Marine Solar Panels: Compare Solar Panels for Boats

By 15 min read

Getting solar panels for your boat will stop your battery going flat and reduce your energy costs

Once you’ve paid for the panels, you have your own free electricity supply

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Imagine never having to worry about your boat battery running flat again. Never coming back after a few weeks’ absence to find your power source giving you the cold shoulder. Never having to miss out on things you want to do because you have to sit on the boat and run the engine instead. Always knowing that, should your engine fail, you still have a source of electrical power.

Just as solar power can be used to provide electricity in your home, it can be used to provide power for your boat too. You can use the sun’s free, inexhaustible energy supply to start your motor and power your lights, TV, computer, fridge and more. The panels only need daylight to work; they’re more efficient in bright sunshine, but any sunlight will do.

What’s in This Guide to Marine Solar Panels?

How Do Marine Solar Panels Work?

house with solar panels

Solar panels on your boat work in the same way as solar panels on the roof of a house. The panels are made from silicon crystals which have been treated so that, when sunlight shines on them, some of the electrons in the crystals start to move, creating an electric current.

The panels are connected to the boat’s battery and feed electricity into it which it uses to power your boat. The battery stores any energy that isn’t being used then and there, so you can still make use of solar power in the dark.

The more direct the sunlight is, the more power the panels will produce. So your panels will probably produce more electricity in the Mediterranean than off the coast of Norway.

You should buy specialist marine solar panels for your boat, as they are designed to be waterproof and withstand the conditions at sea.

Did You Know?

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What Are the Best Marine Solar Panels?

There are a number of brands that produce marine solar panels, but we’ve singled out 3 of the best manufacturers:

1. Photonic Universe: UK brand producing solar and wind power products since 2009.

2. HQST: Affordable solar solutions for the off-grid solar market.

3. Renogy: Award-winning manufacturer of high-quality solar products.

The table below shows you some of the best of marine solar panels produced by Photonic Universe, HQST, and Renogy:

Cell Type
Photonic Universe
50.5 x 44.5 x 2.5 cm
34.1 x 63 x 2.54 cm
54.1 x 63 x 3 cm
119.38 x 54.2 x 3.6 cm
104.1 x 53.3 x 0.5 cm
119.4 x 53 x 3.8 cm
Photonic Universe
84.5 x 67 x 3 cm
100.3 x 99.1 x 3.6 cm
100.3 x 99.1 x 3.6 cm
Photonic Universe
139 x 99 x 4 cm

If you’re unsure what the different types of marine solar panel are, check out the guide below.

Types of Marine Solar Panel

You’ll hear a lot of different names for different kinds of marine solar panel, but they boil down to 2 different types: those you can bend and those you can’t.

Semi-flexible, Amorphous or Thin Film Solar Panels

These are great space savers, as they’re not only lightweight and slimline, but they can bend slightly to fit with the surface they are fixed to.

This means you have quite a lot of freedom over where you put them. You should even be able to walk on them if they are on a hard surface, at least in soft-soled shoes, so you can install them on the deck (make sure the panels have a non-slip coating!). But you still need to treat them with care; there is a limit to how much they can bend!

They will probably cost more than a fixed panel of equivalent power, as monocrystalline and polycrystalline panels (see below) can produce more power from the same area. However, amorphous panels perform better in low light and shade and at hotter temperatures (solar panels become less efficient when they get very hot).

Rigid Solar Panels

These are bulkier and usually have a glass covering (sometimes toughened glass to make them more damage resistant) and an aluminium frame. Like all marine solar panels, they are pretty sturdy, but they can’t be walked on, and need to be fitted somewhere where they can’t be damaged. These panels don’t bend, so need to be on either a flat surface or mounted somewhere like a rail or gantry. They are more efficient, and therefore better value than flexible panels – in good conditions, they produce the same amount of power from a smaller area.

Rigid panels can either be polycrystalline or monocrystalline. Polycrystalline panels are made from small pieces of silicon fused together, whereas monocrystalline panels are made from large individual pieces of silicon. Monocrystalline panels tend to be more efficient – and so more expensive – than polycrystalline panels.

