Solar Powered 12V lighting system

This project is about resilience more than energy saving, though it can also be used to save energy. Total costs should be in the order of £100, but there are ways to reduce that by getting some items from Ebay.

complete installation

This project lets you run lighting off of solar power, effectively storing sunlight for later use. It can be used at home to keep lighting during power cuts, but the same principle can be used to provide power to sheds on allotments, outbuildings or island sites without mains power. Although I have used lighting as an application, such a system can run an electric fence for much of the year if suitable solar panels and battery are used.

The system as described lets you run one or two 12V 1.8W LED lights through the year – my system was able to run mine through the winter and the shortest day where the light would be on from about 6pm to 11pm. In the summer you can also run a laptop computer power supply independently of the main for a couple of hours (these run typically 40W). That is because in the summer you get far more solar energy and you’ll probably use the lighting less.

If you want to primarily save energy or reduce your carbon footprint using solar power, this is not the solution. For that it is best to get a grid-connected solar power installation which will allow you to save energy and get renewable feed-in tariff payments. That sort of thing is on a different scale from this project, and capital costs are usually in the order of several thousand pounds, but the energy savings are much, much greater. A grid-connected solar PV system does not give you resilience against power cuts, because the anti-islanding systems in the grid tie inverter shut the system down if the main power fails, so that a PV system does not send power back into the grid when it may harm power workers trying to repair faults.

Safety First

12V systems have different safety issues from 240VAC mains circuits. 12V is not considered a shock hazard, but FIRE is your enemy with low voltage power systems because of the high currents involved. The reason these schematics include fuses is to safeguard you from fire risks, do not try and save money by eliminating the fuses, and take note of their locations.

Before working on a 12V system, remove any jewellery such as wedding rings, necklace chains and wristwatches, as if these metallic objects bridge the battery terminals they can heat up causing serious injury.

For indoor use, a charge controller and a sealed lead acid battery are mandatory. Using leisure batteries or car batteries indoors is a serious explosion hazard because of the gases given off under some charge conditions. These can be used outside in well ventilated areas, and leisure batteries usually come with a vent pipe, which should be used to lead any gases to the outside if these batteries are to be used in a shed or outbuilding.

Car batteries should only be used in a car because they lack the vent pipe – when charged in a car there is usually a decent headwind of several miles an hour to clear the gases.

Parts list

  • approx 12W 12V solar panel
  • charge controller
  • 12V battery
  • 20A terminal strip (4-way or 8-way if using float charge controller with wire ends)
  • 25A fuse and in line fuse holder
  • 4-way fuse panel (can substitute with inline fuse holder for single load)
  • 2m of 16A red and black zip cord
  • spade crimp kit if the fuseholder needs spade connectors

Tools required

This is a picture of the tools I used

tools used to assemble the solar power system

You don’t need to use all of these if you are prepared to improvise – a good knife can double up for the wire strippers provided you know what you are doing, but they show what I used.

Parts walkthrough

Some of the items are shown in the pic below

solar panel, battery, charge controller and fuse board

The charge controller is in the middle of the picture and clockwise from the top left is a solar panel, battery and fuse panel. Unfortunately for home use the solar panel shown isn’t big enough. It is about right for a shed system that would mainly be used in the short summer nights.

Solar Panel

The solar panel I used is shown on the right – this is occasionally on sale at Maplin for about £40, and is rated at 12W. That 12W you only get to realise in the sort of sunshine you’d get in California, in the UK you can pretty much assume you will get on average 1/10th of the rated power even in the sun. In practice you do a little bit better – in the sun this can charge at about 0.2A through my intelligent charge controller, giving me about 1/5 of the rated power.

I use the light powered from this system regularly, which is why I need such a large solar panel. If you don’t plan to use it daily, then you can get away with a much smaller panel.

As a rough guide to sizing the panel get one that is rated about 10 times your load. Thus if I have sunlight in winter for about 8 hours and use the system for 4 hours at 2W, I need 8Wh of power. A 12W panel for 8 hours is equivalent to 24W for 4 hours.Allowing for it running at 1/10 capacity in the British weather, it gives me  about 8Wh in practice. I get away with that because I use a MPPT controller to maximise the use of the solar panel.


I used a sealed lead-acid (SLA) battery, the sort of thing used in computer uninterruptible power supplies and the like. Mine is a 14Ah 12V gel battery which is about £30 new from Rapid Electronics in Colchester. You could use the 7Ah type commonly found in UPS, either secondhand or these are available from Maplin in town. Maplin isn’t usually the cheapest place for this sort of thing, but you save delivery charges which may swing it.

Two things kill SLA batteries – overcharging and over-discharging. You should aim to never discharge a lead acid battery to less than 50% of its capacity. If your load is a 1.8W LED lamp or a typical electric fence charger, you’re probably running a current draw of 0.2A at 12V, so a 14Ah battery would run my load for 14 ÷ 2 (never run the battery less than 50%) ÷ 0.2 (load current) = 35 hours. This is about three days’ usage in winter, so as long as I get some sort of decent light in the three days I shouldn’t fall short. In summer, of course, I have the opposite problem, lots of sunny days and low usage. The problem of overcharging is solved by the next component.

Charge controller

The charge controller’s basic job is to stop the solar panels overcharging the battery. That knackers it, and makes you sore if you have spent £30 on the battery. The simplest form of the charge controller is something that goes in between the solar panel and the battery, which looks at the battery voltage and when it is full, stops the solar panel charging the battery.

Kemo float charge controller

This works well enough, and is the cheapest solution. For bigger systems you have to size it right for the solar panel as these have an upper current handling, but this is not an issue for a 12W panel as the lowest spec controller is good for 6A.

I wanted a more geeky one which would optimise the usage of my solar panel, as I knew my usage/sizing was marginal, so I used a MPPT controller which tries to match the load specifically to the light conditions to get the most out of the solar cells. It also tells me the battery voltage and load current, and isolates the load if the battery voltage falls too low, which saves me reducing battery life through over-discharge, though this function hasn’t kicked in yet. For the convenience I get to pay £30 for a part that otherwise costs £10-ish

MPPT controller with display

For a small system you’re generally better off spending the extra on a larger solar panel rather than using a MPPT controller to eke out the last of the panel’s performance, but the metering swung this for me.

