Battery Storage vs Solar Panels - What is your thoughts?

[hybe022]

solar panels are cheap and is proven to last a very long time.

lifepo4 batteries are expensive, yes it says 6000 cycles on paper but who knows when the bms or a cell decides to malfunction

solar system designs are not one size fits all - mine may not suit yours.

i went the semi offgrid - overpaneled route with a battery just enough to last whenever the sun is down.

overpaneling gives me way more power on cloudy and rainy days. i do some energy management to ensure to have almost full batteries before the sun sets.

i call it semi-offgrid since i still have the grid service for emergency use.

 

[NC_hydro]

This what you would call a fools errand. If you size it so you’re never “wasting” power then you will fall way short on the days you need power. I’d much rather “waste” power on a lot of days and be able to cover the bad days with batteries/panels. If you have grid then it’s easier to ride the edge and not waste but then you’ll end up buying power.


Fools errand I tell you. Overbuild as you’re able and you can breathe easy on the dark rainy snowy days.

 

[Daddy Tanuki]

solar panels are cheap and is proven to last a very long time.

lifepo4 batteries are expensive, yes it says 6000 cycles on paper but who knows when the bms or a cell decides to malfunction

solar system designs are not one size fits all - mine may not suit yours.

i went the semi offgrid - overpaneled route with a battery just enough to last whenever the sun is down.

overpaneling gives me way more power on cloudy and rainy days. i do some energy management to ensure to have almost full batteries before the sun sets.

i call it semi-offgrid since i still have the grid service for emergency use.

first off... I love that avatar remember, the GDI always wins... Kane is the devil. that being said... best off to have lots of both, panels are cheap, cells are cheap, build your own and ignore the politics of resellers.

 

[hybe022]

first off... I love that avatar remember, the GDI always wins... Kane is the devil. that being said... best off to have lots of both, panels are cheap, cells are cheap, build your own and ignore the politics of resellers.

imagine something breaks in your solar setup and you hear this only for C&C fans


my 9.36kwp, 6kw, 13.44kwh system
will pay for itself in less than 2 years since it is $0.23usd/kwh in my country

so far - can get 50+kwh on an ideal bright sunny day.
20kwh on a very cloudy day.
30+kwh on average
I just plan ahead don't waste energy on that cloudy day.

yes, with prices dropping, there's always room for upgrades
more batteries + more panels!

 

[Daddy Tanuki]

imagine something breaks in your solar setup and you hear this only for C&C fans


my 9.36kwp, 6kw, 13.44kwh system
will pay for itself in less than 2 years since it is $0.23usd/kwh in my country

so far - can get 50+kwh on an ideal bright sunny day.
20kwh on a very cloudy day.
30+kwh on average
I just plan ahead don't waste energy on that cloudy day.

yes, with prices dropping, there's always room for upgrades
more batteries + more panels!

fortunatley I am past that particular sound bite... gotta get weapons production up!

 

[MattMan119]

This what you would call a fools errand. If you size it so you’re never “wasting” power then you will fall way short on the days you need power. I’d much rather “waste” power on a lot of days and be able to cover the bad days with batteries/panels. If you have grid then it’s easier to ride the edge and not waste but then you’ll end up buying power.

If you have grid, if you don’t have enough batteries to cover bad days.. lots of ifs in them statements..

What IF a you did not have that grid option? It is only wasted if you don’t store it and never get to use it on them rainy days.

Fools errand I tell you. Overbuild as you’re able and you can breathe easy on the dark rainy snowy days.

I’m not suggesting anyone build anything, just asking how you would go about coming up with the answer. How much solar and batteries or now much new technology would it take.. just a little critical thinking .. I openly agree that it is not practical in most cases, but there are many cases were it is.

 

[NC_hydro]

If you have grid, if you don’t have enough batteries to cover bad days.. lots of ifs in them statements..

What IF a you did not have that grid option? It is only wasted if you don’t store it and never get to use it on them rainy days.

I’m not suggesting anyone build anything, just asking how you would go about coming up with the answer. How much solar and batteries or now much new technology would it take.. just a little critical thinking .. I openly agree that it is not practical in most cases, but there are many cases were it is.

