How big of a solar panel array do you guys call adaquate?

[AZ Solar Junkie]

i finally updated my signature for these very moments/questions

Ha- around here I wouldn't say N+1 is the answer. More like N TIMES 2 or 3 or 4.....

 

[Bleedingblue]

3205 Ah at how many volts?

48

 

[Bleedingblue]

Unlike lead acid, there is no technical requirement to achieve a certain solar to battery ratio.

If your array can only charge your battery 60% in a day that's ok, what's important is that your array can meet your daily consumption so that your battery is regularly getting fully charged at least in summer.

Going from 100-40% every day and recharging, good, but hanging out in 70-10% every day bad.

Before I bought more cells that is precisely what it was doing in certain times of the year. Mainly late fall through early spring

 

[Bleedingblue]

It is far cheaper to over panel and have only sufficient storage to last a single day or two...

Here in Aussieland where I am, I have a 1.5kw 'temporary' array that charges the 20kwh battery bank (16 400Ah LYP lithium cells) that runs the shed and caravan, but when there is a house to put them on there will be a total of 18kw on its roof (6kw east, 6kw north, 6kw west) on that same 20kwh of battery bank- my 'normal' consumption is about 7-10kwh a day in a house, so with my 18kw of arrays generating in the best conditions about 98kwh a day is vastly more than I need to recharge the bank (and on days of excess I can play in the workshop with the 'big toys' that suck power like crazy, like the mill and lathe etc)- on 'grey overcast' I lose about 50% of my production- on 'really bad' days with 'black 100% overcast' and heavy rain it drops down to about 30% of normal production- but thats still about 25-27kwh a day generated here- still sufficient to cover twice my normal daily needs (I might have to spend the day doing other things rather than pottering around in the workshop lol) but my normal usage needs are still fully covered...

Adding more and more batteries is a mugs game economically speaking- battery storage is still far more expensive than simply over paneling the system instead...

Now just got to finish the house so I can get the whole array up on its roof lol, instead of the panels sitting in the corner of the shed...

Your panels do a lot better job of producing current in the rain. Lol mine produce nothing close to 30% production in rain. It may be closer to 5%

 

[DVD]

Lots of factors going into the answer. I sized my batteries for 3x my average daily load. Then I sized my array for an average 50% daily wintertime replenishment rate.
Wrong answer. Array should have been 75% replenishment. I needed to buy grid power for an equivalent of 3 days use each month during the winter.
Panels themselves are economically priced now. Bigger array is better. Yes, there’ll be a lot of unrealized solar potential during the summer periods.

 

[timselectric]

With lead acid batteries. You have to size your solar according to your battery size.
With LFP you size your solar according to your loads.
As long as you produce (on average) more than you use (on average) you will always be able to charge your battery (no matter what size it is).
Batteries are sized for how long you want to last without production.

Sizing an off grid system is simple.
1. Size your inverter to cover your maximum instantaneous load.
2. Size your battery to cover your loads for whatever time you want to run without production.
3. Size your solar to cover your average loads plus some extra to recharge your batteries.(how much extra, determines how fast you reach full charge)

 

[Bleedingblue]

I looked thru your prior posts, you have a least 6 280Ah and 4 304Ah, running a 48V nominal system. 3205Ah should put you in the 164Kwh area.

You don't say how much usage you have in a day, that would help immensely.



If I drained batteries down to 20% or lower, it will take a few days to get back to 100%.




300Kwh. Where's Tim?

Sure would like to hear your usage per day. With 164Kwh of battery, that is pretty big.

I run about a 7 to 1 ratio of PV Kw to battery bank Kwh capacity. It is adequate but our usage is low and we watch usage and production according to weather forecast.

A 5 to 1 or 6 to 1 ratio will also work. At 164Kwh of battery a 7 to ratio is 24Kw of PV, 6 to 1 is 27Kw of PV and 5 to 1 is 33Kw of PV.

This will depend on your usage daily. I would consider minimum of 7 to 1 so you are undersized from what I have experienced. We can cut usage to minimum on cloudy periods and run 5 days but not 6. This is with limited sun and running off battery mainly. Some days we only discharge the battery with no charging for the day. It's the exception but if you get a week of weather like that, you will be out of battery.

