State-of-the-art solar power, wind and water generators have transformed the efficiency of alternative power sources. Can we say goodbye to diesel? Rupert Holmes investigates

Imagine a future in which there is never any need to fill up with diesel, buy gas, or top up water tanks and the only constraints are those of needing to stock up with food and maintenance of the boat itself.

It’s a scenario that’s much closer than many realise. The past decade has seen an accelerating pace of change, with technologies that appealed only to a minority, or were prohibitively expensive, now firmly entering the mainstream.

It’s already more than five years since the first of Gideon Goudsmit’s 44ft African Cat cruising catamarans sailed from South Africa to the Netherlands without using fossil fuel, even for cooking, watermaking and hot water.

Although many would baulk at the boat’s 80-mile range under power, this is not a quirky vessel in any other respect – it’s a spacious, fully fitted-out, comfortable cruising catamaran with a high level of equipment. In addition to solar and wind generators providing electrical power for the lightweight design, the boat’s electric propulsion motors were configured to be used as generators when under sail.

And it was by no means the first to do this. When Francis Joyon set the fastest time for a solo circumnavigation in 2007/8, his 80ft trimaran IDEC ll did not have a diesel generator. Similarly, Raphael Dinelli completed the 2008/9 Vendée Globe race without using any fossil fuel.

While few owners aspire to this level of self-sufficiency, incorporating some of these ideas can improve reliability and convenience for more conventional yachts, and may also reduce costs. Perhaps the most persuasive reason of all to fit additional means of generating power is that the presence of multiple charging systems improves a boat’s reliability by introducing a degree of redundancy – if one system fails much of the charging capacity remains intact.

Combining several different technologies can also balance the pros and cons of different power sources.

Thin film solar

2013-SNIM-J1-MER (5)

A new development that could be the answer to the African Cat’s short range under its electric motors is extremely flexible giant solar panels that can be attached to sails, or even incorporated into the laminate. The durability of this technology was demonstrated at the end of last year by Daniel Ecalard, who used a pair of 3m2 panels near the head of his mainsail to provide the electrical needs of his Open 50, Defi Martinique, during last year’s Route du Rhum race.

During the race the system stood up to a gale in the Bay of Biscay, in which ten per cent of the fleet retired, and survived the 25-day Atlantic crossing, during which Ecalard logged 4,677 miles, intact.

The system, named PowerSails, was developed by Alain Janet, owner of UK Sailmakers France. Each square metre of the panel is capable of generating 100 watts and, according to Janet, does not need direct sunlight to generate electricity: “In fact, the panels on the sail opposite the sun will generate 30-40 per cent of their maximum output with the indirect and reflected light,” he says.

These panels are made from film that’s 65 microns thick and weighs 100 grammes per square metre. This technology can also be used in other applications – a cockpit bimini shade, for instance, that could generate 1kW on a 50ft yacht.

Prices start at around £700 per square metre of panel, though this is expected to fall as production increases.

Mainstream markets

Janet has produced sails for a Dehler 39 in which a sizeable solar panel is laminated to the mainsail. The technology has also been harnessed by production boatbuilder Arcona, which has announced a version of its 38-footer equipped with an electric engine/regenerating system, sails with solar panels and a big bank of lithium ion batteries.

The boat debuted to great acclaim at this year’s Helsinki boat show, where it won the boat of the show award.

The solar panels in the mainsail are of sufficient size to generate an average of 1,000 watts of power, and the boat has a further 1,000 watts of solar panels. This is sufficient to drive it at four knots under power during daylight hours without taking any charge from the batteries.

Solar power


Almost every aspect of this sector has seen enormous development over the past decade, with worldwide installed capacity having grown by 3,000 per cent since 2005. The resulting economies of scale mean prices have tumbled, while funds are continuing to pour into research and development.

Panels are becoming progressively more efficient, with the best commercially available units now having an efficiency of around 25 per cent, although double that has been achieved in laboratory conditions.

At the moment the thin film panels mentioned above are around 12-14 per cent efficient, but in the future we can expect all types of solar panel to become smaller in area for a given output.

In addition, today’s panels are less susceptible to output drops when in partial shade and give good performance in cloudy conditions. This makes mounting panels on the coachroof, rather than a cumbersome gantry, an increasingly viable option.

Currently solar sells for a very wide range of prices, with most marine grade panels priced from around £200 to well over £500 per 100 watts.


