Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Solar Systems
9 August 2013, 19:01,
Rainbow  Solar Systems
For those of you who may be curious about how I designed my solar set up. It won't be to everyone taste or needs but, as I like to have a play at such things, it'll hopefully give some insight to a solar back up system.

[Image: pv2.jpg]

[Image: pv4.jpg]

[Image: pv8.jpg]

I've designed my system to be flexible ie so I can, with a flick of a switch, change the charging path of selected solar panels to whichever of my four separate systems I want (one 12v system, two 24v systems and one 48v grid tie system). I'm going to only give a basic outline cos I don't want to bore or put off anyone with tons of detailed info. I encourage any questions/suggestions/constructive criticisms. With electrics, there is no such thing as a silly question, electricity can kill so better to be safe than sorry!

I suppose in the interests of legalities I've got to say that any information, advice or recommendations are to be checked by a qualified electrician if there is any doubt what so ever.

Some basics first that you need to know.

- voltages above 50v are deemed dangerous and can kill so 230v ac is to be treated with respect!
- voltages below 25v ac or 50v dc are relatively safe so touching your 12v battery terminals shouldn't shock you
- for battery banks, you need ultra deep cycle batteries, cheapie car batteries are false economy
- you have to have a controller for charging your battery bank from your solar panels
- solar panels have to match up ie DON'T mix n match different panels of different ratings
- solar panels come in different voltage ranges, decide on 12v or 24v setup before you start buying
- site your solar panels in a southerly direction with no shade obstruction from trees/buildings etc if possible
- know what you want powering so you can choose the right inverter ie modified or pure sine wave
- know your power requirements so you can design your system to cope with your power demands
- DON'T underestimate the currents on low voltage systems, cable size is of utmost importance!
- ALWAYS protect ALL circuits with fuses so that any hic ups are protected without unnecessary damage!
- grid tie inverters must be G83 certified as a minimum requirement
- grid tie system will NOT back up your house in the event of grid failure

For a typical solar powered back up system you will need:

- solar panels
- controller
- battery bank
- inverter
- pv cables/MC4 connectors/protection fuses

I would highly recommend that you plan for a 24v set up. This will halve the current to and from the battery bank compared to a 12v set up. To give you an idea what I'm talking about, for a 1kw fire to be powered by normal mains 230v, you can do it on 1mm cable which only has to take around 4 amps. Matter of fact you can power two 1kw fires with this scenario. However, if a 12v system has to power a single 1kw fire, you'll be talking around 80 amps and have to consider 25mm cable! For those who don't know, this is equivalent to the size of cable going to your mains meter/fuse board ie it's huge and expensive. BTW, most solar panel controllers usually handle both 12v and 24v systems automatically so no worries there.

Remember your school days?

V = IR or (volts) = (current/amps) x (resistance)
W = VI or (wattage/power) = (volts) x (current/amps)

Originally, I planned a small 12v system having an entirely independent 12v circuit in the house to power 12v led lights, car radio, phone chargers, tv, etc. All very well but in reality, a 24v set up will give you so much more flexibility through an inverter though, inherently, it's not as efficient. You really need to have a good idea what you want out of a back up system. This will ultimately dictate what stuff you have to get.

So, the simplest and cheapest set up is a single low powered 12v solar panel going straight to a small standard 12v controller going to a single 12v car battery to power either small 12v items or a small modified sine wave inverter for a very low powered mains supply.

So, how much for the cheapest basic set up?

- 10W solar panel with crock clips here £18.99 delivered
- 10A controller 12/24v (this is not PWM or MPPT, more on that later...) here £8.99 delivered
- 12v car battery, new you're starting at about £35 these days as the lead prices have rocketed but have you got an oldie but goodie lying around?
- 12v inverter 150W modified sine wave here £13.95 delivered. You'll have to chop off the car adaptor and fit some crock clips to the leads to attach to the battery. This one is at least colour coded so you don't get the polarity wrong.

So, if you have an old but usable battery knocking about already, this lot will be delivered to your door for £41.93. Double this if you have to buy a new battery.

I do NOT recommend the above, it's just to give you an idea where it all begins. This lot, power wise, won't last you two seconds.

NB/ you can get mega cheap non-controller solar panels that clamp straight onto a battery but they're for sustained trickle charging only and not for keeping a working battery healthy.

The other end of the scale, you can spend well in excess of £10,000 of your hard earned on a professionally installed system without lifting a finger, except to sign the cheque of course.Rolleyes

If you're like me, you're somewhere in between, it's just a matter of where.

