The Eigg renewables project revisited

Among the claimants for the title of “world leader” in renewables development in remote areas the island of Eigg (population 90) off the west coast of Scotland, which since 2008 has been obtaining over 80% of its electricity from a custom-designed hybrid system, probably has the best claim. This post reviews operating data that have become available since I posted Eigg, a model for a sustainable energy future in September 2014. It concludes a) that while the project has delivered good results it is inefficient (overall capacity factor 11%), b) that Eigg will probably never be able to do away entirely with diesel backup and c) that the project owes its existence to the fact that 94% of the capital cost was financed by grants. It is economically unviable on a stand-alone basis.

Data Sources:

The generation data presented below are from a 2015 paper authored by Schmiel and Bhattacharyya , a 2014 paper entitled Off-grid Electricity System at Isle of Eigg: Analysis and evaluation by green energy technology, authored by Bhattacharyya, plus an article from Eigg Electric giving the local perspective.

System Specifications

These were described in the earlier post referenced above, complete with photographs, and will be only briefly recapitulated here. Details of individual units can be found in the above references:

  • Run-of river hydro– Three plants of 10kW, 19kW and 100kW, total 119KW
  • Solar PV: Three arrays of 9.9kWp, 21kWp and 22.5kWp, Total 53.4kWp*
  • Wind: 4x6kW turbines, total 24kW
  • Diesel: 2x80kW generators, total 160kW
  • Total renewable capacity: 196.4kW
  • Total diesel capacity: 160kW
  • Renewable + diesel: 356.4kW

*The project began with the 8kWp solar installation, so at project startup the total installed capacity was 8+119+24+160 =311kW. This number is used in the economic assessment discussed later. The additional 22kWp was added in April 2011 (it was said to be snowing at the time) and the remaining 22.5 kWp was added some time in 2013. The date is not specified but was probably after March.

Additional backup is provided by 60 kW of lead-acid batteries with 3 hours 40 minutes duration at rated output, representing ~220 kWh of storage capacity, sufficient to fill Eigg’s electricity demand for about six hours:

Generation Data

Generation data are summarized in Figures 5 and 11 of Schmiel & Bhattacharyya. Figure 5 plots total monthly diesel and renewable generation from November 2008 through August 2012 and Figure 11 plots diesel and renewable generation broken down by source from March 2012 to March 2013. I converted these into numbers by counting pixels on Microsoft Paint (1 pixel width = 160-170 kWh) and combined them into the November 2008 through March 2013 generation plot shown in Figure 1:

Figure 1: Monthly diesel and combined renewables generation, November 2008 through March 2103.

The increase in the percentage of diesel generation as hydro dries up in the summer months is evident. Also of interest is that in only five of the 53 months (March, October and November, 2009, October and December 2011) was Eigg able to get by with no diesel generation at all. Nevertheless, during the period shown – which covers 4 years and 5 months – renewables filled 84% of island demand, well in excess of comparable projects like King Island (65% projected but apparently yet to be achieved), Gorona del Viento (37% to the end of June 2016) and Gapa Island, Korea (32% after 5 years of operation).

Figure 2 shows the data for the 13 month period between March 2012 and March 13, when renewables generation is broken down by source:

Figure 2: Monthly generation, March 2012 through March 13 with renewables generation segregated by source.

During this 13-month period Eigg supplied 82% of its electricity with renewables – 61% from hydro, 12% from wind and 9% from solar – although hydro generation dried up almost entirely in June and wind and solar could not come close to replacing it. At least some diesel generation was in fact needed to fill demand in all 13 months. Table 1 provides details on actual monthly generation, percentages-of-total and capacity factors (note that figures are approximate):

Regarding capacity factors, the 19% value for hydro suggests that operations are heavily constrained, either because of stream flow restrictions or because production exceeded demand and had to be curtailed, or because of a combination of both. (No data are available on curtailment or on any grid stability problems that may have been experienced.) The 19% for wind seems low and the 10% for solar a little high, but they are both in the general range of what we would expect. Figure 3 isolates the wind and solar components. Wind does not change much from month to month. Solar, however, peaks in May rather than June/July, possibly as a result of cloud cover variations.

