Have solar for my home - Was wondering about getting Batteries

[wattmatters]

I have a 15kw system

I just saw first post again where you said 101kWh/day. Best day I got from my 11kW was 70.5kWh.

I think I had misread another post of yours talking about 200+kWh/day hence thinking you had a big system, that must be on the consumption side.

I dont know what PV means

Photovoltaic. As in solar PV panel.

 

[natesroom]

Thought it was photovoltaic, just wasn't sure. In florida, on the 15kw system it seems to average about 80kwh due to clouds rain etc. So i was thinking also a 18 to 20 backup system probably similar in size to yours

 

[MurphyGuy]

Thought it was photovoltaic, just wasn't sure. In florida, on the 15kw system it seems to average about 80kwh due to clouds rain etc. So i was thinking also a 18 to 20 backup system probably similar in size to yours

Your decision should be based on how often you lose power.. Out where I'm at, power outages are common and can happen 3 to 5 times a year or more and last up to a week at a time if due to a big storm.

But if your historical pattern is single outage once a year for a day or two, then off-grid solar is a very expensive way to go, especially if you're not capable of building it yourself. In this case, I would strongly recommend a generator.. Natural gas if its available, otherwise just a regular generator big enough to power your home and air conditioner. Its a $1500 to $2000 investment that will last almost forever if you take care of it, compared to $5,000 to $10,000 for the off grid system that will eventually wear out its batteries.

 

[natesroom]

I appreciate your input.

Natural gas requires there to be someone providing the gas. In florida (orlando) Historically we lose power about 4 to 6 times a year never more then about 8 hours at most unless its a hurricane then it could be a few days.

Personally i wasn't investing in building a Battery Backup system for the fun of it. As i already have solar production it would be practical to to be able to use that if there is no power. Additionally i am not beholden to any supplier (electric or gas) with the ability to power independently.

As for building it myself i built a 15' 150 sqft block building in my backyard with rebar and a hip roof on a concrete footer, I can "build" this, however i am not fluent in the "Electrical / Math" portion of this so in this sense i would have no idea on how it connects (or the root understanding of how it connects)

 

[wattmatters]

Your decision should be based on how often you lose power

This.

We average 12 longer outages/year (plenty of short outages of a handful of seconds) but typically they are for a couple of hours at a time. I keep stats on our outages.

One was for 2 days. Was just recalling that one as it happened almost on this day 3 years ago as many trees in the district came down, one of which fell on my shed.



For my DIY backup system I spent A$3.4k (~US$2.45k). Before that I used a generator which cost ~A$2k and sparky to wire up the transfer switch and power inlet (so a bit less than US$2k all up).

If I was thinking of a backup system of large scope comparable to my grid tied system, well I wouldn't. But if I were...

then I would instead add a grid tied battery with outage backup capability and which can ensure at least some of the grid tied solar PV system can operate in isolation from the grid.

It would not be a DIY job (it would be illegal to do there where I am) and instead it would be a professional installation. Such a battery makes no financial sense but it makes better sense than a large off-grid solar PV/battery system which sits idle most of the time.

 

[Hedges]

My system has around 10kW of PV inverter, overpaneled with more PV panels.
I have four, 6kW battery inverters but two would be plenty.
400 Ah 48V AGM battery (inverter manufacturer recommends 1000 Ah for 10kW of PV)

AGM is maintenance free, might have 10 year lifespan if only cycled a few hundred times.
Cost was $5k. Some brands are a bit less, and FLA costs less but needs watering.

Two of the battery inverters (Sunny Island) could put out 22 kW surge for 3 seconds to start motors.
The PV inverters carry the A/C operating current and other loads during the day, while keeping batteries floating.

 

[MurphyGuy]

I appreciate your input.

Natural gas requires there to be someone providing the gas. In florida (orlando) Historically we lose power about 4 to 6 times a year never more then about 8 hours at most unless its a hurricane then it could be a few days.

Personally i wasn't investing in building a Battery Backup system for the fun of it. As i already have solar production it would be practical to to be able to use that if there is no power. Additionally i am not beholden to any supplier (electric or gas) with the ability to power independently.

