This is my first instructable covering a project I completed earlier this year. I have a shed which I use as a workshop as well as somewhere where I can train on my bicycle (on a 'Turbo Trainer') and as a general storage area. Although it's close to the house, there is no mains power available and having enough of resorting to using a touch every time I went into the shed in the winter evenings, I decided to have a go at installing a low voltage LED lighting system which could be run from a 12v battery that is charged from a solar panel.
Step 1: Design
I Googled and Googled.... I Googled a lot before I went any further. I had no knowledge of how to put one of these together and so it took a few days before I felt I'd learnt enough to know what I was doing. For those of you who are unfamiliar with the components of a solar charging system, it goes something like this:
You can hook a solar panel straight up to a battery and charge it.... however this all goes very badly when the battery is fully charged and you will actually damage the battery if you push anymore current into it. To prevent this you use a Solar Charge Controller, a device which sits between the solar panel and the battery. This unit is able to regulate the flow of current to the battery and therefore prevent overcharging and also prevents the load from draining the battery too far which also causes damage. There are two main types of controller; PWM and the MPPT Controller. (Thanks for the correction Malkaris)
The first, PWM (Pulse Width Modulation) is better suited to low power applications (< 170W) however it is not capable of dealing with any over voltage generated by the solar array. In comparison, the MPPT (Maximum Power Point Tracking) charge controller is far better at optimising the output from the solar array and can deal with the solar array generating excess voltage which can be harnessed and used to improve charging efficiency by 20%-25% (under the right conditions). PWM has been around a lot longer than the MPPT technology and as a result is generally cheaper and are available in a greater selection of sizes and models.
With all that in mind, I opted for the PWM model and set about buying the other components I needed.
MPPT Controller: eSky Intellegent LCD 30A - £20.00
Solar Panel: 100w Pollycrystalline PV Panel - £70.00
Battery: 12v 35Ah Leisure Battery - £50.00
LED Strip: 5m 12v 5050 LED Strip - £12
Switch: 2 Gang Outdoor Switch - £7.00
Fuse Box: 4-Way Automotive Fuse Box - £6.00
Battery Lead: Ring Terminals, inline fuse and 'Anderson' connector - £5.00
Terminal Block: 4-Row Terminal Strip - £5.50
Panel Connectors: Generic MC4 Connectors - £5.50
Panel Mount: 4x Plastic Mounts - £13.99
Mounting: 10mm Plywood Sheet (400mm x 300mm) - £10.00
Backing Plate: 2mm Aluminium sheet (200mm x 130mm) - £3.50
Cable: 15A Red / Black - £3.00
Bolts: M8 Galvanised - £4.50
Misc: Fork Terminals & Spade Fuses - £2
Total Cost of build: £217.99
This cost can be reduced significantly if you chose a lower wattage panel & smaller battery capacity. I'm sure if you shop around some more on eBay most of the components could probably be found cheaper as well.
Step 2: The Build
For me, the fun part of this project was always going to be the build. I decided I wanted to mount most of the main components on a distribution board which could constructed and then be simply installed and connected in the shed. I chose to use a sheet of 10mm Plywood on which I laid out the controller, connection terminal blocks, fuse and fuse box. The controller itself came with a warning stating that the rear was actually a heat-sink and this should be considered when mounting. I first considered 'stepping' it away from the plywood therefore giving it an air-gap between the rear of the controller and the wood but finally decided to mount it onto a aluminium plate to help dissipate the heat. I cut the sheet about 15mm wider than the controller and rounded the corners (just for aesthetics), marked and drilled the four holes and then screwed it in behind the controller.
I drilled several holes in the board to allow me to run and feed the cable in from behind rather than cluttering up the front. Terminal blocks were placed in proximity to their controller terminals and the 'output' side of the distribution board situated to the right hand side. The output cable from the controller is passed through a hole to the rear of the board and then run out again above the fuse box.