Figure 3: Monthly wind and solar generation, March 2012 through March 2013

Project Economics:

Table 2 of Schmiel & Bhattacharyya, reproduced below, lists the sources of project funding:

Eigg (Island Trust and residents) paid only 6% of the project’s cost. The remaining 94% came from grants. In fact, after winning a £300,000 share of the National Endowment for the Arts and Sciences Big Green Challenge award in 2010 Eigg has come out ahead on the deal.

I made the following crude estimate of the levelized cost of electricity (LCOE) for the Eigg project using the NREL calculator and the following simplified assumptions:

• Cost/installed kW = £1,664,828/311kW (initial installed capacity) = £5,351
• 25 year life, 5% cost of capital (ref. 1)
• Capacity factor 11%
• O&M costs : Ref 1 gives £30,000/year for full time maintenance. Maintenance is currently part-time so I cut this to £20,000. £20,000/311kW = £64/kW/year.
• Diesel fuel costs: 2kWh/liter, 50,000kWh/year, £1.00/liter = £25,000/year. £25,000/311 = £80kW/year. Added to O&M costs = £144kW/year.

The NREL calculator run is shown in Figure 4 below:

Figure 4: NREL calculator run

The levelized cost comes out at £0.54/kWh, over twice mainland retail rates. But Eigg can still sell its electricity at the old rate of £0.20/kWh because it got the system for free. (The levelized cost falls to approximately £0.14/kWh at a capital cost of zero.)

The variable that has the largest impact on LCOE is the capacity factor. A number of previous posts have pointed out that combining a high percentage of renewables generation with diesel backup reduces the capacity factor to low levels and that this has a strongly negative impact on project economics. As shown in Figure 5, Eigg is an example:

Figure 5: Levelized cost of electricity versus capacity factor, Eigg

Concluding Comments:

Despite its small size the Eigg system contains the basic ingredients common to all high-penetration renewables systems, such as energy storage and a smart grid. It also suffers from the same failings, chief among which are its dependence on weather conditions and inadequate energy storage capacity. The project is over-reliant on hydro generation, which dwindles or sometimes even dies out altogether every summer, and the 220kWh of battery storage is again orders of magnitude too small to allow surplus winter hydro to be stored for summer re-use. The hydro shortfalls could be eliminated by increasing solar and/or wind capacity by a factor or four or five, but this would result in substantial curtailment and reduce the system capacity factor even more. As a result Eigg will probably never be able to get rid of its diesel backup, although with 80-85% renewables penetration this is not a major issue.

What is a major issue is that Eigg, like its sister projects at Gorona del Viento and King Island, requires hefty subsidies to make it pay. Renewable energy will never take off until it can stand economically on its own two feet.

Endnote: Demand Management

I was going to write a section on Eigg’s reported success with demand management until I came across this. According to the Case study summary, Isle of Eigg Heritage Trust average (2010) annual electricity use per household is just 2,160 kWh. But according to the Figure 1 data total generation in 2010 was 306,000 kWh, which for the ~38 occupied households on Eigg at the time works out to about 8,000 kWh/household, almost four times as much. The capacity factors on Table 1 further suggest there is nothing seriously wrong with the generation data. I have emailed Eigg Electric to see if they can shed any light on this discrepancy.

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48 Responses to The Eigg renewables project revisited

  1. singletonengineer says:

    Brilliant work, thanks. It would be interesting to see where the real value of the lead-acid batteries lies. Even cursory examination indicates that the system is massively over-engineered, as indicated by the system’s low capacity factor and high capital cost.

    I suspect that the batteries are used for:
    1. Black start capacity independent of hydro.
    2. Source of DC for instrumentation and control in the event of AC failure.
    3. Immediate response capacity for changes in load and/or generation, ie minute by minute and hour by hour.
    4. Minimal value for diurnal load shifting.
    5. Not for storing winter hydro energy for the dry summer months.

    Increasing battery storage capacity in order to store winter hydro for summer use, as suggested, is a different and expensive proposition. The current batteries would only suffice for “about 6 hours” out of the summer’s dry period of 3 months (May – July). The batteries would need to be expanded many times over to achieve anything significant.

