Off grid solar project.

[DAVE HEARSON]

Hi all, anybody going down a similar road to this, I am setting up a solar project for my house in Spain, the gear I allready have in place are,
4 x 30v 250w panels
4 x180a/h batteries = 48v batt bank
2 x 180a/h batteries =24v batt bank
The batteries at the moment are charged via generator,
I will need to have two charge controllers to monitor the charge regime of the batteries as what I would like to do is have the pv array charge the 48v bank and to charge the 24v batts off of the 48v bank via another charge controller.
As anyone out there done anything similar to this, as I realy need some advice on the mppt charge controllers.
Regards Dave H.

 

[SW1970]

I can recommend this book: Solar Electricity Handbook 2012: A Simple Practical Guide to Solar Energy - Designing and Installing Photovoltaic Solar Electric Systems by Michael Boxwell. It has an excellent section about off grid and some links to his website with free system calculators on it. Curious as to why you're wanting to charge one bank from another? Why not parallel up for one larger system?

 

[DAVE HEARSON]

Hi SW1970. Reason being I need to power a 48v ups smart 3000 to power a water pump and the 24v system to power a ups smart 1000 to power a tv and other small appliances, the application is in Spain and works well if I charge the batts by generator, but feel it would be better to give solar a go and use the generatoras backup for winter ect, thanks for the info. Regards Dave H.

 

[SW1970]

Hi, do you mean an APC UPS Smart 3000 and 1000?

 

[DAVE HEARSON]

Hi , yes they are both APC ups units.

 

[SW1970]

Fab. You can pick these up relatively cheaply on ebay compared to typical "posh" domestic solar inverters which are intended for grid connections. Are your batteries internal or external to the units? I'm thinking of doing the same for some off grid circuits in my place.

 

[DAVE HEARSON]

Hi, the batteries are external to the units (very big and heavy) took the apc batts out and run two sets off leads out of the unit with anderson plugs on the ends as they have two sets of 24v apc batts in series for the 48v supply.

 

[SW1970]

Hi Dave, when you were using the generator, were the APC units plugged into a 240v output from the genset? If so, as you say, with the solar solution you'll need charge controller(s) to charge the battery banks. I'm just wondering how the APC units will cope with being permanently disconnected from a 240v supply. Might be worth contacting APC tech support and tell them what you're doing and see what they say. There might be some configurable options either on the internal charge controller or via software to configure the Ah of the connected batteries. I'm planning on doing exactly what you're doing but I'm further behind in the design; would be really interested to see how things go.

 

[DAVE HEARSON]

Hi, the APC units will never be permanently disconnected from a 240v supply, as I am sure you are aware solar systems are OK up to a point for charging batteries, big downfall are days of poor sunlight/ winter periods ect, shortened daylight hours means that the charge controllers do not have enough time to complete there cycle, at the present time I am running a big generator 1hr in the morning and maybe 1 1/2 hrs in the afternoon just to keep the batts at 80 p/cent, putting 20 amp/hr into each batt, and see the solar array as a means of getting a heads up on my charge regime.
I would not rely on the apc unit to charge 4 x 12v 180a/h batteries.

one more thing, getting APC to reply to any e-mail is a lost cause, and when purchasing a ups make sure it is as new as poss and always with a warranty!!!!

 

[SW1970]

Hi Dave, just out of interest, have you done any calcs to see what the cost per kWh is for the energy produced by the generator?

 

[DAVE HEARSON]

No i havnt done calcs, house is in Spain , well off grid, cost of a mains cable running to house 10.000 euros plus link up, plus as here a quarterly bill, so as they say (needs must) till my solar project is up and running the fuel cost will have to be what it is. DH.