Sizing a solar panel for lighting a stable block

I am running two Lumina 18w lights in my stables powered from one 85amp leisure battery.  I am charging from the mains when the battery needs recharging.  Can you please advise what size & type of solar panel, regulator etc I would need to keep the battery charged.  I also run an electric fence from a second 85 amp leisure battery which is situated behind the stables.  Could I put the two batteries together, use one solar panel and run both applications? Regards, Wendy

Hi Wendy,

It all depends how many hours a day you use the lights! If we assume 1 hour a day every day, that's 18 watts x 2 lights x 1 hour, or 36 watt-hours per day that you need to generate from the panels. In summer you could generate that much power from a very small panel - even a 10W panel (such as perhaps the Spectra 10W panel, with a Sunguard regulator).

In the winter, you would need something bigger - but I think a 40W panel should be sufficient even in the depths of winter. In that case you would be best going for the 40W solar panel kit, which includes a 40W Kyocera panel and a Sunguard regulator, and all the wiring you need.

If you use the lights for more than one hour a day on average, you would need a bigger panel in proportion. If less than one hour, you can go smaller with your panel.

Yes, it would make a lot of sense to put the two batteries together and run both the electric fence and the lights from the one bank. Electric fences don't use much power - I think you would be able to run both the fence and the lights from a 40W panel. Very easy to do - you just wire the two batteries in parallel, with the two positive terminals joined by a lead, and the two negative terminals joined with another lead.

best wishes, Andy, Midsummer Energy

Solar panels and inverter for narrowboat

Hi Andy,

Having had a good look around your website, I'm hoping you could give me a bit of advice about renewable energy options, as a novice narrowboat owner who knows very little about boat electrics – so please forgive my ignorance!

Firstly, generating electricity – battery-wise, we've got 3 new domestic batteries connected to an Adverc system, and I'd like to be able to charge these without having to use a separate generator. I was therefore thinking of investing in a sizeable solar array, maybe a single 130w Kyocera panel, or a couple of 65w panels, plus a controller. I'd just like a very rough idea of whether or not this would provide a reasonable amount of power for us, living aboard, without having to run the engine all the time, or whether we should be thinking of investing in a larger array? I know that this is a difficult question to answer without knowing the specifics, but basically, we're not planning to use the fridge over the winter (we've been told that they use a lot of power), so it'll basically be running the lights, water pumps and TV / stereo in the evenings and at weekends over the winter, and then the fridge as well in the spring / summer (when I presume we'll be getting more power, as the light levels increase). We're likely to be cruising most weekends, so we'll be generating power from the engine on a fairly regular basis. Do you reckon the combination of solar panels and sporadic engine-use is likely to be sufficient, providing we're careful with our power usage, or is it inevitable that we'll end up needing a generator of some sort, as some people seem to think?

Secondly, using appliances – we've got a 650w inverter on the boat at the moment, but I'm thinking of upgrading to a 1000w Silverline model. There are 240v sockets down one side of the boat and an external hook-up socket for shore power. It's been suggested that we should just use this system for our normal appliances, rather than muck about with wiring things into the 12v system. We're not going to have a shore hook-up, so it seems that we're going to need to have an inverter more or less permanently connected to the battery bank, with a lead running outside to plug into the external socket, to power up the internal 240v sockets. I'd just like your opinion of whether or not this sounds like a sensible and safe way of doing things – specifically, how efficient are inverters? Are we likely to be losing a lot of power by running our appliances like this? Also, is it safe and efficient to have an inverter permanently connected to the batteries like this – do they still draw power when nothing is connected to them, and do they get hot after prolonged usage? I'm guessing that the unit is designed to just cut-out if overloaded with too many appliances (although we're not planning to run anything more heavy-duty than e.g. a TV and DVD player off it).

Lastly, I'm assuming that all of this stuff is pretty easy to install and connect up to the batteries? At the moment, I'm at the bottom of a pretty steep learning-curve when it comes to most things related to boat maintenance, but I think I can cope with a bit of very basic electrical DIY.

Any advice would be very much appreciated!

