need a simple explanation of battery only install

[haf63]

Hi,
Just started looking into home batteries and possibility of getting one so I can charge overnight and use in the daytime - please ignore the financial viability as I am looking at practical feasibility at the minute.
Daily usage is maybe 3-4kw at the minute but could double as am looking at air source heat pump as well.

My current simplistic understanding is I need
- a 'inverter' of some kind - hybrid? and a certain kw spec (3.5?)
- the battery itself
- some sort of control system (or is that part of the invrstor?)

My main focus is space rests and cabling route.. specifically what happens when the mains cable leaves the meter and goes into the CU.. does it go from CU to invertor and then to battery and also back to CU? Or does it go to invertor direct from meter and then comes back to consumer unit. I have been unable to find a decent diagram/photo that actually shows the wiring route.

Secondly what is the typical size of these things? the battery is easy to find but what a about the invertor as I need a smallish one that can be placed near the CU as the space for battery will be limited..

Any advice appreciated as this may well be a non starter if it look like I don't have the space or simple routes for wiring

[Fintray]

Hi,
Just started looking into home batteries and possibility of getting one so I can charge overnight and use in the daytime - please ignore the financial viability as I am looking at practical feasibility at the minute.
Daily usage is maybe 3-4kw at the minute but could double as am looking at air source heat pump as well.

Likely to more than double regardless of size of heat pump, you would need to work out what size of heat pump is required to heat your house.

My current simplistic understanding is I need
- a 'inverter' of some kind - hybrid? and a certain kw spec (3.5?) Yes, a hybrid(if you want solar PV) see replies below, size depends on how much power you need.
- the battery itself
- some sort of control system (or is that part of the invrstor?) Inverter normally does this.

My main focus is space rests and cabling route.. specifically what happens when the mains cable leaves the meter and goes into the CU.. does it go from CU to invertor and then to battery and also back to CU? Or does it go to invertor direct from meter and then comes back to consumer unit. I have been unable to find a decent diagram/photo that actually shows the wiring route. It can be either, CU/inverter/battery or Mains/inverter, battery/CU.

Secondly what is the typical size of these things? the battery is easy to find but what a about the invertor as I need a smallish one that can be placed near the CU as the space for battery will be limited.. Measure the space you have then check out the specs on likely inverters.

Any advice appreciated as this may well be a non starter if it look like I don't have the space or simple routes for wiring Could also go Tesla Powerwall and site it outside the house.

[AGT]

Plus the requirement to inform the DNO too

[John_S]

I don't think you need a hybrid inverter. What you need is an energy storage inverter where a single unit charges the battery from the mains and discharges the battery into the mains. Hybrid inverters are only needed when you have solar panels as they can also convert the DC from the panels into mains AC. If you are never going to be able to install solar panels, there is no need for the extra expense of a hybrid inverter.

Where are you going to site the batteries? New requirements mean that they have to be installed outside wherever possible and restrict where and how they can be installed inside.
https://knowledge.bsigroup.com/products ... n=standard

A single cable from the consumer unit to the inverter is all that is required and would handle charging and discharging. A sensing cable is also needed which will tell the inverter how much power you are importing so that the inverter can balance it to net xero. The inverter is normally installed near the batteries so as to reduce the length of DC cables which have to be thicker than AC cables as they operate at 48v instead of 230v.

Are you planning to export power or will it all be self consumption?

[Stinsy]

Firstly the financial viability of battery-only installs is at the mercy of actors you cannot control. There was a time when Octopus was the only player in the ToU game, if they’d gone bust when loads of other energy companies were all those battery-only installs would’ve become “decorative”. Even if ToU become less generous because of grid-scale batteries soaking up all the value, the usefulness of your battery-only install is significantly negated. In fact many solar installers (including Octopus) nolonger recommend batteries. There was a time a few years ago where battery-only installs were common, but now solar-only is the thing. Why aren’t you including solar in your plans? Panels are so cheap as to be effectively free! And solar-battery-ToU is an elegantly synergistic trifecta that you’d be silly not to have solar. It also insulates your system from external threats.

Next you need to understand the difference between kW and kWh. And therefore the difference between power and energy. We can only help you once you’ve got that down par.

Right now I can answer your questions:

1) Sure you can install an inverter between your electricity meter and your CU. However that isn’t the normal way of doing things. Generally the inverter sits on a breaker in your existing CU or a mini CU. It uses a CT on the tails to sense current flow and charges/discharges the battery to target zero import/export.

2) if your having batteries only (no solar) then you need a battery inverter. Hybrid inverters are for batteries and solar, great if you’re planning to add solar later, but not needed otherwise.

3) 3.6kW inverters used to be standard because you don’t need to ask permission from the DNO. However nowadays people tend to go for 5kW for the extra power. This is handy if you’re planning to have a HP.

4) Inverters tend to be a similar size to a boiler.

[haf63]

Thanks for the info everyone and will try and answer the questions

1. No solar option as I have a grade 2 listed property I am renovating hence cannot really do anything on the roof. Plus the site is enclosed by large trees so direct sunlight is somewhat limited. So it's battery only or nothing for me I believe.

2. It's a 2 up 2 down detached property and 1 occupent with minimal energy needs plus I am fully insulating all the walls and ceilings plus zoned underfloor heating all of downstairs with 2 radiators upstairs. The energy use outside of winter heat pump use will be minimal energy efficient items used as much as poss as I am doing the renovations.

3. I am not sure installing outside is an option (for reasons I won't go into here) but will look into it - also its a remote site so don't really want to attract thieves with anything valuable outside and building a 'outbuilding' will also be tricky. I was planning to partition a downstairs bathroom to create a 1m x 2m space for both the heat pump HW tank system and batteries (HP will be on external wall of this room). If the invertor is the size of a boiler then that will also have to go into this space.

4. The wiring element is fine now that it's been explained and CU to invertor route is ok for me.

I am currently looking at feasibility of having a battery system or just sticking with normal electric and HP (no gas option either so everything will be electric). The grade 2 nature of the building, the layout and space means I have limited options. I could site the invertor maybe under the stairs or in a hallway by the bathroom but that will impinge on other plans.
It maybe that I am wasting my time and this plan is a non-starter hence doing some research now before I start taking the building apart to renovate.

[AE-NMidlands]

My parents found that their listing was only a single feature: a first-floor oriel window overlooking the hamlet street. If your roof is sacrosanct it might be that you could still have panels close-mounted vertically on a wall or two.
Re inverter power, I would go for bigger than 3.6kW: If I try to export that much the inverter can't supply anything to the house at the same time, which cuts down my evening peak export.
Where there's a will there is a way!
Good luck
A

[shirehorse99]

you would probably need an ac coupled inverter - something like a sofar me3000-sp . this will charge and discharge at 3kw - plenty on eBay - they come up regularly on there - you can then use a time of use charge plan from one of the electric suppliers. I use octopus. the me3000 is 550mm x 350mm roughly.

as regards to batteries its up to you on size - 5,10 or 15kw are the popular ones. fogstar have some pre built . you will need to get the installation signed off electrically, and will have to inform DNO

[Yuff]

I’m thinking of doubling out battery storage, economically with today’s tariffs it makes sense but I’m wary as bi-directional charging would be ideal for us but that seems to get pushed back every year.
It would cost approx £5k and I could export an extra 30 kWh a day.
Seriously tempted

[John_S]

Not only does it always seem to be pushed back, but you will need a lot of other expense

• a new EV

• maybe a new EV charger - who knows if existing ones are compatitable

• upgraded consumer unit with bidirectional RCBOs on the EV charger circuit

• who knows what else

Edited to correct spelling