Simple Solar Panel Help Please

Danno2k

Hello everyone, i hope everyone is safe and well in this bad time we have at the moment
Hello i need some help on this project i was hoping to do, been after doing this for sometime now 2 years +
What my goal is to run a solar system, just to power my home lighting, but unsure on what i really need to buy or do ?
I would like to run some panels and place them in my garden (ground mount) south facing and connect to my consumer unit
I don't want grid tie just want to power my own lighting
What i would like is something like this, This is where i need your help please
So at the consumer unit, add a new wire just for the lighting to a new switch ? that i can turn to say solar or mains (this should be possible) i hope lol
Then at the new switch back to the panels 
The goal is just to run the lighting only, now i don't know what i need, off grid inverter ? and what switches etc
I'm sure some of you must of done this 
All the lights in the house are about 7 to 20 watts, all the house on the top side 200 watts ? 
Been looking at panels and battery's here are what i was thinking 
flee bay
12V 120ah DEEP CYCLE LEISURE Battery  £69.95
Solar Panel 310W Monocrystalline   £155
Any help on this project would be really great full
Thanks 

Martyn1981

Hopefully someone who knows what they are talking about will be along soon, but till then, I'm guessing at lots of problems.
If you connect to the home CU then you'll need to have a certified GTI (grid tied inverter) for DNO compliance, and declare your PV install.

If you separate the lighting circuit, and only run it off the batt, then that might be OK, but will the battery always have enough charge, especially in winter. Also, can you get lights that run DC, otherwise you'll need an inverter between the battery and the lights.

Totally respect what you are trying to do, but you might find that the costs never repay, and some other form of saving / green investment might be better?

Hopefully this is easier than I think, best of luck.

Danno2k

Hello thanks for the reply 

Yes i was thinking of a off grid inverter, i have seen the Triron Inverter which seems cheap and has good reviews
I though it would of been cheaper to setup DIY than get a full system as i only need lighting 

Thanks again 

Undervalued

No experience of solar panels but I do use similar batteries with a comparable load for another purpose.

200 Watts at 12 volts is about 17 amps but that assumes your inverter that steps it up to mains voltage is 100% efficient which I very much doubt. If you are installing a separate system would it be better to install 12 volt lights so as to avoid waste? However you would of course need much heavier weight cable due to the higher current at the lower voltage. Which is better would probably depend on the length of the cable runs etc.

The batteries I use are of a similar capacity, and are rated to be able to supply 25 amps continuous for 3 hours without dropping below 12 volts. So the whole 120 Ah are not really available to you! So, even without any waste you could probably only draw 200 watts for around four hours. Even if that is OK, how many hours of decent light would you need to fully recharge?

Martyn1981

Danno2k said:

Hello thanks for the reply 

Yes i was thinking of a off grid inverter, i have seen the Triron Inverter which seems cheap and has good reviews
I though it would of been cheaper to setup DIY than get a full system as i only need lighting 

Thanks again 

Sorry to be thick, just trying to visualise this. So you have your CU with a light circuit, and the wiring running out to the lights. You intercept that wiring and insert a switch which is mains only, or battery only. Is that right? So the batt/inverter are never actually connected to the CU (and hence never mains / grid tied) they only 'sneak' in to power the lighting circuit when the CU connection is effectively broken by the switch?

If that's anywhere near close, then I see what you mean, and is probably possible. Not sure if it's practical / economic though.

You could build a small ground mount (shed roof etc) PV system, even if only a few panels, then run that with a small GTI or micro-inverters straight to the CU. I appreciate that it wouldn't power the lights, but it would reduce import all the time it's generating, and probably increase your leccy savings, whilst removing the complication of the battery.

Martyn1981

BTW, for help figuring out potential generation you can use PVGIS. I've just stuck a pin in Oxford with optimal pitch and orientation, and for 1kWp of PV you will get, on average per day, 1kWh in December, and 4kWh's in June/July. So that might help you work out how much PV you'll need to meet any particular household demand. Note those are averages, so for December expect somewhere around 0%-200% and July 50%-200% on most days.

Danno2k

Ok great, thanks for the info 

Danno2k

So just a quick update

So every bulb in the house totals = 148 watts, but i would never ever have every bulb on, real would be more like 60 watts for around 5 hours a day, Less in summer 

All the are led, some are 5 watt, some are 7 watt.

So if say i had 2 of them solar panels i said 310 x 2 = 610 watts and say 3 battery's in parallel = 360AH, this should be enough for my lighting needs ? And with 2 panels it should charge fast 

Thanks

Ectophile

You might want to do some sums before you spend hundreds of pounds on this.

Assume 60W in LEDs for 5 hours a day.  Assume electricity is around 17p/unit. Then ((60 x 5) / 1000) x 0.17 = £0.051.

Your system will save you about 5p per day.

To get the thing to work, you need a solar panel, a battery, and a charge controller.  Then you either need to convert your house lighting to 12V, or you need an inverter.  Plus wiring and switches.  I reckon if you could get the whole lot for £250, that's a payback period of 13 years.  Except the battery won't last 13 years, so you need to account for replacing the battery from time to time.  Even if you only replace the battery once, that goes to to more like 16 years.

Danno2k

Ectophile said:

You might want to do some sums before you spend hundreds of pounds on this.

Assume 60W in LEDs for 5 hours a day.  Assume electricity is around 17p/unit. Then ((60 x 5) / 1000) x 0.17 = £0.051.

Your system will save you about 5p per day.

To get the thing to work, you need a solar panel, a battery, and a charge controller.  Then you either need to convert your house lighting to 12V, or you need an inverter.  Plus wiring and switches.  I reckon if you could get the whole lot for £250, that's a payback period of 13 years.  Except the battery won't last 13 years, so you need to account for replacing the battery from time to time.  Even if you only replace the battery once, that goes to to more like 16 years.

Now you have it like this, it's not worth it then really 

Thanks to everyone who has posted and your time

Keep safe

Undervalued

Ectophile said:

You might want to do some sums before you spend hundreds of pounds on this.

Assume 60W in LEDs for 5 hours a day.  Assume electricity is around 17p/unit. Then ((60 x 5) / 1000) x 0.17 = £0.051.

Your system will save you about 5p per day.

To get the thing to work, you need a solar panel, a battery, and a charge controller.  Then you either need to convert your house lighting to 12V, or you need an inverter.  Plus wiring and switches.  I reckon if you could get the whole lot for £250, that's a payback period of 13 years.  Except the battery won't last 13 years, so you need to account for replacing the battery from time to time.  Even if you only replace the battery once, that goes to to more like 16 years.

I certainly agree with that. In fact I would have thought that the battery lasting 6.5 years was optimistic.

As I mentioned, I have no experience of solar panels (although quite a bit with the batteries). Are the panels realistically likely to last that long and still give an adequate output?