Anyone want to shar...
 
Notifications
Clear all

Anyone want to share costs on batteries?

Page 6 / 7

batalto
(@batalto)
Reputable Member
1151 kWhs
Joined: 1 year ago
Posts: 728
Topic starter  

@transparent any thoughts on battery chargers/inverters. I want to add a second as my second batteries can't be used with the pylontechs. But it's pretty scant out there for chargers at the moment. Any recommendations?

12kW Midea ASHP - 8.4kw solar - 14.2kWh batteries
262m2 house in Hampshire
Current weather compensation: 50@-3 and 25@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE


ReplyQuote
Transparent
(@transparent)
Member Moderator
934 kWhs
Expert
Joined: 5 months ago
Posts: 151
 

I have lots of thoughts on inverters @batalto !

Most people assume that an inverter will be able to charge a battery from the Grid and then operate in reverse to supply 240v AC back to the Grid (& home). To achieve this the inverter uses the 50Hz grid frequency to synchronise.

Such inverters must

  • have G98 certification
  • be installed by an approved MCS electrician
  • and have the connection approved by the DNO

G98 dictates a number of basic requirements, amongst which is the crucial one that the inverter must cease export within 20mS of a grid failure. Ie your battery cannot work as a backup device.

AC G99FT 2

If you have two or more devices which can export back to the grid (and/or home) then you require G99 approval from your DNO. The default position is that any inbuild current limitation won't work, and that both devices will export simultaneously. I've written a comprehensive overview of these G-standards and permissions here on the OVO Forum.

 

The sort of inverter I've been investigating over the past year is the type which does not (and cannot) export back to the Grid.

This design has its own internal 50Hz generator, thus making its 240v AC output unsynchronised.

There are far fewer of these inverters, and a great number of manufacturers/suppliers who claim that their particular model works like this. Most also have grid-export capabilities.

I have a Growatt SPF5000ES here, operating as a totally off-grid inverter. It currently supplies a 14kWh battery from either the Grid or solar.

However, this model is extremely hard to buy. I've had more on order from different Far-East suppliers since 4th Feb 2022, and I'll be fortunate to have any arrive by the end of July.

PlantRoomF2

Off-grid inverters fall outside of the requirements for DNO permission and MCS-accredited installers.

There is also no safety-guide beyond the need to have the 240v connections made by a qualified electrician. So there are plenty of ways to make mistakes and damage batteries, inverters and yourself!

This post was modified 4 weeks ago by Transparent

Save energy... recycle electrons!


ReplyQuote
batalto
(@batalto)
Reputable Member
1151 kWhs
Joined: 1 year ago
Posts: 728
Topic starter  

@transparent cheers for that. Any recommendations on what might be in stock and reasonably priced. I'm kicking myself for not buying a used Sofar for £300 last year. Live and learn

12kW Midea ASHP - 8.4kw solar - 14.2kWh batteries
262m2 house in Hampshire
Current weather compensation: 50@-3 and 25@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE


ReplyQuote
Transparent
(@transparent)
Member Moderator
934 kWhs
Expert
Joined: 5 months ago
Posts: 151
 

You'll need to better define what sort of inverter you're looking to buy, @batalto  where the battery connects and what devices you're intending to supply.

Would you feel up to creating a rough schematic of your intended layout and posting it here?

I'm hoping for a pencil sketch with some labels if possible. Please don't try to emulate the colour diagrams I've been posting. We really need something of the level where others will say "I could post something like that too!" Just sketch it, take a photo with a mobile phone and upload it 😎 

Save energy... recycle electrons!


ReplyQuote
batalto
(@batalto)
Reputable Member
1151 kWhs
Joined: 1 year ago
Posts: 728
Topic starter  

@transparent I'm currently drinking gin out and about. I'll see what I can knock up later... 