If you go to 300Kwh of battery, you will need some serious PV.



You seem to be over equipped now with batteries, I think I'd move PV up to the 27Kw or 33Kw area at this point.

Your daily Kwh usage would help...........

Well usage varies. Depends on if clothes are being washed, dishes washed, could be watering the garden (have a well) also have a greenhouse that uses fans, have I think 5 deep freezers and 3 fridges. Also have a seed starter room that is kept warm with grow lights for seedlings. Have 2 shops plus a house...
Just a lot of stuff at different times of the year being used. This time of the year I'm starting seeds and growing them inside and transplant to greenhouse in a month.

Just a lot of stuff uses electricity.

I live on a farm with all kinds of stuff going on. It's not a set amount of electricity per day and that's it. That's why I have a bigger bank I guess.

I think when most try to live grid free and independent they will realize just how much electricity they have to use to grind feed or store meat or vegetables in freezers to last a year instead of going to the store.

Like I said the problem lies in winter months when it's cloudy because of low sun angle and short days. Even in other times of the year if I use a lot of power and it's rainy I could be back on grid.

That's why I posed the question about solar array/ battery size

 

[Bleedingblue]

With lead acid batteries. You have to size your solar according to your battery size.
With LFP you size your solar according to your loads.
As long as you produce (on average) more than you use (on average) you will always be able to charge your battery (no matter what size it is).
Batteries are sized for how long you want to last without production.

Sizing an off grid system is simple.
1. Size your inverter to cover your maximum instantaneous load.
2. Size your battery to cover your loads for whatever time you want to run without production.
3. Size your solar to cover your average loads plus some extra to recharge your batteries.(how much extra, determines how fast you reach full charge)

I guess that's the magical question. No one really knows how much time without production will occur. Besides night there are days or even weeks of not much sun.

Think it was the month of December I had 2 days of sun. Around like 4 or 5 with partial sun/hazy skies and the rest was just cloudy and misty rain. January not much different with almost 10 inches of rain.
Haven't had much snow this year but have had some ice storms in the past that got on the panels and had to wait until the sun melted the ice off.

 

[Bop]

Your panels do a lot better job of producing current in the rain. Lol mine produce nothing close to 30% production in rain. It may be closer to 5%

What voltage are you running your arrays at?- Mine are usually 90v in good weather, charging a 12v battery bank through a MPPT controller (controllers actually)- once the panels manage to get past 28v, my controllers start charging the battery bank...

This was one I took a while back at the old camp site while building the shed...
8AM, 100% grey cloud cover, with showers, the sun is still down behind the treetops and already at 4.4A (38-30A in bright sunlight) so already over 10% of their output in those conditions....)
Look for the 'bright disc' down in the treetops, just to the left of the tree by itself to the right- theres an arrow pointing at it...

or literally at dawn- no sunlight on the panels (look up the top left, you can see the sunlight on the treetops)- only half the suns disc showing above the horizon- and already half an amp flowing into the 13v battery bank, with the panels already at 52v...

(observant people may notice I am in Australia, and I said that was at dawn- yes- those panels are facing SOUTH in Australia... I didn't have the back legs on them at that time- and in fact I never did get them on, too busy building the shed, and they worked well enough they covered the vans needs for the fridge and lights and tv etc- so I just didn't bother as it was all just temporary anyway...)

 

[pollenface]

My rule of thumb is 20% battery size unless this exceeds battery charging rates

 

[DIYrich]

Calculate:
H = highest daily consumption. X=Array size to produce that during that time of year.

W=Array production during worst time of year for one days use. C=Average daily consumption that time of year.

I would want the larger of 3X or 3W. That way you get three days of consumption from one day of production. You could have a string of bad days that depleat your batteries. One good day, and you can ride out two more rainy days.

If you are connected to the grid, then 1.5 times is fine. If you have a long string of bad days, just charge from the grid.

