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

Dehumidifier powered by solar array and micro hydro

I have an isolated house in the middle of France 750m above sea level in a very damp location but with a south facing garden.  The house is unoccupied for long periods of time and I want to install equipment to maintain low level heating and ventilation throughout the four story building to reduce damp and consequently woodworm activity.  There is plenty of strong intermittent sunlight in summer, however in autumn and winter I have access to the overflow from a dammed lake that gushes water - I'd like to set up a microgenerator and connect this to the batteries thereby charging them through solar power in summer and water power in winter.  If you have time to provide any tips I would be most grateful. Thanks, Malcolm

 

Hi Malcolm. It sounds a great little project - but whether it would be practical I'm not so sure! The trouble is that heating and dehumidifying equipment is very power hungry, and you would need a very large (and hence expensive) solar array to provide enough power.  The best thing to do would be to find out the power consumption of the equipment you want to run, and use our solar panel calculator to work out how big a solar array you need.

A little micro-hydro turbine may in fact be a cheaper way of generating electricity, as you are lucky enough to have a suitable location! See http://www.homepower.com/basics/hydro/ for a useful guide. Navitron sell small turbines which might be suitable. regards, Andy, Midsummer Energy

 

Solar and wind power for summerhouse

I have a summerhouse at the end of my garden and would like to power it with a combination of solar panels and wind turbine, hopefully through the same controller. I might want to use computer, stereo CD/radio,two lamps, perhaps 75w soldering iron - probably not all at once but possibly several at one time. Could you give me some idea what wattage solar panel, size of wind generator, and number of batteries I would need? Many thanks - Jenny

Hi Jenny,

A lot depends on just how often you want to use the equipment there! There is a world of difference between a big desktop computer and all the peripherals being used for a few hours a day, and a small laptop used occasionally for an hour or two.

You may find our solar panel calculator useful for working out how much power you would need.

However, a suitable system might include:

• Rutland 503 wind turbine
• Kyocera KC65 solar panel
• HRSi regulator
• 100Ah leisure battery (available from any motoring store, eg Halfords)
• 2 x Labcraft Trilite 16W lights
• 500W inverter (if you would like 240V power as well as 12V)

That would be sufficient for a few hours of lighting and radio use a day; and perhaps say an hour or so a day of laptop / soldering iron use (more in summer, less in winter).

One word of warning about wind turbines - the output does depend very much on the location. If you have many trees around that cause turbulence and restrict the free flow of wind to the turbine, you might be better off going for two solar panels instead!

If the summerhouse isn't used regularly - and mainly in summer - even a single solar panel may be enough for your needs. It is easy to add further panels, batteries, or a turbine to increase the system size when you want to expand the system in the future - so you can always start small and increase as necessary.

Do hope that helps.

Andy
Midsummer Energy

Solar powered laptops - how much power do they need?

Hi Andy,
I want to run 2 possibly 3 laptops off solar instead of using the power chargers all the time. 2 of them are on about 18 hours a day and all the time off  powerpack. If I've used your calc pages properly for one laptop I would need a 1700 w panel to give 138 amphrs for a 12 v system. Surely this isn't right is it? The chargers / power packs are 19v and 4.74 amps and the laptop is on 18 hrs a day. Would it be better to buy an inverter?

P.S. Just wait, it won't be long before the term "Alternative energy" applies to coal, gas and oil....

Hi Alan,

I think the figure of 19V and about 4.74A (19 x 4.74 totals just under 100W power) is the maximum a charger would be drawing; you might well find that the average power a laptop needs is rather less than that. Though just how much depends on many factors! Presumably the laptops aren't actually being actively used for 18 hours a day - much of the time they will be idle, so if you change the power settings to switch off the screen and power down the hard drive, or go into standby while they are not being used, the consumption will go down dramatically. You could get one of those little electricity meters from Maplin if you wanted to measure their actual consumption.

