Understanding grid tie system

[Vic.chrissy]

I like to understand how grid tie solar with batteries bank work .

I thought that while the batteries have charge and the panels and working that any power used in the house would first come from the batteries and the panels and if any other power was needed or if the batteries where low ,it would be taken from the grid ,
Come night time if the batteries where charged once again the power would first come from the batteries.
Is that not correct?

reading a bit more into this it seems I wrong ,
That all power generated from the panels go into the grid which earn income from The power company and the batteries bank is only there should there be a power cut , in which case it will then come into play,

If that is the case what’s the point in having a batteries back up ,
It seems a big investment just in case of a power cut .
I be Interested In being put right by the knowledgeable guys out there .

 

[Hedges]

One mode of operation would be, so long as grid is up, batteries are kept at 100% charge.
No different from GT PV, except battery charger is one more load.
If grid goes down, it becomes an off-grid system.

Could also be programmed to charge battery during off-peak rates (possibly only to the extent charging power is no more than PV power), then discharge into grid during peak rates for higher credit.

Or, charge and discharge as needed to keep grid current at zero (both import and export), draw from grid only if battery is low. Problem here is you might have empty battery just when grid fails at night.

Some systems receive weather predictions, charge toward full if storm is coming.

Start by RTFM, does it mention "SUB", "SBU" etc.?

What brand and model?

What are the terms of your net metering agreement? And rates?

 

[1201]

Different inverters have different modes.

There are systems that optimize self consumption . Ie , even if grid tied they will use the battery until a certain Soc, them they will use the grid. Victron is an example

Some systems will power loads from the grid and change the battery is there is a grid connection, and only use the battery of the grid fails. Example sma sunny island. So is you don't want to charge your battery from the grid you have to disconnect the grid.

 

[Vic.chrissy]

One mode of operation would be, so long as grid is up, batteries are kept at 100% charge.
No different from GT PV, except battery charger is one more load.
If grid goes down, it becomes an off-grid system.

Could also be programmed to charge battery during off-peak rates (possibly only to the extent charging power is no more than PV power), then discharge into grid during peak rates for higher credit.

Or, charge and discharge as needed to keep grid current at zero (both import and export), draw from grid only if battery is low. Problem here is you might have empty battery just when grid fails at night.

Some systems receive weather predictions, charge toward full if storm is coming.

Start by RTFM, does it mention "SUB", "SBU" etc.?

What brand and model?

What are the terms of your net metering agreement? And rates?

Just to be a bit clearer , the system is in a house we about to buy , there a real possibility that the batteries are shots ,
So I’m trying to understand how it works , as if the batteries are there just in case of a power cut , then there no point spending money on new batteries,
As far as I can tell the solar is still going into the grid .

 

[Hedges]

Buy the house for the house, try to not credit any value to the PV system.
Above that, seller needs to document what it is and the condition.

We can help you figure out what it can do, what upgrade if anything it needs.
Give us make/model name & number, wattage and amperage rating where available.

If batteries are lead-acid, likely shot unless quality and used or maintained as required.
If LiFePO4, they could be fine for a decade, unless something went wrong.
If any other lithium chemistry, "Be afraid ... be very afraid."

Lead-acid batteries just for occasional power failure ought to have 10 year calendar life. Cycle life could be a few hundred power failures. That's how I use mine (AGM).

If seller wants to claim batteries have value, invite him to turn on appliances to load at maybe 0.25C or 0.5C and demonstrate battery can power them for 4 or 2 hours.

Power feeding grid - understand what utility rates and terms you have there for backfeed. 1:1 net metering would be great, but some people only get 5% of retail for backfeed. Depends on who pulls the political strings where you are located.

 

[DIYrich]

If you have 1-for-1 net metering, then batteries are there for backup. If you have time-of-use, then batteries help you not buy power when expensive. Some places will pay you to use your batteries like a virtual power plant (dump power to grid when grid is stressed).

 

[kommando]

In the UK only if the installation was by an MCS installer can you sell surplus to the grid and unless there is a FIT scheme in place that selling price will not be much. Octopus were taking non MCS installs but now seem to have stopped. Without a good selling price then the best use for the batteries is to allow excess solar to be stored and used overnight and/or to cover high loads.

 

[k490]

I would find a local solar contractor have them inspect the home before you buy it. There are many variables involved such as if the utility has a grandfather net metering agreement with the old owner. Lot of these agreements if you make changes to the system you lose the agreement and net metering goes away such as going from AGM to lithium batteries. If there is any issues with the roof could be a problem has to be resolved. Try to find a small solar contractor one guy with a few helpers not one of these big solar companies who are out scamming.