 

[Zwy]

Well usage varies. Depends on if clothes are being washed, dishes washed, could be watering the garden (have a well) also have a greenhouse that uses fans, have I think 5 deep freezers and 3 fridges. Also have a seed starter room that is kept warm with grow lights for seedlings. Have 2 shops plus a house...
Just a lot of stuff at different times of the year being used. This time of the year I'm starting seeds and growing them inside and transplant to greenhouse in a month.

Just a lot of stuff uses electricity.

I live on a farm with all kinds of stuff going on. It's not a set amount of electricity per day and that's it. That's why I have a bigger bank I guess.

That changes things considerably. I thought maybe you were just running your house. It appears you must have livestock also so that means possibly a waterer with a heater. Those suck power plenty of power. My dad always had a switch on his, we would turn it on as part of evening chores if it was to be cold out.

I think when most try to live grid free and independent they will realize just how much electricity they have to use to grind feed or store meat or vegetables in freezers to last a year instead of going to the store.

Look to the Amish for ways to cut usage. Around here the Amish who do construction use solar to recharge their cordless batteries (which i find so strange as they can't have electricity on the farm). They suffer from no sun too.

One example is the Amish will use storage like water tanks that are filled every few days so they only have to start a pump a limited number of times. The same applies with solar, you can pump water when sun is available and be able to use it when those cloudy days have limited production.

Meat can be canned as well as vegetables. This doesn't require refrigeration. You get the idea, power storage can come in many forms, you do things when PV is plentiful to get you thru the lean times.

Like I said the problem lies in winter months when it's cloudy because of low sun angle and short days. Even in other times of the year if I use a lot of power and it's rainy I could be back on grid.

That's why I posed the question about solar array/ battery size

You will need way more PV than what you currently have. I did start this thread back in October and you might gain some insight on how others size their array and battery. https://diysolarforum.com/threads/get-a-big-battery.70751/ You are undersized on PV compared to your battery bank and a larger array will allow you to do the heavier loads during the day when the sun is shining. Periods of extended days with low PV production will always happen. That is how you size a battery bank, according to how many days of reserve will you need with limited PV yield.

I'm currently getting ready for installing a system for my shop and it will be mainly load reduction, not off grid. My house on the other hand is mainly off grid. You might consider something similar. Long term you might get a decent return on a large PV system, in my case I'm closer to retirement than starting out. It doesn't make sense financially for me to spend a huge amount of money that might take a good number of years to get 100% ROI even with the depreciation writeoff. When I do decide to slow down or retire, the load will be less and I will have power while working on hobbies.

Panels are cheap so start looking for deals. Panels are cheap today, it seems to cost more for mounts than PV.

 

[Zwy]

I don’t feel there’s much sense in even doing a PV to battery ratio, but rather PV to load consumption ratio. Ensure you have at least sufficient PV to pull in enough power on a daily basis to cover your loads over a 24 hour period (plus enough to cover efficiency losses and some amount of buffer / overpaneling to help get through the winter and get decent power on less than ideal days). Then look at how much battery capacity you want to have to cover your loads through bad weather and grid outages. Sufficient battery to consistently get through the night would be the bare minimum.

But obviously most of us feel that more of everything is better . I just see over and over people doing PV to battery capacity ratios and that just doesn’t make logical sense to me. Maybe I’m missing something?

Some of it depends on time of usage. If loads are mainly during the day, then more PV is a better choice than more battery.

I sized my battery bank based upon the days I could go with limited sun. We increased electricity usage over 12% since installing solar due to shifting loads such as heating to electric dump loads. I've decided to add a little more so I can get thru at least another day.

I also want to be able to recharge the batteries in X number of days with decent sun plus handle loads and usage overnight. Using a ratio can help size the array which I think is what the OP is asking, how to size an array. Just comparing ratios with others shows he is low on PV capacity compared to bank size even without knowing the usage per day.

It isn't a hard set rule but a tool to use for deciding if one needs more PV or should add more battery. The OP was considering more battery but looking at his battery bank size to PV ratio is seems he needs more PV instead. Having the ability to fully recharge within 2 days or less could mean he won't need more battery.

 

[pvdude]

After 3 years working on the solar power project, I still need more panels.
Added more each year, after learning how cloudy days effect production.

