Hi

[AndyT]

Sorry nothing like this - another step beyond.

[tilpol]

Thanks for all the replies

 

The system will be separate with PV and probably wind, powering the office with battery storage. The island grid will power the main house and I will use it to charge the batteries if local generation is low. Hopefully remove the need for a diesel generator. No problem with any DIY aspects of this.  Think I still have bits of a home built wind generator I started after being on a course at CAT in the early 90's run by Hugh Pigott.

 

Heating and DHW is still something I'm thinking about. Thanks for all the advice. I'll use the appropriate forums to follow up on this. 

 

Answering a couple of other comments further up.

 

@jamiehamy Have fun on Eigg. Where are you staying?

 

@Cpd Our friend on Eigg used to be Schellenberg's gardener back in the 90's, might be the same person,. Do you remember his name?

 

@ProDave Thanks for the offer, all help will be welcome.

 

One question has there been any bulk buys been setup before on the forum? I've heard of groups of self builders organising containers of PV direct from China as well as other material direct from manufacturers.

[ProDave]

5 minutes ago, tilpol said:

One question has there been any bulk buys been setup before on the forum? I've heard of groups of self builders organising containers of PV direct from China as well as other material direct from manufacturers.

If anyone is bulk buying solar PV I might well be interested.

[vivienz]

I will need to purchase solar PV at some point this year. I have no idea what spec yet, but definitely plan to include it in the build.

[TerryE]

15 hours ago, Onoff said:

I see lots of talk of battery storage as a possibility. There's another thread just started here ref Sunamp by @AndyT of Sunamp. Let's face it a Sunamp is the place to store it!

 

I've got twin SunAmps and I am delighted with them, but they definitely have a sweet spot -- that is where you need a high thermal capacity density with low heat losses.  If you are looking at onsite wind, some form of solid fuel heater such a an RMH, or infill kW from your 5kW allowance (120 kWh is a  lot of energy to use) then I would have though some some of high capacity buffer (either water or solid) at ~30°C also acting as a DHW preheat might prove more effective or at least cost-effective.

[Nickfromwales]

Can you not just use the diesel genny? In the times of no solar gain it's a near perfect choice. Remote start and silenced it will top up batteries whilst also simultaneously providing waste heat to a thermal store for DHW. You can simply run this more or less on demand TBH, but I'd probably go for an LPG fired one so you can have one bottle bank and use that for cooking too. 

Space heating a passive-esque property will be child's play so I'd go for the fabric-first approach here and go all out for as near a zero energy home as is practicable. 

Great thread btw, I'm ever intrigued by the off grid solutions. 

[ProDave]

LPG cylinders are expensive enough here on the mainland. I expect add the transport cost and they will be eye watering on the island.

 

What do most do for heating?  I expect solid fuel to play a big part but doubt there are enough trees to provide much wood?

[SteamyTea]

I slept in the rain last night (wind changed direction and had window open).

So had a little think about this 'semi' off grid problem.

 

Could you not wire the house a bit differently so that you have light, fridge, freezer,  central heating pump/controls and maybe a couple of spare sockets on the island grid.  It may still be possible to use more than 5 kWp, but mush harder to.  I have no idea what actually happens if you do go over the 5 kWp limit.  Does it blow a fuse and need someone from the DNO to fix it, or trip out and just need a reset?  Or do they do the decent thing and charge £2 a unit.

 

The rest of the house could then be on a secondary circuit, one that is only connected to your own generation and storage.  That way you can use more power if it is being generated or has been stored.

 

As the island increases its renewable generation/storage, they may give you another, higher limit, then it is just a case of transferring a few circuits to the island grid.

 

I also think that it is worth moving away from all combustion technologies.  Shame that the island is going RE electric, then some islanders fill the local area up with smoke and fumes.  Rather defeats the object.

Edited January 15, 2018 by SteamyTea

[Nickfromwales]

With a diesel / lpg genny reinforcing the island 5kw, it can literally just be used on demand. Does anyone on the island have kerosene ( light oil ) delivered / installed ? I'm sure gennys can run off kerosene. 