I'm just saying, I have no grid. And I am 100% okay with "Wasting" Take today for example, batteries were nearly full before noon. They didn't get full for long periods earlier in the winter but also never got below 39%. The best plan is build for your worst days or as close as you can, all the other times you just have lots of opportunities to be generous with your power useage.

 

[MattMan119]

I'm just saying, I have no grid. And I am 100% okay with "Wasting" Take today for example, batteries were nearly full before noon. They didn't get full for long periods earlier in the winter but also never got below 39%. The best plan is build for your worst days or as close as you can, all the other times you just have lots of opportunities to be generous with your power useage.

I am not saying that is the wrong way to do it for your case. The question is a matter of how do you calculate the perfect sized system, where you don't buy more solar or batteries then you need, but you also never run out of power. I am just curious how everyone see the issue from their point of view.

Look at it another way .. You own a resort in the middle of the woods, you have no option for power from the grid and generators would not be appropriate for the site cause of noise, fire hazards, too much maintenance (i don't know pick a reason) .. . But you have 5 cabins or small houses that you want rent. You want to figure out how much solar and batteries you will need so that your tenants never know your solar, but you don't want to spend anymore then you need to cause this will take from your profit..

Like i said this is critical thinking exercise to understand the different ways to solve the problem..

 

[NC_hydro]

Fair point, still.....many critical thinking exercises are fools errands.

 

[MattMan119]

Fair point, still.....many critical thinking exercises are fools errands.

Seems to me there are several methods to calculate this ..

1) Take your current system, see what the grid usage is over the past month (or December or worst month in last year)
2) Take the numbers and work though where and how much you came up short.
3) Calculate a buffer within reason that could happen next time
4) Check that you have enough solar to fill them batteries on not rainy days
5) Adjust battery storage..

You don't need or care about the answer so you avoid the problem .. That does not mean nobody can or will do it or has already .. I'm sure we have many folks on here or off here that are 100% off grid and don't worry about do they have enough X or Y.

I get it you don't need the answer you like your solution .. I'm good with that..

 

[Rmart30]

Currently in my situation between the 2 choices with panels being cheaper and my power consumption being highest during the daytime in summer (A/c, washing drying clothes) , mine will be over paneled vs high storage.
Eventually I will add more battery capacity.

Edit:
Im not off grid. My system was originally for when grid was out due to storms etc. so we didnt have to run generators and keep 45 gallons of gas on hand.
Im slowly incorporating it into taking my higher consumption items off grid when can.

 

[Cmiller]

How to calculate this out will highly depend on your region!

As others have mentioned, panels are cheap! I always say solar panels are the cheapest part of the whole system, for what they do! But with that said, here in Ohio we can have 1,000 panels and still have a few periods in Dec-Feb that we hardly produce any power for a few days in a row!

Personally, last winter, I was short on panels, with a decent amount of battery. (I had a few temporary batteries.) But this winter I started out with less battery, and more solar panels. My conclusion was that you need a certain minimum balance of each, but I don't know if I have a good hard number on that...

We currently use 400-550kWh pr month, or about 15-ish kWh per day during the non-air conditioner weather months, e.g. fall/winter/spring (in summer it climbs a bit higher....) and a very nice "balance" for us is roughly 40kWh storage and 8-ish kW of PV. I have 11.4kW on a 7.6kW inverter, with half east/west facing (east/west are in parallel, so not great production) and half south facing, so roughly like 8kW south facing, if I'd guess.... With this amount, I still expect to have a few days each month that the standby gen runs, but should be minimal.

So, for us, a nice baseline balance is:
PV needed == daily consumption x 0.53 (with proper south facing pv)
Storage needed == daily consumption x 2.67

I'm guessing if I would go with daily consumption x1 for PV and x4 for Storage, I would hardly have any gen run time at all.... ever....

But for you in Florida it'll be completely different, as you get waaaayyy more sunshine than us..... Who would have guessed....? sunshine state and all.... Haha

 

[MattMan119]

How to calculate this out will highly depend on your region!

As others have mentioned, panels are cheap! I always say solar panels are the cheapest part of the whole system, for what they do! But with that said, here in Ohio we can have 1,000 panels and still have a few periods in Dec-Feb that we hardly produce any power for a few days in a row!

