Off-grid power (long)

I response to my other threads here's an outline of our off-grid power system.
A couple of years ago now I asked some questions here about the costs of running diesel generators for domestic power. Some of the numbers I got back almost put me off buying the house, but I, with my partner, did buy the place.
The power set-up as we bought it comprised three diesel generators, all Listers of different power outputs, 1.75kVA, 3.5kVA and 11kVA. This system had evolved over the years.
Historical side note: We have recently made contact with the, now, 94 year old woman who lived in the house from the 30s through to the 70s. She and her husband put in the two lower powered Listers. She, in fact, poured the concrete floors we still have today. Perhaps I should get her back to do the tower foundations!
The house could run directly from any of the generators, the choice of generator was based on what you wanted to do. The lowest was fine for TV etc., the next for a washing machine, the largest was put in by later owners to run a blacksmith's forge.
The generators were used only when needed, evenings, weekends. Thus we don't use a video, say, and we have a gas (lpg) fridge---came with the house.
In addition to the diesel system the previous owners added a couple on small wind turbines (one 50W, one 400W) on the gables of an outbuilding., and a couple of small battery banks with a 600W inverter. This system allowed for lights being used in the middle of the night but not much more.
The whole system is very ad hoc with lots of switches being used depending on what you need to use. So, we decided last year to look at a more modern system or going on the grid.
Going on the grid would cost around 20K. We quickly realised we could spend a lot less than that and have a system based on solar and wind power. We then had to decide whether to go the DIY route or get a supplier fitted system. Luckily we have a company that does renewable systems just a few miles away, which makes for good service. Their quote for a full system was about 15K but as it is an 'approved' system we can get 3-4K of grants to cover some of that.
The DIY route would get any grants and the kit would attract 17.5% VAT instead of the 5% we paid. However, there's probably not much in it in terms of the hardware costs after the sums.
The system we went for, based on our location and needs, comprises 6 110W Solar PV panels, one Whisper H40 (900W) windcharger, a very clever 3.3kW inverter and a bank of 16 6V deep-cycle batteries. In addition there's a solar controller and a wind controller in there. The inverter is also wired to the 11kVA Lister as its back-up charger. It can also patch us straight through to the genset if we use very heavy loads.
All the wiring has been done by the company we got in but the groundworks and preparations are DIY.
The first stage was just the inverter, batteries and genset wiring. This immediately made a tremendous difference as the genny was turned on just for charging for 2.5 hours every 3 to 5 days.
The solar was added next, on the shortest day of all days! We have been surprised at its effect. Even at this time of year it is delaying the need for diesel charging by a few days. The last few days have had record daily inputs of over 60Ah. This is more than enough to cover our normal nightly demand.
The final part is the wind turbine. The charger we have chosen is designed to work in high wind areas and has been used in similar locations to ours (exposed!) in the north of England. We are predicting that the diesel generator will be used very little once the turbine is up and running. In fact we may have to make a decision as to whether to divert its dump load to some use other than heating the inverter shed---possibly to a secondary immersion heater.
We then have to decided what to do with the old system. The Air 303 did suffer some damage in recent storms and an electrical storm fried out 600W inverter. The new inverter is protected from this and the new turbine is better suited to our conditions and will be better installed, though obviously there are no guarantees.
We still feel we need to hang on to the 3.5kVA genset as we like the idea of backup systems. We will probably try to sell the smallest generator, it was built in 1960 so it may be of interest to a collector.
We may used the older wind/battery system to run a DC lighting circuit for the outbuildings with a small inverter there for emergencies.
In fact this raises a final question about the recently discussed regulations on electrical work. Does it apply to a situations such as mine on the other side of the 'meter'? We don't actually have a meter but how does it apply to the old inverter system itself?
Colin
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Colin Blackburn wrote:
<A most interesting piece on living 'off the mains.'>
This is probably preaching to the converted, but if you haven't already visited the Centre for Alternative Technology at Machynlleth then get yourself over there ASAP, as there is much to be learned and many brains there to be picked. (And some very serious batteries to be viewed.)