Have 3 MPPT charge controllers, each rated at 6kw, but rated as 8.5kw OK for over-paneling.
So far, only have 15,560 of PV, distributed across all 3 CC.

55104 kWh of FLA batteries, stay in "standby" service most of the time, as the PV and inverter "grid support"
feature handle the loads most of the time.

Worst case (grid down for weeks, cloudy), I can charge from the genset, but so far, have not had to.
Every hurricane season is a roll of the dice here.....

 

[Zwy]

I don’t feel there’s much sense in even doing a PV to battery ratio, but rather PV to load consumption ratio. Ensure you have at least sufficient PV to pull in enough power on a daily basis to cover your loads over a 24 hour period (plus enough to cover efficiency losses and some amount of buffer / overpaneling to help get through the winter and get decent power on less than ideal days). Then look at how much battery capacity you want to have to cover your loads through bad weather and grid outages. Sufficient battery to consistently get through the night would be the bare minimum.

But obviously most of us feel that more of everything is better . I just see over and over people doing PV to battery capacity ratios and that just doesn’t make logical sense to me. Maybe I’m missing something?

I thought more about your question. Ratio is a good comparison tool as each person's electrical needs vary, some might use 10Kwh per day while others use 60Kwh.

So how does one arrive at the size of PV to install in order to recharge batteries without using grid power as everyone has varying usage? I guess one way is to arrive at an average of PV size to battery bank size.

One thing that is a constant is the available sun on average to every solar system out there. 4 hours of sun during winter on a 20Kw array with a depleted battery of 160Kwh would take over 8 hours or 2 days just to recharge the battery with efficiency losses. That is without any loads during that time. One most likely wouldn't use a 2 Kw array to recharge a 160 Kwh battery as it would take 10 times as long. If one was to assemble a poll and use input from members and run a dot plot graph, you would find an average ratio of PV Kw to battery Kwh. This is due to people adjusting their system size to meet their needs.

As with any average, there will be outliers. But looking at an average gives a baseline to determine if more battery or PV is needed.

 

[Bleedingblue]

What voltage are you running your arrays at?- Mine are usually 90v in good weather, charging a 12v battery bank through a MPPT controller (controllers actually)- once the panels manage to get past 28v, my controllers start charging the battery bank...

This was one I took a while back at the old camp site while building the shed...
8AM, 100% grey cloud cover, with showers, the sun is still down behind the treetops and already at 4.4A (38-30A in bright sunlight) so already over 10% of their output in those conditions....)
Look for the 'bright disc' down in the treetops, just to the left of the tree by itself to the right- theres an arrow pointing at it...
View attachment 195678
or literally at dawn- no sunlight on the panels (look up the top left, you can see the sunlight on the treetops)- only half the suns disc showing above the horizon- and already half an amp flowing into the 13v battery bank, with the panels already at 52v...
View attachment 195679
(observant people may notice I am in Australia, and I said that was at dawn- yes- those panels are facing SOUTH in Australia... I didn't have the back legs on them at that time- and in fact I never did get them on, too busy building the shed, and they worked well enough they covered the vans needs for the fridge and lights and tv etc- so I just didn't bother as it was all just temporary anyway...)

I have 4 strings at 436 volts I think it was. And another string at 288v

 

[Bleedingblue]

Calculate:
H = highest daily consumption. X=Array size to produce that during that time of year.

W=Array production during worst time of year for one days use. C=Average daily consumption that time of year.

I would want the larger of 3X or 3W. That way you get three days of consumption from one day of production. You could have a string of bad days that depleat your batteries. One good day, and you can ride out two more rainy days.

If you are connected to the grid, then 1.5 times is fine. If you have a long string of bad days, just charge from the grid.

My electric bill for December was over $300

 

[Bleedingblue]

That changes things considerably. I thought maybe you were just running your house. It appears you must have livestock also so that means possibly a waterer with a heater. Those suck power plenty of power. My dad always had a switch on his, we would turn it on as part of evening chores if it was to be cold out.





Look to the Amish for ways to cut usage. Around here the Amish who do construction use solar to recharge their cordless batteries (which i find so strange as they can't have electricity on the farm). They suffer from no sun too.