 

[Vic.chrissy]

System was installed buy a MCS installer around 2012 and by what my solicitor have sent me there is a FIT with EDF ,
i need to look into if that can be transferred to me and what the tariff is or what other options there is , (any suggestions)?
the owner of ther house has passed away so I have very little info other then what I seen .
The system is a Growatt with I think 5kw batteries bank and the inverter is a sunny boy ,
A fault is showing on the Growatt as BMS COM fault, so I been told when I phone around that most likely the batteries are shot ,
Growatt said I new a new system, but then they would .
it being an old system they no longer batteries that will fit and a new system is needed , I find that strange one would think other lithium batteries would fit ,
with this in mind is why I am asking the opening question,
As if the batteries are just there as a back up in case of a power cut there really no point spending thousands of pounds on replacing ,
I guessing the solar power being produced with the fault showing is still going into the grid ?

 

[rpdom]

In the UK only if the installation was by an MCS installer can you sell surplus to the grid and unless there is a FIT scheme in place that selling price will not be much. Octopus were taking non MCS installs but now seem to have stopped. Without a good selling price then the best use for the batteries is to allow excess solar to be stored and used overnight and/or to cover high loads.

The Octopus non-MCS scheme was a trial, but there was an up front admin cost of £250 so I doubt it had many takers.

As for export, if you're with Octopus for Import and on certain tariffs you can get a fixed export rate of 15p/kWh which isn't too bad. I use that with their Agile for import to charge my batteries to cover me through the expensive times and I rarely pay over 15p/kWh for import, occasionally lower than 0p/kWh.

 

[kommando]

The FIT is transferrable, the rates for a 2012 install should be good but a lot depends on the install date in 2012 as the rates dropped by 50% during that year.

Feed-in tariffs in the United Kingdom - Wikipedia

en.wikipedia.org

As for the batteries then I would hazard a guess that they either could be recovered or replaced by another battery but unless your geeky side is up to doing it DIY it would be expensive.

However the FIT income should be good and a simple excess diverter to an immersion heater would ensure during the summer your hot water would be free.

One example, I built my own so never used this type

myenergi - Eddi 2.1 Solar Power Diverter CE-EDDI-16A1P02H

myenergi - Eddi 2.1 Solar Power Diverter CE-EDDI-16A1P02H About eddi eddi is a solar power diverter that helps you to make the most of your self generated power rather than exporting it back to the grid. Bring an eddi into your home and you can make the most of the 100% green energy generated...

coolenergyshop.com

 

[DIYrich]

The system is a Growatt with I think 5kw batteries bank and the inverter is a sunny boy ,

Growatt and Sunny Boy is an interesting. combination.
Sunny Boy should operate without the Growatt.

Post pictures so we can see how they are connected.

 

[Vic.chrissy]

Growatt and Sunny Boy is an interesting. combination.
Sunny Boy should operate without the Growatt.

Post pictures so we can see how they are connected.

Don’t have many photo and for now I don’t have access to the property until the sale goes through but here what I do have .
I’m not too sure what the Growatt box does ( charger or a MPPT) any idea guys .

 

[kommando]

Your Growatt just looks after the battery and possibly its own panels, the Sunny Boy does the PV DC to AC and does its own thing so if that is working you get power from the Sunny Boy panels but its not stored if the Growatt is having a hissy fit, any power first goes to the house load and any excess goes to the grid (which you get paid for). You may be missing some PV power form any panels connected to the Growatt.

SP2000 Energy Storage System

The SP2000 Energy Storage System stores excess renewable energy power in a Lithium battery storage pack, giving around 4kw of power which can be drawn when the PV panels are not generating. This simple system can be retrofit to most standard Solar PV installations.

This system is a single MPPT tracking system only and is not compatible with micro-inverters or optimisers. Attention must be paid to compatibility of any inverters including voltage parameters. If necessary check compatibility.

The Lithium Battery Pack is 2 x 48HA 52v batteries in a single cabinet. This battery management system gives a total capacity of 5kw of which 80% can be drawn (you cannot 100% empty a battery) leaving 4kw available. The battery pack has its own inbuilt battery management system which manages the usage, temperature and performance of the batteries to retain the best lifetime performance possible. This battery pack is installed close to the Controller unit and is connected by 2 cables – one for communication and one for transferring the power.

Question is are either or both inverters FIT registered.

 

[Vic.chrissy]

Your Growatt just looks after the battery and possibly its own panels, the Sunny Boy does the PV DC to AC and does its own thing so if that is working you get power from the Sunny Boy panels but its not stored if the Growatt is having a hissy fit, any power first goes to the house load and any excess goes to the grid (which you get paid for). You may be missing some PV power form any panels connected to the Growatt.

SP2000 Energy Storage System

The SP2000 Energy Storage System stores excess renewable energy power in a Lithium battery storage pack, giving around 4kw of power which can be drawn when the PV panels are not generating. This simple system can be retrofit to most standard Solar PV installations.

This system is a single MPPT tracking system only and is not compatible with micro-inverters or optimisers. Attention must be paid to compatibility of any inverters including voltage parameters. If necessary check compatibility.

