This off grid solar system UK guide explains the 6 main parts of a system for cabins, log cabins, shepherd’s huts and glamping pods with no grid supply. It also covers how we size it for a British winter, and how we test and certify the 230V side.
Quick answer
In short: how does an off grid solar system work?
An off grid cabin runs on solar panels charging a lithium battery through an MPPT controller. A Victron MultiPlus-II then turns the battery’s energy into 230V, and a Cerbo GX MK3 shows what’s left. We size the battery first, then the solar for UK winter light. Overall, that’s the off grid solar power system UK cabin owners ask us for most. Finally, we inspect and test the 230V installation to BS 7671.
- Battery sized first, then the solar
- Sized for December light, not June
- Fogstar lithium as standard, Victron throughout
- 230V side tested to BS 7671, with an EIC
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On this page 12 sections
- In short: how does an off grid solar system work?
- What is an off grid solar system?
- What is needed for an off grid solar power system?
- Off grid cabin solar system sizing: how much solar do I need to be off grid?
- 12V, 24V or off grid 48v?
- Complete off grid solar system with batteries UK: kit or designed system?
- Off-grid solar system wiring diagram: why we don't publish a generic one
- Powering an off grid shepherds hut or glamping pod
- BS 7671 inspection and testing: is an off grid cabin safe?
- Off grid cabins and off grid log cabin projects: how we help
- Off grid solar system UK FAQs
- Sources
What is an off grid solar system?
An off grid solar system powers a building with no mains cable running to it. Instead, you make and store everything you use on site: panels on the roof or a frame, a lithium battery, and an inverter charger giving normal 230V. You export nothing, so there’s no grid connection to arrange.
So good off grid solar systems start from how you use the cabin, not from a kit in a box.
Too little battery and the system shuts down on the second grey day. Equally, too much solar on a small battery means you pay for energy you can never store.
We design off grid power systems from three facts: what you run, when you use the cabin, and how much winter light the site gets. The off grid electrical systems we build use Victron Energy equipment throughout, so the whole system reports through one Cerbo GX MK3.
What is needed for an off grid solar power system?
In essence, off grid solar power systems come down to a short list of parts, each with one job.
What's in the system
- Solar panelsRoof or ground frame, sized to your loads and site
- Victron SmartSolar MPPTCharges the battery from the panelsDC isolator at the array
- Fogstar lithium batteryLiFePO4, stores the energyFusing and isolation close to the battery
- Victron MultiPlus-IIInverter charger, makes 230VGenerator input when the sun is short
- Cabin consumer unitmetal, double-pole RCBO 230V circuits
01Solar panels
Panel size and count depend on your loads and your site, so we don’t put a figure on them until we know both.
02Solar charge controller
A Victron SmartSolar MPPT charges the battery from the panels. MPPT tracking gets the most from low, flat winter light, which is when a cabin system earns its keep. Also see our solar charge controllers guide and the controllers in our shop.
03Lithium battery
We fit Fogstar lithium batteries as standard. Victron’s data for lithium iron phosphate (LiFePO4) shows it holding its capacity over thousands of deep cycles and losing little energy in charging. So it suits an off grid battery that works every day. More in our battery types guide, or browse lithium batteries.
04Cerbo GX MK3 and VRM
The Cerbo GX MK3 collects data from every Victron device and sends it to VRM, so you can check the system from your phone.
05Victron MultiPlus-II inverter charger
This is the off grid inverter at the centre of the system. It turns battery power into 230V for the consumer unit and charges the battery from a generator when the sun is short.
Its internal ground relay links neutral to earth whenever there’s no AC input, so the RCDs still operate with no grid supply. We therefore set that relay and the cabin’s earthing up for a standalone system. Our inverter guide explains why we use an inverter charger rather than a plain off grid solar inverter, and the MultiPlus-II range is in the shop.
06Protection and distribution
Fusing and isolation on the DC side, close to the battery and the panels, and a metal consumer unit with double-pole RCBOs on the 230V side. Our guide to fitting a DC isolator to a solar installation covers the array end.
Off grid cabin solar system sizing: how much solar do I need to be off grid?
We size a cabin solar system from the battery outwards. Here’s the order we work in.
- 01
Start with daily use and days in hand
To begin with, we take your daily use and the number of days the battery has to cover with little or no sun.
- 02
Match the headroom to how the cabin is used
A weekend cabin, for instance, may only need a day or two in hand. However, one let out through the winter needs much more headroom.
- 03
Size the solar for the darker months
Then we size the solar to refill that battery in the darker months, not in June.
- 04
Read the site
Site matters as much as size. For example, a cabin in an open field and one under trees in a wooded valley can need very different arrays for the same loads. In particular, hills to the south, tree cover and roof pitch all change what the panels see in winter.
- 05
Plan the backup
If winter use is heavy, the generator input on the MultiPlus-II is the backup. It charges the battery and powers the cabin at the same time, so a grey week in the fells doesn’t leave you without power.
For holiday lets
For owners in the off grid cabin uk holiday market, that’s the key point: we size a cabin let all year for December, not for the summer.
Running several units? For Business answers the common questions from cabin operators.
12V, 24V or off grid 48v?
Larger cabin systems usually run at a higher battery voltage, because the same power needs less current. As a result, less current means lower losses and more manageable cables and protection, which is why Victron’s Wiring Unlimited points bigger systems towards 24V or 48V.
Same power, less current
Current = power ÷ voltage. So if you double the battery voltage, the current halves.
| Battery voltage | Current for 2,400W |
|---|---|
| 12V | 200A |
| 24V | 100A |
| 48V | 50A |
Inverter losses add a little to each figure, but the ratio stays the same.
