Demonstrations of Caribbean people who can’t afford electricity anymore are a sign on the wall that the price of electricity is becoming a serious concern. On the other hand, the Caribbean enjoys a very favourable wind regime. The author, wind energy consultant and environmentalist James Post installed the first utility-grade windmill in Caricom at Paradise Bay Resort in Grenada (http://www.paradisebayresort.net/html/eco.html). He teamed up with international specialists to find the solution to substantially reduce electricity prices, the oil dependency and global warming. Moreover, islands who use this solution can offer tourists a carbon free vacation. In this article, innovative solutions are discussed that allow up to 60% renewable energy penetration – potentially more if hydro power is available-.
 

James Post

During the past decades, wind energy has been the underdog in energy world, where government subsidies and idealists were the main driving forces. The rapid increase of oil prices, global warming concerns and oil dependency made the need for subsidising obsolete. In small markets the situation is even more extreme as the fuel cost per kWh is amongst the highest due to the small size of the operations. With a highly favourable wind regime it is no wonder that the Caribbean is now seen as a prime market for wind energy.

However, current plans are not very aggressive, aiming at a net wind penetration of up to 20%. While this is better than nothing it does not really address the underlying concern and is more a sign of good will than truly solving the issue. The example situation described below shows a typical island energy situation. Many islands face severe financing limitations and therefore often chose the PPA path (Power Purchase Agreement), where an independent power producer (IPP) supplies renewable energy. In cases where the wind penetration is initially set at 15-20%, the vendor with the lowest price per kWh may win the concession. But, there is a string attached –and it’s a big one-.

Most traditionally designed windmills are aimed at low wind penetration. Their natural behaviour destabilises the grid, simply because the wind comes not constant, but with fast rising peaks. As long as the grid is stable enough this works well -for low wind penetration-. But it also closes the door for higher wind penetration and that’s the real pitfall.

The solution is to use windmills that –rather than destabilising the grid- support the grid. There are state-of-the-art windmills out there that first convert AC to DC and then generate a highly defined AC. For the specialists: this opens the door to compensate an inductive grid –which it usually is- by a programmable cosine phi (also known as power factor), in addition to frequency support. But the AC/DC/AC process has another significant –until now less recognised- feature: the ability to stabilise the output of the wind generators.

As long as the nominal output of the wind generators is less than about 80% of the base (minimum) load, a large capacitor bank will do the job and convert the peaks caused by the wind in a smooth output. That is a major winning point for the AC/DC/AC based systems as this allows the wind penetration to be roughly double –without further measures-! This more than justifies the higher cost of these best-of-class windmills; not even counting the other positive effects as described above. But, there is more.

To obtain really high wind penetrations, energy storage is necessary. Typical solutions involve energy storage of 4-8 hours [of the peaks]. This allows to control the diesel plant and let it run in the most optimal fashion, i.e., at 80% load or even switch off in a high wind situation. These windmills are indeed able to run stand-alone! Because of the stabilisation measures needed to support a higher wind penetration, the cost per kWh increases with wind penetration. However, as the effective kWh cost (mix of wind energy cost and diesel cost) goes down with every step, high wind penetration really pays.

The reason why the energy industry in the Caribbean is not massively moving forward towards high wind penetration is the same reason why wind energy in the region lagged behind: lack of knowledge and experience. This is understandable as this is a complex matter, but I am glad to report that there are some utilities who –assisted by external specialists- have seen the ‘high wind’ light.

Another issue that need to be clarified is reports that say the maximum size that can be installed in the Caribbean is 900 kW. However, the state-of-the-art windmills are in the 2 MW range. This statement was true for monopole designs where large cranes were necessary that even made installing the 900 kW windmills a challenge, while traditional lattice towers were considered to be too maintenance-prone. However, in recent years (the recommendations originate before that) new tower constructions were developed, based upon the traditional lattice tower, but with tubular segments. Compare it to a high tech Eiffel tower... The weight is less than a third of the tubular tower at improved strength and without maintenance issues! By placing a top crane on the top of the tower that can lift up the very heavy generators etc., the main crane only needs to have a capacity of 18 tons, even less than required for 900 kW tubular towers.

The 2 MW wind generators have the additional advantage as having a higher tower. A 100 meter tower makes economic sense with a 2 MW, but a 900 kW stops at 65 meter for the same reason. That difference mean significantly more wind.

For good order, with the high wind penetration it may be necessary to upgrade the diesel plants (and if applicable hydro) as the central control system must be able to switch them on or off or at a particular (efficient) load. These costs have not been brought forward here, but neither are the savings associated with these measures.

Finally, for those markets with hydro power installed, pumping up water to the reservoir before the hydro plant is a very attractive energy storage option, cheaper than any other form of energy storage, provided the height between the upper and lower reservoir (. Renovations may be required to be able to switch the plant on and off, in addition to pumping water but these costs are very acceptable compared to the savings.

CONCLUSIONS

• High wind penetration is no longer an unreachable wish, but a technically feasible and economical solution
• To keep the path to high wind penetration open for tomorrow, the right decisions need to be taken today
• The initial investment in the first Megawatts of state-of-the-art AC/DC/.AC windmill capacity may be higher than traditional wind turbines, but it already pays off in the first stage of high wind penetration, not even considering the positive effects on the grid.
• Advanced 2 MW windmills can be installed in Caribbean islands using the latest tower and lifting technology.
• For markets that (will) have hydro, the high wind penetration is the only sensible choice offering dramatic savings.
• High wind penetration reduce the oil independency and –at the very least- stop the increased cost of electricity.
• When the oil price goes up again (most analysts agree this will happen once the world economy recovers) there will be savings in the “fuel” cost of electricity, the substantiality depends on the increase of the oil price

James Post earned his spurs in the high tech electronics industry from 1973. A veteran in system design, customer relations and marketing, he brought his company Ultimate Technology BV to market leadership in the European market prior to merging with Electronics Workbench Inc, later acquired by National Instruments PLC. After resigning as CEO in 2000 he started the sustainable resort Paradise Bay (http://www.paradisebayresort.net) in Grenada, installed a 80 kW windmill, emerged as an advocate for renewable energy and -conservation and became an independent wind energy consultant. He can be reached at: jamespost@spiceisle.com or phone (++1) 473.405.8888 http://www.advancedrenewableenergy.info