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

[Bleedingblue]

Right now I have a 19kw array. Have 3205AH of LiFePO4 and was wondering what size array do you guys think is adaquate for your batteries?

It takes a full day of sun to charge mine up to about 60%. By late in the afternoon of the second day it will be around 100% depending on how much current I use.

Do you guys like an array that is able to charge the batteries up in 1 day or multiple days?

Right now I'd like to double my batteries to around 300,000 watt hours or more. In the summer if there is full sun I don't have an issue with running out of current but starting in november and through march I run out all the time because of clouds and rain. Even during summer when you have days of rain my batteries run out and I'm back on AC mode. So was thinking about eventually saving and buying more batteries. But it would take a while to charge all of em.

 

[Brucey]

3205 Ah at how many volts?

 

[hwy17]

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.

 

[Bop]

Right now I have a 19kw array. Have 3205AH of LiFePO4 and was wondering what size array do you guys think is adaquate for your batteries?

It takes a full day of sun to charge mine up to about 60%. By late in the afternoon of the second day it will be around 100% depending on how much current I use.

Do you guys like an array that is able to charge the batteries up in 1 day or multiple days?

Right now I'd like to double my batteries to around 300,000 watt hours or more. In the summer if there is full sun I don't have an issue with running out of current but starting in november and through march I run out all the time because of clouds and rain. Even during summer when you have days of rain my batteries run out and I'm back on AC mode. So was thinking about eventually saving and buying more batteries. But it would take a while to charge all of em.

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...

 

[timselectric]

I like to get a full charge at least once a week.
I don't care if it takes 3 days, as long as I am usually gaining.

 

[AZ Solar Junkie]

The way I look at it, if my array isn't large enough to charge the batteries to either full or at least more than where they started when the sun went down the night before, it's too small. Mine fully charge every day (at least from Feb through October).

 

[Mattb4]

In my thinking PV needs to carry your daily kWh. Any day it misses has to be made up for eventually. Your battery is a load that is simply part of the system. Like a water storage tank. Water in has to equal water out if the level is to be maintained. Those folks that have an unlimited storage tank, like the grid, have an advantage because the grid is so huge that an individual does not need to worry that they will fill it up or drain it out in regular use. Off grid users do not have that luxury. What they drain from their batteries eventually needs restoring alongside the daily load.

Sizing an off grid system is almost always going to result in periods of feast and famine unless your weather is always perfect.

 

[teal95]

Had an 8kW grid tie system, old enough to be net metered. Have built another system, 20kW panels, 30kWh batteries. Commissioned it late December. I definitely need more panels.

In sure once I get more panels I'll need more batteries.

Rinse and repeat.

 

[Bop]

The way I look at it, if my array isn't large enough to charge the batteries to either full or at least more than where they started when the sun went down the night before, it's too small. Mine fully charge every day (at least from Feb through October).

That's my philosophy- make enough so that no matter how bad the weather gets, I still have more than my normal daily requirements, use the excess when its available, but make sure I always have enough to cover the 'need to haves'

Even my little temporary system- I have been on it now three years (starting at 750w at the camp site while building the shed, now 1.5kw at the shed while building the house)- and in that time I have never used a generator once...

In fact the last time my genrator was actually used was in a cyclone up north back in 2009 or so- much of the time since then it either sat in my storage container or in my sisters garage... I doubt it would even start without a major overhaul lol

 

[ricsun]

I've got 10.3 kW on the roof, and 40kW storage. My house uses 900W/hr +/- 100W, 24/7. Feb-Nov will typically charge to 100% every day. I've got another 280Ah battery on the way, so I guess I'll need to add another 2kW of panels

 

[squowse]

Right now I have a 19kw array. Have 3205AH of LiFePO4 and was wondering what size array do you guys think is adaquate for your batteries?

It takes a full day of sun to charge mine up to about 60%. By late in the afternoon of the second day it will be around 100% depending on how much current I use.

Do you guys like an array that is able to charge the batteries up in 1 day or multiple days?

Right now I'd like to double my batteries to around 300,000 watt hours or more. In the summer if there is full sun I don't have an issue with running out of current but starting in november and through march I run out all the time because of clouds and rain. Even during summer when you have days of rain my batteries run out and I'm back on AC mode. So was thinking about eventually saving and buying more batteries. But it would take a while to charge all of em.

Panels need to be sized for consumption IMO. You cant just keep on getting a bigger and bigger battery to try and survive through shortfalls. A 2-5 day’s consumption is probably about right

 

[42OhmsPA]

I definitely need more panels.

I'm sure once I get more panels I'll need more batteries.

Rinse and repeat.

Words to live by.

 

[teal95]

And more panels always helps. Even on the most dreary days they will make something.

 

[OffGridForGood]

You need to decide what makes sense for you, for your loads, for your lifestyle in your environment.
Never seen anyone here complain "I have too many solar panels"
I have 9.68kW PV and wish I had double this, maybe triple. So that sets the goal, I just have to work at it.

 

[Zwy]

Right now I have a 19kw array. Have 3205AH of LiFePO4 and was wondering what size array do you guys think is adaquate for your batteries?

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.

It takes a full day of sun to charge mine up to about 60%. By late in the afternoon of the second day it will be around 100% depending on how much current I use.

Do you guys like an array that is able to charge the batteries up in 1 day or multiple days?

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

Right now I'd like to double my batteries to around 300,000 watt hours or more.

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 battery bank Kwh capacity to PV Kw. 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.

In the summer if there is full sun I don't have an issue with running out of current but starting in november and through march I run out all the time because of clouds and rain. Even during summer when you have days of rain my batteries run out and I'm back on AC mode. So was thinking about eventually saving and buying more batteries. But it would take a while to charge all of em.

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...........

 

[Ampster]

I think every situation varies based on each of our use cases. I end up the year with a small credit. My True Up is in September and by March I have a deficit of 2,000 kWhs because my winter loads are greater. That turns into a credit by September but I am always worried if cloudy weather will take cost me. I have two EVs and heat pumps for heat. Do not need much A/C in summer.

 

[Bop]

I think every situation varies based on each of our use cases. I end up the year with a small credit. My True Up is in September and by March I have a deficit of 2,000 kWhs because my winter loads are greater. That turns into a credit by September but I am always worried if cloudy weather will take cost me. I have two EVs and heat pumps for heat. Do not need much A/C in summer.

I have to worry about the opposite- cloudy weather (even on my little array) is (just) ok for my current loads, but in summer, the heat kills my panels something chronic- losing me over 20% of their power- and at the same time I want extra power (fridge is sucking down power trying to stay cool and so am I lol)
We just came out of several weeks of 'severe heat wave' warnings for the entire state and my battery pack was lower than it ever has been, even during winter I was fully charged each arvo, yet by the end of it when the heatwave was on, I was hitting it only at 80% often...
(and thank god the LYP's have that wider temperature range- if I had been using LFP's instead- then they would have spent much of each day throttled down because of the high temps...)

 

[G00SE]

i finally updated my signature for these very moments/questions

 

[AZ Solar Junkie]

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...........

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?

 

[G00SE]

The more I think about @Zwy preference of 7:1 the more I like it.
Production estimates seem to be commonly based on 5hrs of production. Ie 5:1
If a battery is equivalent, that leaves no margin for days of below average production, unless battery is also sized accordingly and initiates that down time at full capacity. That incurs additional cost to size for.
Sure there’s a race on here for who will own the biggest battery bank and I fully support such competition, it’s simply far more cost manageable for most to oversize an array for many of those lower production days.