you can get 6 hours of full sun, you are looking in the 7,440WH ballpark of power per day. Depending on your battery bank size, you could run a fridge or freezer off of that. (6) L16 in 2S3P may do the trick depending on the fridge or freezer.

And remember, the currents at 12V when talking about 2000-3000 watts of inverter are LARGE (3000/12=250AMPS!), so LARGE gauges of wire are needed to pulll that from the battery bank. Think in terms of 3/0 (three ought or larger). So that is a topic of further discussion...

 

[Thinwater]

In Oregon you may be looking at only 5000 watt hours per day or less, depending on the season. If you find it is not enough once you put it in use the simple solution is to add a few more panels.

 

[desert knight]

Loup is absolutely correct on wire sizes. i have 4/0 gauge cables on all battery interconnects as well as to the inverter. also, try to keep the cables as short as possible to the inverter to account for voltage drop. the bigger the cables and shorter the distance, the less voltage loss you will have from the batteries to the inverter.

will prowse on youtube has a ton of videos to help with understanding the basics and more technical aspects of a system. he also has a good website to help with components that are needed for different kinds of systems, Mobile Solar Power: Made Easy! DIY Off-grid Solar Power!

 

[etdeb]

It is so confusing for the non technical person. I have panels and wind turbines but I am grid tied. Batteries are so expensive and I am 67 years old and don't know how to maintain batteries. I really want the Lithon Iron ones that only have to be kept from freezing. The lead water flood batteries I think generate a lot of heat so in hot Texas I would have to have AC in the storage room.
I have 168- 200Watt panel and 2 6WK wind turbines mounted at two levels because here we can have wind at 100 ft one min and then its at 120 ft the next. My system was built in 2009 then the company sold out in 2011.

 

[parsonswife]

Loup is absolutely correct on wire sizes. i have 4/0 gauge cables on all battery interconnects as well as to the inverter. also, try to keep the cables as short as possible to the inverter to account for voltage drop. the bigger the cables and shorter the distance, the less voltage loss you will have from the batteries to the inverter.

will prowse on youtube has a ton of videos to help with understanding the basics and more technical aspects of a system. he also has a good website to help with components that are needed for different kinds of systems, Mobile Solar Power: Made Easy! DIY Off-grid Solar Power!

The panels will go on a pole mounts about 50 ft from the battery's, which will be next to the house. Will need to keep batteries outside under the covered patio next to the house. Any reason we should we build a "box" to cover the Batts?

Also if the Trojans get to the 50% discharge spot how long does it take to recharge them (with on grid electricity or from running generator or running a car).

 

[desert knight]

The panels will go on a pole mounts about 50 ft from the battery's, which will be next to the house. Will need to keep batteries outside under the covered patio next to the house. Any reason we should we build a "box" to cover the Batts?

Also if the Trojans get to the 50% discharge spot how long does it take to recharge them (with on grid electricity or from running generator or running a car).

a battery box is definitely recommended to help with temperature regulation and maintenance. ive always put a layer of insulation during the winter on my lead acid batteries, as well as a “battery temp cable” that connects to the charge controller. this helps to maximize charge efficiency.

as with charging times with grid power or generator, assuming you discharged the batteries to 50%, and depending on how many “amp hrs” were consumed, it could take several hours to fully charge the batteries at their recommended max charge current. thats where you need to find out from trojan what the max amps you can safely charge the batteries at so you dont “overcook” them

 

[desert knight]

The panels will go on a pole mounts about 50 ft from the battery's, which will be next to the house. Will need to keep batteries outside under the covered patio next to the house. Any reason we should we build a "box" to cover the Batts?

