Is it economical for a home owner to add storage to already existing rooftop PV?

[jflorey2]

From talking with my neighbors, it seems that first-time batteries last between 10 and 15 years.

That's great. Around here, they tend to last from 3 to 10 years in my experience. The 3 year system was someone with a fairly large (32kwhr) battery bank who drove it very hard; they'd cycle about 10 kwhr through it 3-5 days a week, and it handled generator support in the summer to allow them to run some fairly large A/C's from a 6kW generator.

After the first bank failed I started badgering them about battery maintenance. They'd check levels (all 72 cells) every Friday and wipe down the bank afterwards. Those lasted 4 years.

[SunEagle]

That's great. Around here, they tend to last from 3 to 10 years in my experience. The 3 year system was someone with a fairly large (32kwhr) battery bank who drove it very hard; they'd cycle about 10 kwhr through it 3-5 days a week, and it handled generator support in the summer to allow them to run some fairly large A/C's from a 6kW generator.

After the first bank failed I started badgering them about battery maintenance. They'd check levels (all 72 cells) every Friday and wipe down the bank afterwards. Those lasted 4 years.

I applaud your support of educating someone that a battery system needs to be checked and taken care of like a child. Some people do that and they have been rewarded with long lasting systems that have even exceed a manufacturers warranty.

Unfortunately the mass public seems to be a "plug and play and forget" mode. They do not understand or care about why batteries die or systems fail because they are too consumed with other "important" issues in their lives. That is why I will continue to send out warnings to those that come hear to read about this technology that as of today there isn't a low cost energy storage system for the home that can be used by the typical person because they are still too complicated for the "use and forget" mentality and except for remote places like Hawaii or Germany where the electric rates are through the roof they are not economical to install. Maybe some day but not now.

[DanKegel]

Unfortunately the mass public seems to be a "plug and play and forget" mode. They do not understand or care about why batteries die or systems fail because they are too consumed with other "important" issues in their lives.

That's absolutely correct.

That's what makes the currently arriving wave of storage products interesting: they are designed to be plug & play & forget.

They're not economical yet except in areas with high power prices and storage subsidies.

It'll be interesting to watch the experiences of the early adopters of these newer systems.

[jflorey2]

That's what makes the currently arriving wave of storage products interesting: they are designed to be plug & play & forget.

I have not seen any systems that meet that description. The closet would be the Sonnenschein system, which I think is a well designed AC battery storage system - but it's certainly not plug and play.

[DanKegel]

Maybe 'install and forget' would be more apt.

[J.P.M.]

One big priority for consumer acceptance of any product is ease of use. A big part of ease of use is not thinking about it. Without being easy to use, a product or service will not be as successful.

Whoever/whatever comes up with a scalable storage system - home to commercial to municipal - that can be mostly ignored by the end user(s) and still function with a high degree of reliability will have a successful and profitable product. People will pay a lot of money to be reliably enabled to be lazy, or at least that's the easiest route to getting over a perceived high price.

[ncs55]

Why would anyone choose to replace their batteries every 8 years?