Personally, last winter, I was short on panels, with a decent amount of battery. (I had a few temporary batteries.) But this winter I started out with less battery, and more solar panels. My conclusion was that you need a certain minimum balance of each, but I don't know if I have a good hard number on that...

We currently use 400-550kWh pr month, or about 15-ish kWh per day during the non-air conditioner weather months, e.g. fall/winter/spring (in summer it climbs a bit higher....) and a very nice "balance" for us is roughly 40kWh storage and 8-ish kW of PV. I have 11.4kW on a 7.6kW inverter, with half east/west facing (east/west are in parallel, so not great production) and half south facing, so roughly like 8kW south facing, if I'd guess.... With this amount, I still expect to have a few days each month that the standby gen runs, but should be minimal.

So, for us, a nice baseline balance is:
PV needed == daily consumption x 0.53 (with proper south facing pv)
Storage needed == daily consumption x 2.67

I'm guessing if I would go with daily consumption x1 for PV and x4 for Storage, I would hardly have any gen run time at all.... ever....

But for you in Florida it'll be completely different, as you get waaaayyy more sunshine than us..... Who would have guessed....? sunshine state and all.... Haha

So let me run it on my RV .

I have an average of 22.2kwh this month so far 11 day so that would mean 690kwh monthly usages and working number

PV = .53 * 22.2kwh = 11.7kw
storage = 2.67 * 22.2kwh = 59.2kwh

I have 3700+2400 =6,100 (not south facing.. 3700 flat rv roof. And 2400 shed 40% top, 60% sides.

I run off grid unplugged 3 weeks ago, but I have not had more then two days of rain…

11.7kw of solar .. on a normal day here could produce 50-60kwh at lease if facing south .. I suspect I would be full most of the time but that I would not run out of storage..

The house in my signature has 12.5k and can run 30-40kwh a day, and has zero usage .. no storage on side, it used grid for storage at 1 for 1… shows 12.5k would work here…

Thanks for interesting reply …

 

[CaySol]

I used PVwatts to size my array. I should get around 5 sun hours on my array in the winter and almost 7 during the summer, so my big concern is stormy days that have close to zero production. My sized array should pull in 2x daily usage so that is fine. But I only have 1.2 or so daily usage worth of battery storage. So for me, I will want to expand my storage as prices come down and energy density goes up. Not going with a generator but intend to have the grid as backup.

 

[Zwy]

When the sun shines with clear skies, there is always plenty of power it seems coming from PV.

Most will load up on panels but I have found energy storage holds an edge over more panels. My house loads are mostly when the sun doesn't shine or PV production isn't at peak. Thus more energy storage works well. The shop has loads during the day and little at night. It needs more panels and less energy storage.

I've increased battery bank in the house to 74 Kwh but found if I want to heat entirely with "free energy" except during December and January, the 74 Kwh was not quite enough to heat 24/7 using the mini splits yet still maintain a high reserve SOC and the ability to completely recharge the next day. Yes, more panels would help to an extent but several days of minimal sun needs a larger battery bank. After building the shop bank and the ability to transfer power from the shop to the house system helped as I can transfer some power early in the day to the house bank and if I conserve power in the shop, still hit full charge on both systems. Clouds and morning fog have little effect on the Chargeverter transferring power as it is a constant transfer of power. I am pleased with the extra large size of the shop battery bank, this helps smooth out those days of lower PV yield.

From my experience, having 4 days of battery bank capacity with minimal loads used is the minimum I would consider if you want to cover 90% of yearly usage. This does require discipline running loads if PV yield is low. I now have over 6 days of reserve battery bank with little loads management but if low PV yield conditions are present, then it does require some loads management. The ability to run 3 days without loads management 90% of the time is certainly preferable and I think I am currently there.


I am adding more panels, mainly to help with winter low PV yield. Once the first week of February comes, PV yield is sufficient to recharge the battery banks most days. Longer days help. Winter is always a struggle, there might only be sun for a few hours or no sun due to overcast skies so having more panels can help with that time of year. These additional panels really aren't needed once mid February arrives as I usually hit full SOC by 4 pm and can run what I want during the day.