    Since the contribution of solar+wind is about 21% of total annual demand and peaks are below one third of any individual month’s demand, it is clear that the system is essentially hydro+diesel. Without the solar and wind components, the existing diesel and hydro would be able to manage the entire load, at an additional cost of diesel fuel and with a monthly capacity factor of less than 20%. Even when one of the two diesels is out of service the remaining diesel would be adequate to meet all but the very highest peaks without the need for wind, solar or hydro.

    Further, the frequency control and system synchronization require either diesel or hydro so it is essential that at least one of these be in service 24/7/365.

    Eigg’s solar and wind are only expensive ornaments on an otherwise adequate system.

    The justification seems to be reduced use of fossil fuels. If the residents of Eigg want to feel good about reduced greenhouse gas emissions, what gives them the right to do so while paying only 4% of the up-front costs and thereafter receiving subsidised tariffs?

    • According to Eigg Electric: The overall control of the power generation of the system depends upon a bank of batteries connected to the distribution grid through a series of linked inverters. The inverters allow the flow of electrical energy between the batteries and the grid, depending upon the balance of demand and supply, and they adjust the supply of power from the sources of generation so as to maintain the charge of the batteries. In this way, the inverters ensure that the demands upon the system are met, using as the controlling factor the state of charge of the batteries. The batteries have enough capacity to provide power for the island for periods of up to 24 hours, if energy from renewable resources is not available.

  2. Willem Post says:


    “The levelized cost comes out at £0.54/kWh, over twice mainland retail rates. But Eigg can still sell its electricity at the old rate of £0.20/kWh because it got the system for free. (The leveled cost falls to approximately £0.14/kWh at a capital cost of zero.)”

    It is amazing the LCOE is only 0.14/kWh with 0%/y capital cost, but 0.54/kWh with 5%/y capital cost. The amount of capital used for this set up is enormous.

    Whereas the system may be over-designed, it certainly would be better of with more storage which could be batteries and/or pumped hydro.

    How much storage would be needed to not use the diesels, except for emergencies?

    • jim brough says:

      Eigg is a small island in a small group of islands of the inner Hebrides of the west coast of Scotland.
      The renewables on Eigg survive on grants and subsidies to a small community.
      I suggest you tell how your plan would apply to much larger communities.
      For example… Sydney is a sunny city but I have never seen any proposal to run its electrical rail system on solar energy.

      • Willem Post says:


        I can think of no economically viable plan that would suffice a large city.

        Here in Vermont, US, some RE idiots think Vermont should be “energy independent.” Some idiot legislators even use that mantra to get elected in November.

        So I made a little analysis and sent it to all legislators, and to a few thousand others in Vermont, and elsewhere.

        Vermont Energy Independent?

        RE proponents are using a new, catchy mantra: “Vermont Energy Independent”. Some legislators repeat it as part of their campaign RE rhetoric and talking points. Either they do not know what that implies, or are engaged in another scam of the gullible.

        For Vermont to be truly “energy independent”, it would have to disconnect from the New England electric grid (not use it as a crutch), and produce ALL of its energy, not just electrical energy, which is only 35% of all energy, from HOMEGROWN energy sources, plus have enough energy storage capacity, in various forms (not just electrical), to ensure adequate energy supply to the Vermont economy, 24/7/365, year after year.

        Vermont, population about 625,000, having the equivalent of about 1,000,000 rooftop solar systems, at 5 kW each*, would be a small step towards energy independence, but it would not provide a steady, 24/7/365 electricity supply, year after year, because solar energy is minimal or zero about 75% of the hours of the year. Wind energy could supplement, but it is minimal or zero about 40% of the hours of the year. Many hours of the year, the sum of wind and solar energy is minimal or zero, per ISO-NE website.

        – The capital cost of such a homegrown system would be enormous.
        – The operating and maintenance cost of such a system would be multiples of the existing system.
        – The cost of energy produced by such a system would be multiples of the existing system.

        * Production = 1,000,000 systems x 5 kW/system x 8760 h/y x 0.14 capacity factor = 6,132,000,000 kWh/y, which is about equal to annual utility purchases, about 35% of all of Vermont’s energy requirements.