Fuse panel

LED lights draw a small current of about 0.2A, and using a small fuse allows you to use appropriately thin gauge wire, I used 3A standard twin core lighting mains flex.

fuse panel

The problem arises when you have a fault condition at the lamp end of the cable, say the LED bulb fails short, or the metal of the fitting chafes on the cable and shorts it out. You now have the full battery capacity going into the cable. My battery is rated at a short circuit (CCA) capacity of 84A, and putting that across the 3A cable will melt all the insulation, guaranteeing the short, and eventually catching fire somewhere. I wouldn’t like that very much, so I put a 7.5A fuse between the battery and the cable. By using a 4-way fuse board I can run different things off the battery, so a 15A fuse goes to the 150W mains inverter, and another 7.5A fuse protects another light circuit.

12V lights

The first lamp I used with this was a 12V halogen desk lamp from IKEA which used a MR4 halogen bulb. I simply swapped it for a 12V LED bulb sourced from Ebay, and wired it to my system. The lamp was sub £10. B&Q have a LED 12v desk lamp with a wall wart mains power supply, the LEDs are all in a line and this sells for about £25, which is overpriced but locally available. You need to be able to source a suitable plug and solder it to a cable for the 12V system.

12V modded IKEA lamp

The second was another fine IKEA design which was originally a 240V floor mounting lamp with halogen R50 spots and a SES lamp holder. IKEA don’t seem to have realised how hot these halogen bulbs get. So I gutted the innards and glued a MR4 holder to the SES shell and kept the original cable and switch. Obviously the mains plug wants changing to the 12V system and then a mini-spot MR4 LED lamp was fitted to the socket.

MR4 socket glued in place of the SES lampholder

Complete installation

All these parts, except the solar panel and the light, are mounted onto a wooden board

complete installation

It is worth keeping high-power loads close to the battery and fuse board, typically within 1m to reduce losses in the cables. The solar cells can be mounted on longer cables since this isn’t a particularly high current circuit, and the lighting loads can be several metres away because of their modest power drain. If a mains inverter is used, keep this close to the battery and allow a longer mains cable, since losses are higher in the 12V circuit than they are at 240V for a given selection of cable and a constant load.

Schematic – Cheap Solar Powered 12V system using Float Charge Controller

Solar Powered 12V system - Float Charge Controller

In this version the Kemo charge controller (or equivalent) is placed between the solar panel and the battery. It prevents the panel overcharging the battery. The loads are simply taken straight from the battery via a fuse panel, in the same way as a car 12V electrical system is set up. Here you must make sure that the load is not left switched on, as otherwise, just as if you leave your lights on in the car, you will find the battery discharged fully the next day. That doesn’t do it any good at all. One of the side advantages of a solar system is that it teaches you to value the power and not leave things switched on needlessly, but you don’t want to get to learn that the hard way by having to replace a couple of batteries.

Schematic – Solar Powered 12V system using MPPT (PWM) Charge Controller

Solar 12V system using MPPT (PWM) Charge Controller

Note that the 25A fuse must be located close to the battery – it protects the battery cable against faults. This particular controller also isolates the load if it is left on and the battery runs down, as well as optimising the load on the solar panel, typically getting up to 50% more from it.

charger showing a charge current of 0.2A in the weak winter sun

It also shows battery voltage, panel and load current and lets you switch the loads off via the controller.

61 Responses to Solar Powered 12V lighting system

  1. Joanne says:

    hi all,

    We’re hoping to organise a skillshare session where Richard will show you how to put all this together, along with how to use a couple of electricity monitors to reduce electriticy usage at home. We’ve got the solar system set up here at home and it has worked really well, even through the dark days of winter, and we’ve really reduced our electicity bill too!

    Join & in the forum discussion about this skill share session!

  2. Pingback: 12V Solar Lighting System | Transition Ipswich

  3. sdc2011 says:

    This is easily one of the best pieces I’ve seen on wiring up a small solar set-up, nice job, one of the very few that actually gets into the details of wiring.
    I’m having a job though sorting out a problem. I have been trying to research into making the cable from the battery safe. I’ve seen ANL fuses (in line type), kill switches of various kinds even the kind used normally for AC, switches that are used in boating and car wiring and expensive fuse/switching boxes. So now, in a word, I’m confused!
    I don’t have the exact same set up as here. I have a longish cable coming from the battery (about 6 metres to take it downstairs) then a simple box to plug in a light and another device (for instance laptop or inverter) using a female cigarette lighter attachment. That’s when I realised I had no safety at all. In effect, it is similar to this – just further away. But that is the key because I am not happy mounting a similar fuse box to this at the END of the circuit after it runs a considerable distance.
    So I want to be able to shut the whole thing off, to stop the battery flow and add safety. Should I be looking for a switch or a fuse or both? Do I fix it inline near the battery or is it ok at the end?
    Even here in this set up I don’t see any simple ON/OFF from the battery.
    Then I am unsure of the AMP that the fuse should have because I have read about 50 amps and higher. A local electrician gave me a killswitch with 10 amp fuse trying to convince me it was fine – but I guess he knows as much as I do about 12 volt circuits!!
    Oh dear. You guessed I am no expert. A few pointers would be much appreciated.
    Thanks for reading – and again thanks for this posted info which has been a real eye-opener so far.
    From con-fused!

  4. sdc2011 says:

    Thanks very much for this. I guess that’s clear now. My problem maybe begins because I am using a simpler solar charger – one with only the panel and battery connections (phocos) without the load. So I am running a wire right off the battery not out of the controller. The wire is long because I want the devices downstairs, including the inverter so I cannot keep this last clsoe to the battery. If I put a fuse on this wire from the battery, it then defeats the idea of having a fuse box at the end with other different fuses for the different devices (including the inverter). I will have to get a more sophisticated charge regualator (as the one shown) to fuse the battery separately. Then run the long wire (2mm) downstairs from the load outlets and follow your advice of the separate fuses for the various loads. The inverter will still be 6 metres away! I have no use for it in the bedroom…
    If I could post a diagram I would show but not sure how here.
    Thanks again for your time Richard.