Solar Pros:

√         Improving technology with reducing prices

√         Suitable for a wide variety of boats and conditions

√         Proven ‘fit and forget’ reliability


x         Many boats have insufficient space for a enough conventional solar panels

Hydro generators

Hydro Cruising 300W-970mm - couleur-1

The transom-mounted generators, such as those produced by Watt & Sea, originally came to prominence in the IMOCA 60 fleet, with the 2008 Vendée Globe race used as a gruelling testbed for the prototypes. They are capable of producing large amounts of power with minimal drag and can be lifted clear of the water when not in use.

The company’s cruising units are rated at either 300 or 600 watts, depending on the model chosen. The larger of these produces 120 watts of power amps at just five knots of boat speed, rising to more than 250 watts at 7.5 knots.

Over a 24-hour period that represents a significant amount of power that could alone run the majority of systems aboard many 50-60ft yachts, including watermakers, pilots, lights, electronics, refrigeration and water heating.

On the downside, hydro generators are relatively expensive compared with solar and wind generators, with Watt & Sea’s prices starting at a little over £3,000. Moreover, they are potentially vulnerable to damage when docking. The latter can be a particular problem in the Mediterranean, where most mooring is stern to the dock.

The Sail-Gen from Eclectic Energy (from £2,000) or the towed Aquair (a little over £1,000) from Ampair are more economic, though less convenient, alternatives.

Another option is a hybrid drive system with a regenerating function via the boat’s main propeller. Advantages include an absence of peripheral parts attached to the transom that may be susceptible to damage, or detract from a yacht’s aesthetics.



√         High power output

√         Impressively low drag


x         Transom-mounted types are expensive

x         Vulnerable to damage

x         Only works when the boat is underway

x         Impeller of transom-mounted models may leave the water if boat is pitching in a head sea

x         Towed type difficult to deploy and recover


Methanol fuel cells


These small, lightweight units have many attractions for use on board. Most are designed to monitor battery state constantly and automatically start charging once the voltage falls to 12.2V. They are almost silent in operation, with carbon dioxide and water the only exhaust products.

Output ranges from around 3 to 9 amps and more than one unit can be used to achieve higher charge rates. Given that a fuel cell can, in theory, run for 24 hours a day – unlike a marine diesel generator, which is more usually used for only two or three hours – a fuel cell can pump out a useful amount of power, despite the low amp hour rating.

On the other hand the long-term cost of ownership is a drawback. With retail prices of around £2,300-5,000 they are relatively expensive to buy, although installation costs are minimal. Additionally, the platinum catalyst has a finite life of around 5-8,000 hours. As this is by far the most expensive element, it’s clear that fuel cells aren’t yet up to providing power 365 days a year for long-term use.

A further problem is with the fuel, which to achieve the purity required is expensive and generally only available from specific outlets.

At the moment it looks as though fuel cells have more cons than pros for many yachts, although there are some circumstances in which they may make sense. For instance, they are popular on long-distance short-handed raceboats. A fuel cell may also be useful on a boat with a hydro generator that is self-sufficient on power while on passage, but may need an occasional boost when at anchor for long periods to supplement solar and wind charging.

Fuel cell


√         Unobtrusive, clean and quiet

√         Easy installation


x         Long-term ownership and operating costs

x         Fuel not universally available

Wind generators

D400 turbine 2010

For several decades these were de rigueur for serious cruising yachts. On paper a decent-sized unit is capable of generating the entire needs of a 45-50ft yacht. However, they also have a number of drawbacks, the most commonly cited being noise and vibration in strong winds.

In addition, most cruising routes maximise time spent sailing downwind, which reduces apparent wind strength, which in turn dramatically reduces the output of a wind generator. Similarly, generating power in many anchorages can also be problematic, as the very shelter sought by the skipper also means that wind speed is generally significantly reduced.

Nevertheless, wind generators can be useful in some circumstances; the important thing is simply to recognise their strengths and weaknesses.

Prices range from small units producing just four amps or so for less than £400 to upwards of £2,000, although for most medium to large yachts £1,400-1,900 will buy a suitable system.



√         Capable of producing plenty of power in a strong breeze


x         Noisy and creates vibration

x         Output severely reduced in sheltered anchorages and when sailing downwind

x         Can be bulky and cumbersome

Typical daily power outputs

Power output graphic

Typical power inputs for 12V systems (divide the ah figures by 2 for 24V systems)


Assuming the panels are mounted in an unshaded position, each 100W of rated capacity can be expected to produce, on average, around 33ah of charge per day during the UK summer.

Hydro generators

For a yacht averaging 150 miles per day (6.25 knots), Watt & Sea’s 300W cruising model will produce around 175ah per day. This rises to around 275ah per day at an average speed of seven knots, but falls to 120ah per day at five knots average.