For that reason, we choose the voltage at design stage, from your loads and the Victron equipment that suits them. Our series and parallel wiring guide explains how you build batteries up to a system voltage.
Complete off grid solar system with batteries UK: kit or designed system?
Boxed kits exist, but a cabin works best with a system designed around it. A complete off-grid solar system with batteries uk sellers ship in a box can’t know your loads, your site or your winter use, and those decide everything else.
At Tiny Build Electrics, an off grid solar kit is a custom kit Tom designs after your consult, priced in Xero for your build. In other words, it isn’t a product off a web store. After that, you take one of two routes.
Route 1
Custom kit with Self-Build
Our Complete DIY Self-Build Package comes included free with the kit. You get the parts list and a wiring diagram drawn for your cabin.
Route 2
Fitted
We build the system as a ready-built Victron board in our Witherslack workshop and test it before it leaves.
Off-grid solar system wiring diagram: why we don’t publish a generic one
Why no generic diagram
Every cabin’s loads, cable runs and protection are different, so a generic diagram would mislead more people than it helped. Instead, the Self-Build package includes a diagram drawn for your build. For background, read our guide to selecting the right DC fuse for an off-grid electrical system.
Powering an off grid shepherds hut or glamping pod
01It has to look after itself
An off grid shepherds hut or glamping pod let to guests has to look after itself. For example, the system must cope with a guest who leaves a heater on, without anyone touching it. We set the MultiPlus-II and the battery protection so the battery is never run too low, whatever is plugged in.
02High power loads
We either design high power loads such as kettles, hair dryers and electric heaters in properly, or keep them off the system. So good shepherds hut electrics settle that at design stage, not after the first complaint.
03Monitoring
Above all, monitoring is the big win for owners. A Cerbo GX MK3 reports each off grid battery system to Victron VRM, so you see every unit’s state of charge from home, between bookings. Our battery monitoring guide and remote monitoring service cover the detail.
An off grid shepherds hut on a trailer, or a pod you can move, comes to our Witherslack workshop and goes home already tested. Site operators planning glamping pod power across several units should start with For Business.
BS 7671 inspection and testing: is an off grid cabin safe?
Yes, when we build and test both sides of the system properly. We treat them as two separate steps.
Step 1
The 230V side
A cabin is a fixed building. So we inspect and test its 230V installation to BS 7671, following IET Guidance Note 3: insulation resistance, polarity, earth fault loop impedance and RCD operation. We then issue an Electrical Installation Certificate. We design the earthing arrangement for a standalone supply, with the MultiPlus-II as the source.
Step 2
The battery and DC side
We inspect and check this as its own step, against BS 7671 Chapter 57 (stationary secondary batteries) and Section 712 (solar photovoltaic power supply systems). We also torque every DC connection to the maker’s figure and mark it with a torque pen. Our guide to BS 7671 Amendment 4 also explains what changed for cabins.
Off grid cabins and off grid log cabin projects: how we help
We’re an Authorised Victron Energy Installer, and we supply and fit as one service. We design and build each off grid power system in our Witherslack workshop and test it before it leaves. On-site off grid solar installation is available on request, subject to review.
Customer story
Our work with Unplugged shows how off grid electrical power systems hold up across a run of guest cabins.
Building several off grid cabins, or running a site? If so, our off grid cabin electrics page for operators covers multi-unit projects and the questions that come with them.
Off grid solar system UK FAQs
How does off grid solar system work?
Solar panels feed an MPPT charge controller, which charges a lithium battery. A Victron MultiPlus-II inverter charger turns the stored energy into 230V for sockets and appliances, and can charge from a generator when the sun is weak. Finally, a Cerbo GX MK3 shows the whole system on one screen and online through VRM.
What is needed for off grid solar system?
Solar panels, an MPPT charge controller, a lithium battery, an inverter charger, DC fusing and isolation, and a metal consumer unit with double-pole RCBOs. Then add a Cerbo GX MK3 for monitoring. We size each part to your loads and site, and we inspect and test the 230V installation to BS 7671.
How much solar do I need to be off grid?
It depends on what you run, where the cabin sits and how much winter use you plan. Work out your daily use, size the battery to cover it for the days you need, then add enough solar to refill it in the darker months. So we size it from your loads and the site’s winter light.
Can I install my own off grid solar system?
You can plan it and build the low voltage side. However, a qualified electrician has to design, inspect, test and certify the 230V installation to BS 7671. Our Self-Build package gives you a custom kit and a wiring diagram drawn for your cabin, and we fit and test the rest.
Sources
- Victron Energy, MultiPlus-II 230V manual (installation: ground relay, generator input). victronenergy.com
- Victron Energy, Wiring Unlimited (system voltage and wiring principles). victronenergy.com
- Victron Energy, Lithium Battery Smart datasheet (LiFePO4 cycle life and efficiency). victronenergy.com
- Victron Energy, solar charge controllers. victronenergy.com
- Victron Energy, Cerbo GX and VRM. victronenergy.com
- IET, BS 7671:2018+A4:2026 Requirements for Electrical Installations (Chapter 57, Section 712) and Guidance Note 3. electrical.theiet.org
About the reviewer: Tom Alderdice
Tom holds the 18th Edition (BS 7671) and inspection and testing qualifications, plus NCC training in caravan and motorhome electrics.
Tiny Build Electrics is an Authorised Victron Energy Installer. See Tom’s full qualifications
