Inverter, PV and Battery Storage Location

[Luke1]

I'm working out how best to build a PV and battery storage system.

Log store & shed (not insulated) approx 25m from the main house. 

PV Panels to be installed to log store & shed - 12 x 400W panels.

Battery storage to be added sometime in the near future.

 

Ideally I think I'd like the batteries to be inside the house as I understand they don't operate particularly well below 0C (I'm thinking of the lithium Pylontech batteries)

 

The inverter and batteries can go in the loft space of the house, or in the log store. 

 

Would it be best to keep the DC run short and have the inverter in the shed and batteries in the shed.

Or could I run the DC cables back to the house, or would the losses / cable need to be too big? 

Or do I use a separate inverter for the PV panels and the batteries? (Will this cause me potential control issues?)

 

[Nickfromwales]

You've just described my house and my thoughts tbh. As I've been off-the-chart busy lately I've had to belay my own install.

I'm putting 21 panels ( Solarwatt 400w ) on top of the upper garden shed / pergola ( 50/50 at 11m wide x 4m deep / sloping roof to compliment ) and a further 18-21 panels on the gazebo roof ( upper garden gets hammered by the East sun and gazebo same for West ).

I think you'll want the same that I plan, which is a hybrid inverter, as this allows the panels and batteries to be seamlessly integrated on the DC side. The DNO then only care about the max kW rating of the inverter as that's the only bit of kit 'visible' as AC connected equipment.

My plan is to insulate the shed potion with lots of cheap insulation, but to also plan ahead for cooling it during the summer ( by purging vs fans but not ruling them out as they'd run off excess generation anyways ) and install all of the kit in there, running AC back to the house via a decent sized SWA cable.

I plan to have a load of panels to give me a decent amount of winter generation, as solar irradiance levels drop to ( well ) below 25% for the 3 months or more of UK wintertime. 

[Luke1]

10 minutes ago, Nickfromwales said:

You've just described my house and my thoughts tbh. As I've been off-the-chart busy lately I've had to belay my own install.

I'm putting 21 panels ( Solarwatt 400w ) on top of the upper garden shed / pergola ( 50/50 at 11m wide x 4m deep / sloping roof to compliment ) and a further 18-21 panels on the gazebo roof ( upper garden gets hammered by the East sun and gazebo same for West ).

I think you'll want the same that I plan, which is a hybrid inverter, as this allows the panels and batteries to be seamlessly integrated on the DC side. The DNO then only care about the max kW rating of the inverter as that's the only bit of kit 'visible' as AC connected equipment.

My plan is to insulate the shed potion with lots of cheap insulation, but to also plan ahead for cooling it during the summer ( by purging vs fans but not ruling them out as they'd run off excess generation anyways ) and install all of the kit in there, running AC back to the house via a decent sized SWA cable.

I plan to have a load of panels to give me a decent amount of winter generation, as solar irradiance levels drop to ( well ) below 25% for the 3 months or more of UK wintertime. 

 

Interesting, I think what you're describing makes sense. I should be able to insulate the shed portion fairly well to, so perhaps that will negate some of the winter losses.

 

My plan is also to split my solar across the shed & log store at 35 degree slope and also a future pergola where I will either have them flat or perhaps tilted South slightly, but the gain doesn't seem huge by raising them 10 degrees or so, and I don't really want to see them poking up from the pergola.

 

I've been looking at the voltacon website for budgeting purposes as it gives you customisable sizes and then I just need to account for the electrician, cable etc.

https://voltaconsolar.com/solis-hybrid-5kw-pylontech-us2000-system.html

 

Good Idea on the AC back to the house. I have a 50mm duct going in as we speak, so it's probably worth running 2 cables through it. One for the grid tied side and another with the backup power. 

 

[billt]

Depends which DC cables you're talking about. If it's the 48V battery cables they want to be as short as possible. If you mean between the panels and the inverter, that depends on the string voltage. If the DC voltage is much above 250 then there's no loss in making the DC cables longer than the AC cables.

 

Personally there's no way that I'd put batteries in the loft. LiFePo4 might be the safest Lion chemistry, but you're going to be storing a lot of energy, if it goes wrong with poor access the consequences could be sever.

[billt]

My batteries are outside the house. I disconnected them when we had those sub zero days recently, but that was probably over cautious, as the batteries never got to zero. We don't actually get many days of very low temperatures in most of the more southerly parts of the UK.

 

The issue is that LiFePo4 cells don't like being charged at low temperatures, you can still discharge them if yoou don't use high discharge rates. When I rebuild my batteries I'm going to put heating pads under the cells, thermostatically controlled, for the 2 days a year when it might be an issue.

[Nickfromwales]

45 minutes ago, Luke1 said:

the gain doesn't seem huge by raising them 10 degrees or so, and I don't really want to see them poking up from the pergola.

Not quite. The panels are only typically "self-cleaning" after 12 degree inclination, eg the rain will do the job. Solar irradiance improves quite significantly after the 12-15 degree mark, so I'd re-think my policies there  

[Pocster]

Batteries in the loft would worry me . Not just because if 1 goes pop but access for the future I.e replacing them . Outside definitely best ( unless you have heaps of internal wall space ) . I was considering insulating my SolarEdge battery as it seems to struggle at below zero ; but then airflow especially in summer could be an issue - so I did nothing - easiest solution .

Edited February 11, 2023 by pocster

[Nickfromwales]

1 hour ago, billt said:

When I rebuild my batteries I'm going to put heating pads under the cells, thermostatically controlled, for the 2 days a year when it might be an issue.

I was going to do similar but with some greenhouse tubular heaters, to heat the entire space ( was thinking about inverters etc benefitting too ). Heat pads sound a better ( more targeted ) solution for the batteries, thanks.

[Luke1]

Thanks for the advice. Looks like they'll be outside on heated pads! 

I didn't appreciate that there was still a risk with the new LiFePO4 batteries, but as you say, there will still be a significant amount of energy being stored.

 

Seeing as space won't be an issue for storing batteries in an outbuilding, is there better bang for your buck by getting an older design of battery? 

[Nickfromwales]

2 hours ago, Luke1 said:

Seeing as space won't be an issue for storing batteries in an outbuilding, is there better bang for your buck by getting an older design of battery?

I had considered this, but I've decided to go for something recognised ( with the off-grid community ) and just stick with that.

 

This is the Inverter

 

And the batteries;

 

leoch-lfeli-48100tcan-pd-en-v1.2.pdf

 

48mb-user manual 6dip.pdf

[Nickfromwales]

 

 

The batteries I linked are fully balanced, whereas the cheap Pylontech units aren't. The above is what happens when one cell decides to feel neglected.

[Luke1]

The batteries you linked are twice the price of Pylontech (when adjusted for capacity), but perhaps a small price to pay if they are significantly more likely to have a catastrophic failure. The photos are fairly concerning! 

 

I presume you need to complete the G99 Application if you grid tie that inverter? It seems a bit extreme for my requirements given that I'll probably be doing a grid tie system.