One Man's Adventures into Renewal Energy
Please help me to continue hosting this website & associated costs by donating £2.
In return, I'll email you a ZIP file containing arduino code + all images from the website + some extra ones that aren't on the website...all in high res (370MB of pics!).

Solar Shed Introduction

15th July 2013

It pains me to say it, but after much discussion with the missus, it has been decided that our garden isn't really big enough to accommodate the Solar Tracker I've built.
If I went ahead and installed it, along with two 250w panels, it'd be massive and would take up a quarter of our back garden.
Coupled with the fact we've got two young children running near and around it, it's simply not a good idea.

I am sad about this, but alas, I haven't given up on Solar.

So to satisfy my desires to generate electricity with the sun, I've gone down a more simplified off-grid solar system for my shed.
It won't be too complicated, but it must satisfy a few requirements -
I hope to do all this relatively cheaply, and not too concerned about getting a return on investment...I'll be happy if it just works!

I'm also going to build an Arduino based Solar Monitoring system, that'll monitor various elements of the system.

Like the Solar Tracker, I'll detail every step of the journey on this website.

Shed Solar Panel
Here is the Solar Panel.

It's a 20 watt monocrystalline panel.
I paid £35, including P&P from Ebay.
It feels good quality and well made.

I found some plastic angle brackets in my garage and screwed these to the panel, which were in turn screwed to the shed roof.
You'll notice I've left the panel about 5mm proud of the roof - this is to allow some airflow behind the panel, as it's my understanding that the hotter a panel gets, the less efficient it becomes.

Shed Solar Panel
Here is a side on view.

You can get a better feel for the proudness of the panel.
Saying that though, it maybe doesn't stand proud as much as I'd like. I may increase it to allow more airflow, but I'll see.

You also see in this picture some neighbouring trees.
These trees are very tall and do have a detrimental effect on the panel in regards to shadows.
However, the panel does receive light from 9am all the way through to 4pm, when the shadows start to hit. That's a good 7 hours of sunshine!

Solar PWM Charge Controller
The Charge controller I'm using.
Only cost me £10 from Ebay, but appears to do a superb job.
10 amp version - which will easy handle the 20 watts from my panel, and could easily handle 100 watts if I choose the increase my solar panel area later on.

It's a PWM (Pulse Width Modulation) model, which means it constantly monitors the state of the battery and adjusts the charge current depending.
IE - If the battery volts are low, it pushes more current through to the battery.
If the battery volts are high, it reduces the current and goes into 'float' mode - basically a trickle charge.

This model is also quite clever in that when it detects the battery has become full, it goes into a 10 minute overcharge setting. This overcharge essentially over charges the battery for 10 minutes. This has the effect of cleaning the lead plates of Lead Acid batteries, aka 'desulfation'.
This means you can fit some pretty old knackered batteries to the charger and the charger could, over time, repair them...allowing them to hold more charge, for longer.
I did have the pleasure of catching the charger during this 10 minute over charge stage. You could actually hear the battery ticking as it was being pulsed with a higher charge.

The charger also has some very informative lights -
Solar State - Green when juice coming from the panel, off all other times.
Battery State - Red/Yellow/Green - depending on the state of the battery.
Load State - Green when load is on, off all other times.

You can also set an adjustable timer within the charger for when the charger detects no volts coming from the panel(no sunshine!).
I've set mine to one hour - so for one hour after sun has gone down, my garden lights come on.

For £10, it's a pretty neat little charger and I'm impressed.
You can get better ones, MPPT (maximum power point tracking) for example, but they're a lot more expensive and not really warranted on the scale I'm working with.

PWM Charge Controller Battery Setup
The batteries I've got hooked up.

A 12 volt system, connected in parallel.

Nothing special here -
One is a motorcycle gel type battery rated at 19ah
The other is a standard car battery - probably around 50ah

A friend of mine had these languishing in his garden. To save him the trouble of disposing, I gladly took them off his hands.

