Household Solar setup

Submitted: Sunday, Jun 04, 2006 at 21:06
ThreadID: 34613 Views:2621 Replies:6 FollowUps:8
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I am looking for some advice on a friend’s household solar setup.
Existing setup is approx 10 off 80w panels, a Plasmatronics PL60, 1050AH flooded lead acid batteries. It is a 24v setup. Single item connected to the load is an Inverter approx 3000 watts.
Problem with the setup is a couple of times they have run the batteries down. Reg reported 23% remaining after Easter.
System runs the household power (500 litre fridge, microwave, TV, toaster, fans etc) but not lights, separate 12v solar setup for lights.
There is no backup generator.
We have 8 off 6v 125AH sealed lead acids. I.e. can be configured as 24v 250 AH.
Simply paralleling these batteries would not be recommended. I rang Plasmatronics for advice and was told about the Second battery control option of the PL60. This involves an external relay to switch the solar negative from the PL60 to the second set of batteries.
Basically solar is connected to the PL60 while Batt 1 is being boosted, when Batt 1 reached the float state the external relay operates & connects the solar to Batt 2. When Batt 2 reached max voltage or Batt 1 drops below float voltage then the relay releases & solar is connected back to the PL60. In other words the PL60 charges Batt 1 and any spare solar power is used to charge Batt 2. It was suggested to only connect half the solar via the relay so when the relay operates half the panels are connected to the PL60 & half are connected to Batt 2.
While this setup would work well charging both battery banks, it is a holiday house & both batteries would be fully charged when the house is empty, I have the following reservations about this setup.
This setup is only for running one device, the inverter. Only Batt 1 is connected to the inverter, so for Batt 2 to supplement the setup a battery changeover switch would be needed to connect Batt 2 to the inverter. This of course introduces operator error; the changeover switch would have to be changed to Batt 2 to relieve Batt 1. Then the switch would have to be changed back before Batt 2 was fully discharged. If Batt 1 was run down to 50% then the switch changed then the PL60 would be charging Batt 1, Batt 2 would be running the inverter but would not receive any charge until Batt 1 was fully charged. With Batt 2 being a quarter the size of Batt 1, I could see operator error causing Batt 2 to be fully discharged before the switch is changed back for Batt 1 to run the inverter.
Does anyone have any suggestions on how else to connect this setup? Ideal setup would be for the inverter to be able to use all the battery capacity (1050 + 250 AH) without any operator input to changeover.

From Marty.
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Reply By: Tuff60 - Monday, Jun 05, 2006 at 00:09

Monday, Jun 05, 2006 at 00:09
Someone else on here may know better, but I would assume you could get one way diodes to put in line to the inverter from both batteries, so it could remain conected to both. If diodes come in a suitable size for the current draw.
Maybe this will help, makes sense to me but it is late and I have been at the cans all afternoon.
AnswerID: 176735

Follow Up By: V8 Troopie - Monday, Jun 05, 2006 at 00:23

Monday, Jun 05, 2006 at 00:23
He mentioned a 3KW inverter which _Affordable_Storage_Drawers.aspx big amps at 24V. Big amps means big voltage drop across the big diodes, maybe 1V or more at full load. Too much to waste on heating diodes.
FollowupID: 432787

Reply By: Member - Jerry C (WA) - Monday, Jun 05, 2006 at 00:45

Monday, Jun 05, 2006 at 00:45
Hi Marty,
24v x 125A = 3000w, quite a load, can you give us some details of how the panels are connected together, or the tech spec of the panels?

Cheers, Jerry
AnswerID: 176739

Follow Up By: MartyB - Monday, Jun 05, 2006 at 17:17

Monday, Jun 05, 2006 at 17:17
Hi Jerry,
I can't remember exactly how many panels, but aprox 10 off 80w panels wire for 24v configuration. On the PL60 I have seen up over 30A solar input. 3000w is the max of the inverter, but worst case senario for the appliances in the house would be. TV, Satellite receiver, Fridge on. Then the microwave or toaster is turned on. Only 1 appliance can be used in the kitchen at one time (only 1 power point). I would guess about 1500w max load, but only for a short time. But would be a very large load for just the 250AH battery bank.
FollowupID: 432896

Reply By: Alloy c/t - Monday, Jun 05, 2006 at 07:30

Monday, Jun 05, 2006 at 07:30
The man with the answer is Collyn Rivers , a member of EO who nowadays will not answer questions of this nature on this forum ,, you could try going through his web site ,,,,,
AnswerID: 176749

Reply By: traveller2 - Monday, Jun 05, 2006 at 08:40

Monday, Jun 05, 2006 at 08:40
Or ring a solar specialist like Quirks
AnswerID: 176754

Reply By: Mal58 - Monday, Jun 05, 2006 at 13:08

Monday, Jun 05, 2006 at 13:08
You could try the Rainbow Power Company. It sounds a bit alternative and is, but the technical advice appears spot on.

