Topic: Some Solar System Questions

Some Solar System Questions 

Hi,

After reading the Solar Panels In a Cow paddock article here, I decided that that would be the best way for me to install my solar panels so I don't have to climb on the roof :)

What angle should I set the panels? Where I will be living the latitude is 34.7 degrees north so should I set it to be 40 - 44 degree angle? I read that for best winter collection, solar collectors should be installed at an angle 5 to 10 degrees greater than the angle of latitude at your site. 45 degrees would be easier!

If all I have is an old fridge with a freezer on top, lights, a phone and a computer how many solar panels would I need to run them? I would not run the computer full time, maybe a couple of hours a day. The fridge obviously all time and the lights at night.

I currently have 2 panels - I think they are 90w each - and not installed as well as a couple of deep cell batteries and wired solar box - done when I was going to set up a few years ago, then I went traveling and didn't get around to it! So I have forgotten the specs and won't be able to check them out until next month when I return from traveling and pick them up.

Any other things you think I need to know, please add.

I do have power to the site, not connected at the mo, and would like to not have to get it connected if possible :D

Thank you for your time!

Re: Some Solar System Questions 

How old are the deep cycling batteries, and have they been pampered the whole time you have been travelling? If they haven't been "pampered" for a few months, they are probably no longer batteries but very heavy door stoppers.

An old fridge with a freezer on top probably needs about 1.5 or 2kWh a day - maybe less if it is small but "OLD" doesn't help things. You need to size the panels depending on how many days of no sunlight you want to design to - I have seen systems designed to between 2 days no sunlight (stupid) to 22 days (OTT), and then work out how many Wh (watthours) or Ah (amp hours - watthours divided by 230V) that means - 2kWh a day x 5 days no sunlight say would be 10kWh storage, and for a deep cycle battery to not go below 50% discharge would mean battery size of 20kWh or 87 Ah.

Panels would be 10kWh divided by 4 peak sun hours a day average for the whole year in NZ: so that means 2.5kW - about 30 panels of 90W, and about $3.5k to $8k depending on who is selling! (Suggest you go see an off-grid supplier about a different fridge!!)

But this is not the full story: your battery bank needs to be large enough so that the inverter can draw a large current when the fridge compressor starts up - special off-grid equipment tend not to have such a demand compared with stuff you buy in the regular shops. I have recently had the experience of trying to start a standard, new, small chest freezer through a fully charged battery bank (large-ish but obviously not large enough), through a 2kW inverter, and absolutely nothing happened - the freezer compressor motor simply could not start.

Seeker

Re: Some Solar System Questions 

Oops - panel size calc is wrong - should be less. Your lights and computer won't use much if you are careful about turning things off.

Try this instead (step by step calc):

Re: Some Solar System Questions 

You may find this Wairarapa couple's site of interest - http://thecrateoutdoors.blogspot.co.nz/

Re: Some Solar System Questions 

Thank you seeker for all your advise - I now am guessing that I have very heavy door stoppers :( Oh well, live and learn!

I really appreciate your calculations and at least now I know I need to:
a) get another fridge
b) get at least another 4 panels - they have to be an even number?
c) 2 batteries @ 12 volt 130 ahr which would be more than enough for the 147AH from post 2 above?

Also, do I get 12 volt panels or can I get say 2 24volt panels?

Do all of the panels have to be the same watt? I see that 190w panels are about $500 so a couple of those with my other 2 would reach the 5.1 minimum :D


Cam: Thank you for that link - I appreciate you taking time out to post such a great blog! :D

Re: Some Solar System Questions 

Hi Kainga

The number of panels do not have to be even - but actually depends on how many panels you have in each string, an how many strings in parallel.

A "string" consists of a number of series connected panels, and this is where you determine the voltage of your PV array. So if your panels are nominal 12 V (this usually means they actually operate at between 14V and 16V), then 2 panels in a string would mean a nominal system voltage of 24V. If you have nominal 24V panels, then 2 panels in a string would be nominal 48V - your system voltage. I use 120V commercial panels, so a string of 2 for me would be 240V d.c.

Once your system operating voltage is set, you basically have to double up on the number of strings to give you the actual required output from the array.

With regards different wattage panels, I have heard that systems which have different panels wired together don't work well, even when the panels have similar specs but are from different manufacturers.

If you get an inverter that has inputs for more than one array, then you can have different wattage panels on each leg into the inverter - think this could mean a more expensive inverter though.

There is something else to consider here: once you have your system, you tend to want to put more things onto it. So you have to do some forward planning. The major issue is that batteries must be matched - you cannot increase the size of a battery bank incrementally - a new one added to some old ones would not work well.