12kW Midea ASHP - 8.4kw solar - 14.2kWh batteries
262m2 house in Hampshire
Current weather compensation: 50@-3 and 25@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE


ReplyQuote

ChickenBig
(@chickenbig)
Beginner Member
279 kWhs
Joined: 3 months ago
Posts: 31
 
Posted by: @transparent

Such inverters must

  • have G98 certification
  • be installed by an approved MCS electrician
  • and have the connection approved by the DNO

Can I quickly clarify just what needs to be installed by the MCS electrician; is it just the grid side of the inverter (current clamps, circuit breakers and AC wiring), or does this apply to the BMS, batteries fuses/circuit breakers, batteries and certain inverter settings? Put another way, for a battery storage system what level of self-build is acceptable?


ReplyQuote
Transparent
(@transparent)
Member Moderator
934 kWhs
Expert
Joined: 5 months ago
Posts: 151
 

Good question @chickenbig

The MCS installation certificate is required by the agency who arranges for you to obtain SEG (Smart Export Guarantee) payments. In my case the approved agency was my Energy Supplier (OVO). Unless they can tick all the boxes for your site, then no payment can be made for electricity sent back to the grid.

That pretty well scuppers any DIY input to the process.

An MCS approved contractor has to recoup the expense of the training courses and annual fees for the business. So they're going to be pretty strict in having everything specified and done by themselves... right down to the screws used to fix PV mounting rails to your roof.

Whatever they install for you must be equipment that has been tested, approved and listed on the MCS database. If any component part isn't MCS-approved, then the contractor can lose their licence.

That means the only battery storage systems available to you are the mainstream commercial units. To obtain their MCS accreditation, those batteries will have been required to have inbuilt BMS, fuses etc.

 

If you want to use DIY knowledge and skills, then you're restricted to energy storage systems that do not export to the grid.

For similar reasons you're not allowed to install your own Heat Pump or EV charge-point. Both of these devices are categorised as Low Carbon Technology, requiring approval from your DNO. The process includes identifying the approved contractor.

Save energy... recycle electrons!


Mars liked
ReplyQuote
ChickenBig
(@chickenbig)
Beginner Member
279 kWhs
Joined: 3 months ago
Posts: 31
 

@transparent Thanks for the info. I now know what (Australian) Andy from Youtube channel Off Grid Garage feels like; his power company prevented him extending his home's solar panel setup so he took his garage (and EV charger) off grid.

It seems as if the MCS has the PV/energy storage/heat pump market stitched up! I can understand the safety reasons for this, but I can't help but feel it may somewhat slow down adoption given the limited pool of MSC approved installers.

In my case, I am part of a group-buy scheme but the winning installer wants to install LiFePO4 batteries (Fox ESS) in the loft. Aside from the increased weight on the ceiling, storing charged LiFePO4 batteries in a hot loft will cause them to degrade very rapidly. Hence my desire to install an inverter and self-built batteries (to save some money) elsewhere.

Trying to find a way to work with the "If you want to use DIY knowledge and skills, then you're restricted to energy storage systems that do not export to the grid" statement, is it possible for a DIY-er to install (or manage the installation of) some G100 approved battery storage inverter (connected to self-built batteries) and keep export to grid set to 0W (or some small positive value) to prevent exporting self-generated solar power? Not being able to export energy at peak times takes away some of the economic motivation for installing an energy storage system (peaking using Octopus Agile), but there is some justification to maximise solar self consumption.


Mars liked
ReplyQuote
Transparent
(@transparent)
Member Moderator
934 kWhs
Expert
Joined: 5 months ago
Posts: 151
 
Posted by: @chickenbig

the winning installer wants to install LiFePO4 batteries (Fox ESS) in the loft

And how will their system protect the batteries against damage from charging below freezing? See this reference.

Posted by: @chickenbig

is it possible for a DIY-er to install [...] some G100 approved battery storage inverter (connected to self-built batteries) and keep export to grid set to 0W [...] to prevent exporting self-generated solar power?