        – The capital cost of solar systems = 5,000,000 kW x $3600/ kW = $18 billion for systems that last about 25 years.
        – The capital cost of homegrown systems for the other 65% would be another $25 billion.
        – The capital costs of the various energy storage systems would be many billions.

        Sayonara to Vermont’s economy.

  3. pyrrhus says:

    90 people…..All this engineering and mixture of systems for 90 people…..and it still needs diesel power to actually work, at a levelized cost that is 4-5 times what many people in the US are paying…

    • A C Osborn says:

      This is basically an extension of a small commune being “off grid”, it may work for them but perfectly illustrates the idiocy of trying to be green for anything larger.
      Add any kind of energy intensive industry or transport and the whole thing collapses.
      It would not exist at all but for the CAGW scam and demonisation of life giving CO2.

  4. edhoskins says:

    To power Germany for 24hours for a would require day would require all the batteries in all the vehicles in the world plus another 80% more. See

    As David Mackay said “numbers not adjectives”

  5. Gavin D says:

    I suspect that those involved, including the engineers, never had any illusion about the cost viability of this project (or el Hierro for that matter). These things are all tied up in the emotions of self sufficiency and global warmist mumbo jumbo.

  6. So to follow up on the capacity factor comment

    What does the cost look like if it were just a hydro/diesel scheme?

    • The cost would probably go up because Eigg would have to buy more diesel fuel. Without solar and wind renewables supplied 61% rather than 82% of demand between March 2012 and March 2013, so diesel would have had to generate about twice as much electricity.

  7. Does anyone have any thoughts as to how Eigg stabilizes its grid at +80% renewables penetration?

    • Olav says:

      From your 2014 post was “aggressive demand management practices” mentioned. On a small community it is possible to do. Then they have batteries for a while until diesel is started.

  8. auralay says:

    Euan, do you have any feel for the number of people employed to run the system? My suspicion is it would need at least one skilled person 24/7/365 – a staff of 3+ so a cost of perhaps £100,000.

  9. auralay says:

    Euan, do you have a feel for the number of people needed to run the system? It must need a skilled operator 24/7/365 and must need at least 4 full time. Cost £100,000 to £150,000?

  10. I just received a response to my query on household electricity use. It seems that the Eigg estimate is more or less correct and that there are a lot more residences, businesses, churches, schools etc. on Eigg than I had been led to believe. Here’s the response.

    Hello Mr. Andrews,

    Maggie Fyffe has passed your query to me for reply.

    I have read with interest your review of our electrical system and the papers to which you refer.

    According to my own figures the power generated by Eigg Electric for the year to which Bhattacharyya refers was approximately 307MWhrs. This represents the total power fed into the grid by the hydros, pvs, wind farm and generator in providing the island with all of its electrical needs. Of this, according to my count 45 households used an average of 2371kWhrs. The remainder was used by:

    * the businesses on the island, the school, the doctor’s surgery, holiday lets, the community hall,

    * the two churches on the island, agricultural buildings and the harbour lights

    * In addition, power surplus to these requirements was supplied to community buildings, primarily during the winter months, in the form of electrical heating, and as you will be aware plays a role in the control of the system.

    * Finally, there are system losses – transformers, HV and LV cables, battery-inverter etc. – which are an integral part of the running of the system.

    Together, these made up the 307MWhrs.

    I hope this answers your query.

    Thank you Mr. John Booth. I only wish the people on El Hierro were as responsive.

    • Euan Mearns says:

      Mr Booth, thank you very much for your reply.


    • Euan Mearns says:

      Roger, £1664828/45 households = £36,996 per household. 46% of this from the EU – no wonder Scotland voted “remain” 😉

      Do we know if all the wind and solar produced actually goes to the grid / storage and is balanced by hydro?


      The levelized cost comes out at £0.54/kWh, over twice mainland retail rates.

      How would this compare with a 100% diesel system?

      Eigg’s performance certainly beats El Hierro hands down.

      • Roger Andrews says:

        According to 2014 data from Lazard the LCOE of diesel is $225 – 404/MWh, or £0.17 to 0.31/kWh at current exchange rates.

      • Roger Andrews says:

        And no, we don’t know whether all the wind and solar goes to the grid. We would need generation data at 5 or 10-minute intervals to figure this out and I don’t know whether Eigg Electric has such data available. .