Many thanks, Jon

Hi Jon,

It's certainly possible to run narrowboat electrics all through the year just from solar panels - I manage it on my own boat! That said, even with a biggish array (about 200W) I do have to be pretty careful in winter to keep usage down.

I would think a 130W panel would be a good choice based on what you expect to run. That would certainly have no problem at all in keeping up with lights, water pump and stereo use (though having energy efficient fluorescent or LED lights is well worthwhile to make sure of that). Fridges and TV do take a lot more power - but if you are happy to turn your fridge off in the winter, and are also able to get a bit of charging from the engine at weekends, I would think a 130W panel would be ample 90 or 95% of the time. Just occasionally if you are using systems heavily, and have a few overcast days, you might have to turn on the engine to charge - but I would think that would be rare.

Inverters are about 90-95% efficient, and draw a pretty low current when nothing is connected, so yes, they can be a sensible way of running appliances. It's no problem to leave them on all the time, and they do have thermal cut-outs if you do ask too much of them. I run a 240V fridge in summer for example - it was about 1/3 the cost of the equivalent 12V version, it means I can get away with thinner wiring, and there is little difference in the power it draws.

Wiring of a solar panel is extremely simple - two wires from the solar panel to the regulator, and two from the regulator to the battery. An easy DIY job. Wiring an inverter is equally easy - two big fat wires from the inverter to the battery. Having said that, they are 240V appliances, so if you are then wiring the inverter into a distribution system, you might want to have someone qualified to make sure it's all safe. Also, running a cable outside from the inverter, to then bring it in again through your shore power inlet is perhaps not the neatest way of doing things - it shouldn't be hard to simply rewire your distribution system direct to your inverter.

hope that helps, Andy

Losing charge through a Sunsaver controller?

Andy I think the Morningstar SunSaver solar regulator SS10 is draining my batteries at night. Every night I read the volts on the solar side -.04, -.09, -.16 ; No load on 2 x 85amp leisure Batteries in parellel.  Batteries increase around .25 volts a day and topped out at 13.29 yesterday night then dropped to 13.09 tonight.

What's your verdict?

What are the best batteries to use with the Kyocera 130 watt solar panel?

best regards, Scott

Hi Scott,

If they are only dropping to 13.09V there is nothing to worry about! Anything above 12.8V for a 12V battery is basically as fully charged as you can get it. Although the voltage will rise slightly above that during the day while charging is happening, it's quite natural for it to settle slightly overnight even if there is no load on the battery. If it was going down to 12.5 or so without any load on the batteries I would think there was a problem - but over 13 is a very healthy battery!

You do always measure a small negative voltage on the solar terminals when they are not receiving charge - if you actually measure the current along that wire however you should find it is negligible.

Standard leisure batteries like you are using are absolutely fine for use with that panel. They should last at around 5 years or so if they are kept well charged - which it sounds like yours are. 'Sealed' or 'gel' batteries would last longer - but they are so much more expensive that it's not really worth it.

A bank of 2 85Ah batteries is fine, but on the smaller end of the bank size I would recommend - you could easily add another couple of batteries if you want to have a bit more reserve for times when you are using the power heavily.

Hope that helps,

all the best,
Andy

Variation of output with mounting angle

Where can I see a chart/graph showing the relationship between solar incidence angle and current output for a solar panel.  I am interested in the BP380 but I assume that most units are similar.  I am trying to assess the need for providing a tilt mount.
Thank you. Edward.

 

Hi Edward,

http://www.yourhome.gov.au/technical/fs67.html is quite useful, particularly the graph that shows the variation of solar panel output with orientation and tilt angle. The figures are for Australian latitudes - but you can get the idea at least!

Solar panels do give pretty good output even when not angled directly towards the sun. The graph shows that, for 35 degrees latitude, the optimum angle is 35 degrees (not surprisingly) but a horizontal panel will still be around 85% efficient, and a vertical panel will still be around 65% efficient.

Note that the difference is smaller during overcast conditions, when light is scattered anyway. At those times, there is practically no difference in output between a panel mounted horizontally, and one mounted at the optimum angle.