Wind generators

These have by far the biggest range of potential outputs, with many units averaging less than ten per cent of their rated output over a full year. That would equate to a mean of around 50ah per day for a model with blades of around 1.2m diameter.

However, there are few average days and a 24-hour period with steady 15-knot breeze would see the same unit produce more than 100ah per day. In a 25-knot wind it would be 500ah.

Fuel cells

The daily output of fuel cells is very predictable. For example, a model rated at 5 amps would produce 120ah per day, if run constantly for 24 hours.

It’s worth noting that, as the catalyst nears the end of its life this figure will tend to reduce.

Daily power table

Battery monitors

The more complex a yacht’s systems, with multiple power inputs and outputs, the harder it is to keep track of the battery state. However, a properly calibrated battery state monitor will measure all the power flows in and out of each battery bank. This makes it easy to keep track of power consumed and keep charge levels above the 50 per cent of battery capacity needed to ensure good battery life.

Reducing power requirements

Despite the increasing complexities of many of today’s yachts, new technologies mean that power requirements are steadily reducing in many cases. Whereas only a
few years ago the accommodation of a quality 60ft cruiser might have been lit by 400W of halogen bulbs, low-power LEDs can reduce that by 90 per cent.

Despite their growing size, TVs can now draw less power than a couple of 12V lights did a decade ago. Similarly, tablets and smartphones are increasingly used for activities that not so long ago could only be done with a power-hungry laptop.

Pragmatic solutions for cruisers


For most yachts it’s worth combining a number of different types of technology, depending on how you sail and where. Here are some options for a range of different scenarios:

1. Cruising in Northern Europe

Despite a reputation for inclement weather, solar power can be a very viable option here, thanks to long daylight hours and relatively cool temperatures. The latter may sound counter-intuitive, but the efficiency of solar panels reduces at higher temperatures.

Whether wind power is worthwhile may depend on where you’re planning to sail and the time of year. In mid-summer in the southern half of the UK, for instance, the wind is typically less than ten knots for 50 per cent of the time, so wind generators are of limited use. However, in western Scotland towards the end of the season you could generate plenty of power, which would compensate for the reduced solar output.

With the longest passages most yachts will make being 300-400 miles, a hydro generator is likely to be of less use than for boats making longer voyages. An exception might be for those planning to spend a lot of time at anchor and who therefore value the ability to arrive at an anchorage with batteries fully charged.

2. Mediterranean cruising

While many marina-based yachts, with ready access to shorepower, in the western Med appear to have been slow to adopt solar power, the opposite is true in the eastern Mediterranean where there are increasingly few privately owned yachts without an array of panels.

As an example, Alan and Deborah Mackenzie’s Lagoon 410 catamaran, based in the north-west Aegean, has three 100W semi-flexible panels. This has proved fractionally too small for their needs – to power a fridge, freezer, powerful fans and a 19in TV/DVD in addition to the boat’s systems. They plan to solve this with an additional panel.

Owners of monohulls tend to be more restricted by the space available to mount panels, although the new thin-film panels clearly offer a wider range of options. Given the relatively short distances most yachts travel on each passage, the same considerations regarding a hydro generator in northern Europe apply here.

Equally, in most parts of the Med, wind power is not viable for much of the time.

3. Caribbean

Here it would be easy to assume that solar is the best option. However, while it can certainly be useful, as the main sailing season is winter, when daylight hours are restricted, daily output is smaller than many owners expect. Given that the islands are in the tradewind belt, wind generators stand to produce a good output here.

4. Tradewind passagemaking

Here it’s clear that hydro generators (or power generation via a hybrid drive) have advantages and can deliver a good charge. Wind power, however, makes less sense for tradewind sailing, owing to the reduction in apparent wind speed when sailing downwind.

The output of solar will also suffer from the restricted number of daylight hours on a typical east to west Atlantic crossing. There are, however, more factors in favour of solar on a west to east crossing, as it is likely to be at a higher latitude – with more daylight.

5. World cruising

If you’re going further afield combining as many options as possible will yield the best rates of charging over a wide range of conditions. This is exactly the route taken by Jimmy Cornell, founder of the ARC, whose new Garcia 45 is fitted with solar, a Sail-Gen water turbine from Eclectic Energy and a wind turbine.

The water generator will create 50W of power at four knots of boat speed, rising rapidly to more than 250W at 7.5 knots. The wind turbine, from the same company, is also a high-power model, with a 1.1 metre rotor diameter, producing approximately 100W in 15 knots of wind, rising to 235W in 22 knots.

For more information:

Eclectic Energy:


This is an extract from the June 2015 issue of Yachting World