[TerryE]

9 hours ago, Nickfromwales said:

Can you not just use the diesel genny?

 

Nick, Costing the Earth did a really good podcast on Eigg's energy solution, and one of the major goals was to provide at residents with a guaranteed supply so long as they stuck to the <5 kW cap, and one of the aims was to get rid of all the noise polluting Diesel generators.

 

All houses have a 20A trip on the supply.  Basically its such a PITA losing your supply that most islanders just learn to shape their demand to avoid getting tripped.  I can't see anyone needing 120 kWh a day, so the issue isn't the overall capacity but how you proactively manage your demand to avoid the 5kW trip.   

 

[Nickfromwales]

On 15/01/2018 at 11:03, TerryE said:

 

Nick, Costing the Earth did a really good podcast on Eigg's energy solution, and one of the major goals was to provide at residents with a guaranteed supply so long as they stuck to the <5 kW cap, and one of the aims was to get rid of all the noise polluting Diesel generators.

 

Ok, thanks. A bit of thought adjustment from the Welsh Neanderthal needed then  

Dhw is a bit of a sticking point, so even more argument to heat a whopper of a Sunamp by trickle charging it and drawing space heating and Dhw from that. A bit of discipline with use / duration of Dhw should suffice then. 

[TerryE]

That podcast is well worth listening to, BTW. 

[tilpol]

The difference in noise pollution on the island from before the grid was installed is pretty significant. All you used to hear was the noise of generators where ever you went. Most folk still have them as backup but I don't think they have ever been used since the grid was installed.

 

Don't think my neighbours would be best pleased if I had a generator that was running occasionally. Even one that is "silent", the noise would travel for some distance when you have complete silence.

 

Most folk live happily with the 5KW limit (its 10KW for businesses like the shop and tea room). I believe at present the system is approaching it's limit not so much on generation but storage for any new builds on the island. I think there is moves to add more batteries. This is one reason I wanted to generate some of our own electricity as well as I like to play around with these things. I'm an electronics engineer and have worked in renewables in the past (although it was wave power).

 

There is plenty wood on the island and most folk have a wood burner. The problem up till now has been it has not been managed properly. There is now an initiative to address this  and people employed to ensure there is a sustainable supply of decent wood for heating. So BIomass is an option for hot water. Most people have a back boiler on their wood burner along with solar thermal.

[SteamyTea]

42 minutes ago, tilpol said:

Most folk live happily with the 5KW limit

I could easily live with that restriction, but it is nice to be able to get up in the middle of the night and make some tea and not have to worry about whether the water is heating or not.

43 minutes ago, tilpol said:

There is plenty wood on the island and most folk have a wood burner.

A m² of biomass will yield around 2 kWh/year, a m² of PV will give about 130 kWh/year.

To put that into perspective, in December, that same m² of PV will yield over 10 kWh. Not much I grant you, but a lot better than the 'sustainable' biomass option.

 

Eigg has a total surface area of 30.5 million m², at 0.25% efficiency (about what plants produce) and at an annual irradiation level of 90 kWh/m², the island could produce about 7 MWh/year of biomass energy.

There is no 'sustainable' biomass plan for the island.

 

[Onoff]

7 minutes ago, SteamyTea said:

I could easily live with that restriction, but it is nice to be able to get up in the middle of the night and make some tea and not have to worry about whether the water is heating or not.

 

 

[SteamyTea]

Yeah right, I can use a bedpan to save to ever getting up as well. 

[Nickfromwales]

20 minutes ago, Onoff said:

 

 

Buy a black one and bingo, solar heated coffee. ( or tea ). 

Dragons den ?

[TerryE]

@tilpol, if you are doing a newbuild and can get your wall U values under 0.15, windows & doors under 1.0 and avoid the "acres of glass" that so many architects love, with a decent insulated slab, good airtightness and MVHR then you should get your space heating needs down under 2 kW even for typical Jan / Feb. 