  11. Another super-prompt response from Mr. John Booth on the question of grid stability. This should be of interest to the electrical engineers among us:

    Hello again Mr. Andrews,

    No, the intermittent nature of renewable generation causes no grid stability problems – the battery inverter system ensure this. We have a battery bank of approx 720kWhr capacity attached directly to a grid transformer via SMA Sunny Island inverters which allow up to 60kW to be transferred essentially instantaneously in either direction – thus when there is insufficient power supplied by the renewables to match demand, power flows almost instantaneously out of the batteries to compensate and when there is a surplus of renewable power the reverse happens. So, we achieve a stable grid 24/7.
    Of course additional factors come into ply as the batteries tend to discharge below a selected level (generator comes on) or when the batteries tend to become fully charged (a sequence of events)

    If you are interested in our system, and you have a chance, you might consider visiting us, when I will happily discuss the system with you.

    • Euan Mearns says:

      Its a good reply. One of the best ways to create stable output is to process supply through storage.

      Mr Booth – Roger lives in Mexico and is unlikely to take up your kind offer and day soon but I live just up the road and may well visit one day. One thing that would interest me is knowing if there are ancillary benefits for the Islanders. For example has the electricity project created a greater sense of community? And do folks feel good about going Green?

    • Greg Kaan says:

      The amount of battery power (60 kW) is almost as high as the total of intermittent generation capacity (24 kW + 53.4 kW) and the hydro generation (119 kW) dwarfs both. This makes the system far more stable than GdV could ever be.

      I’m puzzled by the battery capacity, though. This article says 220 kWh, Mr Booth states 720 kWh, The 2015 Schmiel and Bhattacharyya paper lists 4 clusters of 24 Rolls Surrette 4KS25 PS batteries so I guess it depends on the discharge rate.

  12. Does not the question of the stability of the system depend upon a complex array of solid state electronics, not especially cheap items. In the mainland system these control mechanisms and the large transport distances from renewable sources to the Grid, constitute a significant component of our mainland electricity. Grid stability is purchased at a cost; yes National Grid will do, but no mater how complex it becomes we have no alternative but to pay up; and let us not forget that these costs are not itemised on our electricity bills, out of sight-out of mind.

  13. PhilH says:

    Another ‘island’ grid (wind/solar/battery/diesel) system for you to study is to be built at Coober Pedy in South Australia:

  14. jacobress says:

    Many small countries (whole countries, not tiny islands) achieve 95% (or 80%) “renewable” electricity thanks to hydro.
    Examples: Uruguay, Costa Rica, Bhutan.

    Eigg is essentially a hydro system. Nothing unique or remarkable about it.
    Wind and solar are irrelevant, just an adornment, for the sake of attracting all that outside, ideology motivated money.

  15. Jean-Marc says:

    Good day Roger,

    First, thanks for the analysis provided on Eigg project.

    Now, as far as capacity factor for Hydro, my calculations point to a 20% capacity factor and not 65% as mentioned in article (119 MW * 24 h * 365 days / 213,600 kWh).

    Nevertheless, the overall capacity factor (11%) points to the fact that a great number of generating facilities (wind, hydro, solar, diesel,…) have been installed but are barely used to produce electricity for the island’s requirements. I believe the whole system could be optimized by installing more wind turbines (capacity factor 19%) vs solar generation (capacity factor 10%). By installing more wind turbines (instead of solar) could still achieve the 80-85% of renewable generation on the island and lead to lower costs since solar would be replaced with a more efficient source of energy.

    Obviously, your calculations point to a cost of £0.54/kWh and compare such cost to the cost of electricity in mainland Scotland. From this point of view, this is a high cost and leads to a conclusion: renewable energy sources are not competitive… and would be further “negative” if all electricity would be generated by renewable sources.

    But I disagree on this. I believe one should compare these costs with the “normal” alternatives, i.e. all electricity produced by diesel or installing an underwater power cable to supply electricity to the island (a 10 km underwater cable is feasible and a proven alternative).

    For instance, without any renewable source, cost of producing electricity would be > £0.60/kWh (rough estimate derived from your assumptions of a £0.50/kWh for diesel generation + O&M) using diesel generation or £?/kWh to feed the island with an underwater cable. So, system’s costs using renewable have to be compared to these 2 “normal” alternatives and not compared to the average cost of electricity in Scotland.

