Off-grid experience

[Originaltwist]

How about a wood burning stove and a heat bank? A 14kW Clearview 750 with a 7kW back boiler works well for your size of house. You get almost permanent hot water and heating too. Twin tanks are best. A gas boiler is a good addition and will get little use to trouble your wallet. I had this arrangement and used to run the boiler for 10 minutes every morning just to make sure the showers were in the bank. Gas use was so low that caravan type bottles were sufficient.

Then bigger PV and battery along with a Victron Quattro to pull in a generator occasionally. Then Robert's your father's brother.

[jack]

2 hours ago, Muellar said:

 

lol... you've reminded me of a Father Ted sketch @Conor, thank you! And yes, it's how I felt when I saw the calcs come through I just couldn't believe the figures being presented but they stood by their calcs and this is an area I get confused in so I left them to their stuff being told by the architect they were good and could 'work wonders with NIE'.... unfortunately not the wonder I'd hoped for.

 

If they did calculations, then they ought to be able to present them and explain their maths. You've paid for it, so demand they show their working.

 

40 kW is 166 A.

 

Like you're planning, I have a "big house all electric" (290 m², 5 kW ASHP, 7.2 kW car charger, 3 ovens + induction hob) and my very conservative electrician was more than happy with our existing 100 A supply.

[saveasteading]

1 hour ago, Muellar said:

from his experience would need 35-40kVA

You need someone with more experience then.

 

Do you have a schedule of the power needs? Ask for it.

You don't just add it all up. I think the term is divergence, for not all toasters, hairdyers etc being on at the same time.

[SteamyTea]

4 hours ago, Muellar said:

tried this and got myself in a pickle

When I am free from n a couple of days (only got one day off this week), I shall try and knock up a generic spreadsheet.

 

Is NIE Northern Ireland?

Think they have different rules there.

[jack]

29 minutes ago, saveasteading said:

I think the term is divergence, for not all toasters, hairdyers etc being on at the same time.

 

Diversity.

[saveasteading]

 

I understand that multiple electric car chargers can also sort themselves out in some way.

[jack]

Yes, I think some of them can. In my case, even 2 x 7 kW car chargers and the ASHP pump running flat chat on top of ordinary background loads wouldn't take me anywhere near the limit.

[Muellar]

1 hour ago, SteamyTea said:

When I am free from n a couple of days (only got one day off this week), I shall try and knock up a generic spreadsheet.

 

Is NIE Northern Ireland?

Think they have different rules there.

 

Yes, Northern Ireland Electricity. I've made my own attempt at a sheet but I got an even larger figure... duh. Thanks for offering to knock one up for me, i'm very grateful.

 

 

Edited December 24 by Muellar

[Muellar]

3 hours ago, Originaltwist said:

How about a wood burning stove and a heat bank? A 14kW Clearview 750 with a 7kW back boiler works well for your size of house. You get almost permanent hot water and heating too. Twin tanks are best. A gas boiler is a good addition and will get little use to trouble your wallet. I had this arrangement and used to run the boiler for 10 minutes every morning just to make sure the showers were in the bank. Gas use was so low that caravan type bottles were sufficient.

Then bigger PV and battery along with a Victron Quattro to pull in a generator occasionally. Then Robert's your father's brother.

Now I'd originally thought of having something like that, but was told 'don't be silly'. i'd seen a Woodfire EX15 that i'd quite liked, and had seen that not only would it be a nice feature, but we'd also have back up should things go bad - like recently during the storms and power went down.

 

This whole experience with the cost of power has really made me think that maybe i'd dump the whole induction hob thing and go with Calor gas tank for cooking use and also a boiler to be used now and then, with adding in the Woodfire EX15 for use during winter and as a back-up.

 

Then go back to NIE and ask 'how little can you give me' just for small power and other items.

[ProDave]

Do NIE ask for calculations?  If not just pick a low figure like 12KVA and re apply.  They are not going to connect you with a thinner cable just because you ask for a low rated supply.

 

If they question the change, tell them your original estimate was made by someone not understanding how it is done, and now you have a more accurate understanding of the energy needed for your house.

[Originaltwist]

The Woodfire EX15 looks nice although I have no experience with them.