The system I'm finding really versatile is my main 24v set up using:

- up to 5 x 24v 250W (= 1.25kW max) solar panels (switchable so I can have anywhere between 2 - 5 panels connected at any one time)
- 60A PWM (MPPT type also good) controller
- 6 x 12v 125Ah ultra deep cycle batteries (ie 3 x 24v)
- 2kW pure sine wave inverter

From memory, this lot cost me over £2,200 but that does include cabling, connectors, specialised tools, roof rails and brackets, meters, etc, etc. Expensive, I know, but it can back up the whole house if the grid goes down (not the likes of kettles, electric showers etc) and heat our hot water. It should last many many years if treated properly. Solar panels have a life expectancy in excess of 20 years, batteries (if the "depth of discharge" [DOD] is kept shallow) I reckon should be good for at least 10 years, the inverter and controller (if not abused and decent quality) again, 10+ years.

Worth noting the obvious that energy prices will only continue to climb as demand becomes more intense and supplies become more depleted. I estimated that my system will pay for itself within about 2 years. After that, it's all free energy. Also, in the event of SHTF, energy-wise, I should be in a better position than most, whether that's a good thing or not I don't know.

NB2/ Batteries. All batteries are lead acid. The difference is in the construction. In general, the Lead Acid battery is made up of plates, lead, and lead oxide (various other elements are used to change density, hardness, porosity, etc.) with a 35% sulfuric acid and 65% water solution. This solution is called electrolyte which causes a chemical reaction that produce electrons.
The Gel Cell and the AGM batteries are specialty batteries that typically cost twice as much as a premium wet cell. However they store very well and do not tend to sulfate or degrade as easily as wet cell. There is little chance of a hydrogen gas explosion or corrosion when using these batteries; these are the safest lead acid batteries you can use. This is why I keep my AGM battery in the garage, very little explosion risk. The other batteries can leak explosive fumes and are kept outside in a vented enclosure.
Lead acid batteries include the starting battery in your car. They also include deep cycle batteries that have thicker plates than starting batteries. Thinner plates (in the electrolyte) can deliver higher current, necessary for starting loads in a motor vehicle. Thicker plates are better suited to long slow discharges which is why they weigh a ton.
The Absorbed Glass Matt (AGM) construction allows the electrolyte to be suspended in close proximity with the plates active material. In theory, this enhances both the discharge and recharge efficiency.
The gel cell is similar to the AGM style because the electrolyte is suspended, but different because technically the AGM battery is still considered to be a wet cell. The electrolyte in a GEL cell has a silica additive that causes it to set up or stiffen. The recharge voltages on this type of cell are lower than the other styles of lead acid battery.

NB2/ DOD or "depth of discharge" for deep cycle batteries. This is the amount of charge you take away from a battery when using it. AGM deep cycle series offer approximately 250 cycles @ 100% DOD, 500 cycles @ 50% DOD and 1250 cycles @ 30% DOD. If a voltmeter's connected, I personally never want to see a battery go under 11.9v (24.0v for 24v systems) when under load. You can go much lower but you shorten the battery's life span. Nice thing about inverters is that they have a cut off at a certain low voltage to save your batteries :-) Here's an example of usage:

say you've got a load connected to your 100Ah battery which draws 5 amps. Working on 50% DOD, 50% of 100Ah = 50Ah, 50Ah/5A = 10 hours usage. You can easily double this time by wiring two 100Ah batteries in parallel and so on. Most manufacturers I've seen quote 500 recharge cycles at 80% DOD. Only do 20% DOD and the recycling can jump up to 2,500 cycles!

PWM and MPPT Controllers. Basic controllers seem to just pass all available charge to the battery and stop when they reach a certain voltage although I suspect some will even over charge. PWM (Pulse Wave Modulation) controllers are the next step up. They monitor and regulate the battery far better by varying the charge pulses/voltages as the battery becomes recharged. This, in effect, prolongs the life of a battery and is far more efficient. MPPT (Maximum Power Point Tracking) is better yet. Here it converts high voltages from solar panels and converts the charge to more amperage. This means that the charge voltage can be kept at an optimal level while the time required to fully charge the batteries is reduced. It's worth noting that you get what you pay for eg the 60A PWM controller I have for one of my systems was expensive but can be programmed to suit whatever battery type I use, cut off voltages I want and monitors all that's going on etc.

Inverters. Two types, modified sine wave and pure sine wave. Modified are electronically manipulated waves that are squarish in nature so basically more on/off in it's voltage delivery whereas pure sine wave is what you have in your house mains ie a smooth curved wave which is gentle on your electrical items and not abrupt. There are some items that don't like modified sine waves and can be damaged by them like power tool chargers. The big difference is in price, basic modified sine wave inverters are only a fraction of the price of a proper pure sine wave inverter which will handle anything.

