Photovoltaic Propulsion of Boats in the Netherlands

by W van Zanten, CADDET Dutch National Team

Introduction

The use of photovoltaic power in the Netherlands must be encouraged if it is to reach the projected share of 0.3% of national electricity generation by the year 2010. Currently, only 5% of installed photovoltaic power consists of grid-connected systems. Successful and visible applications will stimulate acceptance of solar systems, and an improved market should reduce prices.
 Water sports occupy large areas in the Netherlands and the government, councils and owners are looking for quieter alternatives to the internal combustion engine. The advantage of engines powered by photovoltaic solar energy is the complete absence of emissions, fuel and noise.

Propulsion Tests

An investigation on Novem's behalf by Ecofys, a consultancy and research organisation, estimated the technical potential of photovoltaic propulsion for recreational vessels in the Netherlands, as shown in the table. Projected for all of Europe, this accounts for several hundreds of MWp.
 In 1993, Ecofys started a test for Novem with 18 recreational vessels using photovoltaic electrical propulsion, totalling 5.2 kWp. Research has shown that two combinations operate satisfactorily: a 60 Wp system for small vessels used only at weekends, and a 400 Wp system for intensively-used saloon vessels. An annual shortage of energy of 6% for small vessels and up to 28% for saloon vessels used daily is to be expected.
 The goal of the project was to obtain experience with photovoltaic electrical propulsion. Most units are built into vessels that were not specially designed for this kind of propulsion. About half of the test vessels were equipped with a small (100 Wp) system and the other half with a larger system of around 400 Wp. Two additional excursion ships also participated in this experiment. Their capacity was more than 600 Wp.
 Some 5,000 electrically propelled vessels are currently in use in the Netherlands. Consequently, sizing of the engine expressed in terms of nominal power presents no problems. An electric engine need be only half to one-third the size of the combustion engine required to provide similar sailing characteristics. The engine's power should be more than 500 W/tonne.
 The capacity of the battery chosen was capable of covering one week's sailing. For small systems, this was between 2 and 4 kWh, and between 3 and 11 kWh for larger systems. Most of the solar panels were made by, Solarex and Sunware. They are slightly flexible and capable of sustaining pressure caused by standing on the panel.

Monitoring

Monitoring was carried out to obtain more knowledge of the capacity of photovoltaic electrical propulsion. Of special interest were: energy consumption, power required, energy supply and the yield of the photovoltaic/battery systems. This information was obtained from measurements on board, surveys of employers and inspections of logbooks. An energy balance sheet was drawn up for all systems. Global solar radiation data, gathered from one of the Dutch weather stations, were sufficiently accurate for the project.

Type of vessel

Number

Photovoltaic potential

Open vessel

22,000

> 1 MWp

Saloon vessel

122,000

49 MWp

 Total

144,000

 > 50 MWp

Results

The performance of the photovoltaic systems can be expressed as a performance ratio: the number of hours a day the system can deliver its nominal power in relation to the total solar supply. The expected performance ratio in stand-alone photovoltaic-battery systems is between 0.2 and 0.4, ie 20-40% of all solar radiation is used effectively.
 In this test, the performance ratio is lower between 0.04 and 0.37 because not all panels are mounted favourably and their use is not constant. They are designed for weekend use only. If a vessel is not used for a weekend, the battery is fully-charged and all extra solar energy is "wasted".
 The solar panels can supply enough energy for weekend use in the summer, excluding holidays. On average, the vessels sailed about 50 hours per season. Generally, all components operated satisfactorily.

Conclusions

Stand-alone photovoltaic systems are suitable for propelling electrical recreational vessels. A photovoltaic power of 100 to 400 Wp is sufficient for weekend summer sailing. On average, the engine is used for 50 hours a year, although owners are tempted to overestimate the number of sailing hours. Shortage of energy during holidays can be temporarily overcome by extra battery capacity or by charging the battery from the grid or from an auxiliary generator.
 For more information contact the CADDET Dutch National Team in Sittard.

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