I go for the Clearview because:

Stainless steel back boiler - quick to replace if it fails - which they don't

I never go more than 50% heat to water - condensation on the back boiler and not enough to the room otherwise.

Clearview stoves don't break.

Chuck a big log in and they will stay in all night - saves a fortune in matches.

 

I guess it's just down to what you fancy in the end.

[Roger440]

For what its worth, before we bught this place, we looked at a place a few miles away that was off grid. Was running on a ramshackle collection of old gennys, some lead acid cells etc.

 

That would be no use to me. I rang these guys. https://www.energy-solutions.co.uk/applications/off-grid/residential

 

At the time, £40k, all in, solar, batteries, generator, control system etc. Completely automatic. So long as its filled with diesel. The cost of a connection would far exceed that, and if you take out the capex on it, your actual cost per unit of electricity was way way lower than the grid.

 

I thought it was quite a sensible solution. Didnt buy the house though.

 

The one we did buy has an 11kv pole directly behind my barn. I wanted 3 phase in the barn. Still came in at £17.5k plus VAt with me doing the trenching. Im sure that the minute they think you might spend money, they start adding in loads of extra stuff, that would normally be "maintenance and replacement" and get you to pay for it instead.

 

I dont have 3 phase. 

 

It does mean, however, with both a house and barn needing heating, oil remains my only sensible option as otherwise overall load starts to get to high if ASHP's were to run both along with everything else. But, tough, not paying £20k. To have higher priced electricity than a domestic supply.

 

Its a good thing that back in the 50's when they were connecting houses to the grid for the first time, they operated in a rather different way!

 

 

[Alan Ambrose]

OK, supposing in December you use 90% of your proposed 40,000W / 175A supply. There are 744 hours in December, so that’ll be 744 x 40 x 90%  = 26,784 kWh. At, say, 20p per kWh, that’ll be £5.4K for December. Maybe £30K of electricity a year given that you’ll be using far less in the summer? Is that what you’re expecting?

 

No? Why not? So, perhaps you won’t be using that much electricity and maybe you don’t need that big a supply. Search for ‘Veyron’ on the forum and you’ll see related discussion around this subject.

 

 

Edited Wednesday at 07:31 by Alan Ambrose

[SteamyTea]

Right, have knocked up something to estimate energy usage (electrical).

The first sheet "Loads" is where you list everything you have that is electrical and there power.  Usually you can find the power on the appliance, or take a good guess.  Better still, for plug in appliances, get a cheap energy monitor from Lidl.

Fill in Columns Loads and Power/W (A and B).  Note that they are all in W [watts].

 

So once you have filled in the first column (A), you have to fill in the Utilisation Factor column (C). This is for how long you actually use the appliance.  This will be your best estimate. The Utilisation Factor is a decimal fraction of a day, so if used for 1 hour a day, 1/24 = 0.04, 15 minutes a day 15/60/24 = 0.01.   I have used my house as an example on a typical winter day (23/12/2024).  It is not perfect, but gives a good first approximation.

 

Columns G and H show the maximum possible load i.e. absolutely everything on at the same time, the mean power, in kW, and the estimated daily energy usage in kWh.

 

The next two sheets Smart Meter Data and Home Monitoring Data are bonus sheets if you have the data.

Usually you can download a daily file from your current supplier and just paste the data in (use paste special as dates can be weird).  I have built my own energy data logger so have included that, but you can ignore it, though it does show a useful metric of Zero Power, which is useful for off grid living as there may be a minimum power draw needed (off grid would not work very well for me as my loads are so low the lights would not switch on).

 

The final sheet "Analysis" is just a summary of the other sheets for comparison.

 

 

Household Loads - Copy.ods

Edited Thursday at 09:20 by SteamyTea

[Gus Potter]

Hi all and @Muellar

 

Here is a bit of a story but some ideas for you to have a look at. I'm and SE and Architectural designer but here is some of the stuff I've picked up along the way. Servicing a site can be expensive.. a decider often.

 

I look after a house for a great friend who's husband died. It's around 500 - 600m^2 and well out in the country. We ( the husband who was the techy guy) both did a self build at the same time (mine was a lot smaller) but Clive (the husband) who was a scientist / technologist say like @SteamyTea and @Alan Ambrose were well ahead of his time and brought loads of info to the table as he use to work in Finland / Sweden etc. In some ways the bigger the house the easier off grid is to do. The house I look after also has some 5 acres of land so plenty scope to "do stuff".