As for building it myself i built a 15' 150 sqft block building in my backyard with rebar and a hip roof on a concrete footer, I can "build" this, however i am not fluent in the "Electrical / Math" portion of this so in this sense i would have no idea on how it connects (or the root understanding of how it connects)

If your heart is truly set into a battery backup system and your electrical skills are only so-so, then here is what I would suggest for a high quality problem free, bullet-proof system.

Two Sunny Island's and a bank of Trojan SIND (Series-Industrial) batteries. That's it! That is all you need.. The Sunny Islands are (by far) the best off-grid inverter made in the world.. There isn't even a close second place, although there are other good inverters out there. They can be found on ebay for about $3000 each and you'll need two of them to create a 120/240 split phase system..

The Flooded Lead Acid Trojan batteries are amongst the highest quality lead acid cells you can get.. Up to 17 years of life backed by a well known company. No fancy lithium BMS issues to deal with, no fire hazards.. You just need to spend a few minutes each month making sure they are watered like a house plant and maybe exercise them every six to eight weeks to keep the sulfation at bay.

You'll spend about $10k on the system but it will be a problem free reliable workhorse that is simple to build and easy to understand.

 

[Hedges]

Two Sunny Island's and a bank of Trojan SIND (Series-Industrial) batteries. That's it! That is all you need.. The Sunny Islands are (by far) the best off-grid inverter made in the world..

Agreed, but I want to consider how his grid-tied inverters behave. If they don't do frequency-watts (linearly decrease power output in response to increasing AC frequency), they'll constantly cycle on and off every 5 minutes.

 

[MurphyGuy]

Agreed, but I want to consider how his grid-tied inverters behave. If they don't do frequency-watts (linearly decrease power output in response to increasing AC frequency), they'll constantly cycle on and off every 5 minutes.

Good point, but my guess is that if his solar system hasn't been on his roof for 10 years and he had someone install it, then they probably used a name brand modern inverter.. and don't all the newer units do the freq shift thing?

I guess we won't know until the OP comes back....

 

[Hedges]

I think frequency-watts is an optional feature which can only be used if utility agrees.
Remaining online for 299 seconds within rectangular voltage frequency limits is the basic UL-1741-SA requirement.
There were a couple staircase steps of small & large voltage and frequency excursions.

With relay disconnecting every 5 minutes for the basic requirement (or disconnecting immediately and reconnecting after 5 minutes for my original UL-1741 inverter), something might wear out.

The frequency-watts feature if implemented probably has to be enabled using an installer code.

 

[MurphyGuy]

I think frequency-watts is an optional feature which can only be used if utility agrees.
Remaining online for 299 seconds within rectangular voltage frequency limits is the basic UL-1741-SA requirement.
There were a couple staircase steps of small & large voltage and frequency excursions.

With relay disconnecting every 5 minutes for the basic requirement (or disconnecting immediately and reconnecting after 5 minutes for my original UL-1741 inverter), something might wear out.

The frequency-watts feature if implemented probably has to be enabled using an installer code.

Yeah, that wouldn't be optimal. My grid tied Sunny Boy's have a setting for that 5 minute timer, I suppose it could be set to 15 minutes or 30 minutes....
FLA batteries don't mind shallow DOD cycling.. Not good for lithium, but doesn't harm FLA cells..

Waiting for OP to come back and respond with inverter model number...

 

[natesroom]

Wow, just getting back into this as i had the last few months completing that building i was talking about earlier.

My inverter is a SolarEdge SE7600H-US - I currently have two of them.

 

[Hedges]

Wow, just getting back into this as i had the last few months completing that building i was talking about earlier.

My inverter is a SolarEdge SE7600H-US - I currently have two of them.

I see reference to the frequency-watts feature, so you should be able to use it with one of the battery inverters that does frequency shift.
Sunny Island, of course. I think Schneider. Others from Outback and SolArk, but some people have said high frequency inverters aren't as stable for AC coupling.

https://www.solaredge.com/sites/default/files/application_note_power_control_configuration.pdf

"P(f) – Power Frequency: This is used when frequency-based power reduction is required. This defines a linear graph set by two points. The inverter de-rates power according to the defined graph, until the frequency reaches the trip value and the inverter disconnects (the trip point is preset per country therefore does not need to be defined as one of the two points)."