Newboy looking for a little advice.

[newtoallthis]

Hi,

My Introduction

I live in a very efficient house (ICF, Triple glazing, MVHR, loads and loads of insulation) that we self-built in 2011. It is entirely electric apart from a small woodburner in the living room.

I was an occasional poster on Navitron but have not paid much attention to the Energy saving scene for a few years, however, prices are rising and hence I am keen to do something.

We have solar thermal and immersion heaters on E7 to heat the thermal store and power the downstairs underfloor heating.

We have a 3.68 KW south facing PV system attracting the highest rate FiT.

Our current rolling 12 month consumption of grid Electricity consumption is around 6000 kWHr per year, however as a result of the kids leaving home (for good ?) I anticipate that our current import projected for a year is around going to be around 4500-5000 KWHr

We self-use about 1000 kWHr of PV generation. About 3000 kWHr of PV generation is exported.

We live in a village which is powered by overhead cables and power cuts are relatively common.

I would like to store some of our generation in a battery and self use it when it is not sunny, and I would also like some off grid capability when the mains power is off.

I keep a spreadsheet containing weekly Daytime/Nightime/PV generated/PV exported figures taken from my Saturday morning meter reads - this data goes back years.

If I had a sufficiently sized battery it looks like we could be self sufficient for about 7-8 months a year, and probably avoid day time imports for another few months.

Current Plan

I am actively considering a Victron MultiPlus II system with something like 7-10 kWHr of Pylontech batteries. It might make sense to stick another PV system on our East/West garage but that would be a possible upgrade for the future.

I would install the Victron in the garage and perhaps build a small fire-proof battery house either inside or close to the garage.

I appreciate that at the moment this does not make financial sense, but I am a firm believer in fixing the roof when the weather is good, and there is no time like the present.

A few questions.

Am I correct in saying that a Victron MultiPlus can be configured as a whole house UPS if coupled to sufficient batteries ?

Can such a system be configured to use any surplus PV generation to charge the batteries rather than exporting to the grid ?

Is it possible to configure such a system to part charge the batteries on E7 in order to ensure that there is always a few kWHrs of charge in the batteries at the end of then E7 cheap rate ?

Am I missing anything obvious ?

Thanks in advance for any advice that the experienced posters on here might make.

One way or another I will keep you guys posted on whatever we finally decide to do.

Regards

P

[Stinsy]

Welcome!

• I believe the MultiPlus can be configured to provide whole-house backup.

• You'd be better to split off UPS and non-UPS circuits. EG: cooker, EV charging point, resistive electric heating, and maybe utility, can be excluded. This dramatically reduces the size of inverter that you'll need.

• Yes such a system will store energy from your solar that will otherwise be exported and power your house overnight. However you'll need to put-aside a portion of your battery for power cuts.

• Yes you can charge batteries from cheap-rate too. I haven't heard of a "good" E7 tariff, many of us are on Octopus Go.

• No need for the battery store to be "fireproof" LiFePO4 batteries are intrinsically safe and cannot catch fire no-matter what you do to them!

[openspaceman]

• No need for the battery store to be "fireproof" LiFePO4 batteries are intrinsically safe and cannot catch fire no-matter what you do to them!

That's interesting as it has been my chief worry having my 6kWh one sited in the hallway byt the front door, why are they so different from the lithium ion ones that do catch fire and are difficult to extinguish?

Newtoallthis this thread is along the lines I want to go although I only produce 3MWh a year and although it's impractical to store all the shortfall I have in winter we do only use 6-8kWh per day and will still need to buy in 450kWh in winter.

Our house is the opposite of yours, leaks heat like a sieve but a woodburner just about keeps us comfortable in winter.

[newtoallthis]

Welcome!

• I believe the MultiPlus can be configured to provide whole-house backup.

• You'd be better to split off UPS and non-UPS circuits. EG: cooker, EV charging point, resistive electric heating, and maybe utility, can be excluded. This dramatically reduces the size of inverter that you'll need.

• Yes such a system will store energy from your solar that will otherwise be exported and power your house overnight. However you'll need to put-aside a portion of your battery for power cuts.

• Yes you can charge batteries from cheap-rate too. I haven't heard of a "good" E7 tariff, many of us are on Octopus Go.

• No need for the battery store to be "fireproof" LiFePO4 batteries are intrinsically safe and cannot catch fire no-matter what you do to them!

Splitting the UPS/non-UPS circuits makes a lot of sense however, as the overwhelming amount of the overnight consumption is electric charging of the thermal store via an Immersion heater, it might not make sense as I will find myself without a user for PV electricity stored in the batteries. I will need to do a bit more analysis of the numbers.

Its good to hear that I don't need to worry about batteries bursting into flames and hence it is much more likely that the battery will go in the garage.

