Battery Energy Deliverd VS Energy to Recharge

Ok so here is my dilemma, I have a lead acid battery bank in my basement that is quite old and requires care and attention to maintain. I have taken measurements using a “Kill a Watt” meter and it seems it takes about 7.5 - 9 KWH of energy to recharge my bank after I have used it all night and thanks to sense, I now know I have used about 6KWH overnight. This represents an efficiency of approx 77% of power delivered vs energy required to replenish that same power. I am wondering if anyone has any experience with battery banks and thinks this is typical efficiency for lead acid flooded cells. I wonder is newer more efficient batteries would make a difference or if my charger (Xantrex 3012) is too old and inefficient. Also I am wondering if the general consensus is that batteries are really more trouble than they are worth today until a breakthrough in battery technology happens. I would consider getting rid of the entire battery setup and just having the solar supplement the daytime usage then live with the nighttime usage, my area does not have TOU billing so that is not an issue.
I like the battery setup, my solar (3.8kw in a very sunny area) is more than adequate to charge the batteries; reheat the hot water tank; and recharge the Prius Prime using only about 4kwh from the grid in a 24 hour sunny day period. That would be a light day with no dryer or central AC running or other large loads.
I’d like to keep the battery setup and improve it along with adding another KW of solar or more but I’m just not sure about putting more money into batteries and charger/inverters as that part of the system is quite pricey. Any thoughts or ideas. I’m just fishing here, lol.

(Link) - Is solar battery storage worth it, given the current solar battery costs?

Although I’ve decided not to implement a solar installation for my home, I remain intrigued by the idea reducing my on-grid usage!

What type of specific maintenance needs are you experiencing and do they lessen the benefits of having the battery bank?

My personal montra is simplicity is the base of all things!

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Wayne… My 2 cents… Couple of things … Efficiency of the 1. Invertors and 2. The charger. Not sure how old your charger is, but is it a transformer type or inverter type. And I can’t answer to the efficiency of the transformer type, but I think the inverter types are more efficient. If it is heavy when you pick it up it is a transformer type. I have used both, but use the inverter type most of the time now. Think of the fluorescent bulbs as compared to LED bulbs. I just changed out 30 in my barn and now … measured am using almost half the power. Now the inverters converting you r DC to AC… The ones I have looked at on the web have spec sheet the have the efficiency listed. I’m going to say around 95% ±. . …So net…when you charge your batteries, charger at 80 % efficiency… 120 watts to replace 100… The inverter converting back to AC at 95 %… 105 watts to make 100… Hope this helps… You have losses in the conversion both ways… Maybe someone else can explain it better then I did, but this will get you started… Gerry

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My big negatives are as follows:
Space required. The lead acid batteries require a sealed box that is ventilated to the outside of the house to expel the generated hydrogen gas. The space required in my case is about 4x4x3. This box has a plastic pipe attached that uses up more space to travel to the outside of the house, which required drilling a hole through the wall.
Filling with distilled water. My batteries require periodic topping up with distilled water and monitoring water/acid levels to ensure they stay within range.
Equalization. Once a month or so I equalize the batteries to ensure they stay balanced to help prolong the lifespan of the batteries.
Temp monitoring. During the equalization process I monitor the cell voltages and temperatures during this process to ensure none of the batteries is starting to fail. Any battery getting warmer than all the rest work indicate an elevated internal resistance problem. If not closely monitored and allowed to escalate the individual cell could fail catastrophically resulting in severe damage to the house. A leak of sulphuric acid from an overheated and cracked cell jar would severely damage a concrete floor. I may make my box liquid tight to mitigate this issue.
Disposal. If any or all of the batteries need to be disposed of this is a big deal. Flooded lead acid cells are difficult to transport and dispose of properly. On the plus side you get paid at the scrap yard for lead acid cells
Life span. As these batteries age, they are already about 20 years old thus I got them for free, their efficiency continues to degrade. Luckily they were a standby bank in their previous life so they never really saw any discharging till after I inherited them. They are performing pretty well thus far but not sure how many more years of life I can get out of them.
These are some of the main issues that are driving me to think about upgrading the battery/inverter/charger system. The upgrade would be expensive but so far the battery storage solution is very attractive and my local utility is moving to TOU billing very soon so I will likely stay with some kind of battery storage solution. When I can run my 1800 sq’ home on 3 or 4 kWh in a 24hour period of a sunny day without seriously compromising lifestyle I am hooked on the battery storage idea.

On the efficiency of the inverter/charger. I have two Stacked Xantrex 3012’s. This gives me 6000 watts continuous at 240vac with a peak o/p of 12,000. This seems adequate for most of my loads, minus: central air, hot water tank rewired for 120 instead of 240v, hottub off, electric heated floors off, two small window shaker A/C units installed in the two main bedrooms.
The inverter/chargers are very heavy, 60lbs each, and contain a huge transformer in each. My 77% efficiency was calculated going both ways from ac to dc to charge then back from dc to ac to supply the house. Since there is loss in each direction I suppose 77% efficiency is not too bad? Are the newest units transformerless?

Have you looked into the Tesla powerwalls or similar devices? https://www.tesla.com/powerwall
They do weigh 250lbs each so are not that light.
I know that the powerwalls can be configured to pre-charge(or do it automatically) before a storm comes through the region. They also look considerably smaller than lead-acid setups.

Getting more competition in this field should drive the prices down and capabilities up.

Lithium batteries (Powerwalls etc) is undoubtedly the way to go but the huge caveat is the longterm recyclability of pretty much any (ion) battery system.

If logistics permit, I would seriously consider a super-sized super-insulated hot water tank as your core “battery”. PV solar to hot water is very efficient. The trick is to have your heating system integrated with that hot water store. In the ideal world you could use the hot water battery for cogen to then providing cooling. In the real world, using Sense metrics gathered from your usage patters, especially the EV, and solar generation, you can perhaps do enough load shifting that “simply” upgrading your hot water storage to huge & well insulated will work.

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My feeling on battery from purley a financial point - What are your net metering rules in your state?
I’m in Massachusetts where the utility buys back everything at matching rates. The only thing I would pay each month if I had a solar system and was generating more than we use on a monthly basis is the $7 “you exist” fee.

If your net metering rates are not good, then storage starts making more sense from a financial standpoint. If you buy from them at 15c/kWh, but they buy from you at 5c/kWh, then it makes more sense to charge your batteries during the day and use them at night when you can’t generate. Thus maximizing the power from your actual panels

The other thing to check out if you are considering a battery product (PowerWall, LG Chem, Generac etc…) some states have demand offset programs.

In Massachusetts, depending on your power company, if you have an approved battery system, they will pay you over the summer to trigger your battery to discharge during a high usage period. So your battery gets a signal from the power company at a certain time and the house will switch to drawing from the battery first, vs the grid. This reduces load on the grid. According to documents, this can be around $1000 a summer paid back by the power company if you opt in each time they send an alert.

Good point @ben, demand offset is something that will be widely deployed eventually (NY also has it). Migrating from a “dodgy” (to insure?) lead acid setup to a “demand offset programmable” PowerWall system is a likely future-proofing. You also get the major benefit of easier load-shifting.