  5. richard says:

    If I put a fuse on this wire from the battery, it then defeats the idea of having a fuse box at the end

    In that case put a fuse of about 15-30A at the battery, depending on the cable rating to protect the long cable and protect you from the fire hazard. You can still use a fuse box at the other end with smaller fuses for your equipment, that way if you have an equipment fault the load fuse will go. Having a long run from a battery without protection isn’t a great idea IMO.

    I would feel uncomfortable with that unprotected – having once tried to faultfind a car starting solenoid as a youth by jumping it with a iece of 10A cable, fortunately held in pliers, I gained great respect for the current reserves of a lead-acid battery. The insulation melted off the cable in a flash before I could react 😉

    FWIW the same philosophy is used for your home mains distribution – the electricity board’s main fuse is 60-100A and is upstream of the consumer unit, where the largest fuse/MCB is probably 30A. So under nearly all fault conditions the consumer unit trips go out, but the electricity board’s main intake fuse is there as a safeguard of last resort.

    You will lose significant power via the long cable to the inverter under heavy loads. How much depends on the load – for high loads it might make sense to use a car type relay to remote switch the inverter if the load on that is high, say > 50W. Cable losses in low voltage systems are very counterintuitive because not only are the I2R loses higher due to the higher currents but the system voltage is lower. A voltage drop of 2V at 240VAC is no big deal, the same at 12V is a significant part of your source and could represent a > 10% loss of power.

    • sdc2011 says:

      Thanks again for this insight.
      I got hold of another solar controller – not as sophisticated as this, yes one of the cheaper Chinese models, but with the 3 outlets – and a couple of in-line fuse holders to carry bayonet fuses. So I will be wiring it up as suggested with the fuses now.

  6. Wendy Baird says:

    Thank you for the article – exactly what I was looking for! Just one question: in your picture captioned “Complete installation” is the thing(s) on the right your inverter? Do you just use one socket?

  7. richard says:

    the box on the right is the inverter, with a elecricity usage monitor plugged into it.

    Note that the size of the battery and solar panel are such that the 12V lighting is the main usage. I can run 4W of lighting for all the time I need it in the shortest day, but if I were running a 40W load every day via the inverter I’d probably only get about 1/2 hr of running time then.

  8. Markusace says:

    How would this differ in usage and setup with Li ion batteries?

    I am looking to store the excess from my panels (some days up to 20kwh excess from 16 FEC 240w panels which I do’t want to give to British gas). So would be looking for a bigger set up. Would it be simpler (but less efficient) to use an inverter from the batteries? Also am allowed to put this back into my lighting circuit when I am connected to the GRID (assume they have no way of knowing) or would I have to disconnect it and run from battery/inverter only? I would probably employ an electrician . By the way this is the best and clearest tutorial I have seen for a long time. You could go professional.

    • richard says:

      @Mark The cheapest and easiest way to store 20kWh excess would be using a grid-tie inverter and the National Grid. To use batteries you have to size the batteries right. A 85AH 12V lead-acid battery would do about 400Wh (you can only use about half the battery capacity for optimum lifetime). Lead acid is ususally the cheapest option for a fixed installation, though you’d have to pay serious attention to venting the battery room.

      Li Ion has a much better energy density and you can use most of the battery capacity, but you do have to use a charger designed for the chemistry and capacity of the cells. You’d be better off reconfiguring your panels for a higher voltage to reduce copper losses and possibly aim for a 240V or 120V system and use a charger that has a internal switch-mode, these don’t mind running off 240VDC. But you have to know what you’re doing, these voltages are very hazardous.

      You may only provide locally generated 240VAC power to a circuit which normally carries grid mains voltage via a transfer switch fitted correctly so there is no chance of back-feeding the mains. This sort of work is covered by Building regulations Part P certification requirements An electrician carrying out this sort of work would be able to certify.

      There’s no fundamental technical reason why you can’t do what you want, though the battery costs are likely to be prohibitive and need to be researched first. The regulatory issues will add overhead to the project.

      I’d be tempted to mod the lighting circuit to use 12V. 12V running is common for things like halogen bulbs and accent lighting, and electricians are familiar with that. You need to use the right grade of cable because the current is higher, but the bulbs are widely available, both LED types and the much higher power halogen types. The service life of the halogen bulbs may be slightly lower on DC unless you reverse polarity every so often. However, if you want to use your existing lighting there’s no reason why a transfer switch can’t be used for just that circuit to feed an inverter to it.

  9. Markusace says:

    another post

    What to you think about using battery powered LED lighting e.g. Mr Beams range which uses 3C or 3 D type batteries? Could use rechargeable and recharge them from solar in the day sounds safe, cheap and easy to install (lights though are around 20 pounds with motion detectors).

    • richard says:

      Main issue there is swapping the batteries is a lot of faff. 12V to D cell and C cell chargers are easily availble, so there’s no problem in doing it. This sounds like a dear way fo sourcing lighting, your payback period is going to be long…

  10. SolarMon says:


    Firstly, a great article – very useful and informative.

    Secondly, I have a query regarding the Charge Controller you have mentioned in this article – this looks like an EP Solar one. I cannot find this exact looking model on the EP Solar website ( The nearest equivalent is the VS**24N

    But this is classed as a PWM charge controller.

    On some other websites it also suggests this “EPIP20” model is a PWM one and not an MPPT one?

    • richard says:

      It was sold to me on Ebay as a MPPT, and observing the response to cloud to sun transitions it appeared to me that there is some adaptive processing going on. On a drop in light level the current falls, then seems to pick up again a little. Whether this is an artifact of lag in the metering or real adaptation I haven’t investigated, I may try getting a scope on the current at some point.

