navitron
 
Renewable Energy and Sustainability Forum
Welcome, Guest. Please login or register.

Login with username, password and session length
News: Anyone wishing to register as a new member on the forum is strongly recommended to use a "proper" email address - following recent spam/hack attempts on the forum, all security is set to "high", and "disposable" email addresses like Gmail, Yahoo and Hotmail tend to be viewed with suspicion, and the application rejected if there is any doubt whatsoever
 
Recent Articles: Navitron Partners With Solax to Help Create A More Sustainable Future | Navitron Calls for Increased Carbon Footprint Reduction In Light of Earth Overshoot Day | A plea from The David School - Issue 18
   Home   Help Search Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: Small battery backup system for on grid house  (Read 2202 times)
blob127
Newbie
*
Offline Offline

Posts: 10


« on: January 03, 2014, 11:45:43 AM »

Hi all i have a 4 kilowatt solar pv array i'm looking at getting a small battery backup system and i am looking at the victron inverter charger does anybody know if they switch across themselves from batteries to grid when a load is too much and back to batteries when the item has been switched off
Logged
biff
Global Moderator
Hero Member
*****
Offline Offline

Posts: 11956


An unpaid Navitron volunteer who lives off-grid.


« Reply #1 on: January 03, 2014, 12:19:48 PM »

Hello Blob,and welcome to the forum,
         We need a bit more info,Are you charging from the grid or from a generator,? Perhaps you could give us some more details.There are members here who can help but they need to know what you have in mind.
                                     Biff
Logged

An unpaid Navitron volunteer,who has been living off-grid,powered by wind and solar,each year better than the last one.
blob127
Newbie
*
Offline Offline

Posts: 10


« Reply #2 on: January 03, 2014, 02:25:43 PM »

Hi i am looking to charge batteries from my pv panels in the daytime and use from the batteries at night . my house uses about 3 to 400 watts through the night. Just like to know if anybody else is done this is it worth doing what sort of costs involved.
     Blob
Logged
biff
Global Moderator
Hero Member
*****
Offline Offline

Posts: 11956


An unpaid Navitron volunteer who lives off-grid.


« Reply #3 on: January 03, 2014, 03:08:26 PM »

Well blob,
           What can I say. You are talking about a standard off grid set-up which most of us off-gridders have.But you state that you already have 4kw of pv.So I must assume that you are already using this in some form or another.Could you clarify,?
                                                   Biff
Logged

An unpaid Navitron volunteer,who has been living off-grid,powered by wind and solar,each year better than the last one.
jonesy
Hero Member
*****
Offline Offline

Posts: 839



« Reply #4 on: January 03, 2014, 03:27:28 PM »

Hello Blob and welcome
This topic comes up pretty regularly http://www.navitron.org.uk/forum/index.php/topic,21341.0.html & this is sort of related http://www.navitron.org.uk/forum/index.php/topic,21438.0.html.  If you search the forum there quite a few this year.

It's an expensive business storing leccy.    IIRC members that are off grid talk around 15-20p/unit solar to battery to mains.
Logged

1.1kWp PV & SB1700. 7kW log burner.
billi
Global Moderator
Hero Member
*****
Offline Offline

Posts: 8943



WWW
« Reply #5 on: January 03, 2014, 04:56:56 PM »

Quote
i'm looking at getting a small battery backup system and i am looking at the victron inverter charger does anybody know if they switch across themselves from batteries to grid when a load is too much and back to batteries when the item has been switched off

Yes
Logged

1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
freddyuk
Sr. Member
****
Offline Offline

Posts: 436


« Reply #6 on: January 04, 2014, 08:10:48 AM »

Victron Multiplus will do this automatically via inbuilt transfer switch and can be programmed for various scenarios. Also computer control via USB Dongle available. Just match your usage to the battery/inverter. I assume you mean 3-400 watts per hour overnight. If you are on cheap rate then charge from mains overnight. Use solar during the day with decent energy controller and charge batts with any spare. I am hoping a new device is coming out soon which will be effective for grid tied systems wanting diversion from GT solar to DC supply with certification for UK.
Logged
pj
Sr. Member
****
Offline Offline

Posts: 286

Nom de Plume


« Reply #7 on: January 04, 2014, 11:14:14 AM »

I assume you mean 3-400 watts per hour overnight.
I think Blob had his units right - not sure what 3-400 watts per hour means?
Personally, I see 150-250 watts on my OWL monitor whenever I get up in the night, so I average approx. 200 watts running all night. Guess from say 11Pm till 8am that's about 1.8kWh.
Logged
blob127
Newbie
*
Offline Offline

Posts: 10


« Reply #8 on: January 04, 2014, 12:59:11 PM »

Hi thank you for your comments Yes i did mean 3 to 400 watts per hour. does this mean i will not need a very big inverter charger is that right as it will cut straight back to the grid if i put a big load on it
  blob
Logged
w0067814
Full Member
***
Offline Offline

Posts: 239


« Reply #9 on: January 04, 2014, 01:19:26 PM »

Yes i did mean 3 to 400 watts per hour.