I am currently on a very cheap EDF E7 deal that runs until Sept 2024 (I swapped for a long term contract when I started suspecting that the electricity market was going to go crazy in Sept last year) When this deal comes to an end then I will investigate Octopus as they seem very popular in this parish.

I have a 3.68 KW PV system that I assumed was registered under the old G83 system, when I install a battery I believe that I will need to make an application under the G98 rules - is this correct ?

Thanks for the answers -it is very good of you to take the time to help a beginner, and they give me confidence that I am heading in a reasonable direction.

Thanks again.

P

[nowty]

I have a 3.68 KW PV system that I assumed was registered under the old G83 system, when I install a battery I believe that I will need to make an application under the G98 rules - is this correct ?

Thanks for the answers -it is very good of you to take the time to help a beginner, and they give me confidence that I am heading in a reasonable direction.

Thanks again.

P

No because you are already at the limit of a G98 application. It will be either a G99 Fast Track (up to another 3.68kW battery inverter) or a G99 application for a larger inverter. Note, both these are Pre-Install applications.

[ALAN/ALAN D]

Mr Stinsy wrote.

" No need for the battery store to be "fireproof" LiFePO4 batteries are intrinsically safe and cannot catch fire no-matter what you do to them! "



Best not to buy. “ LG Chem ICR18650S2 LiCoO2 cells and use inside the house “


Results indicate that LG Chem ICR18650S2 LiCoO2 cells pose a CH4 explosion hazard from a cell internal short circuit. Under specified test conditions, A123 Systems 26650 LiFePO4 cells were safer than the LG Chem ICR18650S2 LiCoO2 cells at a conservative statistical significance level.

[Stinsy]

Splitting the UPS/non-UPS circuits makes a lot of sense however, as the overwhelming amount of the overnight consumption is electric charging of the thermal store via an Immersion heater, it might not make sense as I will find myself without a user for PV electricity stored in the batteries. I will need to do a bit more analysis of the numbers.

The battery system will power all circuits when the grid is up, up to its maximum. Going over the inverter max is no problem, the grid will supply the rest.

In grid-down situations the inverter has to supply all the power, so you either need a huuuuge inverter or you risk tripping it. The solution is to split the circuits to supply only some circuits in grid-down condition.

[Stinsy]

• No need for the battery store to be "fireproof" LiFePO4 batteries are intrinsically safe and cannot catch fire no-matter what you do to them!

That's interesting as it has been my chief worry having my 6kWh one sited in the hallway byt the front door, why are they so different from the lithium ion ones that do catch fire and are difficult to extinguish?

Newtoallthis this thread is along the lines I want to go although I only produce 3MWh a year and although it's impractical to store all the shortfall I have in winter we do only use 6-8kWh per day and will still need to buy in 450kWh in winter.

Our house is the opposite of yours, leaks heat like a sieve but a woodburner just about keeps us comfortable in winter.

LiNiMnCoO2 and LiCoO2 batteries suffer “thermal runaway” this is where: the batteries getting a bit hot starts a reaction that generates even more heat and this keeps going until they start a fire that is exceptionally difficult to extinguish.

LiFePO4 batteries do not suffer thermal runaway. The energy density isn’t quite as good so LiFePO4 isn’t used in BEVs (or phones, or laptops) but for stationary applications they’re a bit cheaper, last longer, and are a WHOLE LOT safer.

[openspaceman]

Thank you

[sharpener]

<Am I correct in saying that a Victron MultiPlus can be configured as a whole house UPS if coupled to sufficient batteries ?>

Yes. If you connect your PV on the output side then it will stay operating during a power cut. On the input side it won't but you can get away with a smaller Mutliplus as it does not then need to have the same rating as the PV system.

I have the whole house on a 5kW MultiPlus, because it has 50A passthrough capability and splitting out the critical circuits would have been a nightmare, you might need this much as you cook by electricity. Others on this forum would disagree and suggest 3kW is enough if you are careful.

<Can such a system be configured to use any surplus PV generation to charge the batteries rather than exporting to the grid ?>

Yes, using the Victron ESS Assistant the priority order for using the PV is 1 house loads, 2 battery charging, 3 export

<Is it possible to configure such a system to part charge the batteries on E7 in order to ensure that there is always a few kWHrs of charge in the batteries at the end of then E7 cheap rate ?>

Yes, you can schedule up to 5 charging periods, with separate SoC target values. There is a limitation in that discharge is not allowed during charging periods even if the battery is more than full enough. But with 7 kWh of batteries a 5 kW Multiplus will charge them at 50% per hour so I only need a short top-up period before the E7 goes off. You can get round this and do more complicated programming in a visual language called Node Red.

<Am I missing anything obvious ?>

No, that about covers it, you have obviously done your homework!