One example is the Amish will use storage like water tanks that are filled every few days so they only have to start a pump a limited number of times. The same applies with solar, you can pump water when sun is available and be able to use it when those cloudy days have limited production.

Meat can be canned as well as vegetables. This doesn't require refrigeration. You get the idea, power storage can come in many forms, you do things when PV is plentiful to get you thru the lean times.


You will need way more PV than what you currently have. I did start this thread back in October and you might gain some insight on how others size their array and battery. https://diysolarforum.com/threads/get-a-big-battery.70751/ You are undersized on PV compared to your battery bank and a larger array will allow you to do the heavier loads during the day when the sun is shining. Periods of extended days with low PV production will always happen. That is how you size a battery bank, according to how many days of reserve will you need with limited PV yield.

I'm currently getting ready for installing a system for my shop and it will be mainly load reduction, not off grid. My house on the other hand is mainly off grid. You might consider something similar. Long term you might get a decent return on a large PV system, in my case I'm closer to retirement than starting out. It doesn't make sense financially for me to spend a huge amount of money that might take a good number of years to get 100% ROI even with the depreciation writeoff. When I do decide to slow down or retire, the load will be less and I will have power while working on hobbies.

Panels are cheap so start looking for deals. Panels are cheap today, it seems to cost more for mounts than PV.

Ya I bought some 250 watt panels from santan solar. Have 104 of em I think it was. Was going to put them on my shop with some facing east and some pointing west. My dad died unexpectedly before I got them up. And I took on the building of his solar for his place which my mom and younger brother still live. I have an older brother that said he would get a solar loan and have someone install some panels and hook everything up. As of now nothing has been done on that project that's was signed off on 14 months ago. Guy took half the money from the bank and hasn't done much of anything.
I can't use my panels I bought because of SHTF I have to use those panels over at my mom's. I even have 96-280AH cells over there that I got configured up .
At my place I got food stored up not only for my house hold but my mom/brother and my older brother who only has an apartment. That's why there is a lot going on around here. We have 3 big gardens we eat off of and also I feed my grandmother as well.
If that shyster actually put up the solar panels and hooked them up I could then put up another solar panel array.

I have 4 inverters that each have 2 PV inputs and only using 5. I also have spare inverters that I could use to just charge batteries

 

[OffGridForGood]

Lots going on.
Ground mounts may be quicker easier way to go, if there is space available in open area. - just a suggestion.
If I were you, I would get some wood and duck bill anchors and get some of those 100 pv panels out in the sun pronto, get them collecting something and cut that monthly elect billing down.
then later you can work at getting them into a more final location, or what ya need to do. Having cells, inverters and PV but not connected is not getting ya anywhere today. just saying. hope it works out for you.

 

[Bleedingblue]

I thought more about your question. Ratio is a good comparison tool as each person's electrical needs vary, some might use 10Kwh per day while others use 60Kwh.

So how does one arrive at the size of PV to install in order to recharge batteries without using grid power as everyone has varying usage? I guess one way is to arrive at an average of PV size to battery bank size.

One thing that is a constant is the available sun on average to every solar system out there. 4 hours of sun during winter on a 20Kw array with a depleted battery of 160Kwh would take over 8 hours or 2 days just to recharge the battery with efficiency losses. That is without any loads during that time. One most likely wouldn't use a 2 Kw array to recharge a 160 Kwh battery as it would take 10 times as long. If one was to assemble a poll and use input from members and run a dot plot graph, you would find an average ratio of PV Kw to battery Kwh. This is due to people adjusting their system size to meet their needs.

As with any average, there will be outliers. But looking at an average gives a baseline to determine if more battery or PV is needed.

That would be a very interesting graph to see. I know when solar installers come around they try and sell ya on a 8kw system and make ya think it's all your ever gonna want or need. When actually it needs to be at min 2x that size for a smaller house.

When the government mandates everyone has to have an electric vehicle and no gas stoves, washers, water heaters etc then your usage will skyrocket. Would probably need a solar system of 30kw and battery bank of 200kw