You can also get portable solar panels that you can put up temporarily and take down again – some even come with a stand that you can fold away.

How Much Do Marine Solar Panels Cost?

The prices that we researched in April 2018 started at around £70 for the smallest panels (30 watts). Expect to pay several hundred pounds for panels of 100 watts and over – so if you are living on your boat and using a lot of electricity, you could be looking in the region of £500 to £1,000, depending on how many panels you need.

With some manufacturers, prices will include everything else you need, including the cables and the regulator; with others you will buy those separately. You will also need to decide whether you want to fit the panels yourself, which you can do, or get a qualified installer to do it for you. You’ll be looking at around £600 upwards for supply and installation of a 200watt system and £1,050 for a 400watt system, plus the solar controller on top.

If you live on your boat or use it a lot, you should recoup your costs within around a year.

The Benefits of Solar Panels for Boats

The electricity they produce is free. Sunlight is free (no one’s taxed it yet) so once you’ve paid for and installed the panels, they cost nothing to run – you have free electricity.

They’re easy to use. Better than easy – the panels work automatically in daylight, so you have to do precisely nothing.

They’re silent. Without solar or wind power, many boat owners rely on running the engine to charge their batteries, which is noisy, costly and can make the cabin uncomfortably hot if you’re already somewhere warm.

They’re environmentally friendly. Solar panels produce no pollution, don’t contribute to global warming and don’t use up natural resources.

No flat batteries. The solar panels will charge the battery while you’re away from the boat – so it’s ready to roll when you are.

You’re independent. You’ve got your own, 100% reliable source of power – there’s daylight every day. Your life isn’t ruled by the need to run the engine to charge the battery and you won’t need to spend time and money refuelling so often.

They need very little maintenance. All you need to do is wipe the panels with a damp cloth and some mild detergent to remove dirt and salt, and check the equipment now and again for wear and tear.

They last. You can expect your solar panels to be with you for at least 25 years.

Your engine will thank you. Using solar panels means less wear and tear on your engine and consequently less maintenance.

Your battery will thank you too. Letting your battery go flat can damage it and shorten its life.

The Disadvantages of Solar Panels for Boats

Solar panels don’t really have many significant disadvantages. There is the initial cost, of course, and the fact that aesthetically they are not to everyone’s taste.

What is worth pointing out, which we will discuss further down, is that the panels will of course not work at night and will work considerably less well on cloudy days or in the shade. So the power they supply will vary from day to day and it would not be wise to expect to rely on solar panels alone to supply your energy.

What Size Solar Panels Do You Need for Your Boat?

The power of a solar panel is measured in watts. Panels can range in size from a teeny 10 watts to a mighty 250 watts or more. The more power your solar panels have, the more they can do.

The aim is to balance the power going in from the solar panel with the power going out of the battery. So what size panel you choose will depend on how much power you want.

Recommendations vary but as a rough guide:

If you just want to keep the battery topped up while you’re not on the boat: 30 to 70 watts (batteries lose some of their charge when they’re not being used)

If you want to power electrical appliances when you use the boat: between 100 and 200 watts

If you’re living on your boat: 250 to 300 watts or more

Using the boat every now and then for holidays: 165 watts

Living on the boat in a mooring with no power, or on a very large barge: between 660 watts and 990 watts (at this point, you’re not far off a system which would power a small house!)

These are rough estimates. Here’s how to work it out more precisely …

How to Work Out How Much Power You Need

1. How Much Energy Do You Use Each Day?

First, you’ll need to total up how much power all your electrical appliances are likely to consume.

Each appliance should have a sticker telling you how many watts it needs. You should multiply this by the number of hours you’re likely to use it for each day. Do this for each appliance and add the total together. This figure is known as the total watt-hours that you need.

For example, if you expect to use a 30-watt CD player for 2 hours a day, you will need 30 x 2 = 60 watt-hours of power.

If there’s no wattage on the appliance or in its handbook, look for the current in amps or A and multiply this by your battery voltage (usually 12 volts) – this will give you the number of watts. (Remember that equation from school: P=IV? This is one of its uses.)