    Last comment: yes, overall system costs have been assumed by grants and subsidies from government and local agencies (94%) and one would conclude that such high public investments is a subsidy to local customers on behalf of other ratepayers. But this public funding of renewable should be compared with the case where no renewable is installed on the island but a subsidy is granted for producing electricity using diesel. My point: subsidizing renewable on the island leads to smaller or similar costs than those which would be assumed by Scotland’s ratepayers for electricity generated on the island using diesel or an underwater power cable.

    • gweberbv says:


      I doubt that today a 10 kW wind turbine on a remote island has a cost advantage over a 10 kW PV installation. The scaling of the instaalation and maintenance costs as a function of installed capacity is different for both technologies. To be more specfic, PV is much more favourable for small-size installations.

      • Greg Kaan says:

        Installed capacity yes but if you factor in the “capacity” factor (quoted since it really isn’t true for solar and wind), then the costs are comparable

        • gweberbv says:


          for a 6 kW wind turbine system I found prices (in Germany) of about 25.000 euros. For the same money, you could get nearly 20 kW of PV. And this is just the installation costs. The wind turbine has moving parts that need (real) maintenance, which leads to much higher M&O costs compared to a PV system.

          The situation is different when you consider a farm of several turbines in the MW range, because then economies of scale kick in.

          So, even if the wind turbine has 3 times higher CF, for small-size installations it is still a bad deal compared to PV.

          • Greg Kaan says:

            I don’t see how larger numbers of wind turbines decrease the unit maintenance costs – they are discrete units.

            Hydro still does the lion’s share of generation in any case and diesel is still a necessity when hydro has run out.

          • gweberbv says:


            the technician who has to travel to the island of Eigg for maintenance will charge less per turbine if he can work on a few dozens of them compared to a single one (of four of them).

            On the other hand it would be much cheaper to to do maintenance of a single 600 kW turbine (still a very small one) compared to 100 6 kW turbines. (But of course, Eigg has no use for utility-scale turbines.)

            Bottom line: When it comes to residential-size power generators, wind is in general much more expensive than PV.

      • singletonengineer says:

        That is nonsense, gweberbv.

        To match 10kW nameplate of wind turbine at 19% CF will require not 10kW of PV, but 19kW at 10% CF. Furthermore, this isn’t a 10kW installation – it is 356kW total.

        Besides which, there are several months each year when the PV is essentially useless. Nameplate ratings are irrelevant when the sun isn’t shining. What matters is the energy sent out measured in MWh and the ability to schedule that electricity for times when the users need it.

        10 or 20 kW in this system makes no real difference to the ultimate result. Both wind and solar on Eigg are ornamental. The real work will continue to be done by hydro and diesel unless more free money for bigger and better wind and solar and battery storage is wasted on it.

        • Thinkstoomuch says:

          I would not really say complete nonsense.

          When I look at figure 1, figure 2 and table 1 a couple of things seem to leap out at me.

          First a big hat tip to Roger for deconstructing graphics!

          IF(!!!) I am spending other people’s money and I want to use the diesel as little as possible. Solar seems like the perfect solution. The two months needing the most help are June and July. Figure 1. To a limited extent May and possibly April.

          Extra wind would just be curtailed in the fall and winter when hydro is covering demand, Figure 2. A guess on limited information. One year’s data is a stupid way to plan a multiyear system life.

          One problem. Seems like wind and solar are limited(curtailed?) to around 7,200 kWH a month. This is based on April, May, June and July numbers in the table.

          It looks like the battery storage is what is limiting Solar, and probably Wind. But that is a big guess.

          Without more detailed information we are not going to be able to identify the problem much less come up with a solution.

          Again all that is predicated on the fact that it, It Ain’t my money or my tax money.

          Have fun,

          • Jean-Marc says:

            Thanks to all for your comments.

            Now, as far as subsidizing renewable projects in remote areas, let me share our experience here in the province of Quebec.