Striking a balance between battery bank size and panels needed is not always easy. It will depend on when the majority of power will be used. I like a larger bank myself, it allows the ability to run more optional loads and capture as much PV yield as possible. We have cut our propane usage down to less than 1/2 per year and 90% plus of hot water is now heated with electricity instead of propane. I looked at hot water power usage as it hit 1 year since installing the heat pump water heater and it used 993 Kwh for the year. That comes to about $200 worth of electricity which is cheaper than propane usage of 250 to 300 gallons/year at $1.45/gallon.

 

[CaySol]

When the sun shines with clear skies, there is always plenty of power it seems coming from PV.

Most will load up on panels but I have found energy storage holds an edge over more panels. My house loads are mostly when the sun doesn't shine or PV production isn't at peak. Thus more energy storage works well. The shop has loads during the day and little at night. It needs more panels and less energy storage.

I've increased battery bank in the house to 74 Kwh but found if I want to heat entirely with "free energy" except during December and January, the 74 Kwh was not quite enough to heat 24/7 using the mini splits yet still maintain a high reserve SOC and the ability to completely recharge the next day. Yes, more panels would help to an extent but several days of minimal sun needs a larger battery bank. After building the shop bank and the ability to transfer power from the shop to the house system helped as I can transfer some power early in the day to the house bank and if I conserve power in the shop, still hit full charge on both systems. Clouds and morning fog have little effect on the Chargeverter transferring power as it is a constant transfer of power. I am pleased with the extra large size of the shop battery bank, this helps smooth out those days of lower PV yield.

From my experience, having 4 days of battery bank capacity with minimal loads used is the minimum I would consider if you want to cover 90% of yearly usage. This does require discipline running loads if PV yield is low. I now have over 6 days of reserve battery bank with little loads management but if low PV yield conditions are present, then it does require some loads management. The ability to run 3 days without loads management 90% of the time is certainly preferable and I think I am currently there.


I am adding more panels, mainly to help with winter low PV yield. Once the first week of February comes, PV yield is sufficient to recharge the battery banks most days. Longer days help. Winter is always a struggle, there might only be sun for a few hours or no sun due to overcast skies so having more panels can help with that time of year. These additional panels really aren't needed once mid February arrives as I usually hit full SOC by 4 pm and can run what I want during the day.

Striking a balance between battery bank size and panels needed is not always easy. It will depend on when the majority of power will be used. I like a larger bank myself, it allows the ability to run more optional loads and capture as much PV yield as possible. We have cut our propane usage down to less than 1/2 per year and 90% plus of hot water is now heated with electricity instead of propane. I looked at hot water power usage as it hit 1 year since installing the heat pump water heater and it used 993 Kwh for the year. That comes to about $200 worth of electricity which is cheaper than propane usage of 250 to 300 gallons/year at $1.45/gallon.

How are you transferring energy from the shop to the house? I might have to do something similar as space in the house is an issue for more battery storage.

 

[MattMan119]

From my experience, having 4 days of battery bank capacity with minimal loads used is the minimum I would consider if you want to cover 90% of yearly usage. This does require discipline running loads if PV yield is low. I now have over 6 days of reserve battery bank with little loads management but if low PV yield conditions are present, then it does require some loads management. The ability to run 3 days without loads management 90% of the time is certainly preferable and I think I am currently there.

Yes, I am at 3 days with minimal loading.. most of the time even at the solar worst production days, I can get 5 or 6 days … I have been wanting to take the RV up to get weighed to know if I can take on another battery .. that would put me in that sweet spot you have outlined above.

I am adding more panels, mainly to help with winter low PV yield. Once the first week of February comes, PV yield is sufficient to recharge the battery banks most days. Longer days help. Winter is always a struggle, there might only be sun for a few hours or no sun due to overcast skies so having more panels can help with that time of year. These additional panels really aren't needed once mid February arrives as I usually hit full SOC by 4 pm and can run what I want during the day.

When you say recharge most days you are talking about normal average daily recovery… what I am getting at you not talking about recharging to 100% each day while you have thunderstorms all the time, or heavy show days..