Also if the Trojans get to the 50% discharge spot how long does it take to recharge them (with on grid electricity or from running generator or running a car).

also, dont be discouraged with all these tips and advice, it can definitely be quite technical and overwhelming like the above poster said. i was a complete newbie 6 years ago, knew NOTHING of off grid solar, and its easier than i expected. you have a good startup system for sure, and with a few tips and adjustments, i think you will be happy with what a solar system can do and provide for self sufficiency

 

[buttie]

So here's a map with your solar insolation Solar Maps for the USA | Solar Insolation & PV Potential with this info you can now fairly accurately estimate power production. We've lived off-grid since '08 so it's a familiar process for me. The other factor is if there are obstacles that will shadow your panels during the winter solstice.
To get the most out of the system timing is everything. Using FLA (Flooded Lead Acid) battery power will cost you about 45% of production. So try to time your usage to when the batteries are full and you're using the power directly from the panels. We switched to LiFePo batteries a couple of years ago and they are much more efficient. The hit for using battery power is now around 7%. They are expensive though.
Another useful tool is a BMS (Battery Management System) they work like a fuel gauge to know what the state of charge of the batteries are. I use the Tri-metric meter.

 

[Dennis Olson]

Please use the HELP prefix when asking questions.

Thanks!

 

[LoupGarou]

It is so confusing for the non technical person. I have panels and wind turbines but I am grid tied. Batteries are so expensive and I am 67 years old and don't know how to maintain batteries. I really want the Lithon Iron ones that only have to be kept from freezing. The lead water flood batteries I think generate a lot of heat so in hot Texas I would have to have AC in the storage room.
I have 168- 200Watt panel and 2 6WK wind turbines mounted at two levels because here we can have wind at 100 ft one min and then its at 120 ft the next. My system was built in 2009 then the company sold out in 2011.

The freezing battery issue with Lead Acid is not an issue unless the batteries are at a VERY low SOC (State of Charge). As the charge drops, the sulfur sticks on the plates and the electrolyte (the liquid between the plates) become less and less acidic, and more like water. Here is the rough breakdown of the temps needed to freeze the electrolyte at any given SOC.



Given the fact that most batteries should not be pulled down past 80% SOC, and none should be pulled past 50% SOC, that gives you a range of -4 degrees F to -94 degrees F to play in.

 

[parsonswife]

Delete

 

[marsofold]

You need to have a more technical person to help you since you really don't know enough to make informed choices. The fact that you have three L16 batteries which adds up to 18 volts tells me that you don't know what you are doing. There are no 18 volt inverters on the market. They are mostly 12 volts, 24 volts, and 48 volts. Adding another is a problem since aged batteries don't mix well with new ones. Plus you have no information about the current state of charge the batteries you now have. If they have been sitting forever without being charged, then they are all dead. Letting a lead battery go below 50% charge kills it quickly. You have four 37 volt panels. Since charge controllers cannot go above 140 volts without damage, the only way you can connect the panels is two series strings of 74 volts, and the two strings are connected in parallel. The MPPT charge controller is the correct type. The 3000 watt inverter is rather large as inverters go, and you need to know if it is a modified square wave unit, or a pure sine wave unit. I paid $1700 for my 2000 watt Outback Power inverter, so I'm guessing that yours is a cheap modified square wave unit. Modified square waves are hard on motors, so I've given away the one I used to have. If you choose a new inverter, get one that also has a charger built-in so you can charge from a generator or the grid in winter to keep the batteries from dying. Outback Power inverters aren't cheap, but they do have this function and are pure sine wave units. Your panel watts add up to 1240 watts, slightly less than mine. As a rule of thumb, your 24 hour averaged power available in summer will be around 13% of the peak power available from the panels due to inefficiencies and 5 hour sunlight usefullness. That means that your average power will be around 160 watts. That's right, only 160 watts and no more. That assumes that all of the stuff running will be 24 hour a day continuous loads.