      However, TBH the economics don’t really stack up at this low power level to pay any MPPT premium for the controller. The essential features are solar overcurrent protection and isolating the load on a low-voltage battery condition. I was probably rushed by the MPPT claim on the Chinese ebay ad and should have stuck with the bog-standard model and spent the £20 difference on more solar panels 😉 There again, I quite like the metering and this device has been in use for nearly two years now without any trouble, and it would have cost a lot more from a non-Chinese supplier so I can’t really complain!

      • SolarMon says:

        Hi Richard,

        I am by far not an expert, but I now realise that all, if not most, charge controllers use PWM for its charging mechanism. Then it comes down to whether the charge controllers use/support MPPT to adjust (down convert) the charging voltage (and up convert the amps) accordingly, as opposed to just taking the panel voltage down to 12V (for a 12V battery) and performing no down/up conversion. It is confusing, and misleading, when charge controllers are classed as either PWM or MPPT.

        But yes, the metering and display panel of the model you have is nice. In my basic setup (for an *ahem* off-grid climbing frame) I’m using the EP Solar EPHC10:

        Which has no display panel and basic metering with just load and battery status LEDs.

        • richard says:

          That one is probably the best value for a small system, and was widely available on ebay ISTR 🙂

          People do seem to be moving to PWM for controllers and you probably have to for any charge currents of > 2A, less than that and a regular linear voltage regulator works okay but you’re losing power as heat. So PWM is the first stage of improved efficency and seems to be the economic sweet spot here

          Although the canonical way to do a MPPT is to use a micro and sample the resutls of perturbing the operation point and chasing a maximum of dI/dV This TI article seems to indicate that you can win half the battle by targeting a cell voltage of 0.45V, which might open the way to a gonzo version using something like the venerable TL494 PWM with the reference string targeted at the input side rather than the output

          • SolarMon says:

            I’ve seen a video that suggest PWM charging can , depending on PWM frequency, also cause noticeable pulsing/flickery issues for LED lights:


            Have you come across this issue with your setup?

          • richard says:

            Haven’t observed any flicker, and I wouldn’t expect any with the battery slugging any PWM pulses 🙂 It’s a lovely light to read by, a very even field compared to typical task lighting.

            Now running them on 12V AC, as I did to see I could use an old halogen lighting transformer, that does give you the most horrendous flicker. The LED regulator full-wave rectifies the AC, but the LED is either fully on or fully off, giving a harsh juddery flicker on movement. Don’t do that 🙂 However, off the battery it is absolutely fine. I’m unable to discern any flicker in thel ight and it doesn’t strobe with my video camera

  11. RPoon says:

    Hi Richard,
    Great job. Precise and clear detail in explaining your solar setup.
    I am staying in a high rise apartment in Singapore with some windows in my balcony facing East and some facing West in another room. So I have 06 pieces with total of 250 watts solar panels facing East and West to catch the sun light since December 2011. My 3 AGM gel batteries totalling 84 AH, 20 amp charge controller and 500 watts inverter are in the balcony powering 04 units of 7 watts LED lights, 1 unit of of 16 watts lights, cigarette charging station for my samsung phones, Iphones and Ipad.
    I had linked a cable from this charge controller called station A to another 10 amp charge controller in a room 50 feet away charge by another solar panel – station B powering my wireless modem and wireless extender. I have circuit breaker and fuses at start of long cables and loads. Is it possible to add a 100 AH battery in station B and still power by batteries from station A? Can the linking cable from station A take this load without shorting out? I want to power more appliances. I am saving 40% off my power bills every month now.

    • richard says:

      50 feet is a long way for a 12V system. The charge controller should always be close to the batteries as it needs to know the battery voltage and the current accurately. If it feeds a battery via a long cable then the loss in the cable will make it believe the battery is not charged enough, resulting in overcharging over a long period of time.

      You could look at your system as two isolated systems for 12V and power different items from system A and B matching the load to the sun and battery capacity at each location. If you need to power something a long distance form the batteries then the long cable should be on the output of the inverter, your losses will be much lower at the higher 220V output voltage. The problem with a 50 foot cable at 12V is the losses if you’re drawing much more than an amp.It isn’t so much that the cable will burn out if it is sized for the current, it’s the loss in voltage and power that will be hard to work around for any reasonable size of cable.

      Big solar systems run at higher voltages – 36 and 48V are common and some rooftop systems can be 200V or more, which reduces this cable loss problem. You may need to consider a higher system voltage, in which case perhaps go for a grid-tie inverter. Sounds like it is much more sunny in SIngapore!

  12. RPoon says:

    Thanks Richard,
    You are right. 50 feet from the batteries is too far for 12 volt system. My 7 watts LED light in station 2 is dimmer and flickers. Other lights in station1 are brighter and do not flickers. I will take your advise and make 2 isolated solar power systems.
    As I am staying in high rise apartment, I am unable to install grid tied solar panels. 90 % of Singapore 4.5 million population stay in high rise buildings. Only 10% of population stay in landed houses such as terrace, semi detached or bungalows. We only have a land area of 680 square km.
    We have lots of sunshine being only 200 km north of equator.

  13. Aaron Griffith says:

    Hi Richard
    At last a UK posting of solar charging. Too many on YouTube are based in the states!!
    Like you I have the same set up but have only just started, so still working out a few things.
    For now, thanks to a friend at BMW, I have 4 BMW car batteries. Yes I know not the best for the job but they are free and do the job for now. They are 12v 70a sealed.
    I have the same controller as you and want to replace / add as backup, my normal 50w halogen bulbs and use LED 12v bulbs.

    My current set up at home is using GU10 LED bulbs but running off the normal electric setup. I have to admit the the LED are not as good covering / flood lighting the rooms as the halogen bulbs, but if I add more LED then it should cover the area.

    My house faces south and the front has sun on it from sunrise to sun set. My long term plan is to put up solar panels on the roof, curtesy of my bro in law who installs them for a living, and then run most of the house from them and battery backup.

    I also have a wind turbine and a hydro turbine, later projects to help add more juice to the battery bank when solar is low.