 

It was Clive that got me into UF heating systems /off grid stuff / electrical diversity and trying to get the maximum kVa out of a transformer on a pole that is several hundred meters away (voltage drop see later)... and that was 30 years ago. This worked for us as we were well out in the sticks and we use to have power cuts for days at a time when the temperature was regularly -15C and at one time hovered between - 19 and -23 deg for three days in a row.. even our drink froze / the diesel vans did not start, my German Shepard got a bit cuddly and that was a great experience big dogs are warm! This is the Scottish Borders I'm talking about when we used to get hard winters.

 

Basically we flew by the seat of our pants and hoped it would work in the Scottish climate. We had no internet to research and a set of Y fronts each! they came before Speedos I think. .. for the younger these are male under garments that we use to wear. I'll come to the off grid stuff which I love later.. on my bucket list.

 

Ok what Clive did was to have a LPG gas generator for when the power went off. My power cable which was right at the end of the line was a 95mm^2 aluminium three core cable, each core! What the electricity board was to connect all the cores together so we got single phase (220 -250 volt) but delivered through each of what could have been a three phase supply. This mitigated the voltage drop.

 

But the big cost saving was me digging my own track and backfilling.

 

DNO obligations, diversity and demand:

 

My level of understanding is pretty basic @ProDave may chip in to clarify. Also @Carrerahill is off line at the moment, but I'll see him early next year and he does this stuff as a day job.

 

Anyway @Muellar I would come at this from a different direction.

 

Generally the cable that comes to your meter is protected by a main fuse. These tend to be sand fuses and work in a different way from everything after, usually the tails to the meter. I'll call it a sand fuse as there is a table in BS 7176 that lays out how they perform. @ProDave can you correct my interpretation if my laymans explanation is off the mark? Now lets say you have an 80 amp sand fuse. That is the one in the meter box that has a seal on it. Up stream you have a DNO cable ( belongs to the lekky board) which they are interested in protecting and everything up stream of that only. Your in house system is of little interest to them.

 

Now a sand fuse / breaker does not blow like a fuse / MCB you have in your consumer unit. I'm trying to find the BS 7671 table but you could draw several hundred amps through a sand fuse over a few seconds before it blows.. and that is why you should not tamper with it!. Sand fuses work by heating up and then they blow, the sand stops the fuse blowing when say you blow a socket in the house and you get a surge of current.. but the MBC's etc on your consumer unit stop you getting killed as they trip quickly.. hopefully. The stuff in your consumer unit works on miliseconds.. the sand fuse in minutes.

 

Now say you had an 80 amp sand fuse and you were drawing 100 amps.. it may last a few minutes before it blows. The whole objective of the leccky board fuse is to protect their equipment and not yours. Where I live here is a local transformer that has a fuse rated at 600 amps. but it I think serves 10 -15 houses. The electricity board apply diversity depending on the number of houses. Again their fuse at the sub station is not the same as the ones we have in our consumer unit.

 

 

Ok lets put some sums to this and why.

 

Copied from internet to be lazy..

 

In the UK, the declared voltage and tolerance for an electricity supply is 230 volts -6%, +10%. This gives an allowed voltage range of 216.2 volts to 253.0 volts.

 

Now your supplier has a legal obligation to meet the statutory voltage range... and that is easier said than done! @Muellar this may lie behind the quotation you have. Try and get to the bottom of this. If you have long cable you get more voltage drop prid pro on on the cable area. It may not be the amount of kVa that is the sticking point... could be their obligation for voltage? If the cable is too thin /  long it causes a voltage drop that could expose your suppplier to a claim if your appliances stop working.

 

The sums are Kilo Watts =  Volts  * Amps.

 

Say you have a 15 kVa transformer up steam. It's the current that overheats a transformer generally. How many amps could you draw if you were the only customer at 216 volts. ?

 

15000 watts / 216 = ~69 amps continuously... like for an 20 min to an hour say . Transformers are designed to cope with a surge in loading and that is why they are oil cooled and have fins for example. But if there are other folk using the same transformer it gets more complicated.  A good example here is that you get a DIY guy that likes to do a bit of welding. They may be drawing a lot of amps but only for a few seconds.