Technically, yes.

Legally, no!

The mechanism by which grid-export is kept to zero is itself subject to DNO approval. In effect, if the combination of component parts you wish to use is not already on the ENA approved list, then you won't get the G99 certification from your DNO.

I have a PowerVault 8kWh storage battery with inbuilt export limitation controlled by software and a current clamp (ie G100 certified). However, when seeking G99 approval to add a Growatt string-inverter, the DNO required that to be of no greater throughput than 3.6kWh. Ie because that combination wasn't on the ENA list, the current-limiting system within the existing (G98-installed) PowerVault battery was no longer 'trusted'.

The DNOs are not trying to make life awkward. There are very good technical reasons why they will not allow such possibilities of grid-export, particularly from single-phase sites.

I've benefited by being part of the OpenLV Project, working with monitored substations, and talking with network engineers. I was astonished at the losses being incurred on the distribution grid, and I'm fully supportive of Ofgem requiring DNOs to reduce these under the new RIIO-ED2 licence arrangements.

 

This post was modified 4 weeks ago 2 times by Transparent

Save energy... recycle electrons!


Mars liked
ReplyQuote
batalto
(@batalto)
Reputable Member
1151 kWhs
Joined: 1 year ago
Posts: 728
Topic starter  

@transparent this is my current layout (but I have a bigger battery now). Ideally I just want to put it along side after the first one to pick up anything excess. Because my PV is over 8kw I often have excess PV in the summer. We do dump a lot into AC, or the swimming pool heater, but there is always plenty left. Ideally I also want grid tie to make maximum use of Octopus Go in the winter.

Screenshot 2022 04 02 21 11 22 47 e2d5b3f32b79de1d45acd1fad96fbb0f

 

12kW Midea ASHP - 8.4kw solar - 14.2kWh batteries
262m2 house in Hampshire
Current weather compensation: 50@-3 and 25@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE


ReplyQuote



ChickenBig
(@chickenbig)
Beginner Member
279 kWhs
Joined: 3 months ago
Posts: 31
 

@transparent Can I query the mechanism you use to prevent grid export for your system, as described in one of your previous posts in this thread?

Posted by: @transparent

It currently supplies a 14kWh battery from either the Grid or solar.

Alternatively, what was the plan for the retrofit system for @hydros in this post?

 

Posted by: @transparent

because that combination wasn't on the ENA list, the current-limiting system within the existing (G98-installed) PowerVault battery was no longer 'trusted'

I take it the problem is coordinating two independent limiting systems to limit the total power exported at any given moment, hence the combination needs approval. Would some kind of independent G100 limiter device somewhere between the meter and the exporting unit meet the DNO's requirements? Yes, the linked to device does not have a price, and if you have to ask ...

 

After this journey into uncertainty about fitting batteries/inverters, I can't decide between

  1. getting no storage (and probably not bothering with solar panels);
  2. getting solar panels and storage installed in one go (and have the batteries cause the ceiling to sag, and lithium plate/cook in the loft);
  3. getting solar panels, DIY-ing batteries and taking the bulk of the house off grid (topping up in winter using a battery charger to ensure energy can never flow back to the grid).

The first option will probably happen in my case, since the group-buy scheme has 35% more takers than expected, and I suspect finding more capacity for installers in the area will be pretty tricky/unprofitable.


ReplyQuote
Transparent
(@transparent)
Member Moderator
934 kWhs
Expert
Joined: 5 months ago
Posts: 151
 

Let me address the point made by @batalto first...

Posted by: @batalto

Because my PV is over 8kw I often have excess PV in the summer.

Exactly. You've hit the nail on the head.

What you need is a double-pole switch to divert one of your two solar arrays from the existing grid-tied inverter, and connect instead to a separate off-grid system. This video clip shows the arrangement operating in a self-built "string combiner" box.