    My questions are :-
    1. What is the best way to link the all 4 batteries up, positive to negative or in line pos to pos ?
    2. When I set up wind and hydro, I know I have to use different controllers, but how would I link them to the battery bank ?
    3. Should I use step battery banks for each system and link them to the main switch load board ?
    4. Can you see any issues or alarm bells with my planned set up ?



    • richard says:

      You link the batteries in parallel, ie positive to positive, if, and only if, all are the same voltage and that is your desired system voltage. Since you are using car batteries you must, must, must, think about how you are going to vent the gases to the outside, rather than letting them build up in an enclosed space. This is easy in a BMW as when you are charging you have the headwind through the radiator grille and the engine compartment isn’t an enclosed space…

      Assuming you have the batteries like so

      —– (+)—-(+)—-(+)—-(+)


      you take your output off the top LHS and bottom RHS or vice versa to try and balance the high current drain, i.e. don’t take the power off both RHS or LHS else the battery nearest the output will do most of the work.

      If you had the choice to raise the system voltage to 24V using two in series parallel another two in series that would lower the current requirement and hence cable demands, but your loads seem to be 12V only so you probably don’t have the choice.

      You can usually parallel the controllers to the same battery bank, though consult the manuals of the specific controllers.

      Your 50W halogen lamps are far too high a load for this sort of system, running that will raise the cost of your battery backup and the required number of solar panels if you want to maximise the off-grid runtime. You must change these unless you have access to a lot of free solar panels and batteries 😉

      Running your GU10s via an inverter is less efficient than running the system at native 12V, though this is still far batter than native 12V halogens!

      Finally, you need to have an extremely good reason to want to run off-grid using battery backup in the UK. The economic case massively favours using a grid-tie inverter and using the National Grid for storage instead of batteries.

      We are at a latitude of 50 N – there is about a 10:1 ratio between the power available at midsummer and midwinter. That means if you want to run off-grid in midwinter your system will be 10x overdimensioned in summer. With grid-tie that is power you can sell back to recover your economic outlay, without that is just dead capacity.

      Your USB charger can be just bridged across the 12V system with a switch in line (these things tend to draw some power even when not charging something). It works well, I have one of these too.

  14. Aaron Griffith says:

    Sorry forgot to add,
    I have a 12v to 5v unit with USB for charging phones, tablets, game controllers and recharge batteries for the tv remotes.
    Can you see where I would fit this into my set up ?
    Also I want to add a inverter for other things that the family might use around he house.
    Would it be better to monitor, using the same plug monitor you have, the machines I want to use in an inverter then decide if the system can handle it ?

    The end game is to be as “off grid” as possible, using the above, I suppose that’s most people’s idea ?

  15. Aaron Griffith says:

    Sorry my diagram was wrong I meant as your diagram and understand the drain.

  16. rogue lj says:

    This is a great write-up. Do you foresee any issues with just daisy-chaining solar panels together? My idea being that it could be an on-going expenditure, rather than one big outlay (i’m looking to start running a lot of devices of this type of setup, maybe using a couple of Powersonic 12v 26AH batteries).

  17. Diane says:

    Hi, This is a great write up! and very helpful for me.

    I am trying to use it to to help me design and fit a solar lighting system for a small stable block – two 12ftx12ft stables, one 6ft x 12 ft tack room, a feed room (8X6ft) and a 12ft x 9 ft hay shed. I only need lighting at the stables on 3-4 nights per week, and not every night of the week so hopefully the charging capacity of the panel will be okay.

    I have purchased a 20W solar panel and charge controller – with max 5 amp output. This will be connected to a 65Ah car battery (in ventilated space) [i might parallel clamp in another battery too]

    So far for lighting i am thinking this for lighting – please correct me if i am wrong as I am trying to work from A level physics some time ago!

    Max 5amps output through the charge controller, therefore with Power (watts) = I (amps) X V (volts) this means the max power i can have on the 5 amp circuit is 60W … correct so far??

    A local electrical shop sells some DC directional lights which can have the ‘MR16’ 3.5W bulbs in – so should be a current of 0.29amps using above equation…?

    if each one pulls 0.29A then i can have 15 in the circuit no problem on the amps side, and the watts side? is this correct?

    using a 4 fuses board as shown will be able to give me a different circuit for feed room/hayshed/tack room/ both stables together? again – what do you think?

    BUT do i need a fuse board as my charge controller cuts the output if more than 5amps?

    As this is for a stables, i will be using switches on the walls rather than using the lamp switch – do these have to be plastic covered do you think?

    I would love a radio up there too – can i just solder connections onto the battery section of my AC radio up there (that used to work off a generator that no longer works – but that is another project!).

    Thank you in advance for your help,

    • richard says:

      Hi Diane,

      You power is not limited by the capacity of the panel, but by your battery. It’s your runtime that is limited by the capacity of the panel combine with the power you draw and the amount of sun you get. You mainly need light in the winter, where you have least sun 🙁 As a rule of thumb your 20W panel (in full noonday California sunshine) will charge the battery at about 2W in the sun in our midwinter, ie at about 2/12 ~=150mA for 6 hours – the sun isn’t particularly useful for a solar panel at the beginning and end of the day when it is low in the sky.

      If you use the light for 1 hours of those 6 hours you could use up to 12W of lighting. Your usage pattern is about half the time, which hopefully makes up for the overcast days.

      In practice use the LED 12V lamps, or possibly the sort of caravan 12V fluorescent lights, though I’ve found these to have a poor service life if they get damp. The LEDs draw about 2.4W – you could use up to five of them if you had the sort of 1:6 usage pattern. If you need more light or more runtime you need more solar panels. More battery won’t help you, you just won’t be catching enough energy from the sun for the amount you are drawing out. On the other hand, were you to only need it for 5 minutes, you’d get away with 100W of lighting. Yo have a lot of area to serve – you’ll make it easier if you illuminate only one room at a time. A 12V circuit isn’t a shock hazard, though everything will corrode more if it gets damp.

      We use a old car radio at the Oak Tree farm directly off the battery, with a car door switch on the main door to turn the radio off via the ignition connection when people lock up. That works fine – if your radio is 12V you can take the battery straight in, but it’s an unusually high voltage for a portable radio so you may want to double check that.