 

The problem with a wood fire is that you will have a great deal of difficulty keeping the power output under 6 kW if you want it to run efficiently, and the burning efficiency of stacked wood isn't good; anything less than 2 years drying, terrible.   A bit of a dilemma, really. 

 

In principle the RMH approach solves this by burning at a high output for shortish period, once every few days and dumping the heat into a thermal store (typically cob) which you can then draw down as needed into the house fabric through UFH or whatever.  A quick search gave this interesting thread.  As this thread points out there are a lot of issues such as no commercially available appliances with HETAS certification.  A difficult one.

[Simplysimon]

@tilpol a 350mm jji stud wall/roof with blown cellulose will give a u value of .1, windows at .6, just had an excellent price for upvc windows, i really don't want upvc, however, other half is going 'i don't care, look at the price'! have to say it's difficult to argue.

airsource heat pump 2-3kw power input dependent on size (ecodan)

[tilpol]

Don't think I've ever not been able to get a cup of tea at any time of day and night when I've visited as well as getting a hot shower in the morning. It's just about adapting to the circumstances.

 

I can't speak directly for the people who currently live on the island but they have to use the resources they currently have. In general it is a low income island and not everyone has the finances to change. So for most burning wood is the only option. Therefore the initiative to try and manage the wood resources better.

 

My preference is not to use any wood and I'm in the process of trying to persuade my wife that the wood burner is not necessary.  We are used to one however as I put one in our current house about 20 years ago. We were forever having power outages in the winter and needed some form of heating we could rely on. Very few power outages these days but we still use the fire, I have a free source of wood offcuts and it still provides most of our space heating.

 

Thanks for the info on walls U-values. I had been looking at kits with a value of 0.12 but I was concerned about the costs of transportation. JJI joists does sound like an option. @Simplysimon Can you tell me your supplier?

 

 

 

 

 

[pdf27]

Apologies for the slight thread necromancy, but I started reading this while looking up something else and started to wonder if what would normally be the right approach really isn't here.

 

Electricity looks to be slightly expensive (http://euanmearns.com/eigg-a-model-for-a-sustainable-energy-future/ gives 20p/kWh - probably gone up a little since then) but not ridiculously so, and emissions are very low (85-90% renewables with the rest from diesel) so PV will only save you a bit of cash and not much else. Given that 5kW is actually quite a bit of power and well insulated houses don't need much heat (Passivhaus is 10W/m² at design conditions - so ~3kW of thermal power, ~1kW of electrical power from a heat pump) then some sort of automated load shedding system is probably enough when combined with good insulation. There are a number of off-the-shelf items (mostly from Germany) that can do this, and cooking up something with Smart Grid Ready appliances should be quite easy (e.g. SG-ready heat pumps have an "inhibit all" contact which you could use whenever power consumption goes over 4kW).

[SteamyTea]

10 hours ago, pdf27 said:

right approach really isn't here.

I think you are probably right.

Part of the problem is that we are now used to having unlimited electrical energy on demand.

Reading some of the comments on that Eigg report shows that a lot of people are missing the point, including the author.

Comparing, what is in effect, a stand along system by using the ratio of demand and installed capacity is just wrong.

But there are some relatively easy upgrades they can make i.e. more storage (thermal and electrical) and much larger wind turbines.

 

[pdf27]

We're also used to the grid being based around fossil fuels with marginal load being picked up by coal or gas, so any additional renewable generation will reduce emissions. In the case of Eigg, 90% of the time there is excess renewable capacity and the other 10% of the time they're reliant on diesel but with very limited renewable resources. That suggests to me that expanding generation won't really help (essentially it's likely to reduce the output of the existing grid renewables), but that demand shifting would be helpful to some extent. The main issue is that most generation is hydro-based, so periods of low/no generation are likely to come in large blocks rather than over a few hours which makes the storage task rather more demanding.