Perhaps you could email/talk with Independent Power in Albany about what you want to do - they sell all of this off-grid stuff and is where I bought the super insulated freezer I use. I'm sure there are others I just haven't dealt with them. Also have wander around www.rpc.com.au - I remember seeing some d.c. fridges on the website.

Seeker

Re: Some Solar System Questions 

thank you seeker for that and the Independent power in Albany - http://www.independentpower.co.nz/ I will contact one of their dealers closer to my area :D

I appreciate all of your help and time :D

Re: Some Solar System Questions 

Hi You don't need an expensive fridge to get an energy efficient one. I have a samsung fridge/freezer that uses 339 kw per year, only $550 on special.
( actually uses less than that in situe)
A very good american site for asking solar power questions is the Wind Sun forum, Do lots of homework and it will save $ in the long term.
Good thing now solar is getting cheaper and more main stream .

Re: Some Solar System Questions 

thanks for that tearai - do you know what litre size it is? I am guessing from looking it up about 238litres?

Once again, thank you for your time :D

Re: Some Solar System Questions 

The model I got was SR237nme. So I think 237L , not a big fridge/freezer , but we find it adequate.The build quality is not as good as the ecold and grams but i felt good value for money. Was $559.00 inc gst 2years ago.

Re: Some Solar System Questions 

once again thank you for the information tearai - there is only me so that fridge would be great - it is still about the same price so all good!

Re: Some Solar System Questions 

Hi Kainga

Powersmart solar have an energy audit on their website for off-grid systems.

http://powersmartsolar.co.nz/off-grid-solar

(see the link energy audit)

You just have to fill it out what appliances you want to be able to use and make a good guess at how long you want to be using them everyday. They'll be able to give you an accurate system design for your needs. Powersmart sell the complete system, so this might not be helpful if you are doing it DIY.

Re: Some Solar System Questions 

thank you for that link - even though I am going to dim (do it myself) having that spreadsheet will be a great help :D

Re: Some Solar System Questions 

Just found this for anyone else who goes down this path and is trying to find out how to work out what they need :D

http://www.folders.co.nz/solar.cfm is a link that has
- loads calculator
- array size calculator
- battery calculator

so using it I can work out what kind of load I will have, the array size that I need (allowing for all seasons or just one depending on when I am there) and how many ah of batteries I need (allowing me to choose how many days without charge so used the 5 days as seeker suggested :D

Re: Some Solar System Questions 

Kainga

There are some power usage meters/monitors on the market (check Trade Me) which would allow you to actually measure what your fridge/other gadgets is using now, so apart from the issue of startup requirements, you can actually accurately measure power usage and see where you are at. These meters help people who want to go off grid to carefully analyse their power consumption prior to sizing the system, and is much more accurate than estimating the number of hours anything is on.

Seeker

Re: Some Solar System Questions 

thank you for that seeker :D

I have actually decided that I am not going to have a fridge as I don't really need one - even in the cities where there is power I use powder milk! *LOL*

As for meat, there is plenty of seafood at my doorstep and veges in the garden so a fridge would be a waste as would not really be used.

I wouldn't be able to work out my power consumption as the place I am staying at the moment has lots of electrical things and when I get home next month I am not even going to bother connecting the mains power - why create a bill when I don't need it?

I do know the theory about getting a system that can be expanded later, but my needs are simple and it is my retirement place - if the kids or grandkids want more then when it is theirs they can pay for it :D

And my motto for life is avenge yourself - live long enough to be a problem for your kids - and this may do it :D

Re: Some Solar System Questions 

I want to know the cost and maintenance of system ....

Re: Some Solar System Questions 

depends on how much power you intend to use. Solar power is more expensive than grid power, It can be cost effective when the grid is not at your door ,and a long cable is needed from the line company to your house.. I run a holiday home off solar, 1200 watts of pv panels, 1800 watt inverter 900ah of batterys.
Pv can be purchased for less than $3.00 per watt. Batterys $2500. Inverter maybe $2000 To $4000.
Cables , circuit breakers fuses etc ???
Charge controller $400 to $1300. Labor???
Mounting of panels ??? THE list can go on.
Conservation is a big part of a solar set up.
Regards Peter

Re: Some Solar System Questions 

@tearai
How Long It will Live if I use 1200w PV Panels!!1

Re: Some Solar System Questions 

Panels last for 25 years to 80% of rated output.
My system runs water pump stero , lights, and fridge frezer. Hot water is gas .Cooking is gas. Heating is wood.