10 Years off grid

Ten years ago we resigned ourselves to going off-grid for electricity; these days we wonder why everyone isn’t doing it!

At that time we were building our home on a tight budget. The electricity utility provider quoted £24,000 to connect it to the electricity grid. We knew we could install a solar-based energy system for much less. So we were forced, kicking and screaming, into what has turned out to be one of the best decisions we’ve ever made.

I don’t know anything about building a solar energy system (or I didn’t back then) – but I don’t mind learning how things work; what devices …and with what power ratings we’ll need; and then building it myself. As the roof wasn’t slated when the off-grid decision was made, I even designed and built my own solar panel mounts for fifteen panels – saving more money.

Ten years ago these were the main components which made up our energy system:

• Fifteen south-facing solar panels offer 4kWp
• The inverter/charger is a MultiPlus 48/5000/70
• The original battery storage was from 8 x 12V AGM Deep Cycle batteries of 220Ah each. We changed them for Lithium Battery Smart after seven years …though I still use some of the original Lead Acid batteries on my boat.
• There was a BlueSolar MPPT solar charge controller – now a SmartSolar MPPT 150/100 solar charge controller. The difference between them is principally that the latter has Bluetooth on board.
• We had a CCGX which has now been upgraded to a Cerbo GX data communication centre device. It harmonises all component parts of the system passing data between them, and also allows the system to be accessed from anywhere in the world via the free to use platform VRM. We can view real time data, install firmware updates when necessary, or even change system settings – from anywhere.
• We have a GX Touch screen display which allows us to do all the things above, at home.

The biggest mistake I made on the original build was to bring the wiring of each panel into the house before daisy chaining them into groups of three. This meant that the solar energy harvest had to travel through almost 200 metres of 4mm cabling. My thinking was that I could check that each panel was functioning correctly at any time without climbing onto the roof. Perhaps that idea was okay in the early days because I did find one or two of the MP4 connections I had made were dodgy after a year or two – having been poorly crimped.

The system worked fine, but after seven years I decided to upgrade the cables from 4mm to 6mm, and to daisy chain them on the roof (halving the cable run). I immediately noticed an improvement of over 15% in the solar harvest. Our 4kWp array will occasionally max out at 4.6Kw for short periods!

Inverter Charger

We have a MultiPlus 48/5000/70 inverter/charger. During the last ten years I don’t recall that it has been overloaded by our needs except on two or three occasions. If the washing machine is on a hot wash drawing 2kW, at the same time as I’m heating twenty litres of water for beer-making – also drawing 2kW, and the immersion heater was also on – consuming 3kW – that would result in an overload shutdown. We are aware of the limitations of our inverter and consequently would allow the immersion heater (3kW) to run at the same time as one other big consumer (up to 2kW). Whilst running big loads, the power draw from more incidental consumers – such as lights (we have LED) and standby currents – are not great enough to overload the Inverter which in any case is capable of providing short term power of up to 10kW.

The MultiPlus is the AC charging device for our back up generator. It has a generous charging capacity of 70 amps; in practice we have set the generator current limit to 23A. Setting it higher than that we notice that the generator will experience an over temperature shut down after about 30 minutes – so it’s great to have the facility to limit the generator charge current setting to a level which works for us exactly.

The MultiPlus is capable of running my stick-welding machine – but it’s harder to strike an arc if I’m using it far away from the inverter, on an extension lead, and the cable length is too long.  Whilst welding, it tickles me to know that stored sunshine is melting my weld metal.

Batteries

For the first seven years we used Lead Acid batteries offering 440Ah at 48V. They were perfectly satisfactory, and we were careful not to deplete them beyond 50% State of Charge (SoC). Key to this was only running large energy consuming devices – such as the washing machine – around the brightest part of the day wherever possible …or if it was overcast, delay the job until tomorrow, if ‘tomorrow’ was forecast to be sunnier.

If lead acid batteries are habitually allowed to drain below 50% SoC they will age prematurely, lose capacity, and need to be replaced much sooner than hoped.

We changed our batteries after seven years when I judged that their capacity had fallen to about 80% of the original  – 440Ah had reduced to 350Ah. For the new battery storage we chose Lithium. That change brought an immediate advantage – as well as the usual long-term advantages:

One of the frustrations of using Lead Acid batteries becomes obvious during winter months when the days are short. Winter sun can be very bright because cold air carries less humidity, resulting in more irradiance for solar harvest. But Lead Acid batteries can only be charged relatively slowly – a 100Ah battery can only be charged at 20A, and in order to avoid boiling the battery even that charge current must be gradually reduced once the SoC climbs over about 80%. (Remember that you can only use the top 50% of SoC, in any case).

Lithium Batteries have much lower internal resistance – allowing them to accept charge at a much faster rate – the recommended charge rate for a 100Ah lithium battery is 50A – two and a half times faster – and they can accept that level of charge almost until they have reached 100% SoC. All this is a long way of saying that on short winter days when you may only get a couple of hours of decent sunshine, the difference between lead acid and lithium in terms of solar energy storage is remarkable. A lithium battery can frequently be fully charged from solar on days when lead acid will never get there.