 

As a very rough approximation, and assuming from the earlier discussion on PV that reducing emissions is a priority:

1. Reduce demand. Given the large percentage of Hydro on the grid, concentration should probably be more on reducing demand for hot water rather than heating since a lack of water is unlikely to be a problem during winter in the Hebrides.
   1. Shower heat exchangers are a good place to start, as is thinking about how the hot water is generated - some sort of heat pump is probably a good idea, and given that the diesels are likely to kick in at times of good weather which will give the best COP.
   2. Assuming that the main system isn't electric resistance heat (immersion heaters) then at least think about hot fill for appliances - for dishwashers it's pretty much a no-brainer (they clean a lot better on hot fill in my experience), not nearly so clear for washing machines however. Then again, washing machines are straightforward to program to run overnight when demand will otherwise be low.
   3. Reducing heating is a good thing from the point of view of comfort (draughts, etc.), but won't actually have much if any environmental impact beyond a certain point as the source will be pretty much 100% renewable with spare capacity. It does make using some sort of smart grid based system to avoid exceeding the 5kW limit much easier however - the smaller the draw from the system, the easier getting everything to work together is.
2. Increase heat/power storage in the design. I'm actually not totally sure how far this can be practically taken given that times when the diesel plant is running will tend to be quite extended.
   1. Hot water - storing big volumes of it is actually quite easy, but to make a meaningful difference compared to a standard cylinder it needs to be really, really big and that might well not be practical given the fact it would need to be shipped to a very remote location.
   2. Heat - storing low-grade heat within the structure is relatively easy, e.g. by building a thicker slab with lots of rock in it but doesn't get you very much of a benefit as it's unlikely to be needed much when generation is low.
   3. Batteries work better at a grid scale than the individual scale, since demand can be averaged at grid scale and so they are used when needed and only when needed at a grid scale, something difficult to implement at a domestic scale (they have to be integrated into the grid control system). Again, if the problem is rare periods of extended diesel running, batteries don't help very much.
3. Increased microgeneration - normally a good option, but doesn't do much in this special case.
   1. PV is the best of bad lot since it is easy to turn the wick down on it and there are ways (Sunny Island, etc.) to stop it affecting the grid - but given the unusual circumstances it's quite a lot of money to pay for not much improvement.
   2. Solar Thermal might actually be appropriate here for a change since integrating PV is more expensive than usual and hot water is likely to be a major demand at times when the diesels are running. For all that, it's quite expensive and maintenance intensive compared to some of the alternatives.
   3. Small wind, micro hydro, etc. have the same problems, plus when they're generating the grid should be just fine so you aren't saving much.

Personally in the circumstances I'd probably follow the US "pretty good house" concept - push the insulation up towards but not reaching Passivhaus, then spend a bit on some things to shift load about (heat pump time programmer, boiling water tap, that sort of thing) and invest the budget otherwise assigned to PV with the island power co-op if that's possible, since it would do far more good there. Obviously, a lot depends on what people are comfortable with and what will make them happy - quite a few people out there want to generate all their own power even when on grid where it doesn't make financial or ecological sense.

[SteamyTea]

I just had a look at the weather data for Tiree (probably not so different from Eigg).  I have only looked at the temperature so far and compared it to Camborne.

The interesting thing is that if you take the heating period as anything below 12°C (I use 10°C in a slightly improved 1987 minimum building regs house), the heating times are start only 3 weeks earlier than Camborne and and 2 /12 weeks later.

I shall now have a look at sunshine hours to see how much generation could be had from a PV system up there.

I still think that a single larger turbine would be a cheap way to generate RE power (larger turbines are more efficient, are high up so get higher windspeeds for more time and are cheaper per kWp to install).

Here is a chart to be going on with, it shows the median monthly temperature by month from the last 40 years.

 

[SteamyTea]

And now the sunshine hours and rainfall.

The solar resource is pretty good, though the power will be lower for Eigg than Camborne.

The rainfall is a bit higher in Eigg, though again, not by much.