There is a graph of optimum angles for solar panels across Europe on our information site.

regards,
Andy
Midsummer Energy

Can you charge a 24V system with a single 12V solar panel?

Is it possible to use 1 solar panel to charge 2 12volt batteries connected in series (24 volt) via 2 seperate 12 volt charge controllers, one linked to each battery? - Richard

Unfortunately, no.

The negative solar and negative battery terminal on most charge controllers are connected together internally - it's only for convenience that they provide you with two seperate terminals to connect the wire.

If you were to try putting two controllers in series, you would be joining the positive battery terminal of the first charge controller to the negative battery terminal of the second. If you then attach the negative solar panel lead to both solar negative terminals you have the following situation:

1) positive battery terminal of first controller is connected to negative battery terminal of second...
2) ... which is connected internally to the negative solar terminal
3) ... which is connected to the negative solar panel lead
4) ... which is connected to the negative solar terminal of the first charge controller
5) ... which is connected internally to the negative battery terminal

In short, you've connected the battery positive to the battery negative. That's called a short circuit, which is a cause of wires melting, fire, grieving next of kin etc etc.

If you must try it, I'd recommend making your will first. I can't see any reason why you couldn't put two 12V controllers in series with seperate solar panels, though don't take my word for it. However, it's more usual to simply wire two 12V panels in series to a single 24V controller. See our handy 24V solar panel wiring diagram.

24V system with a 12V solar panel?

Is it possible to use 1 solar panel to charge 2 12volt batteries connected in series (24 volt) via 2 seperate 12 volt charge controllers, one linked to each battery? - Richard

Unfortunately, no.

The negative solar and negative battery terminal on most charge controllers are connected together internally - it's only for convenience that they provide you with two seperate terminals to connect the wire.

If you were to try putting two controllers in series, you would be joining the positive battery terminal of the first charge controller to the negative battery terminal of the second. If you then attach the negative solar panel lead to both solar negative terminals you have the following situation:

1) positive battery terminal of first controller is connected to negative battery terminal of second...
2) ... which is connected internally to the negative solar terminal
3) ... which is connected to the negative solar panel lead
4) ... which is connected to the negative solar terminal of the first charge controller
5) ... which is connected internally to the negative battery terminal

In short, you've connected the battery positive to the battery negative. That's called a short circuit, which is a cause of wires melting, fire, grieving next of kin etc etc.

If you must try it, I'd recommend making your will first. I can't see any reason why you couldn't put two 12V controllers in series with seperate solar panels, though don't take my word for it. However, it's more usual to simply wire two 12V panels in series to a single 24V controller. See our handy 24V solar panel wiring diagram.

Andy

Solar panels for yacht in the Med

Hello
Can you help me with some advice on solar panels. I have a yacht based in the Eastern Mediterrian, it has 3x 155amp/hr domestic batteries and a seperate engine batterry. I'm looking to try and keep the domestic batterries charged whilst sailing and at anchor. The main power user is the fridge which uses about 50amp hrs per 24hrs.
Currently I have a Sterling Power Management system which displays the battery position and amps being used and total amps consumed. This system counts down amps when on charge either by engine or mains charge.
To start with I plan hang them on the guard rail.
What would you recommend? Regards, Martin

Hi Martin,

Fridges do consume a lot of power unfortunately, so you would need a reasonable array of solar panels to replace what the fridge is using. As a guide, in the UK summer you would need about 120 watts of solar panels to generate about 50Ah per day (assuming you have a 12V system). As on a yacht it is difficult to keep the panels always pointing towards the sun, you may get a little less than that.

I would recommend perhaps a pair of Kyocera KC65 or KC85 panels http://midsummerenergy.co.uk/buy_solar_panels/kyocera_framed_solar_panels.html. They should certainly deliver most of the power you need for your system - perhaps not all, but then again you will be getting some power from the engine anyway from time to time. Dimensions are on the datasheets linked from the product pages on the website. We can supply the most appropriate regulator and suitable cables too.

Alternatively, we can get in some Sunware solar panels which can be attached directly to the deck, and can be walked on. They are rather more expensive than the framed panels, but if they would be of interest do let us know.

best wishes, Andy, Midsummer Energy