No!, You were right first time. It is important to understand the difference.

A WATT or a KILOWATT is a measure of POWER.
A WATT HOUR or a KILOWATT HOUR is a measure of ENERGY.

ENERGY and POWER are two different things. ENERGY = POWER * TIME.

If you are stating POWER then you are correct with 3-400 WATTS or if you are stating ENERGY then you should be using WATT HOURS or KILOWATT hours.

There is a massive difference between the battery requirements to support a load of 3-400 WATTS for say 12 hours, than if you are stating that you only use 3-400 WATT HOURS in total over night. 3-400 WATTS * 12 HOURS = 3,600 to 4,800 WATT HOURS or 3.6 to 4.8 KILOWATT HOURS if you prefer.

400 WATT HOURS = 33 AMP HOURS @ 12 VOLTS.
4.8 KILOWATT HOURS = 400 AMP HOURS @ 12 VOLTS.
Logged
billi
Global Moderator
Hero Member
*****
Offline Offline

Posts: 8943



WWW
« Reply #10 on: January 04, 2014, 03:07:51 PM »

I understand it as  a constant draw of 3-400 WATT during the night , so say 12 hours X 300-400 watt = 3.6 kWh -4.8 kWh during non PV times ....


Surely the Victron can switch on and of the Grid AC in put , but the tricky part will be to allow PV-grid power in to be switched through during the day for house consumers and battery charging , but switch Grid Power off when PV sleeps , but also allow grid assistance when needed....

Not sure what the new Victrons in relation to FiT do, but as as self-made idea , i would use a bigger Victron Multi and a time-clock that switches of the grid/PV during the night



Logged

1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
freddyuk
Sr. Member
****
Offline Offline

Posts: 436


« Reply #11 on: January 06, 2014, 08:38:51 AM »

Glad we cleared up the technical definitions but my point was the OP had indicated an incorrect figure for total hourly watts drawn. Overnight it is normal for the load to be static around 300-400 watts so I was clarifying the actual loads across the night which would be say 350watts PER HOUR for the sake of argument. Then you can work out the total loads based on kWh while the solar is disconnected.
The Multiplus can be programmed to make use of AC Mains whenever required. If battery requires charging during the day when there is insufficient solar it will kick in. No Victron kit is grid connectable in UK but they are working on an option to get round this.
Logged
w0067814
Full Member
***
Offline Offline

Posts: 239


« Reply #12 on: January 06, 2014, 09:27:41 AM »

Glad we cleared up the technical definitions but my point was the OP had indicated an incorrect figure for total hourly watts drawn. Overnight it is normal for the load to be static around 300-400 watts so I was clarifying the actual loads across the night which would be say 350watts PER HOUR for the sake of argument. Then you can work out the total loads based on kWh while the solar is disconnected.
The Multiplus can be programmed to make use of AC Mains whenever required. If battery requires charging during the day when there is insufficient solar it will kick in. No Victron kit is grid connectable in UK but they are working on an option to get round this.

Watts per hour is a rate of change of power.

http://en.wikipedia.org/wiki/Kilowatt_hour#Misuse_of_watts_per_hour
http://en.wikipedia.org/wiki/Watt#Confusion_of_watts.2C_watt-hours_and_watts_per_hour

But yes, it has been established that the OP would require something in the order of 4.8kWh of usable battery storage to support a 400 watt load for 12 hours. The OP has not stated the length of the night, so this could be feasible (short summer night with long day) or unfeasible without an abnormally large PV array (long winter night with short day).

Total battery capacity would also need to be larger to some degree than the usable capacity to prevent degradation of the batteries. How much larger is a trade off of capital costs vs on-going replacement costs, factoring in capacity related losses.
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.20 | SMF © 2013, Simple Machines
SMFAds for Free Forums
Simple Audio Video Embedder
Valid XHTML 1.0! Valid CSS!