      You must must must fit the fuse at the battery end. It protects you against equipment failure and shorts, that could otherwise be a fire risk

  18. Diane says:

    Thank you for that, it helps to know i am on the right track I would hope that with me generally not needing the lighting on consecutive days it will mean even in the rubbish english winter i will get enough power from my solar panel. As two days charging will be for one evenings usage.

    Just another question about the fuse. There is already one in the lead between the charge controller and the battery – which is the one you were referring to as a must. My question was about the 4 fuse-fuse board – which sits between the charge controller and my light circuits? is that required if the charge controller cuts the current if it gets over 5amps, so acting like a fuse itself?

    Luckily my old ‘ghetto blaster’ (it is quite large!) is 12v, so i can solder connections straight onto the terminals.

    Also – what cable do i need to specify and purchase for the lighting system – i have seen 6amp black-red cable, but is that too high. someone in maplins said speaker wire would be sufficient?

  19. Justin says:


    Very clear, and I now have the confidence to put my components together as per your system using MPPT Controller.

    1). Can I confirm that you are using the 16A wire to connect the fuse board to the controller and also the battery to the controller. I have a 10A controller and was going to use 15A wire from Maplins (although could go to 20A if you think that is safer) – my Battery to controller cable run is only about 50cm.

    2). My controller doesn’t have a meter, and so I have purchased a small LED voltmeter of ebay. Can you advise me where I should place this in relation to your circuit diagram. I have been told that I can place this straight across the battery terminals, although I assumed it should really be across a load.



  20. richard says:

    @Justin Don’t worry about the difference between 15 and 16A cable – particularly with such a short run.

    Your LED voltmeter will present a continuous small drain, so it wants to be after the controller, because in the end you are interested in the voltage for the load, and should you run the battery down it would get cut off by the controller undervoltage protection.

    You don’t need a meter – I got a controller with a meter because I was geeky that way and was worried about the amount of solar charge not being enough for the lights. I have one of these meters – they typically draw about 10mA so you would be drawing about 240mAh a day, similar to running the example light for an hour and a half

    I have now passed the third winter solstice with this rig and I can say the meter was not needed 🙂

  21. Justin says:

    Thanks for the reply.

    If I am honest I am only interested in the voltmeter as a small side project for fun. The meter was only £1.49 from Hong Kong (which included P&P) so my expectations are not very big. However I thought it might be fun to mount the LED on the board next to the controller and then take a circuit in parallel across the battery and in parallel across 2 loads, all wired straight to the LED. Using 3 push type switches, the LED is always off unless I choose one of the 3 circuits and push down and hold on the switch. The LED would then light up and show the voltage across the battery OR one whichever load I have chosen. The drain will be utterly insignificant as it will be in use for a second or two at a time.

    I hope that makes sense. I guess I am just killing a bit of time and improving my 12v skills.

  22. Katherine Melvin says:


    In a previous posting you say that you can have multiple solar panels in parallel as long as the voltage is the same. Do you need to match the panel power as well.

    I am asking because I had a 5W panel into a 5A controller, but I have since replaced this with a 20W panel. However the 5W panel is working fine and now sitting on a shelf in the garage.

    • richard says:

      If the voltage is similar then that’s fine. Most solar panels have a diode so the strongest one wins unless the load is heavy enough and then it’s shared. You can find out by putting a voltmeter across the main panel in the sun with no load- the voltage will rise to somewhere around 20V. Shade the small panel and put it in parallel – you shouldn’t lose much voltage. If you do lose > 5%, there isn’t a diode, and it’s probably not worth the bother of running them together unless you’re prepared to wire a 1N4001 or similar diode in series with the small panel with the anode to the small panel positive

  23. eldicko1 says:

    Thankyou for your valuable information, I have done solar here a few years ago but now plan to follow system with 12v leds and a pulse width modulation charge controller, there have been so many improvements in the last few years. I will let you know how I get on, Best regards Eldiko1.

  24. david says:

    Thanks for a great article. I have a similar geeky ‘need’ for a readout of various information on the MPPT charge controller and the one I am looking at is on ebay here . The question I have is that the specs say it is for a battery of >= 100ah. Do you think this would still work on a battery in the 20-30ah range?

    • richard says:

      Difficult to say what the specs mean in the Chinglish 😉 This was a worrly for me as my EPIP20 says the battery setting is >=50Ah and my battery is only 18Ah. It’s worked fine for the last 3 years. The only problem is that the A display only reads to 1 decimal point – I believe that is what you set when you set the battery capacity, so if I up the battery capacity to 100Ah from 50Ah the display only reads 0 or 1A as opposed to 0.1A and up.

      It’s not a big deal. I just winged it and got away with it, the controller looks for the battery voltage and temperature I believe.

  25. thornwarbler says:

    thanks for this………..simply explained clear instruction

  26. andy says:

    Hi have read the posts and im looking to set up a 12v off grid dc system in my cabin with about 10 x light led downlighters and a 12volt fridge freezer . Im thinking about 4x100watt panels with an mppt controler and 2x 100watt hour batteries . do u think this would be viable as i plan to live in it permenently . And forgot was thinking about a generator backup tied into the system for any shortfall in winter months . regards

    • richard says:

      The 12V fridge freezer will kill your system unless it’s really tiny and efficient. There’s a reason why the fridge in my campervan is only powered by 12V when the engine is running rather than the 12V auxiliary system – it’s designed to run off gas otherwise. That’s not a bad option for your cabin – a lot quieter, too.

      If you’re going to live there you need more solar panels relative ot the battery storage. Here at a 51 degree latitude there’s a 10:1 ratio in average daily energy got from solar panels between summer and winter. That ratio will be lower at lower latitudes, but probably still 5:1 in the US.

      So if your system could keep up in winter it’ll be overdimensioned in summer. The economics of a generator work fine to cope with occasional peaks, but it’d be ugly with a daily shortfall.