I do have one customer who has set up a solar powered webserver using a laptop - I think he reckoned on nearer 30W rather than 100W. See the gallery page or his web page.

Having said that, you are right that you would still need a large array if you want to be able to power the system all through the winter with solar panels alone. The fact is that you get very much less power in winter than summer with solar, so to size the system such that you get enough even in the depths of winter means that you do need a big system. I reckon on solar panels rated at 20x the average power consumption. So if you have a 30W load on for 18 hours a day, thats 75% of the time, so an average of 22.5W - to power that fully in winter would need approximately 450W of solar panels. In summer you would get away with not much more than 100W of solar panels per laptop.

Hope that helps! All the best,

Andy

Powering everything under the sun!

Hi. I am having a narrowboat built and would like some information on solar panels.  I have set aside an area approx 6ft long on the roof and between 3 and 4 feet wide (chimney). I wish to run a TV/fridge/laptop/printer/ lights/12v w/machine/ induction hob (2 ring)/ combi microwave.  Heating will be by a solid fuel with capability to bake potatoes etc and by diesel c/h. I would also like to be able to heat water with the electrics on days that I do not move.  How many solar panels would I need and how big could my battery bank be? I may also need a little solar panel for the envirolet loo.

Thanks, Kath

Hi Kath,

Some of those appliances use a huge amount of power. Whilst it is relatively easy to power energy efficient lights and a radio by solar power - they typically only consume tens of watts - it's a completely different ball game trying to power an induction hob, which will consume thousands of watts when it's on! Laptop and TV are somewhere in between - definately possible by solar, but it won't be a small array.

I do know one narrowboat owner who cooks by electricity. He has 8 180W solar panels that take up most of his roof, and an enormous wind turbine - and he still has to run a generator every day if he wants to boil his kettle.

On a 6' x 4' section of roof you could fit a maximum of 3 Kyocera 130W panels - so a total of 390W of power. I suggest you play with our solar panel calculator to see roughly what appliances you can expect to be able to run from 390W of solar panels. They will certainly make an enormous difference - but you shouldn't expect to be able to run anything that requires heat on a regular basis from a solar array of that size.

The Envirolet can be wired into the rest of your 12V system; there is little point in having a seperate battery and solar panel for it. But even they are quite energy hungry. Envirolet recommend a 50W solar panel to provide sufficient power.

hope that helps - and sorry not to be more positive! regards, Andy - Midsummer Energy

Multiple regulators on one battery bank

Hello. I have 2 sets of solar panels (200W each) with their own regulator, and a wind generator with its own regulator. However they are not all charging efficiently. Even though the battery bank is fla,t when it is sunny and windy the wind regulator slows the wind gen down and one solar reg beats the other down. So I am getting maximum recharging from only one source not all 3. I think the regulators are sensing the charging voltage of the dominant regulator and thinking the battery is fully charged. Any suggestions? I have been looking for a regulator to manage 3 inputs (and 2 outputs would be good) but can't see any. Could I wire all 3 regulators to a 4th regulator for the bank? Thanks. Stephen.

Hi Stephen. You are right that whenever you are charging a battery, the voltage will increase, and therefore any other charging sources attached to the battery will see a higher voltage and think the batteries are slightly more highly charged than they actually are. That's pretty much unavoidable.

The effect should not be very large, however, and it's not necessarily a bad thing, as it prevents overcharging. PV arrays trickle charge batteries, and with a healthy battery bank and decent sized cables between the battery and regulators, you shouldn't see a massive voltage increase. If you are - if they are cutting out even when you think the batteries are flat - it's suggesting the voltage is rising above 14.4V (the usual cut off), even with a relatively low charging current. That suggests to me that the batteries are on the way out.

Regulators are designed to be used in parallel in the way you have them wired, so I very much doubt you will find any difference if you do change the regulators. Trying new batteries is in my opinion far more likely to give you good results.

Hope that helps.