            We are 98% hydroelectricity (huge dams and reservoirs) and 75-80% of residential heating systems are electric. But there are a few islands (Magdalen Island) and remote Northern areas where there’s no transmission lines to serve those customers. Therefore, electricity is generated with diesel at a high cost. But these clients carry on the same rate as all other ratepayers in Quebec (namely 6 cents/kWh) and not the cost of actually generating electricity from diesel. Therefore, all ratepayers are subsidizing these people but there’s a social consensus that this is OK.

            Now, if we were to install renewable systems in those areas, cost of installing and maintaining such systems should be compared to the cost of generating electricity from diesel. And, if the renewable are cost competitive, then it’s OK. We (as ratepayers) would be subsidizing those renewable but what’s the difference between subsidizing renewable or subsidizing diesel to generate electricity in remote areas? My point: renewable systems in remote areas should be compared to the cost of delivering electricity using “conventional” means such as diesel and not the “per se” costs of such renewable systems.. If cost are lower or equal then great. If not, then let’s forget about it.

            Also, to comment on singletonengineer, I fully agree: PV have a very low CF (10%) and replacing those systems with wind turbines (CF 19%) would improve wind’s CF, improve system’s overall efficiency (CF 11%) and, probably, cost less for the same basic generating capacity.

            All this to say, if cost of renewable are compared to cost of generating electricity solely from diesel then renewable on Eigg Island are cost effective. And system could be optimized by installing renewable who have best CF, which would improve overall CF of 11% and lower the £0.54/kWh computed by Roger.

          • singletonengineer says:

            Don’t forget the batteries. Wind and solar need to be supported by a reliable additional source, probably either batteries or hydro, in order to maintain frequency and to bridge the no-wind and no-sun periods. I imagine that local capacity factors are as low as those experienced on Eigg.

            The capital cost for a full swap from diesel to wind+solar+batteries will be quite high, thus also a high LCOE. Possibly this can be justified on social grounds but if the primary motivating factor is reduced fossil fuel use, your provincial government might find cheaper and less risky ways to do so.

            Most of all, the residents must understand the risks that are inherent in intermittent power sources such as wind and solar and the effects of limited energy reserves in any battery backup.

            As always, the advice is “Do the maths”.

          • Jean-Marc:

            Thanks for picking up on that error. Mea culpa 🙁

            The CF for hydro is indeed around 20% (I get 19%), not 65%. I’ve altered Table 1 so that it now contains the right number and made a few modifications to the text in the next paragraph. Overall it doesn’t change much except that it make the system look even more inefficient than it was before.

            Thanks again.

  16. Greg Kaan says:

    the remaining 22.5 kWp was added some time in 2013. The date is not specified but was probably after March.

    According to this site, the last block of PV was installed in July 2013

    There are more details about Eigg and other UK island mini-grids on this site, as well

    • Greg: Thanks for those interesting links. When time permits I might try to put together a post that summarizes data from all these projects to get an idea of the current state-of-the art. (I think I already know what it is but confirmation is always nice to have).

  17. Jean-Marc says:

    Good day to all of you from Montreal,

    Let me throw in another option: underwater power cable to feed island’s customers, with diesel station as a backup (if only one cable is installed). From my previous comments, I derived the fact that generating electricity solely through diesel would induce costs > £0.60/kWh. And, with renewable as computed by Roger, LCOE is £0.54/kWh.

    Now, Eigg is 10 km from mainland Scotland, which is a short distance for an underwater power cable. For an ongoing underwater power cable project in the Northumberland Strait (roughly 10 km), they’re installing 2 new cables, at a cost of 140 M$ CDN (80 M£) for a total capacity of 360 MW and a life expectancy of 40 years (

    Let’s make a few approximations to transpose this project to Eigg’s configuration:

    1) 80 M£ * 360 kW / 360 MW = 80,000 £ (project cost for 2 underwater cables)

    2) 80,000 £ / 2 = 40,000 £ (only one cable installed)

    3) 40,000 £ / 40 years = 10,000 £ per year (capital cost)

    4) 10,000 £ / 350,000 kWh = 0.03 £ / kWh

    Let’s figure out a cost of 0.05 £ / kWh as the approximate cost of delivering electricity through an underwater power cable to Eigg from mainland Scotland, the diesel station supplying electricity only in case there’s a fault with underwater cable.