From there I wired the switch (there was a reason for a 2-gang switch which I will go into later in the instructable) and ran the cable that would connect to the LED Strip and finally tacked it all in place. The shed is roughly 2.5m long so the 5m LED strip could be cut half way and mounted either side of the centre beam in the roof (and connected at the far end with a small piece of cable run between the two)
For the solar panel, luckily the shed faces north / south so one half of the roof was south-facing and therefore perfect for maximum exposure of sunlight. The panel was bolted to the panel mounts (using M8 bolts) and then bolted to the roof of the shed (again, using M8 bolts) with butterfly nuts to allow for easy removal. The mounts allow air to flow under the panel as well as channelling it over the top to reduce the risk of it being torn off in high winds. I constructed a cable with MC4 Connectors on one end to connect to the panel, and fed the other end back into the shed through a hole I had drilled. I then passed it from behind the panel through one of the holes and crimped on the fork terminals before attaching them to the terminal block. All other cables were prepared in a similar fashion.
The Anderson plug on the battery lead is quite an 'industrial' piece of kit! The pins can be crimped if you've got a tool that's up to the job however I used a small pencil blowtorch and soldered the cable into the pins instead.
Fuses are really important in a system like this. 12v systems aren't generally considered dangerous and are therefore perfect for this use; however there is a real possibility that a short circuit could cause a fire. As I've already said, the controller is able to deal with shorts in the output side but we should also make sure we protect the battery too. The lead I chose (see photo) to connect the battery to the charge controller has an inline spade fuse (which is currently a 10A). The output side also has a fuse to protect the lights from shorting damage too. Currently I am using a 5A fuse on that side.
Finally, using what was left of the sheet of plywood, I made a box to place the battery in as it was going to live on the floor, I wanted to protect it from wear, tear, knocks and bangs.
Step 3: Switching On
As soon as I plugged in the MC4 connectors to the panel, the charge controller came to life and started giving readings of charge rate, panel output etc.
It took a bit of fiddling around with the controller before I understood the settings.... unfortunately the manual that came with the eSky controller was lacking in its English translation!
I mentioned earlier that I'd chosen to use a 2-gang switch.... the reason for this is that I wanted to fit a second strip of LEDS that could be controlled independently..... a red set! I'm an amateur astronomer and it's a real challenge to set everything up in the dark.... however using a torch or turning on a normal light destroys the sensitivity of the eye... unless it's red light. Fitting this second strip means I can use the shed light to illuminate the area while I am setting up and even as a place to sit and remotely observe (using a laptop etc.) if it's really cold outside!
The one question I wanted answering when I was first researching this was 'How long will my battery last with the lights turned on'. This is actually far more difficult to answer than I first thought. Theoretically my 35Ah battery should be able to deliver 1A for 35 hours before its exhausted. The white LED strip draws 1.5A so this would mean about 23 hours of operation with a full battery. The problem is that these are just the theoretical values.... they don't take into account variables such as temperature & battery health which affect things massively. The other thing to consider is that lead-acid batteries don't operate anywhere near the theoretical maximum.... in fact at best you should expect about half of what is potentially possible. Saying that.... if it powered those strips for 10 hours, I'm happy with that!
Charging performance also relies heavily on external variables, not least the need for direct sunlight. With this in mind it follows that your battery will charge much better in the spring / summer months than during the rest of the year. Charge time is very difficult to calculate and until I have a monitor installed I can't say how this rig performs.
Step 4: Future Expansion
I am planning several more instructables covering a home automation and monitoring system I am currently implementing. One module of this will be a solar charge monitor which will feedback information about current battery charge, panel output etc. from this system. Once I've finished it, I will link it back to this instructable for continuity.
I am also looking into using the battery to power a mains invertor to allow 240v operation of some items of equipment for short periods of time.
Step 5: Any Questions?
That's about it for this first instructable from me. I hope that you've found it useful and would ask if you think I've missed anything, have something wrong or have any general questions, please don't hesitate to ask in the comments section below.