A short distance off the west coast of Scotland lies the island of Eigg, area 15 square miles, population 87 (2005). It has never had a grid connection to the mainland, so historically its residents have either had to generate their own electricity from diesel generators or go without.
Then on the 1st of February 2008 everything changed. Eigg proudly switched on its new power system, which generates around 90% of the island’s electricity from renewables and feeds it to consumers through a smart grid. In 2010 the system won a £300,000 share of the National Endowment for the Arts and Sciences Big Green Challenge award and also the prestigious Ashden gold award for energy efficiency. It’s been hailed as a example of how renewable energy can be made to work, and as a model for a sustainable energy future.
So using Eigg as our model, let’s see what a sustainable energy future might hold for us.
First some details on the Eigg electric system (data sources are listed at the end of the post). It has a total installed nameplate capacity of 333 kW, made up of three hydroelectric plants of 100, 10 and 19 kW. Here’s the 100 kW plant:
Plus 24 kW of wind in the shape of four 6kW turbines:
Plus 30 kW of solar panels (8 kW to begin with, 22 kW added later):
Plus two 80 kW backup diesel generators (no picture available) to deliver power when renewable generation is insufficient to meet demand. (80 kW is the capacity given by Eigg Electric. According to the Isle of Eigg Heritage Trust there are two 64kW generators that operate alternately. However, the diesel generators provide less than 10% of the electricity used in a year.)
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:
Power from these different sources is integrated into the the local high-voltage (no details on how high) smart grid through a series of inverters and a multicluster box:
The total cost of the system was £1,664,828, or £5,353/kW for the 311 kW in the initial installation, which is not out of line for a small-scale remote installation. Eigg’s residents also get remarkably cheap electricity considering the island’s location, paying a flat rate of £0.20/kWh for power consumed plus a daily standing charge of £0.12 for a 5 kW connection and £0.15 for a 10 kW connection, not much more than they would pay on the mainland.
And since the system was installed Eigg’s CO2 emissions have fallen by 47%, from 8.4 to 4.45 tonnes/year per household.
So what’s not to like?
Well, there are a few things.
First, the Eigg system is almost unbelievably inefficient. Eigg Electric Ltd. publishes no performance data, but based on the data that are available the annual load factor for the total 333 kW of installed capacity on the island is less than 4%. Here are the numbers (if anyone has better ones please feel free to present them):
333 kW installed capacity times 8,760 hours/year = 2,917,180 kWh/year at a 100% load factor.
Average annual electricity consumption = 2,160 kWh per household, times 50 households = 108,000 kWh/year.
Load factor = 108,000/2,917,180 times 100 = 3.7%.
If we exclude the 160 kW of backup diesel capacity and its ~10% contribution to total generation the load factor for combined hydro+wind+solar is still only 6.4%.
Second, the Eigg system is hopelessly uneconomic. The levelized cost of Eigg electricity given by the NREL calculator assuming a 20-year life, £5,000/kW installed cost, a 4% capacity factor, a 3% discount rate and a £150/kW/yr O&M cost is £1.38/kWh. (Eigg Electric can get away with charging only £0.20/kWh because it got the system effectively for free. The island contributed only ~4% of the project’s £1,664,828 capital cost – £92,761 from the Isle of Eigg Heritage Trust and local residents less maybe £35,000 recouped in hookup fees – and this expenditure was more than offset by the £300,000 award Eigg received from the National Endowment for the Arts and Sciences in 2010. The other ~96% came from grants from organizations such as the European Regional Development Fund and the Scottish Households Renewables Initiative.)
Third, the system makes no attempt to match supply to demand. Instead it manages demand by setting low consumption limits to begin with and then by cutting the power off (and fining the violator) when these limits are exceeded:
Eigg manages electricity demand mainly by capping the instantaneous power that can be used to 5 kW for a household and 10 kW for a business. If usage goes over the limit, the electricity supply is cut off and the maintenance team must be called to come and switch it back on again. If the limit is exceeded and one of the maintenance teams is called out to turn the power back on, a £20 charge may be levied …
All households and businesses have an OWL energy monitor, which displays current and cumulative electricity usage and sounds an alarm when consumption reaches a user-defined level, usually set a few hundred watts below the actual limit.
Demand is also managed by warning the entire island when renewable energy generation is lower than demand and the diesel backup generators are operating – a so-called ‘red light day’, as opposed to ‘green light days’ when there is sufficient renewable energy. Residents then take steps to temporarily reduce electricity demand further still, or postpone demand until renewable energy generation has increased.
(The emphasis on “renewable energy generation” suggests an unwillingness to start up the backup diesel generators even though they should be more than capable of filling demand. One can question whether there’s any point in having them if they’re not going to be used to keep the lights on, but keeping CO2 emissions low seems to be the priority at the moment.)
Fourth, despite the aggressive demand management practices there have still been a number of “red-light” days when renewable energy generation failed to deliver. A prolonged period of red light days occurred just before Eigg received the Ashden award in the summer of 2010, when the island enjoyed an extended spell of unusually fine weather during which the wind died, little rain fell and the reservoir level dropped below the turbine intake. For some weeks the islanders were back to boiling kettles with gas, but they took it all in stride. As one of them interviewed by the Daily Mail said: “Of course the drought has hit us hard. But whatever people say, there’s no question the project’s been a massive success. We are all delighted with it here.”
So there you have it. Despite its defects Eigg’s model of a sustainable energy future is regarded as a triumph by the island’s residents:
But whether it will play in Peoria, Paisley and Paris is another question.