  27. Sam says:

    Hello there
    Fantastic job and I love it, pls tell me is the set up or bit more higher one able to light up a three bed house with every room having light ? If so what do I require to do that

  28. Pingback: Transition Ipswich | living 12 volt

  29. Scotty A says:

    Hi Richard and thanks for your post. I see that although it dates back to 2011 there have been steady interactions right up to late 2014!

    I am in Australia and have just set up a larger system for 3m * 6m shed. It is running a 100w Solar Panel and 150AH sealed battery with a PWM controller. The shed is in my backyard and I have no mains power running down there so I thought I would do this, get some lights on in the shed and around my backyard and learn a bit about 12volt at the same time.

    At this stage there are a couple of things I am confused about and they are really revolving around making sure I have the correct wiring gauge and how I can run multiple circuits from the controller. Here are my questions:

    If I have different wiring gauges (eg I have some led strip lighting with thin guage and a 10w led floodlight with thicker guage what is the best way to address this … power distribution (fuse box)? I am a bit confused by your wiring as I was thinking to use a power distribution fuse box with one in and multiple outs on the +ve and then a terminal strip on the -ve. Practically you have wired two wires (+ve and -ve) coming from the charge controller lights and battery terminal and then when they hit the terminal strip and fuse panel they do a little loop out. Could you explain or direct me to some readin on what this is. I’ve seen it before but I dont understand it.

    One last thing is your mount to wood. I was going to mount my stuff to MDF (currently the controller is just screwed into some treated pine wall studs). If 12v is such a fire risk why would this be a good idea?

    Thanks again for your help just from your posting. Its great.


    • richard says:

      Your wiring gauge is relatively simple – in needs to be comfortably (at least 5x or more) current rated greater than the fuse protecting it on the input side. That way if you get a dead short because a critter chomps through the cable the fuse blows rather than the cable heating up and starting a fire somewhere along its length.

      This is why I use a multiple fuse box, so for light loads I can use a 3A fuse and cheap 16A thinwall cables. For the inverter, which is located close to the fusebox I can use 80A cable.

      There is another issue with 12V systems in that long runs need much heavier gauge cables than you’d think, due to IR losses. Say your floodlight is 10m from your fusebox, you use a 3A fuse (plenty because 10W ~ 1A@12V) and 16A cable at typically 1mm^2 cross-sectional area at .0185 ohms/m. So you have 20m of this in series, 0.37 ohms so you drop ~0.37V. That’s absolutely fine. Put that floodlight 50m away and you take a 1.85V hit, nearly 10% of your supply voltage lost. If you use exactly the same setup at 240V the loss is less that 1%!

      > I was thinking to use a power distribution fuse box with one in and multiple outs on the +ve and then a terminal strip on the -ve

      That’s pretty much what I do – each circuit has its own fuse but I’m only showing one load. It’s easier if you use a fuse panel where all the supply sides of the fuses are common, and use a all-metal earthing block, which is what I’ve used when replicating this in a shed in pretty much your application.

      I mount to wood because I have taken precautions against the fire risk. These are: the output fuse panel, and then for issues like a faulty controller or a faulty controller and shorted solar panel (could happen from lightning induced surges) there is the catchall 25A fuse as a last resort at the battery +ve terminal before the battery cables start to run parallel. I actually changed this for a 15A fuse in the house, because I don’t run any exceptionally high loads.

      Because you tend to use thinner cable for economic reasons for light loads eg your LED strips you must protect those thin cables with a lower rated fuse. 11A cable is .037 ohms/m. Say you have a 10m run of that, total resistance 20*.037=0.74 ohms. Develop a short in the far end and you will draw 16A, so the 25A battery fuse will be happy. That cable is now a 192W heater if you don’t protect it 🙁 A fuse will typically carry twice the rated current for a while before rupturing, but not 5x for any great length of time

  30. Scotty A says:

    Thanks very much for that detailed reply Richard.

  31. Randy says:

    greetings Richard. Thanks for taking the time to write this article and consistency in engaging with all the replies.

    I have recently set up a 12V solar system and would like to connect up some LED lights, a cig lighter socket and a usb socket. I’ve got basically the same set up as yours, panel, charge controller, etc. What gauge of wire would you recommend for a set up such as this. My LEDs came with 2m of 0.5mm cables 16A rating. Can I connect a larger gauge cable from the CC to the fuse box and terminal strips, then down to a smaller gauge from the box and strips to the load?

    • richard says:

      > Can I connect a larger gauge cable from the CC to the fuse box and terminal strips, then down to a smaller gauge from the box and strips to the load?

      That’s right – you can see this philosophy on the third output to the right with my fuse box which is in fact a thinner cable going to a LED lamp, and that’s a 3A fuse (and similarly a 16A rated cable).

      Presumably your USB socket will use one of those Ebay Chinese coverters, or maybe a car adapter for the cig lighter socket? Bear in mind these have some standby drain – my Chinese Ebay device has a 10mA standing drain. That’s not good in these dark winter days so you’ll want a switch in there, or pull the fuse when not using it. 10mA doesn’t sound much, but it’s about 3Wh of waste a day.

      My system is coming up for its fifth anniversary and still running on the original gear and battery, though I’ve upgraded the LED lamp to a brighter 3W one and added a couple of other lights

  32. joanna says:

    Hi your article & responses to all the comments have been really illuminating (ho ho). I am trying to work out a completely 12v system for lights, mobile & laptop charging etc for a small off grid house. Could you recommend any books? I really want to get a handle on everything!

    Thank you very much

  33. Tim C says:

    Hi Richard,
    Great to see a useful UK based article, thanks for posting all those years ago.

    Re you comment about updating the LED lamp, could you say what you are using now? I am hoping to put something similar in my Summer House and I would like to have some more conventional lights for main lighting.

    I have a spare 100 Watt PV and 2x100AH 12v Lead Acid Batteries, due to the MPPT I am using it makes sense for me to use the batteries as a 24v bank which I think will also help me running my laptop from DC (rather than using a 230v inverter) I may also uses a 230v inverter for other things but I should have a decent reserve of power with my system.

    However I am not sure about drivers for LED lights and what options exist sure for decent overhead handling lighting. Any ideas?