The way to tell what you can power is to buy a heavy duty extension cord and a $26 gadget called a Kill-A-Watt. You plug the Kill-A-Watt meter into a wall outlet and then the extension cord into it. You then plug all of the stuff you'd like to power into the extension cord. The Kill-A-Watt unit will then measure the total power consumption (in watts) of the gadgets you plug into it. If the total exceeds 160 watts, then it is too much for the solar setup to power 24/7. Your only choice is to unplug one thing from the extention cord, reset the Kill-A-Watt and try again. My old small meat freezer pulls an average of 90 watts in summer. A 100 watt-equivalent LED light only pulls 17 watts. Laptops don't use much, especially since they are mostly not on for 24 hours a day. Never use incandescent lamps as they use 6 times the power of an LED for the same brightness and you can't afford that. Add and subtract different loads to see what you can power up to 160 watts total.

If you don't pay attention to the state of your batteries, then you WILL kill them by accidentally going below a 50% charge state. A few incidents like that and your expensive batteries will be dead. If you really can't monitor your battery state vs loads, then you shouldn't be using solar at all. Sorry, but that's the hard truth and the truth is always your friend.

 

[parsonswife]

You need to have a more technical person to help you since you really don't know enough to make informed choices. The fact that you have three L16 batteries which adds up to 18 volts tells me that you don't know what you are doing. There are no 18 volt inverters on the market. They are mostly 12 volts, 24 volts, and 48 volts. Adding another is a problem since aged batteries don't mix well with new ones. Plus you have no information about the current state of charge the batteries you now have. If they have been sitting forever without being charged, then they are all dead. Letting a lead battery go below 50% charge kills it quickly. You have four 37 volt panels. Since charge controllers cannot go above 140 volts without damage, the only way you can connect the panels is two series strings of 74 volts, and the two strings are connected in parallel. The MPPT charge controller is the correct type. The 3000 watt inverter is rather large as inverters go, and you need to know if it is a modified square wave unit, or a pure sine wave unit. I paid $1700 for my 2000 watt Outback Power inverter, so I'm guessing that yours is a cheap modified square wave unit. Modified square waves are hard on motors, so I've given away the one I used to have. If you choose a new inverter, get one that also has a charger built-in so you can charge from a generator or the grid in winter to keep the batteries from dying. Outback Power inverters aren't cheap, but they do have this function and are pure sine wave units. Your panel watts add up to 1240 watts, slightly less than mine. As a rule of thumb, your 24 hour averaged power available in summer will be around 13% of the peak power available from the panels due to inefficiencies and 5 hour sunlight usefullness. That means that your average power will be around 160 watts. That's right, only 160 watts and no more. That assumes that all of the stuff running will be 24 hour a day continuous loads.

The way to tell what you can power is to buy a heavy duty extension cord and a $26 gadget called a Kill-A-Watt. You plug the Kill-A-Watt meter into a wall outlet and then the extension cord into it. You then plug all of the stuff you'd like to power into the extension cord. The Kill-A-Watt unit will then measure the total power consumption (in watts) of the gadgets you plug into it. If the total exceeds 160 watts, then it is too much for the solar setup to power 24/7. Your only choice is to unplug one thing from the extention cord, reset the Kill-A-Watt and try again. My old small meat freezer pulls an average of 90 watts in summer. A 100 watt-equivalent LED light only pulls 17 watts. Laptops don't use much, especially since they are mostly not on for 24 hours a day. Never use incandescent lamps as they use 6 times the power of an LED for the same brightness and you can't afford that. Add and subtract different loads to see what you can power up to 160 watts total.

If you don't pay attention to the state of your batteries, then you WILL kill them by accidentally going below a 50% charge state. A few incidents like that and your expensive batteries will be dead. If you really can't monitor your battery state vs loads, then you shouldn't be using solar at all. Sorry, but that's the hard truth and the truth is always your friend.

I realize I need 4th battery. The ones I have were a brand new, a gift from a relative. Just now found a 4th and having it shipped to us.

