Friday, 22 June 2012

Solar Observations.

Solar Panels, more observations.

I have had some correspondence with others about the use of solar panels on a boat. I have written a bit about them in the past and I have described my system previously. There are a few common misconceptions about panels and how they work as well as what you can realistically expect to get from them.

There are almost an infinite number of variables that can be used to calculate costs and savings. Getting a handle on costs is in my opinion good if you are on a tight budget. However, I found myself and others debating in the finest detail each factor while doing a cost/benefit analysis. It took me some time to realise that costing a solar system on your boat to such fine detail can give you a nice warm comfortable feeling. The reality is however the variables are many and the real cost would elude all but the most fastidious of people.

First you have to decide why you might want to use solar panels. Some people will want to lower their carbon footprint. The use of solar will help you to do that. For others they will want to reduce engine use for recharging leisure battery bank. The use of solar will help you to do that as well. The big thing is that Solar is not the beginning and the end, but just one part of an overall electrical power package. There are other viable alternatives to solar. The way in which you operate your boat will also play a significant part in how efficient and cost effective the solar panels can be.

Will you be mooring your boat in a marina for long periods?

Then if you have an electrical hook-up available the use of solar will give minimal benefit. It would not be cost effective and the use of mains powered 240v white goods as against 12 volt white goods would be a much cheaper option.

Will you be moving your boat every few days?

Then an alternator control control system would be a better starting point. Most alternators are inefficient a charging a battery bank. Lead acid battery systems are poor at storing the charge from an alternator. Modern alternator controllers will help to charge your batteries quicker and also include multi-stage charging, to prolong battery performance life. Look at the Sterling Power Product range for alternator controllers. (ProReg B - AR12V Alternator Regulator)

Will you be staying in one place off mains for extended periods?

In this instance Solar will provide an additional option to you electrical power provision. Unless you are using a substantial solar system other changes should be made. Such as installing LED lighting systems and changing to white goods than can be powered at 12 volts. I would look to run as many electrical items off low voltage as possible. Thus reducing the requirement for a mains power inverter system.

Even with a solar power, there are going to be times when the electrical output is going to be less than your daily requirements. You will periodically have to run the engine and charge the battery system. The solar system will reduce the amount of engine hours required. On long sunny periods you may go days without needing to start the engine. On overcast dull days, you may need to provide a boost more frequently.

Pointing a solar panel at the sun will allow for more of the suns output to be captured. However it may not be practical to do so especially when away from your boat. Like an alternator controller your solar panels will also need a controller. There is only one serious kind of controller to purchase and that is an MPPT type. This will improve the output of power from the solar panel into the battery bank.

The next variable is Sunlight, which everyone knows is not a given in our climate. If you can only get a certain amount of solar power from a given amount of sunlight. Shade is also a problem, as the sun moves across the sky surrounding objects will put your solar panels in the shade and reduce their effectiveness. Choosing a shade free mooring becomes second nature after a while. However, the clouds will also reduce the amount of sunlight falling on the solar panels from time to time.

I wanted an output into the battery bank of about 6 hours per day at 10amps or 60Ah (ignoring charging efficiencies) That equates to a power of 120 watts. I then built a solar system which should give me twice that as the three panels are rated at a total 240 watts.

The weather recently has been very poor with a great number of over cast days In the last 28 days the solar panels have added 575Ah into the leisure battery bank. That's a little over 20Ah each day. Now if I work that back (rule of thumb) and look at what I would need to do to generate that much power from our standard engine alternator I estimate that would be around 18 hours. That's 18 litres of diesel and 18 hours less wear and tear on the engine system.


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