Do solar panels make sense financially?

A typical residential narrowboat installation

A 80 Watt panel kit with a suitable solar controller and wiring costs less than £300. How long will it take to recoup the money?

During the summer months, an 80 Watt panel will provide around 30Ah per day to a 12 V battery. That's about one third of the capacity of a typical boat battery. The amount of electricity used per day varies a great deal depending on the appliances you run. However, 30Ah should be enough to cover the use of lights, radio and water pump for the typical user. Fridges consume rather more power, so you might need a bigger panel - but on the other hand if you use energy efficient lights such as LED or fluorescent lighting, you may find your energy requirements are considerably lower.

A 40A alternator on an engine would take close to an hour of charging to provide the same amount of energy. So from spring to autumn (about 180 days) you may expect to save up to 180 hours of charging. In the winter, light levels are much lower, and you may still need to rely on your engine or generator to top up what the solar panel supplies. However you should still expect at least 6 or 7 Ah in charging each day from the solar panel through the winter, which corresponds to about 30 hours less engine use.

Quick payback!

So, in a year, we might save roughly 200 hours of charging from the engine. Red diesel now costs well over £1 per litre from boatyards, and a diesel engine will burn over a litre an hour when used for charging.

Even at a conservative estimate, if you install a solar panel to charge your batteries, then fuel bills should be reduced by about £200 per year. Wear and tear on the engine is also reduced, particularly as charging from an alternator provides a rather light load to a diesel engine. You should also find that because the batteries are kept topped up, they should need replacing less frequently. A lead acid battery won't last a year if it is frequently left flat - but will last 5 years or more if kept well-charged. To replace a typical 200Ah battery bank costs well over £200.

It's rather hard to quantify just how much reduced engine maintenance and depreciation, along with less frequent battery replacement, will save you. It depends on factors such as whether you do the maintenance yourself, or get a boatyard to do it. But £50 per year is not an unreasonable figure to expect in savings.

So in total, by installing a solar system, savings achieved are approximately £250 per year, which means you should recover the cost of the panel in considerably under 2 years. Please note that this estimate is for a boat in continuous use and without a connection to the national grid. If you only use your boat occasionally, payback time will be slower.

But remember.... it's not just about money! Even if for you it might end up being more expensive to use solar panels, remember that by doing so you are doing less damage to the environment. Your neighbours may also be grateful for not having a noisy, smelly engine rumbling away next door - and you can enjoy the peace yourself.

Take a look at the kits we can offer.