It’s wise to add a bit extra to your final total – at least 10% – to give you some leeway for unexpected use.

house with solar panels

2. How Much Power Will You Get from Your Marine Solar Panels?

Ideally, you’ll want the watt-hours your solar panels supply to match or exceed the watt-hours you need. But for reasons of space or cost, you may decide that you’re happy to have less powerful panels that just supply some of your needs.

The power produced by a solar panel, also in watt-hours, can be estimated by multiplying the panel’s power rating (in watts) by the number of hours of peak sunshine you can expect in a day where you are.

As a rough guide, the UK, northern Europe and Canada average 1 hour of peak sunshine per day in winter, and 3 to 4 hours in summer. So a 30-watt panel would be expected to produce 30 watt-hours of power on an average British winter day, and 90 to 120-watt hours of power in summer. Some experts consider this a conservative estimate and would hope for up to 180-watt hours.

This may seem low, but a solar panel will not usually give the wattage it says it gives. Manufacturers test panels in bright sunlight at 25ºC, and quote the output accordingly; particularly in the UK, we are not usually blessed with such conditions. How much sun your panel gets will be affected by your latitude, the time of year, the time of day, whether you’re in the shade, whether it’s cloudy or hazy, how hot the panel is (their efficiency decreases as their temperature goes above 25ºC) and how old the panels are. There will also be some power loss through the cables and the solar regulator. Shade can have a big effect on output, as if even 1 or 2 cells are in shadow and not producing power, they can massively drain the power that the other cells are producing. This is one big advantage of amorphous panels, which cope much better with shade. If you can, get panels with bypass diodes to stop this happening.

Most experts would recommend that you oversize your panels by at least 20% to allow for things like particularly poor weather and unexpected energy use. So if you’ve worked out that a 200-watt panel will cover your needs, you should actually go for at least a 240-watt panel.

While we would not want to advise you to spend more money than necessary, in our experience it is always better to err on the side of having too much power. Your needs can vary considerably from one day to the next – in a very warm climate, for example, the fridge and fans may use more energy than you expect. Some manufacturers argue you can’t have too much solar, as more powerful panels will charge your battery more quickly, and your solar regulator (see below) will stop the battery overcharging.

Marine Solar Regulators

A solar regulator, also called a solar controller or charge controller, has 2 functions: it prevents your battery from overcharging (which can damage it), and stops power flowing back out of the battery when it’s dark.

There are 2 types of solar regulator: PWM (pulse width modulation) regulators and MPPT regulators. PWM regulators are simpler and less expensive, but MPPT regulators are more efficient, so will deliver more power.

A regulator will use some of the power produced by the panels, but most manufacturers recommend one for all but the tiniest wattages. The regulator should be installed somewhere that’s cool, dry, well ventilated, easily accessible and as close to the battery as possible. If you don’t have a regulator, you’ll need a blocking diode anyway to stop power coming back out of the battery at night.

Prices start from around £20 to £30 and go up to more than £100. It’s helpful to buy a regulator which has a digital display, so you can see data like how much power the panels are producing, how charged the battery is.

How Do You Get the Most Out of Your Marine Solar Panels?

Experts differ on the best way to position your panels so they benefit from maximum sunlight; we would generally say that horizontally is the best option. You can also get tracking panels which automatically tilt to follow the sun’s path through the sky.

• Make sure the panels are not shaded or obscured by anything else on the boat – this will hamper their efficiency.

• Try to keep the panels cool: rigid panels will need a small gap underneath them to allow air to circulate.

• Use energy-efficient appliances; this is just a good idea anyway.

• Some boat owners replace halogen light bulbs with LEDs; others recommend getting 12-volt fridges or TVs (your fridge is likely to be one of your biggest power users).

• Avoid positioning the panel somewhere where it’s going to interfere with the benefit you get from favourable winds.

Jonathan Whiting

An eco hero with a head for numbers, Jon’s data visualisation skills are legendary. Whether it’s determining what countries will survive climate change or the animals most at risk from it, he has the planet’s best interests at heart.