This is the balance of using 100% of pv and batteries on low sun days, and then having enough to move in a positive direction day after day to recover the battery usage.. for example I can run storms for 4-5 days and then for the next 3-4 days my end of day high watermark can be 10-15% of prior day.. so if I am way down it make take a few days to get back to 100% each day..

Striking a balance between battery bank size and panels needed is not always easy. It will depend on when the majority of power will be used. I like a larger bank myself, it allows the ability to run more optional loads and capture as much PV yield as possible. We have cut our propane usage down to less than 1/2 per year and 90% plus of hot water is now heated with electricity instead of propane. I looked at hot water power usage as it hit 1 year since installing the heat pump water heater and it used 993 Kwh for the year. That comes to about $200 worth of electricity which is cheaper than propane usage of 250 to 300 gallons/year at $1.45/gallon.

Not that is a real game changer, converting real $$$ out of pocket for propane to solar.. I did this same switch over just a few weeks back.. I can’t do it when traveling with 24x7 hot water will have to use heat use shutoff method for traveling without the extra solar shed power.

 

[MattMan119]

How are you transferring energy from the shop to the house? I might have to do something similar as space in the house is an issue for more battery storage.

He uses chargeverter .. here is his video about it ..

 

[Crowz]

Seems to me you all are overthinking it. Too complicated.

My method is as follows :

1. If you bought panels last then buy batteries.

2. If you bought batteries last then buy panels.

3. Repeat

 

[MattMan119]

1. If you bought panels one of the last two times then buy batteries.

2. If you bought batteries the last 2 time then buy panels.

3. Repeat

I think I would update it this way …

 

[Crowz]

Well there is the even simpler version for those of us that are getting older and have poor short term memory....

1. If stuff stops working at night buy batteries.

2. If stuff stops working during the day buy panels.

3. Repeat

 

[Zwy]

He uses chargeverter .. here is his video about it ..

It is pretty slick, during the day if one system is way ahead of the other, I can push power to the lowest SOC system. Yes, there is some conversion loss. With the Shelly plugs, I can control the power transfer from anywhere using the phone app.

 

[Zwy]

Yes, I am at 3 days with minimal loading.. most of the time even at the solar worst production days, I can get 5 or 6 days … I have been wanting to take the RV up to get weighed to know if I can take on another battery .. that would put me in that sweet spot you have outlined above.

It should be 3 days without much load shedding to really have enough battery from my experience. There will be times one thinks the sun will shine the next day and find that it isn't. Having that little extra battery capacity can carry power needs thru to the next following day if only minimal loads are ran.

When you say recharge most days you are talking about normal average daily recovery… what I am getting at you not talking about recharging to 100% each day while you have thunderstorms all the time, or heavy show days..

With the large battery bank in the shop, I can push power down to the house and get the house bank up to 100% even if the sun isn't shining. This is huge, it is just like having a PV system that can produce on overcast days.

Shop loads are mainly constant thru the day and I have the option to cut one string of lights off and just rely on the remaining 2 strings. It takes about 900W per strings (all LED) and thus 1/3 of base load is gone. I might install motion sensors on lights that are at the outside edges or in corners as those fixtures don't always need to be on.

Yes, it does draw the shop bank down. Usage in the shop is minimal over winter, it will take over 2000 Kwh per month in summer compared to 600 to 700 Kwh on average in winter. Usage in the house is higher in winter and I do use what I can for heating purposes. In summer, it won't take as much power as winter.

This is the balance of using 100% of pv and batteries on low sun days, and then having enough to move in a positive direction day after day to recover the battery usage.. for example I can run storms for 4-5 days and then for the next 3-4 days my end of day high watermark can be 10-15% of prior day.. so if I am way down it make take a few days to get back to 100% each day..

Since the shop system was up and running, I rarely run the shop bank under 50%.

Not that is a real game changer, converting real $$$ out of pocket for propane to solar.. I did this same switch over just a few weeks back.. I can’t do it when traveling with 24x7 hot water will have to use heat use shutoff method for traveling without the extra solar shed power.

It makes the payback for the heat pump water heater much faster. A little icing on the cake.