This is my take on that question. Because the user is not instructed on the importance of how to properly maintain their batteries. Or the charge controllers are not programed as per the specific battery manufacturer specs. The user ignores what they are being educated to do for maintenance. The battery array was not properly sized for the users load requirements. The user has no backup power to help keep their batteries healthy during periods of heavy use and low solar input. Or the recommended DDOD is exceeded on a regular basis. It seems that an 8 year lifespan is considered max life for batteries in off grid. I see a lot of the solar specific AGM batteries being used and the customers are being told that they will last 10 or more years. When they fail in 5-7 years, it is like, what the heck for the customer. I dug into this and called the manufacturer of one of the most popular brands of solar specific AGM's being sold in my area and asked them to explain how they calculate the longevity of their battery life. In the end it came down to the amount of their recommended daily depth of discharge of their batteries. They say their batteries will last for ten years with no problem if the DDOD is maintained at 15% and went on to explain the percentage of battery life in relation to higher DDOD. (and by the way you have to ask the manufacturer for this information if it is not readily available on their website). At a 15% DDOD in an off grid application, it would take 3 times the amount of that type of battery to give me the same useable power and lifespan as a properly set up and maintained LA array of which another manufacturer says that it can last for ten years at a 50% DDOD. I use LA 2V cell batteries in my off grid system with Classic 250's and modules on trackers. If I let the batteries float before I start pumping water for instance and it is sunny the battery array never even comes close to 50% DDOD. During low solar input and still having to pump water I will take them down to 50% before I have to use backup power for recharging and this array is just at 14 years old. So, for me it is a trade off of a lot of maintenance vs more frequent replacement. Also more frequent replacement is not in my opinion sustainable. I am actively looking for a future replacement for this array that can handle pumping water on top of the normal load profile without so much maintenance. Lithium is the latest breakthrough. But consider this about lithium. There are only two mines in the world that produce this. It is highly toxic from raw materials to the end product. And no one has figured out how to recycle it, yet. If you look at the whole picture and in my opinion lithium is not the way to go as it is not really a sustainable solution for large scale or off grid applications. Neither is the AGM solution.

[SunEagle]

This is my take on that question. Because the user is not instructed on the importance of how to properly maintain their batteries. Or the charge controllers are not programed as per the specific battery manufacturer specs. The user ignores what they are being educated to do for maintenance. The battery array was not properly sized for the users load requirements. The user has no backup power to help keep their batteries healthy during periods of heavy use and low solar input. Or the recommended DDOD is exceeded on a regular basis. It seems that an 8 year lifespan is considered max life for batteries in off grid. I see a lot of the solar specific AGM batteries being used and the customers are being told that they will last 10 or more years. When they fail in 5-7 years, it is like, what the heck for the customer. I dug into this and called the manufacturer of one of the most popular brands of solar specific AGM's being sold in my area and asked them to explain how they calculate the longevity of their battery life. In the end it came down to the amount of their recommended daily depth of discharge of their batteries. They say their batteries will last for ten years with no problem if the DDOD is maintained at 15% and went on to explain the percentage of battery life in relation to higher DDOD. (and by the way you have to ask the manufacturer for this information if it is not readily available on their website). At a 15% DDOD in an off grid application, it would take 3 times the amount of that type of battery to give me the same useable power and lifespan as a properly set up and maintained LA array of which another manufacturer says that it can last for ten years at a 50% DDOD. I use LA 2V cell batteries in my off grid system with Classic 250's and modules on trackers. If I let the batteries float before I start pumping water for instance and it is sunny the battery array never even comes close to 50% DDOD. During low solar input and still having to pump water I will take them down to 50% before I have to use backup power for recharging and this array is just at 14 years old. So, for me it is a trade off of a lot of maintenance vs more frequent replacement. Also more frequent replacement is not in my opinion sustainable. I am actively looking for a future replacement for this array that can handle pumping water on top of the normal load profile without so much maintenance. Lithium is the latest breakthrough. But consider this about lithium. There are only two mines in the world that produce this. It is highly toxic from raw materials to the end product. And no one has figured out how to recycle it, yet. If you look at the whole picture and in my opinion lithium is not the way to go as it is not really a sustainable solution for large scale or off grid applications. Neither is the AGM solution.

I agree with you. A smart designed system that is taken care of can last longer than what the manufacturer predicts.

Unfortunately the number of people that seem to really understand the dynamics of maintaining a battery system can be counted using maybe both of my hands. I will always enjoy learning what these people have done and hope others learn too.

[SunEagle]

That's absolutely correct.

That's what makes the currently arriving wave of storage products interesting: they are designed to be plug & play & forget.

They're not economical yet except in areas with high power prices and storage subsidies.

It'll be interesting to watch the experiences of the early adopters of these newer systems.

I am truly hoping that someone will some day soon develop a low cost energy storage system for the masses. Once that happens I will be in full support of that technology.