The cost of lithium batteries is falling. At the time of writing the purchase price of lithium batteries is about two-and-a-half times the price of Lead Acid batteries per Ah. In the long run, however, the picture changes – Lithium batteries are the cheapest because they can achieve as many as ten times the number of charge-cycles of a lead acid battery. And during each one of those charge cycles more of the Lithium battery’s stored energy can be used – 80% for lithium vs 50% for Lead acid. The Lithium battery charge rate is faster (as already noted); and the charging process is more efficient – less energy is lost as heat, so more energy gets stored. Lithium Batteries store more than 95% of the energy they receive – Lead Acid might not manage much more than 80%. Get Lithium batteries if you can.

We don’t heat our home with electricity, neither do we drive an electric vehicle. Some off grid homes do. Off-grid (and grid-tied) solar energy systems can be built to huge scale – even allowing homeowners to warm their home with an air/ground source heat pump during the winter …and to charge an EV. Victron Lithium NG batteries offer a maximum storage capacity of 385kWh in a single bank which must be controlled by the Lynx Smart BMS NG battery management system. More battery banks can be added by parallel connection of additional Lynx Smart BMS NG devices.

Field array of solar panels for an off-grid home in the UK which uses an air source heat pump.

The size of the a solar energy system is only really limited by budget …and the availability of land to site what is likely to be more than 100 solar panels – usually ground mounted at this scale.

(Large solar energy systems employ high voltages and are unsuitable for amateur build – they must be installed by a qualified electrician.)

The great news is that any sized solar energy system will pay for itself within six or seven years, typically. The lifetime of the installation – excluding the batteries – will be more than twenty years. Even a lithium battery which is well looked after has a life expectancy of more than 13 years.

No sun?

Unfortunately it doesn’t matter how big your solar array is, if the sun is obscured by fog or covered by dark clouds for days on end your energy harvest will be miserably small. To secure themselves against those eventualities, off-grid owners usually have a back up electricity generator. Ours is rated at 5kVA – last year we ran it for thirty hours. We didn’t need to run it even for that length of time as our lowest battery state of charge during that period was 51% (of a 21kWh capacity); but because we used to have lead acid batteries we still haven’t quite got used to the idea that you can safely discharge Lithium batteries down to 20% SoC. The generator is an SDMO Silence 6000. After ten years it starts first time, is easy to maintain, and runs quietly.

Our energy use is about half the typical household usage in the UK – there are only two of us. Our energy demand last year was met by Solar (95.5%) and Generator (4.5%). The cost of fuel for the generator was just over £40/$54/€46.

The current UK energy cost, per annum, for a typical household is £1720 – 26p per kWh for electricity and 6p per kWh for gas. In addition there are standing charges of £187 per annum for electricity and £110 per annum for gas.

Make mistakes!

I prefer getting things right first time – but it doesn’t teach me anything!

• In the original system build I fused the solar panels with ‘auto’ style fuse holders of poor quality – I noticed that they would often get quite hot. We now use professional breakers.
• I got quite confused with the communication cables between devices – eventually I was forced to read the manual!
• My MP4 terminal making was poor – I ended up remaking all of them after a couple of years. I know better now.
• I tightened connections to the battery terminals using a double ended spanner with no insulation – when the other end accidentally touched the opposite terminal of the battery it resulted in a short-lived but impressive firework display.

Making mistakes led to a virtuous circle which I wasn’t expecting …increased knowledge was followed by a higher degree of self-reliance when problems arise – I became more confident that I could find out how to fix it. Analysing the problem gives rise to hunches which may help identify the cause. It may be covered in the troubleshooting section of any product manual – or if that doesn’t throw light on the problem someone else may have had a similar experience on the Victron Community. It includes a DIY space for less technical people like me.

Off gridding is life-changing!

The more you do, the more you can do. I found that a willingness to try new skills of which I have no experience works every time! All it takes is the confidence to begin by taking the first step. Practical skills are learned by doing. I’ve taken it to extremes: I designed then built our home – carrying out every trade.

We’re off grid for all utilities; we heat our home with wood felled, sawn and split ourselves; I found a fresh water spring which is now tanked, pumped and filtered. And we have a private waste treatment plant. As a result the only bill that arrives in the post is a community charge (aggregated local service tax) at a cost of about £1100 / $1500 / €1275 per annum.

I love to cook – so I built a ‘summer’ oven…

and then a smoker!:

Apart from the cost-savings, building your own power system allows you to really understand how it works. The advantage of that isn’t immediately obvious – but when something goes wrong you can fix it yourself rather than wait for an engineer to visit …who will then leave you with a bill which is bigger than you’d hoped!

In the UK, we have a rather old fashioned proverb. Before I tell it to you I need to explain that we used to have a 1200-year-old monetary system in which 12 pennies were equivalent to one shilling: The proverb was: Weekly income one shilling, expenses one shilling-halfpenny – result misery; Weekly Income one shilling, expenses eleven-pence-halfpenny – result happiness. The same reassuring philosophy applies to living with off-grid electricity. There are two sides to it – how much energy you harvest on any particular day, and how much you consume. Sensibly managing that ‘income and expenditure’ leads to happiness.

Knowledge is power – it’s changed the way we live, providing us with independence and security; and it has completely slashed our cost of living. With a minimal outgoings we can choose how we work – resulting in lifestyle choices that wouldn’t be available to us if we were burdened with debt.