BS 7671 certainly applies. There's a whole section (Section 551) applicable to "generating sets" - the definition of which extends beyond rotating machinery and so includes your inverter, PV cells and batteries. It covers the ELV sources (<50 V AC or 75 V DC) as well as 'mains voltage' stuff. Parts, but not all, of it are concerned with interfacing safely to a public supply - interlocking, separate earthing and so on. These won't apply to you, but there is much that does, mostly concerned with the co-ordination of protective devices (i.e. fuses and circuit breakers) and fault levels, to ensure that bad things (like cables catching fire) don't happen if there's a short-circuit somewhere. Earthing bonding and shock protection are also covered.
Whether Part P applies is a moot point: The SI says:
"'electrical installation' means fixed electrical cables or fixed electrical equipment located on the consumer's side of the electricity supply meter;"
If there's no meter there can be no consumer's side, so you could argue it doesn't apply. Dunno whether that would stand up in court though.
--
Andy

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You say 16.6v? You mean 13.6 I guess? which are more commonly called 12v batteries, even though theyre not exactly..

why not feed it into the main dc system?
You must have wired over the washing machine thermostat so it doesnt heat electrically.
BTW are you using the gen exhaust heat to heat the house? If the gen runs much in winter, you get around 20kW out of an 11kW gen exhaust, at full tilt.
Is all your lighting 12v? 12v loads are generally more efficient than running things on 240, as theres no invertor losses in the way..
If you want to inevst a few more hundred, solar flat plate space haeting is an excellant payer.
NT
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What's the best way to do this ? I assume some sort of heat exchanger but are there ones that you can place on the exhaust without a) disintegrating or b) messing up the running of the genny ?
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Our charity's is a watercooled lister and we fitted the watercooled exhaust manifold from the marine version of the same engine to recover a small amount of exhaust heat into the coolant circulation, this was then passed through a multitube heat exchanger with the central heating circuit as the secondary.
AJH

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On 2 Feb 2005 12:06:20 -0800, snipped-for-privacy@meeow.co.uk wrote:

With just the solar input the OP said the gen only runs for 2.5hrs every 3 - 5 days. Once the wind gen gets turning it'll be even less often. The invertor is 3.3kW so should cope with most normal loads without (auto starting?) the genset.
I sort of wonder if 11kVA isn't a bit on the large side but I guess if the invertor drops everything over to the genny for loads over 3.3kW it's not so bad. Bit daft running up an 11kVA genny for an extra few hundred watts...
I'm actually quite curious as to how this clever invertor does it's thing. Say you put something on that means the total load is greater than 3.3kW, what happens whilst the genset starts and comes online?
--
Cheers snipped-for-privacy@howhill.com
Dave. pam is missing e-mail
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thing. Say you put something on that means the total load isgreater

We wait to hear... there are not many options though. It either current limits, causing Vout to drop, shuts down if its a poor design, or switches off some loads.
NT
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snipped-for-privacy@meeow.co.uk wrote:

We don't have a main DC system. There is a small DC system that runs to the garage and workshop. There is a DC line to the house but it is used solely for an alarm system.

Nope. The washing machine will start quite happily off the inverter. When the load rises, ie the heater comes on, the genset kicks in to take over the high load. The inverter controls this. It then leaves the genset on for a period of time after the high load has dropped this is to prevent the genset having to start up again. The inverter will happily grab use of the genset for charging the batteries during this period.
However, at the moment we will often switch over manually to the middling generator and do the washing with that. This is in part because the generator needs exercising from time to time.

No we're not but it is certainly something to think about. The generator is an air cooled Lister in an outbuilding a few metres away from the house so I don't know how feasible this would be. The exhaust at present discharges through a hole in the wall and warms the sheep in the adjacent field!

The house is wholly 240V AC (except for the alarm. This is historical as the original occupants used direct generator power only. Once the wind power is up and running we are likely to, generally, have an excess of power so the inverter losses would be insignificant. Certainly not worth the additional costs of putting a DC line across to the house and wiring up a DC lighting circuit.

We are hoping to review our whole heating set-up later this year, once we have a feel for our electricity situation, so any suggestions are welcome.
Colin
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Colin Blackburn wrote:
circuit

to
used
Normally one has both 12v and 240v, as putting some of the loads on 12v reduces the necessary invertor rating and eliminates the invertor power losses for the 12v loads. 240 only systems cost noticeably more.

doesnt
I think thats usually regarded as a bit of a no-no with solar and wind power. To use the leccy for heating increases the system cost unnecessarily. I guess its a case of well, since youve got a genny...
The good news is that if in future you make the setup more efficient by addressing this, you'll have some more leccy to play with. This will all help to get you off the generator hopefully.

gen
exhaust, at

generator
present
I would expect very feasible - if you continue using the gen anyway. When youre loading it at 3kW you're going to get somewhere in region of 6kW out of that exhaust pipe. An exhaust heat exchanger is a fairly elementary thing to make.

than
excess
that would be a most unusual situation if you didnt use the genny.