Solar panels. Here you have to know what you're planning. There are panels that are only for 12v outputs and panels that are only for 24v outputs. You can wire two 12v panels in series to give 24v but forget about knocking a 24v panel down to 12v without a lot of hassle. Very important to match up your panels, not only in voltage but in ampage. One unmatched panel can and will affect the whole system adversely. The electrical law here is thus:

Panels in series, add the voltage of each panel, but limited to the lowest amp panel in the string.

20V/3A + 12V/4A + 22V/6A + 18V/4A => 216W ie 72v x 3A (the lowest ampage panel). You are wasteing the watts from the higher amp panels.

Panels in parallel, will drop to the lowest voltage panel but the amps will add.
example (same panels):

20V/3A + 12V/4A + 22V/6A + 18V/4A => 204W ie 12V x 17A but you are wasting the volts of the higher panels.

throw away the 12v panel and you get:

20V/3A + 22V/6A + 18V/4A => 234W ie 18V x 13A The next highest voltage factors into your calculation.

So you can see, it's not just a matter of buying any panel and connect to any battery with any controller or use any inverter!

Congratulations if you haven't fallen asleep yet! I'll stop here to see if I've put everyone off...Rolleyes
I'm NOT political so DON'T correct me!
9 August 2013, 19:34,
RE: Solar Systems
Excellent Nix, well done. That was a lot of work I can see.

Well I scan read it and have just cut and pasted it int o a word doc for archiving and also so I can read it off line. (Power is a bit on and off up in the hills today)

Cheers mate
72 de



STATUS: Bugged-In at the Bug-Out
10 August 2013, 15:21,
RE: Solar Systems

Weather - depending on where you live, what season you're in and the weather will dictate what you get out of your solar panels. On a dark damp short winters day, you'll get very very little power, a mere trickle charge. In contrast, on a long sunny summers day, you'll have so much power coming in, you won't know what to do with it! On days like we've been having recently, by late morning I've got the immersion tank full of boiling water, all the batteries fully topped up and the grid tie inverter doing it's best to make the meter spin backwards at a high rate of knots!

MCS - Microgeneration Certification Scheme, this is the mark of quality and demonstrates compliance to industry standards. You don't have to get MCS panels but, given the choice, it's probably best to do so as they've had to meet certain standards. Recently there's been issues raised by the EU over the Chinese dumping their cheap panels and under cutting ones made in the EU. They wanted to levy a dumping tax to make them more expensive for the likes of you and me. Long story short, it looks like they've finally sorted it out between them and we can continue to buy at a reasonable price from China. Don't be put off by the Chinese stuff, they are just as good as EU ones, most with MCS accreditation and much cheaper!

MC4 - these are the weather proof connectors for your panels. Don't skimp here cos they're not that expensive and could save you a lot of hassle if a non waterproof connection goes duff and you're contemplating going up on the roof when it's snowing and -10 outside!
[Image: 75410_image.jpg]

Solar Panel Mounting - this is where many will hit a brick wall. For me, going up alone when it's freezing cold and start drilling holes in a perfectly sound slate roof went against all my instincts! But then again, I've not always been that bright. [Image: tongue3.gif] To comply with your house insurance (which these days seem to automatically include roof mounted solar panels), you must roof mount securely ie bolt into the principal rafters will do nicely. BTW, these 250W panels are heavy (about 50lbs each) and awkward to man handle up ladders. It was the only time I had to rope in a mate to give a hand, no way I could do it alone. Oddly enough, the biggest danger with roof systems is the force of the wind trying to suck those babies up rather than any weight issues with the panels themselves. Re the mounts, again, don't skimp! You want proper secure mounts that are corrosion proof and made for the job.

Alternative to roof mounting is mounting on a frame on the ground. Nothing at all wrong with that and if you've got an ideal secure place, go for it. They may be more vulnerable to theft or other issues but they'll be a dream to maintain and you can even make a swivel mount so you can follow the sun if you are so inclined!

Last but by no means least, you can have a portable set up that you can take in at night and put out during the day. These will inevitably be small low powered foldable units but if your requirements are small then why not?