    • richard says:

      All I did to change the LED lamp was to swap it for a brighter one. I only changed it because I wanted to pinch the original to replace a halogen bulb in a van and the old one fitted perfectly.

      You’re in for a world of hurt in the wallet if you go 24V 😉 You can get 24 V to mains inverters for trucks and some LED lamps will tolerate 24V, but read the specs, most won’t. It probably won’t be the optimal cost solution.

      For the laptop use a standard native 12V car laptop converter (12 to somewhere between 19 and 21V depending on the laptop) . They’re more efficient than going up to 240V and then using the original laptop PSU. Plus you get to charge the laptop in your car if you want.

      You don’t need drivers for 12V LED lamps on a battery system. You only have them in bathrooms etc because they are swapping out the legacy 12VAC transformers designed for the original halogen lamps. Those drivers are therefore taking the 240VAC and making them into 12VDC, which is the same as your battery.

      Just put your LEDs in parallel across the 12V supply from the battery, after a suitable fuse of course. There’s a little inverter inside the lamp that matches 12V to the LED requirements, and a bridge rectifier so it doesn’t matter which way round you get it. You can use any standard 12V light fittings such as those for bathrooms.

  34. john w says:

    Hi Richard
    I have just set up a system for lighting in my garage.
    I have a 100w panel and 20am charge controller and a 75 ah agm battery.
    I have trouble working out cable sizes from charger controller to fuse box and then
    from fuse box to led lights.
    My led strip lights 5 metres long and draw about 8.5 watts. 8.5 divided by 12v is less than a amp how do you size the wire. I worked it out and the wires seem quite thin
    2mm. Fuses do you oversize them against the ampage rating of the cable.
    thanks john

    • richard says:

      @John W,

      You never oversize the fuse. Always oversize the cable, so that the fuse is the weakest link. In practice make the cable grade several times the fuse rating.

      A 100W panel can in theory deliver 100/12 ~= 8.3A. You are unlikely to ever get that in the UK, but it gives you a general scope. Size your maximum system capacity around a 10A fuse at the battery, and use something like 33A automotive cable (3mm2) or 50A, this fuse must be at the battery end, usually fitted at the + terminal. Take the same grade to the fuseboard and earth block.

      For the cable run to the light use a 2 or 3A fuse in the fuseboard. That means you can use light duty 11A automotive cable ~0.5mm2 after that fuse, which will save you money for that run. Typical resistance is about 0.1 ohm/metre, so at 1A you will lose 1V after 10 metres. If you have a run longer than that then if cost is more important to you then you live with eating the loss of power and a dimmer light up to about 30m, else you will have to uprate the grade of the cable to save voltage loss (roughly 20A for 20m @ 1V loss and so on.) Leave the fuse at 2 or 3A.

  35. john w says:

    Thanks Richard
    So the fuse between the charge controller and battery should be 10a and situated as close to the battery as possible is that right.
    My set up is the same as yours.
    I just wondered why you had a 25a fuse near your battery in the diagram.
    Sorry for all the questions I am on a steep learning curve.
    Thanks again

    • richard says:

      The original rig had a 25A fuse because some of the people building systems in the early days of the project wanted to use bigger panels than mine and one had ambitions of running more than lights.

      For a lighting rig like yours and mine, in practice 10A is plenty at the battery. As a general rule use the smallest fuse that will carry the current safely. Though the light would be happy with a 2A fuse there, the charging current is likely to exceed that.

      The reason the fuse at the battery is necessary is because a battery can deliver a huge short-circuit current. That fuse is stands between you and a serious fire hazard, should for some reason the positive be shorted to negative. A mouse chewing through cables can do that…

      The second fuse lets you save money on the cable run to the lights while staying safe

  36. john w says:

    Thanks Richard
    I properly end up charging phones ,running a laptop and a led 18w stoplight off the
    System as well as the led strip light would I have update the fuse at the battery or put a small circuit breaker

    • richard says:

      laptop is typically 40W so your have a combined load of ~60W which is 5A@12V, so you’ll be okay with the 10A fuse.

      You’re going to struggle running all that lot in the short days and weak sun of winter unless you keep the usage very short…

  37. john w says:

    Thanks Richard
    I am learning all the time

  38. James Harrison says:

    Hopefully this thread is still “live”.

    I am hoping to build a micro-hydro system rather than solar to power a garden lighting system. Would the charge controller requirements be the same? The battery bank will be about 30ft from the hydro plant and the light run will be about 50 ft from the batteries. Or I guess I could have the batteries right by the hydro with a longer run to the lights.

    As I will be able to charge constantly – would I be better running a 24V system and if so, how do i reduce back down to 12V closer to the lighting run.

    It is very difficult to find any guidance on line to DIY hydro and battery charging systems – any links and wiring diagrams would be gratefully appreciated.

    Many thanks – James

    • richard says:

      > charge controller
      You’d need to ascertain what type of controller is needed for hydro.There are two basic types. For solar you use a series controller, which increasingly disconnects the batteries as they get charged up. The other sort is a shunt regulator, which is generally used on wind, because as the wind increases you most definitely do not want to disconnect the load from the generator, which will overspeed. So you divert the generated power to a dump load (sometimes water heating) keeping a load on the wind generator.

      My guess is for hydro would be ok with a solar type controller, but it’s worth checking with the generator manufacturer, I have no hydro experience.

      With 80 foot of cable it probably would be cheaper on cable to run a 24V system because of the lower current. Nowadays 24V capable LED lamps are a bit more common, so you’d need to do the calculation on whether the slight extra cost of 24V capable lights beats the extra cable cost at the max 12V load current you are running. You also need to take into account any cost difference in the generator end and controller between the two options.

      If you really don’t want to run your lamps at 24V you can get 24V to 12V DC-DC converter blocks on ebay or the like, these are designed to run 12V kit in trucks with a 24V electrical system. You could use 12V lamps after one of those, sharing one converter with several lamps, but you need to put the light switch in the 24V line because the converter blocks have some static power drain even if the load is disconnected. Switching the input gets rid of that drain, saving your battery if you have a generator fail for a long period that you don’t notice.

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