and
the solar panels are remote as well? I dont know anything about your alarm setup, but even a wimpy alarm cable can be used to supply a steady current 24/7 to a secondary house battery, enabling some amount of 12v load use. Alarm cable is very low current rated, but it has several cores and can charge that battery 24/7, so it might be usable. But with what you spent I imagine you dont want to bother with 12v stuff.

once
If you want to play, I'd also look into a tracking heliostat to provide DHW and partial CH too. If youre into diy theyre quite low cost, and can produce quite serious power output, as hot water. Redrok.com.
NT
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snipped-for-privacy@meeow.co.uk wrote:

They probably do if one is running on the edge but even with only the solar set up, in winter, we have no problems finding enough power (ignoring the washing machine for now) for normal needs. There are only two of us, we have low energy lighting, we don't normally run a central heating pump, etc.. In that case the losses via the inverter really are negligible *for our needs*. Certainly not worth investing in a new wiring circuit in the house. If at some point in the future we have the house rewired---it is on the cards as like everything else it has been piecemeal in its development---then we will consider putting in a DC circuit at the same time.

Regarded as a no no by whom? As I say, it is not a concern with our set-up at present. If we address our issues of water heating---at the moment that is by an oil-fired Rayburn---then we may look at using the hot water directly but as it is we do one load of washing a week and that exercises either generator, both of which we would have to exercise at some point anyway.

Eh? Do you know how much electricity we use then? We live in an area with strong wind almost every day. There is very rarely a calm day. We have very open skies when it is sunny. I will be more than happy to post back here saying I was wrong but looking at the inputs and outputs on the inverter even now it is hard to imagine us being short of power.

Remote to what? The panels are ground mounted in the garden. The feed into an outbuilding which contains the batteries and inverter charging system. Power is then delivered to the house via an underground cable.

As explained above. I don't think it is an issue worth addressing at present. Also, the DC alarm cable comes from a completely separate outbuilding which is not directly connected to the new supply system.
Colin
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You say 16.6v? You mean 13.6 I guess? which are more commonly called 12v batteries, even though theyre not exactly..

why not feed it into the main dc system?
You must have wired over the washing machine thermostat so it doesnt heat electrically.
BTW are you using the gen exhaust heat to heat the house? If the gen runs much in winter, you get around 20kW out of an 11kW gen exhaust, at full tilt.
Is all your lighting 12v? 12v loads are generally more efficient than running things on 240, as theres no invertor losses in the way..
If you want to inevst a few more hundred, solar flat plate space haeting is an excellant payer.
NT
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snipped-for-privacy@meeow.co.uk wrote:

no he said 16 6V which I read as 16 * 6V = 96V I assume the inverter uses that to generate 240V AC
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snipped-for-privacy@ntlworld.com says...

16 x 6V batteries powering a 24V inverter
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Rob Morley wrote:

Yes, thanks. They are wired as four serial banks of four in parallel together.
Colin
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Ah, a 24v system. Those work nicely with the 3 wire system, but its moot if youre all 240v.
NT
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I wonder if you looked at the gas bottle solar engine at: http://www.amasci.com/freenrg/minto.html
I've never played with one, but on the surface it looks like it could produce serious power for peanut money. Anyone know anything about it? NT
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Thanks for this Colin, Much appreciated.
How does the VAT thing work? Why would you have to pay 17.5% VAT if you were DIY'ing it?
Which Inverter are you using?
Also, how much are the installation costs? (If that isn't too cheeky a question) It is crazy that they won't allow DIY installation for grants as DIY reduces costs and would therefore encourage more installations. f'n' government organisations!.
Cheers,
Alan.
Please keep us updated on how you get on with it.
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I suspect because they think it is too easy for you to fleece them, or not complete the installation.
Christian.
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Christian McArdle wrote:

Probably. Though the grants are authorised on quotes but are paid on completion of the works. In our case the installer was able to verify that the works had been completed and we were able to verify that the installation was working and that we were happy with it.
Colin
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Alan wrote:

If you buy the parts they are just ordinary bits that have ordinary VAT. If you buy "a power system" then it attracts the same VAT rate that heating and power fuels do.

It's a Trace pure sine wave inverter. I can't recall the model number but it is rated at 3.3kW and takes 24V input.

I'd have to get back to you on that one. To be honest whatever they were I'm grateful! One of the guys spent the best part of two days trying unsuccessfully to wire in the ignition box for our generator. The ignition box was an unnamed, probably home made, thing that used a key and push button system. He went home, had a eureka moment and then came back and sorted it out. It isn't a job I could have done at all.
Colin
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