 

In summary I would try and understand what is lying behing the quote from the Electricity board. Most of their Engineers are quite helpful and will be happy to share their technical knowledge. You could ask the question.. can I have a 40 / 60 amp fuse, all sealed so it protects your network? Funnily they may be more than happy to engage once the find out your plans for off grid / with a bit of back up. They may support you a lot as they could use this as part of their environmental accreditation?  Sell it to them! Write to the head honcho! Many ex council houses have 60 amp fuses so this is quite common.

 

@SteamyTea has done a spread sheet on diversity.. but I would start with the main fuse to get this issue out the way and then you can play with you off grid stuff to your hearts content.

 

To finish the DNO . I would love to have another go at doing an off grid house.

 

OFF grid!

 

Love this but the key for me is to do it and still be able to sell the house when you move on.  Another poster has made the point that it is a neice market. True.. but if I was doing it I would keep it as simple and stupid as I can and keep some data on performance and an operation and maintenance manual. Make sure you future proof things like underfloor heating pipes.. the things that can't be easily changed.

 

@SteamyTea Combined heat and power is fantastic. If you have a bit of ground then grow some willow, encourage wildlife and as it grows like fury it could well be enough to keep you warm in the winter. I'll need to stop here.. but @Muellar love your idea.

 

Don't forget.. you can write to the head honcho of the leccky board.. lay out your case and they may suppport you! Get your ducks in a row and you may get a nice surpise and support.. this lunch won't be free but..

 

 

 

 

 

 

 

 

 

 

Edited Thursday at 22:56 by Gus Potter

[Iceverge]

Great post @Gus Potter

 

From an amateur point of view, does this mean that if you could convince the DNO to give you even a tiny supply, with a very small fuse, you could make it function ok with appropriate losd spreading and battery storage downstream of the meter?

[SteamyTea]

2 hours ago, Iceverge said:

could make it function ok with appropriate losd spreading and battery storage downstream of the meter?

Yes it does.  Why I suggested that a generator, or CHP unit with some battery storage, is probably the better way to go.

 

It really comes down to your views on combustion technologies.  It is hard to get away from them when off grid, and PV is quit cheap.

As I originally studied automotive engineering, designing and building a small CHP unit would not worry me, but for others off the shelf units may be a better option.

The biggest problem with ICE generators is the noise.

[Gus Potter]

On 27/12/2024 at 01:35, Iceverge said:

Great post @Gus Potter

 

From an amateur point of view, does this mean that if you could convince the DNO to give you even a tiny supply, with a very small fuse, you could make it function ok with appropriate losd spreading and battery storage downstream of the meter?

Thanks for the compliment, much appreciated.

 

The amatuer point, well I still qualify as that as this sort of stuff is complimentary to my day job.. SE / Architectural designer.

On 27/12/2024 at 04:30, SteamyTea said:

Yes it does.  Why I suggested that a generator, or CHP unit with some battery storage, is probably the better way to go.

 

It really comes down to your views on combustion technologies.  It is hard to get away from them when off grid, and PV is quit cheap.

As I originally studied automotive engineering, designing and building a small CHP unit would not worry me, but for others off the shelf units may be a better option.

The biggest problem with ICE generators is the noise.

Great succinct writing.

 

The house I look after is big. I forgot to mention that it also has a large "garage" which has space for a few cars and a games room. That has it's own boiler that runs off oil. I think Clive's thinking was to have options.. switch from a big LPG tank to oil if the price changes. He really future proofed the place. But that comes at an upfront cost.

 

@MuellarIn terms of protecting your asset (when you come to sell) then connecting to the grid, even if you have a small main fuse is probably the sensible thing to do. But you do have the standing charge. Much will depend on the value of the house cf the capex cost of connecting to the grid. That said if you are a bit strapped for cash then you could set up your own of grid system and get grid connected later, so long as you plan for it then you may have options.

 

 

 

 

[Kelvin]

The advice I was given by someone who works for a DNO was to keep questioning the estimates you get from them and get a breakdown of the cost. Although they are reluctant to go into detail until they move the estimate to a quote. They all seem to start off high. My initial estimate was £26500. In the end it cost us less than £500. I did need to do all the trenching etc myself.