After much serious reading and research from books, Internet (I recommend Victrons “Energy Unlimited”) and cruising people we met on our travels we decided to have the following setup:
- Four 90W Phaesun Solar panels
- Blue Sky MPPT Regulator
- Six 225AH Trojan deep cycle 6V Batteries
- Victron 2500W /120 amp Multi Plus Inverter / Charger
- Victron 3.6 KW Isolation Transformer
- Upgraded DC Busbar system
- Upgraded DC wiring
- Dedicated Windlass/Bow thruster Battery
After reading Victrons online book “Energy Unlimited” it became clear that their way of looking at a DC charging system was carefully thought through. Allowing for some “Sales” talk I believe the concept of making the batteries the heart of a small scale energy system is based on sound logic.
To start with an exact figure for amp hours per day usage was needed. This was calculated in Excel (download the file here and modify to suit) initially the solar panel output was a guess but after one year use it is now based on actual output figures. The new system looked something like this:
(download larger image)
My thinking was that in the summer months from say May to September enough days with sunshine were available to support all loads as last year (2007) we always had amps to spare. In other words even though we used the washing machine once a day (powered by the inverter), run the watermaker for three hours per day and run all other consumers the batteries were charged by 3:00pm. The exception to this was when there was a cloudy day or indeed if we had rain. On these days it was necessary to run the new suitcase petrol generator (much quieter) for an hour to top up the batteries via the 120 amp battery charger in the Victron.
Spray’s first DC system consisted of three 110 AH ‘leisure’ batteries giving 330 AH total and one 110 AH engine start battery. The alternator on the engine was a 55A ‘normal’ car type which came with the engine. I figure one and a half hours of engine run per day would re charge the batteries. With one day per week in a Marina to top up water and do washing and maintenance. When I designed the system it was based on a total AH consumption of 60 AH per 24 hours. This was based on adding up all the consumers such as light bulbs, fridge and so on. At the time the only other charging source was a battery charger which was run off an 5kw petrol generator. Below is a rough sketch of the system.
This all worked well all the way to the Med as we had to use Marinas in Portugal and in Spain. Once we got to the Balearic’s everything changed. Marinas were very expensive in the summer months. In some places like Ibiza and Majorca up to €60 per night. So this meant using the petrol generator a lot. Not so good in quiet anchorages as other boats had to put up with the noise.
In 2003 our three ‘leisure’ batteries would not hold the charge so we replaced them at a cost of €300 to three more ‘leisure’ type batteries as this was the only thing available on Menorca. They looked more like car batteries than our previous ‘leisure’ ones. We needed to have a serious re-think
We decided as we were going to have a refit in 2005 as the paint system failed (another story see the Paint System Categories) we would upgrade the whole charging system integrating solar panels, inverter battery charger to run a washing machine and a watermaker. This also meant changing battery banks as 330 AH was not sufficient to support all these new loads.