When I got them and checked the voltages, they were in a pretty poor state. The 19ah battery was at 10v, the 50ah was at 7v!!!
Now this is where it gets interesting - Everything I've read on the internet suggests that when a lead-acid type battery goes below 10v, it's beyond repair. The suggestion is that it simply will never hold a charge again.
Me being the kind of person to persevere, I'm willing to let my little PWM charger have a go at repairing them with its 10 minute overcharge mode.
I'm hoping, with enough sunshine, and enough time, the batteries will go through many desulfation cycles over the next few months, which will get them back to a reasonable state.
I'll report back on the progress of this in a few months time.

In terms of capacity, I've used some basic calculations -
My lights consume 25 watts of power
I've used 50Ah as a conservative estimation of my battery capacity.
So for a 12volt system, 25 watts = approx. 2 amps.
Leaving the battery with approx. 50% capacity (you never want to completely discharge your battery).
2 (amps) x 10 (hours) = 20 amp-hour runtime before battery gets near 50% charge.
So I'll get 10 hours of runtime before my batteries are drained.

So based on the fact I only run the load (garden lights) for 1 hour a day, I'll get 10 days before my batteries are drained.

A good bright 7 hours worth of sunshine will feed 4.5 amp-hours into my batteries, effectively filling back up the batteries from the previous nights consumption + another 2.5 amps extra.
But in England, 7 hours of good sunshine is simply not gonna happen every day. The big test will be on the dark winter days' - but we'll have wait and see for that.

I plan on purchasing a 1500w Pure Sine Wave Inverter, which I'll install in my shed.
Primarily, I want to be able to mow my lawn using the power of the sun...and that's why I need the inverter, to convert the 12 volt battery system to 240 volt.
I'm struggling to find an inverter of this size for anything less that £100 - and I simply can't justify paying that amount of money on my crazy scheme, but I do have lots of alerts on various auction sites, in the hope of finding a watch this space!!!

28th July 2014

100watt Solar Panel
A number of people have asked about my 100 watt panel.
So here is a pic of it mounted on the back of my house.
This panel, in addition to my 20watt panel mounted on my shed roof, gives me a total of 120watts.
I bought this 100watt panel from Ebay for around £75. Brand new.
I took this picture in the morning and you'll notice heavy shading. This panel really only gets going around 1pm when the Sun comes round...but gets good sunlight all the way through to 7pm.

Solar Shed Battery Bank
Here is the latest pic of my battery bank.
I've now collected a number of sealed lead acid batteries from various sources.
I reckon I've probably got around 40ah worth of Sealed Batteries. In addition to the 43ah car battery on my mower, I've now got 83ah total.

The picture doesn't show great detail, but you'll notice I have two bus bars at the top. One positive, one negative. These make it really easy to add batteries.

You'll also notice the Arduino and relay unit sitting on the top shelf.
You'll also notice the huge car battery I had (see 4th pic from top, above) has gone.
This is because it was below 10v when I hooked it all up and I was hoping to desulphate it. Long story short, it didn't work, so I dumped it.

Next - Monitoring my Solar Shed


Robert - 02/06/2014 07:45:34
I also have a solar shed! i have 3 12v 8ah in parallel on a 20w panel. i am currently repairing a 24v lawn mower that i will just place the batteries into when needed. in the future i plan to wire a pair of relays so that i can charge @12 and run @ 24v. Just some food for thought!

- 14/11/2013 08:34:23
Hi Rav - Yes, I increased the size of my panel array. I have been meaning to get around to updating the website with pics....just haven't had chance yet.

Rav - 13/11/2013 17:34:39
Hi, Just reading your brilliant project "Shed" - Just a little observation though, on your Stats page, you state that your Solar Panel is 120W, but in your introduction, you note that it is a 20W panel that cost you 35. Regards, Rav

- 02/09/2013 14:26:11
Thanks Mike....I'll have a look around for one :o)

Mike B - 28/08/2013 09:07:29
Depending on the lawn, the B&D "Lawn razor" if still around would be a good start ??

- 27/08/2013 09:57:26
Hi Mike. Thanks for your question. I have been contemplating the lawn mower situation and decided instead that I'm going to make a 12volt lawnmower. I just need a donor lawnmower for the base and a reasonable power motor. Watch this space - I'll keep you all updated with this.

Mike Blake - 25/08/2013 08:47:05
Have you done the maths on the inverter ? You would have no chance of powering the trimmers etc. with the panel you have.


Email Address (won't be shown)

Human Check - What colour is the sky?


Copyright 2020