 

Please note that the double-pole Manual Transfer Switch must be DC rated. Each of the four pairs of switching contacts has its own arc-suppression 'ladder'. When the contacts open, a pair of magnets pulls the resulting arc into the ladder's plates and quenches it. This is a safety requirement.

DC switches/MCBs like this are marked with their polarisation and must be connected the right way around.

The switch in the above video is manufactured by FEEO in China. The coloured tags on the levers have been added by me.

This post was modified 3 weeks ago 3 times by Transparent

Save energy... recycle electrons!


ReplyQuote
Transparent
(@transparent)
Member Moderator
934 kWhs
Expert
Joined: 5 months ago
Posts: 151
 
Posted by: @chickenbig

Can I query the mechanism you use to prevent grid export for your system, as described in one of your previous posts in this thread?

Yes, please do query. This is a very important point!

I alluded to the mechanism I use to prevent grid-export higher up this thread, but it warrants being repeated here for clarification.

Posted by: @transparent

The sort of inverter I've been investigating over the past year is the type which does not (and cannot) export back to the Grid.

This design has its own internal 50Hz generator, thus making its 240v AC output unsynchronised.

And here's a generic diagram of such an arrangement:

Off Grid battery5spD

 

There is only one parameter on the UK electricity grid that is a constant - and that's the 50Hz frequency.

It is not possible to connect any generation source to the grid unless the frequency is first aligned.

I've seen this for myself at a hydro-electric plant where a turbine was being run up. The engineer watched a gauge until the arrow pointed directly upwards. At that point it was safe to 'throw the switch' without the fuses blowing!

Exactly the same principle applies to my tiny 5kW inverter. Since it contains its own 50Hz oscillator, it is unsynchronised to the national 50Hz grid. If I were to try connecting it to the grid then it would be pitched into an unequal battle against the combined power from all the commercial generation plants of Europe. Guess who's going to win?!

In conclusion, a solar inverter must fall within one of two possible categories:

  • it is grid-tied, using the external 50Hz frequency to synchronise its output to that of the National Grid
  • it is off-grid, creating its own 50Hz for its output from an internal oscillator
This post was modified 3 weeks ago 3 times by Transparent

Save energy... recycle electrons!


ReplyQuote
Majordennisbloodnok
(@majordennisbloodnok)
Active Member
1016 kWhs
Joined: 6 months ago
Posts: 144
 
Posted by: @chickenbig

... 

2. getting solar panels and storage installed in one go (and have the batteries cause the ceiling to sag, and lithium plate/cook in the loft);

...

I realise your installer wants to install the batteries in the loft, but let's not forget you're the customer. You don't even need to argue on technical grounds; if you want to retain the loft space as somewhere to install your Scalextric track, that's what the installer must work around.

105 m2 bungalow in South East England
Mitsubishi Ecodan 8.5 kW air source heat pump
18 x 360W solar panels
1 x 6 kW GroWatt battery and inverter
Raised beds for home-grown veg and chickens for eggs

"Semper in excretia; sumus solim profundum variat"


ReplyQuote
ChickenBig
(@chickenbig)
Beginner Member
279 kWhs
Joined: 3 months ago
Posts: 31
 
Posted by: @transparent

I have a Growatt SPF5000ES here, operating as a totally off-grid inverter. It currently supplies a 14kWh battery from either the Grid or solar.

OK, so I mis-read the post about your current setup and assumed that there was an AC link from the grid to the inverter. I am now just a little unclear about how you charge your battery from the grid. Do you use some kind of high powered charger (e.g. an Elcon 3.3kW battery charger which can be controlled over CANBUS) to move energy one way (from the grid down to the batteries) with no possibility of trying to feed the energy back? If this is the case (and similar to the V2G trial mentioned) what are your efficiencies like?


ReplyQuote

Page 6 / 7



Share:

This website uses cookies to improve your experience. We'll assume you're OK with this, but you can opt-out if you wish. Accept Read More