Solar power for electric boats has made significent progress in recent years. The Sidney solar ferry and many other solar ferry services have been in service for years.More solar ferries are on the way. The Swiss MW line of solar assisted commercial tour boats has had an big impact in europe. The sun 21 crossed the Atlantic with solar power alone (with battery storage) in 2007. Many solar boats are now on the market including the Canadian Loon by Tamarack Lake Electric Boat Company. This web page will introduce you to the utilization of solar power for electric boats by dividing solar power into some useful categories. In addition some basic design and installation information will be provided as well as references to take you to the next step.
This has been demonstrated many times. The most spectacular demonstration may have been the trans atlantic crossing by the 46 ft Sun 21 under solar power alone (with battery storage). It used battery power at night. Durring the day, the solar panels provided enough power to charge the batteries and. produce a good cruising speed. This use of solar as the sole power is rare because of the imense cost of solar panels. The Sun 21 used 10 kw of solar modules. At a local boat catalog price of US$1000 for a 123 watt panel that would translate to 81 thousand US$. ( I don't represent this as the ammount paid by the Sun 21 team).
Of course there are more economical ways of powering an electric boat by solar alone. I designed and built a 16 ft electric launch powered by a built in 24 volt trolling motor, 2 Type 27 12 volt batteries and 2 - 20 watt solar panels. The total cost for the boat was about 1600 US$. The solar panels were about 250 US$ each. I used this boat for many years without charging the Batteries except for a few exceptional uses of the boat. I kept it on a private dock at a lake with no electric service at the dock. We used it about 2 or three times a week for about 45 minutes each trip (one circuit arround lake). This was an economical way to use 100% solar. As a bonus, there was nothing to do but turn on the switch and un-tie the boat to use it. By the way, the canopy also served as a boat cover when dropped down. This is the boat shown on the first page of this website.
This may be the most exciting and fast moving sector of the solar power story to date. Many Hybrid powered boats are appearing. Many if not most electric boat manufacturers offer a hybrid option. Most often this consists of a diesel generator on board. Often solar panels are offered as well to supplement the other power sources. We are now seeing multiple supplemental power options integrated with sophisticated contols. The Australlian Solar sailer may be the best example of this.
This is really just another form of hybrid. I separated it because the loon and other small boats have made a success of this concept, streching out ranges and providing extra power for equipment while maintaining relative simplicity over generator equiped electric hybrids with elaborate control systems.
Multiply the number of 12 volt batteries in your power bank by the amp hour rating. If you have 6 volt batteries, divide the number of batteries by two then multiply times the amp hour rating. Divide the above amp hour capacity for your battery bank by 2 for the power you need to replace with solar panels. This assumes that you will not normally allow your battery bank to go below 50% to increase the lifespan of your battery bank. Now multiply this amp hour number by 3 to obtain the watts in solar power output you will need for 100% replacement of the charge in the battery bank.
If you wish to fully recharge in one day, use the above number.
If you wish to fully recharge in 7 days, divide the above number by 7 to obtain watt output of required solar array.
Example for a system with two 105 amp 12 volt batteries which needs charging over a 7 day period.
2(number of 12 volt batteries) X 105 (amp hours per battery)=210 amp hours
210 (amp hours) divided by 2 = 105 (50% of battery capacity in amp hours)
105 amp hours divided by 7 (days) = 15 amp hours
15 (50% of battery bank capacity over 7 days) multiplied by by 3 = 45 watts of solar panel advertised output
Once you know how many watts you will require from the solar panels you will need to map out the placment. In most configurations, the same panel size type and manufacturer should be employed for all panels. You need to avoid shading of any part of any panel as well as possible. Shading of a part of a panel causes a drastic reduction in the power output. The best place is the cabin top of a powerboat. Catamarans electric launches and pontoon boats can be outfitted with a hardtop sun shade which is an ideal location. Although such a hardtop looks best with a curve, or even a compound curve, flat is best for solar collection. Solar panels and a support structure adds a lot of weight high up where it could affect stability to an unsafe degree. You must address this issue. Check with the boat manufacturer. An electric boat manufacturer has probably made some stability, calculations which consider the addition of solar panels.
Solar panels used for marine conditions should be robustly built for those conditions. Check the warantee lenth for panels you consider. Select panels with 33 to 36 cells to ensure high enough voltages to fully charge batteries. You will need voltage regulators and posibly diodes if not incorporated in panels.
The panels need to be robustly mounted on the decks or roof top. Marine mounting brackets are available for some solar panels. No wire connection should be made on deck between the panel connection point and the deck seal. Only marine quality wire and connections should be used. Be sure to wire to marine standards. The wire should be oversized relative to the length of the wire run and the amperage carried for a minimum voltage drop. The recommended book below (by Nigel Calder) goes into more details. A Marine electrical wiring book is also recommended. If you are uncertain about the electrical wiring, it is advisable to employ a marine electrician to perform the wiring or to check the wiring prior to any battery connections.
I recommend the Nigel Calder book titled "Boatowners Mechanical and Electrical Manual" for its extensive design and installstion section for solar panels. In addition you may want to check out the following websites.
UK Electric Boat Association Solar Page Solar Panel FAQs