 

[lostinaz]

You should consult with a solar dealer that can help you would with what you need. This is an example only, not an endorsement. Shop around for the best deal and service. Find a local guy if you can. These guys have lithium solar deep cycle batteries and systems you may want to look at since you can take lithium batteries down to almost 0% without harm, unlike lead acid batteries. If your lead acid batteries can only use 25% of rated AH to prevent them from having issues, then that's really the only capacity you can use. For example, you have 740 AH, you really only have useable 185 AH. With Lithium you get like 90% of the AH available, which gives you more capacity to play with, even though they may have less AH for the dollar spend. If your panels are going to be a long distance away you may want to run your batteries such that you can go 24v or 48v. Your cable sizes are huge for 12v, making it expensive.

100 Ah 12V GC2 LiFePO4 Deep Cycle Battery

 

[desert knight]

for the last 6 years, i have run my entire cabin on (6) 6volt golf cart batteries. the total amp hour capacity was 690ah. so really only about 345ah of useable power. granted, this is mainly a weekender or getaway cabin, so only sporadic use of 2-4 days at a time, but we ran our coffee maker, microwave, furnace, all the lights(LED), 32in tv(LED)with satellite receiver, water pump, on demand water heater, and a 18 cubic foot fridge/freezer. now, of course we were careful on what we had on at the same time, and mindful of the consumption, but those 6 batteries powered all we needed for 5 years, until i got a new 3300 watt inverter/charger, which has a selectable built in charger up to 100 amps. made a big mistake in trying to charge those golf cart batteries at 70 amps, thinking i could charge them in half the time. wrong. i cooked them and bulged every terminal, so be careful on the max amp charge you put into the batteries. ive now switched to lifepo4 which can handle much higher current and like lostinaz said, they can use most of their capacity without degrading cycle life.

 

[parsonswife]

I need all you all's opinion on solar cable wire to solve a disagreement between two realitives who are helping set up our solar system.

One says I need 4ought wire from local supply house (expensive) another says to order 10 awg online and save some money. Hooking up 4 310watt panels to a midnite solar Combiner box. Distance is about 45ft.

I am in charge of "gathering" all materials from them to install in a few weeks. The cable is the last of it...

 

[LoupGarou]

I need all you all's opinion on solar cable wire to solve a disagreement between two realitives who are helping set up our solar system.

One says I need 4ought wire from local supply house (expensive) another says to order 10 awg online and save some money. Hooking up 4 310watt panels to a midnite solar Combiner box. Distance is about 45ft.

I am in charge of "gathering" all materials from them to install in a few weeks. The cable is the last of it...

A lot of variables still not known. What is the nominal voltage and amperage on the panels and are you planning on hooking them up in parallel for the nominal voltage but 4 times the amperage, or in series for 4 times the nominal voltage but the amperage being the least of the panels nominal amperage? If the voltage is high, and the current is low, as in the case of a series solar array, then a single pair of 6AWG would work, with only a little loss. If the panels are in parallel, then you might get away with four strands (4 positive bound together, and 4 negative bound together of 6AWG) OR use 2 strands each of 2AWG conductors. Voltage drop at 12V with a handful of amps even over 50 feet can be nasty and demand a lot thicker wire than just is needed to carry the current alone. 4-0 is a bit overkill.

If your charge controller is a MPPT one that can handle the higher voltage input, then I would definitely suggest wiring in series and then the 6AWG would run fine. 10AWG can handle 30 amps if it is THHN or THWN insulated, but the voltage drop would be in the 5-10% range for 8-10 amps of power coming in from the panels. And here is a good chart for 2% drop specs on a nominal 12V system over at: choosing-right-wire-size - Web


Looking at this chart, this gives you the worst case scenario for 12V use. The 310 watt panels are probably 24V nominal, and with that, are probably looking at making around 8-9 amps each. If the panels are all in parallel, then you are looking at up to 36 amps of power to have to go the 45 feet.

 

[parsonswife]

Thanks Loup. Lots to talk over with DH