    This raises 2 questions:

    a) why have the authorities not installed, at this time, an underwater power cable since delivering electricity through this medium is far less expensive then generating electricity locally, with diesel, without any renewable?

    b) notwithstanding environmental considerations, what’s the purpose of going on with renewable systems since LCOE are far more expensive then using an underwater power cable to feed the island?

    • gweberbv says:


      again you ignore the scaling of costs. For your power cable you will have a certain offset that you have to pay independent from the transmission capacity.

      • Jean-Marc says:

        Good day gweberby,

        “Ignore scaling of costs”?

        From a rough estimate, I get 0.03 £/kWh, which I’ve rounded to 0.05 £/kWh.

        Now, double or triple this cost and you’re still way below diesel generation or renewable installation (LCOE of 0.54 £/kWh).

        So, pls come on with data and facts and not generic statements.

        • gweberbv says:


          as you cannot order undersea cables at your local electrician, it is hard to obtain exact numbers for the costs. But here you might get an idea about it: (seems to be data from about 20 years ago)

          Bottom-line: You need to spend a few millions per km just to pay for the experts and special equipment to install an undersea cable.

          • Jean-Marc says:

            Good evening gweberby,

            You are right: one must base such propositions on proven projects.

            Actually, I’ve provided a “real project” being carried on, ie. the Northumberland Strait. Look at the reference provided by CBC coverage.

            Now, this project has awarded a contract to a South Korea manufacturer to supply the cables (approx 54 M$ CDN) and the overall project cost is 140 M$ CDN (including cables, experts and special equipment to install such cables). And the cable length is 10 km, same as Eigg.

            So, I’ve based my proposition not on a project carried out 20 years ago or some theoretical solution but an ongoing project with real costs established.

            Therefore, I stand by my figures since this proposition (install underwater power cable) is based on a real project with proven costs.

          • gweberbv says:

            Jean Marc,

            the costs to install the cable are fairly independent from its transmission capacity. Therefore you have a lower limit for the transmission volume below which the undersea cable makes no (economic) sense. I guess this limit is order of magnitudes higher than the electricity consumption on Eigg.

          • Jean-Marc says:

            Good day gweberbv,

            Yes, you are right: there are fixed costs (cable installation and layout) and the cost of cables per se, which is variable depending on length, capacity,…

            So, from my computations, only the cost of the cables (54 M$ CDN) could be “adjusted” to the required cable capacity for Eigg, on a prorata basis. But there’s still 86 M$ CDN which seems to represent “fixed costs” independent of cable capacity and related to cable installation.

            Now, as a junior P. Eng, I had to lay out a power cable between mainland and a small island (approx. 1 km long and very few customers). The technique was simple: using a specially designed ship (small), cable was laid down to rest on sea floor. And it was covered with a layer of concrete as to protect cable from anchors,… no expensive machinery, no need to dig a trench,… And installation costs where small using this approach.

            So, as far as Northumberland cable is concerned, layout and installation costs are expensive since demand is high (360 MW) and special care has to be taken to ensure continuous supply to the island. But, in case of Eigg, using a “standard” cable installation on sea floor, I still believe that we could make this option feasible.

  18. There are a number of important omissions in the article.

    The real purpose of renewables – attempting to avoid the most extreme climate change scenarios – is subsumed beneath a largely irrelevant discussion of cost. Renewables do not have to compete on price. They only have to reduce carbon emissions. In an emergency you have to act decisively by pursuing the best options available at the time.

    We should also question the claim that renewables actually are more expensive. The article does not mention that oil and gas etc also receive subsidies. The cost analysis would look different if these had been considered.

    There are significant external costs associated with the old technologies quite apart from future climate change impacts – eg pollution. Once these are included, studies have shown that wind is the cheapest way to generate electricity – and the cost of renewables continues to fall year by year.

    Finally, it doesn’t make a lot of sense to use one tiny island as an example off the wider benefits of renewables. The true potential of wind etc is only realised within smart, continental-scale supergrids where demand management and the sheer scale of the system can relieve the issue of intermittency.

    Even so, Eigg seems to have a pretty successful set-up. We also should consider that advances in battery technology may allow the diesel generators to be retired in the near future.

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