Grid Tie - as I mentioned before, grid tie inverters must be G83 compliant to make sure you and others are safe. G83, amongst other things, ensures that if the grid goes down, it will disconnect and not electricute some tired engineer trying to get the grid back up. Important to note that grid tie inverters rely on the mains being on to work. If the grid goes down, so does the grid tie inverter, you get nothing from it. I fitted one to use my excess energy and save on electric. If you have an old style meter ie the disc that goes round and round then you should find your meter going backwards on sunny days! Recent smart meters don't do this. Very grey area with respect to legalities but a lot of people do it. Energy companies don't like this cos it'll eat into their miniscule profits and are reduced to eating only bread and drinking only water.[Image: doh.gif]

Switches and Fuses - although controllers and inverters have their own protection for circuits, it's a must that you fit your own fuse from the battery in case of a short. DON'T underestimate the power from a little battery, it can cause a fire just as much as mains! Also good idea to fit an appropriate isolation switch (ie a switch with the correct ampage rating) so you can conveniently turn off the system for any maintenance work. My teenage daughter last week accidently plugged in the vaccuum cleaner into my 12v to mains system and melted one of the switches! It was carrying 110 amps (12v side) and it was HOT! What annoyed me was that the plug from the inverter had a 3A fuse (230v side) that didn't blow despite passing double the ampage. Lesson learnt, now all my systems will have in line quick blow fuses direct from the batteries.

I suspect that I may have put too much info up here and people will think it's too complicated or expensive and not bother. Please, it IS worth it. Whatever your budget, you can at least get something going to keep your mobile phone charged and some LED lights burning all through the night if need be. At the end of the day, you're connecting a solar panel to a controller that is attached to some batteries. That is then connected to an inverter for your mains back up. It's just a matter of how big a system you want/need. You can always start small and build on it.

Simples! [Image: grin.gif]
I'm NOT political so DON'T correct me!
10 August 2013, 17:35,
RE: Solar Systems
not had time to read this yet but after a quick skim I'll definitely be reading it in detail once I get back from the In Laws
25 September 2013, 16:58,
RE: Solar Systems
(10 August 2013, 15:21)Nix Wrote: ...

I suspect that I may have put too much info up here and people will think it's too complicated or expensive and not bother. Please, it IS worth it. Whatever your budget, you can at least get something going to keep your mobile phone charged and some LED lights burning all through the night if need be. At the end of the day, you're connecting a solar panel to a controller that is attached to some batteries. That is then connected to an inverter for your mains back up. It's just a matter of how big a system you want/need. You can always start small and build on it.

Simples! [Image: grin.gif]

Great and easy to understand first hand explanation Nix. Thanks for sharing your knowledge.

Not too complex IMHO, very well balanced.

On the strength of your recommendations I have this afternoon ordered a significant value of components to get a serious PV system in place here.

Especially useful was the battery advice. Without it I would surely have gone for Lucas branded cells, and would have been an expensive mistake.

A question though. In mid winter, cloudy conditions what is the typical output you see from each of your 250w panels? I have to deal with quite cold conditions here and am trying to gauge expected power available taking account of reduced panel output and increased internal losses in the accumulators.

Again thank you.
72 de



STATUS: Bugged-In at the Bug-Out
25 September 2013, 17:15,
RE: Solar Systems
Thanks - I was bemused by the photos which showed a couple of ladders.
I'm surprised that the Health and Safety Mob didn't demand scaffolding
like they did on mine :-)
25 September 2013, 17:56,
RE: Solar Systems
As I did it myself, there were no H&S people knocking about.

Photos were only intended for "during" and "after".

Did any of that blurb help btw?
I'm NOT political so DON'T correct me!
25 September 2013, 18:01,
RE: Solar Systems
(25 September 2013, 17:56)Nix Wrote: Did any of that blurb help btw?

Yep, 24 carat quality blurb Nix :-)
72 de



STATUS: Bugged-In at the Bug-Out
25 September 2013, 20:13,
RE: Solar Systems
(25 September 2013, 16:58)Lightspeed Wrote: In mid winter, cloudy conditions what is the typical output you see from each of your 250W panels? I have to deal with quite cold conditions here and am trying to gauge expected power available taking account of reduced panel output and increased internal losses in the accumulators.
There are different technologies of PV and they vary quite a bit in terms of how much power they can create in winter but the short answer is expect in the region of 1% to 10% of full rating! (Yes it can be just a few percent)
Cold should actually improve the performance of the panels a few percent (of output, not of rated) but the batteries dislike cold more than the PV like it.
Increased losses in the system should be negligible.
Doctor Prepper: What's the worst that could happen?
25 September 2013, 20:50,
RE: Solar Systems
Out of curiosity, is there any way we can help to protect our batteries during the winter months, to ensure we get the best out of them,.... without putting central heating into the shed
A major part of survival is invisibility.

Forum Jump:

Users browsing this thread: 1 Guest(s)