The Lithium Battery Pack is 2 x 48HA 52v batteries in a single cabinet. This battery management system gives a total capacity of 5kw of which 80% can be drawn (you cannot 100% empty a battery) leaving 4kw available. The battery pack has its own inbuilt battery management system which manages the usage, temperature and performance of the batteries to retain the best lifetime performance possible. This battery pack is installed close to the Controller unit and is connected by 2 cables – one for communication and one for transferring the power.

Question is are either or both inverters FIT registered.

Thanks for your reply , very helpful .
First May I say Your comments about the lithium set up is on the ball it’s exactly as it is ,

To answer your question , is the inverter FIT registered,
I would as say so as I seen a MCS certificate and it has a FIT license with EDF .

If I could ask a few question as I really want to understand how this system works please.

You say the Growatt box just look after the batteries?
How do you mean ? Act as a charger? or regular power going into the batteries?

if the system was all working ok , ( fault wasn’t showing ).
Would that mean that power from the PV would first go to charging the batteries and suppling the house ,
With grid topping up if need be ,
In other works the grid would only come into play if the PV or batteries couldn’t cope with the draw .
If this was the case then it be worth replacing the batteries if needed or having a bigger bank .

As I posted above the Growatt box show a Com BMS fault,
Growatt without seeing it say the system batteries are shot and there no parts or batteries and I would need to change the lot .
I read it could be a communication problem maybe a wiring problem .
even so the little I know about solar from my system on my boat I can’t understand why a new bank of batteries can’t be fitted unless for some unknown reason the Growatt box in the photo will only work with a special set of batteries.
And if that was the case , if the batteries has their only BMS why can’t the batteries be connected to the inverter and add an charger to the batteries and remove the Growatt box of tricks .

Any comments please ?

 

[kommando]

The Growatt comes from a period where addon units were designed to take DC from the PV panels before the existing inverter and push it into the battery so creating a hybrid system of dubious operation. How it works I have never looked into, the systems have been taken over by full hybrid systems and no longer made, hence why Growatt want to replace the whole system probably including the SB too.

As the SB is working, you have a FIT payment giving income and solar lowering your consumption, then fixing the SP2000 issue is IMHO wasted money unless you want to cover a powercut. If you do got for a complete replacement then you will either lose FIT or have to go through hoops to retain it.

I would leave the SB in place and sell the Growatt and battery on ebay as not working for spares and take the FIT for the next few years and only then maybe upgrade. That German made SB will soldier on for years more and the panels too.

Goodwe did an addon unit too, most failed like yours.

 

[MisterB1959]

Where in Suffolk, we're in Clacton .... If it's registered under FiT then you're on a bonus, but buy the house because it's what you want, not because of the system. Ask the seller for details of payments via FiT for the last two years ....
We have a FiT system and added batteries and an additional inverter so as not to affect the payment

 

[Vic.chrissy]

Where in Suffolk, we're in Clacton .... If it's registered under FiT then you're on a bonus, but buy the house because it's what you want, not because of the system. Ask the seller for details of payments via FiT for the last two years ....
We have a FiT system and added batteries and an additional inverter so as not to affect the payment

We live near Ipswich but the house is in Cambridgeshire.
Here the problem the owners have pass away so we have very little info ,
I don’t have any info how it works , how to get info what going in or out , without going into the loft to look at the inverter , I’m guessing there be some kind of app .
I need to look into it .

I only know about the FIT because of some paper work we come across .

 

[Hedges]

Sunny Boy display shows it is working. Only 201W at the moment, probably not much sun.

28862 kWh lifetime production / 10 years / 365 days = 7.9 kWh/day
7.9 kWh/day / 5 hours average effective sun = 1.58 kW capacity.
Although the inverter is a 4kW model.

Maybe this means only about 2kW of PV panels connected, or limited sunlight due to orientation, shading, weather.

How much does your power cost? If $0.25/kWh, the system has saved previous owner $7215 over its lifetime.
Best you could hope for is similar for the future, but older equipment more likely to fail and need repair. So let's assign 50% value.
Consider the Sunny Boy system worth $3600
(Growatt not working, so consider $0)

Adjust for your electric rates, I'm not immediately pulling those up.

I've had a Sunny Boy system with 5 inverters operate for 17 years, 2 failures (one repaired under warranty). MTBF calculated out to 32 or 34 years.
Yours has been operating 10 or 12 years. Reasonable life is 20 years (for a quality system like SMA, less history for Growatt, you have one example.)

I would attribute $3600 value maximum to the system (based on $0.25/kWh).
If you end up owning it, can consider ratings of the two PV arrays, consider feeding both into Sunny Boy if it is only loaded to half its wattage rating.

 

[Mattb4]

Not knowing UK laws but in the US that it is held that once a person dies most agreements, contract and Warranties are over. You have to establish new ones at that point. I would certainly check with the local electrical provider before coming to any conclusions.