Inverter and battery storage sizes

[Saints1]

Good evening all,

 

I wondered if anybody could help. 
just trying to do some calculations in regard to our self build and solar panels. 
So within my plan I have added 16 integrated 410wp Marley solar tiles to be fitted on the roof. Although this has been calculated, one thing that hasn’t is what size inverter and battery for storage. 
I just wondered if there is anyone out there that has some good knowledge in this field?

 

To give some perspective on the build it is a fair sized 4 bedroom detached house (approx 300square meters) that will have 2 electric vehicle charging ports and an ASHP. 
There will be two adults and a teenager living in the house. 
 

Any help or advice is greatly appreciated. 
 

[SteamyTea]

Have you run the system though PVGIS, I think they have a storage calculator now as well, but not sure on that.

 

 

[JohnMo]

PV, battery and inverter can be confusing.

 

So looking at battery first and how it powers the house. You need an inverter big enough so it passes enough kW to house so you don't draw too much from the grid. So for example if you have a 3kW inverter, every time you put the kettle on you could be drawing peak electricity in to cover base load, Same when cooking your tea.

 

We have a 6kW and that suits our life style well enough.

 

Then there's the question of DC or AC coupled battery. DC coupled generally will only supply a dedicated circuit in a power cut, AC can/will provide whole house.

 

Then there's the panels and there relationship with the inverter, you can over clock (way more kWp than the kW rating of inverter), 90% of the year you loose nothing, a good summer day when you are producing bucket loads of energy the inverter will clip this back. 

 

So loads to think about.

 

First MCS install or self install?

G98 export limit (3.76kW) or unlimited or something in-between?

Do you have power cuts?

[Saints1]

3 minutes ago, JohnMo said:

PV, battery and inverter can be confusing.

 

So looking at battery first and how it powers the house. You need an inverter big enough so it passes enough kW to house so you don't draw too much from the grid. So for example if you have a 3kW inverter, every time you put the kettle on you could be drawing peak electricity in to cover base load, Same when cooking your tea.

 

We have a 6kW and that suits our life style well enough.

 

Then there's the question of DC or AC coupled battery. DC coupled generally will only supply a dedicated circuit in a power cut, AC can/will provide whole house.

 

Then there's the panels and there relationship with the inverter, you can over clock (way more kWp than the kW rating of inverter), 90% of the year you loose nothing, a good summer day when you are producing bucket loads of energy the inverter will clip this back. 

 

So loads to think about.

 

First MCS install or self install?

G98 export limit (3.76kW) or unlimited or something in-between?

Do you have power cuts?

It will be an MCS install

i am having three-phase electricity supply if that makes any difference. 
I am very new to all this so please allow for my lack of knowledge. 
 

Don’t have any power cuts whatsoever. 

[Saints1]

15 minutes ago, SteamyTea said:

Have you run the system though PVGIS, I think they have a storage calculator now as well, but not sure on that.

 

 

I haven’t but I’ll certainly look at it, thank you 

[SteamyTea]

Excess can also be easily and cheaply stored as domestic hot water

[JohnMo]

3 phase (still no idea why anyone needs it in a domestic house) allows 16A per phase export on G98. So about 3.6kW X3. G98 you tell DNO after you start generating.

 

But how you manage the phases, to make best use of the solar is something I have looked into. As most the house will only make use of a single phase.

[Mattg4321]

Currently most cost effective to have a battery big enough to see you through 24 hours in the winter when there is little generation. 
 

Charge it overnight to 100% at cheap rate then export any excess solar at higher unit price than you buy in for overnight. If you think you’re saving the planet by using maximum amount of generation on site, then that changes things. 
 

[Dillsue]

12 minutes ago, Mattg4321 said:

Currently most cost effective to have a battery big enough to see you through 24 hours in the winter when there is little generation. 

That will be a whopping battery to run an ASHP for 24 hours in freezing weather. Not sure it's cost effective to have a battery that size rather than use peak time grid eleccy for the few freezing days a year most people have???

[Mattg4321]

3 minutes ago, Dillsue said:

That will be a whopping battery to run an ASHP for 24 hours in freezing weather. Not sure it's cost effective to have a battery that size rather than use peak time grid eleccy for the few freezing days a year most people have???

In that case worth looking at something like octopus cosy as there are multiple cheap rates during each 24h period. 
 

As you say though, it’s worth weighing up whether it’s best to not worry about the very coldest of days. 

[JohnMo]

38 minutes ago, Mattg4321 said:

Currently most cost effective to have a battery big enough to see you through 24 hours in the winter

Or big enough for a cosy tariff and charge 3x