Get More From Your Solar Array!

By Ted Russ

Do you have a solar array? A number of solar panels interconnected together to charge your batteries? If you do, there's a good chance you can get an extra hour's charging out of your array. Every day. That can add up to a considerable amount of extra capacity of an existing installation, or save the cost of several panels in a new installation.

I believe this will work with almost any installation of two or more panels, and will cost only a few dollars to implement. It should not damage your installation, but you do need to have some knowledge of electrics and solar technology before attempting it.

If you make commercial use of this idea, please give credit where credit is due, and make arrangements with me to sponsor this site on an ongoing basis.

The idea itself is simple enough to describe. With any solar panel array, there is a period in the morning and in the evening when incident light is just too weak to produce the voltage required for successful operation of the charging circuits. This is a period of around an hour at each end of the day, when your expensive solar panel array is just sitting there shading the house. Unless you fit panel rotators or some such mechanism, that is almost two hours of completely wasted daylight. And even if you do have a tilt mechanism, quite often this does not really increase the useable output of the array.

If it's a cloudy day, quite often the voltage from the panel arrays will drop to below useable levels, and no tilt/rotate mechanism will be of any use in this situation either. This idea of mine, however, will produce useable energy even at these times.

Enter - the Relay.

My basic idea - as yet untried because I do not have a two panel system to test it out with - is so simple that I am surprised it has not been done before. I have a relay with a 24V coil and two sets of change-over contacts, and by experimentation, I've found that this relay will pull in successfully at about 16V, and drop out at about 8V. Had I not had this particular relay, I could have used a 12V relay and a voltage trigger circuit instead.

I've wired the solar panel I have and a mains 6V plugpack (as a replacement for a 12V solar panel that I don't have) so that when the relay is energised, the two are in parallel and connected to the charging circuit, and when the relay is de-energised, the two are placed in series by the contacts and connected to the charging circuit. The ideal would be to have two solar panels, but so far no-one has stepped forward to sponsor me... (hint hint!)

The coil is attached to the most shaded of the two solar panels' outputs, and what happens now is simple. While ever there is too little voltage to operate the charging circuit, which is morning and afternoon and during periods of extreme clouding, the relay is de-energised and the two devices I have (which should be two solar panels, remember) are connected in series. The two voltages, which are individually only 8V or less, are added together to produce 16V or more, at which point the charging circuit works, albeit we are only operating at half current - but remember we would not be charging at all if it weren't for the cells being in series.

As the voltage on the most shaded cell increases, eventually the relay pulls in, and now the two devices are placed in parallel, and charging can continue at maximum current again.

Notes:

• I could have used a few power MOSFETS and a voltage trigger circuit to produce the same effect, and saved a few nano-amps of current.
• To prevent damage to your solar panels, they should include anti-reverse bias protection, otherwise inequalities between cells might produce enough current to damage a panel.
• While it seems that this technique produces only a miniscule benefit, it should actually produce quite a marked benefit, because even two hours extra charging a day at half current or less will still be a 5% - 10% increase in available power.
• With a little bit of thought, it can be seen that this technique can be applied directly to solar panels, i.e. the cell series/parallel switching can take place right in the panel itself and provide a useable output for longer each day. If you use this technique in your commercial or manufacturing process, I ask you to play fair and recognise/recompense me for the concept.
• With a little bit of thought, it can be seen that this technique can be applied directly to solar charging circuits, i.e. the leads from each solar panel in an array can be brought to the charging unit and the charging unit can juggle cells into series or parallel as needed and thus provide a useable output for longer each day. If you use this technique in your commercial or manufacturing process, I ask you to play fair and recognise/recompense me for the concept.
• The other usefulness of this technique is during periods of solar occlusion such as cloudy periods, where tilting mechanisms can't increase the yield of energy, but this technique can. If you use this technique in your commercial or manufacturing process, I ask you to play fair and recognise/recompense me for the concept.

That concludes this article, if you would like to help me test this by providing me with two reasonable solar panels, a solar charger, and battery, I would be grateful, and acknowledge any such sponsorship on this site. If you have any software that will allow me to produce circuits and sketch drawings of these ideas, I will produce drawings and circuits and post them with these articles, and acknowledge your sponsorship on this site. If you are a solar energy business and would like to discuss several other ideas which I have, please contact me.