They have a website at

AnswerID: 176801

Reply By: MartyB - Monday, Jun 05, 2006 at 17:38

Monday, Jun 05, 2006 at 17:38
Thanks for all the replies, one suggestion I came up with at work is. Inverter connected to Batt 1, very large diode (like what you get in a welder) between Neg terminals of Batt 2 to Batt 1, so current can only flow from Batt 2 to Batt 1. Theory is, at first both Batts are at 28.8v, approx 0.5 volt drop across diode so Batt 1 would supply all the current to Inverter. When Batt 1 drops to 28.3v both Batteries would be supplying current (probably 3/4 from Batt 1 1/4 from Batt 2 due to sizes of batteries). All solar current is into Batt 1 so when solar input is greater that load all current is flowing into & out of Batt 1. Batt 2 would not receive any charge until Batt 1 reaches 28.8v (Possibly only of an afternoon, some days Batt 1 would not reach 28.8v), Batt 2 would only supply current when Batt 2 voltage is 0.5 v above Batt 1 (probably sometime after midnight). This would have the effect of having Batt 2 as a backup to supply some of the current when load output exceeds solar input. When load is less that solar input, Batt 2 would simply float. Both batteries would fully charge when house is not occupied or when load is less that input. In practice the heat & resulting loss of power over the diode might mean it won't work. I am trying to come up with a theory using a voltage dependant relay between the batteries. As some have suggested I will try ringing some gurus for advise & more ideas.
Gives me something to think about anyway.
from Marty.
AnswerID: 176866

Follow Up By: Member - Meggs - Monday, Jun 05, 2006 at 19:51

Monday, Jun 05, 2006 at 19:51
Marty I am assuming that it was installed by a professional and the cable sizing is correct and that batteries are located close to the solar panels.
The PL60 has a 30 day data logger built into it and with the addition of a $100 interface unit you can read the logger with a computer or via a GSM modem. You can still read the logger from the front screen but it is a real pain in the neck but it can be done.
With the installation tell your friends for starters to throw away the electric toaster as that is a serious waste of battery power use gas. You mention "etc" on the demand what does that mean as your friends will have to practise some power conservation measures especially by eliminating the use of any heating appliances.
With the system and the demand you are showing it would be very doubtful if the main battery reached float voltage as the demand is too high.
I think it is a case of getting some info out of the data logger before going any further.
FollowupID: 432915

Follow Up By: MartyB - Monday, Jun 05, 2006 at 21:11

Monday, Jun 05, 2006 at 21:11
Hi Meggs,
Yes a professional install, yes cable sizing is correct, batteries are in a purpose built shed with the panels on roof. Inverter mounted in shed, approx 2m of 35 or 50 sq mm cable from battery. Batteries in box vented to outside.
House has a "very large" gas stove for most of the cooking. Also a wood BBQ is used . It was my suggestion to try & use the toaster & microwave. Yes they use a lot of electricity, but also save a lot of gas. Eg previously the griller on the large stove was used to make toast, used a lot of gas just to toast a couple of pieces of bread. Toaster uses 800w but for how long? Only a couple of minutes a day. Same with the microwave, approx 800w but only for minutes a day. Gas savings are significant, 45kg gas bottles are swapped on the mainland, expensive to swap, expensive to transport to the island.
We monitor the usage from the screen of the regulator, usage is ok if the couple who own the house are there by themselves. A week of my family will leave with the batteries at above 90% capacity. Christmas is another story, the couple plus about 4 of their grown kids plus spouses plus various grandkids (you get the idea) this tends to run down the system.
The idea is to increase the battery capacity by aprox 25% so they don't have to worry about conserving power as much. Yes they will still run the system down, but not as quickly, they would get through the Christmas period with a bit more battery capacity left. Once the house is left vacant for a couple of weeks the batteries are back to 100%.
Most of the advice the owner recieves is fit an autostart generator as backup, yes this would be the easy way out but where is the fun in that?
FollowupID: 432941

Follow Up By: Member - Meggs - Monday, Jun 05, 2006 at 23:11

Monday, Jun 05, 2006 at 23:11
I should have asked before where is this installation? I think a manual start generator would be a pretty good suggestion as there is nothing in reserve a dull day and you are really going backwards. I think the visitors should be told to bring their own generator when they come.

My suggestion on the toaster is to reduce the demand, I appreciate it is a few minutes for each person using it but it all adds up and the system is up to its limit with no reserve for dull days even if you area able to connect the extra batteries in you still have to get the energy back into the batteries.
FollowupID: 432959

Follow Up By: MartyB - Tuesday, Jun 06, 2006 at 17:24

Tuesday, Jun 06, 2006 at 17:24
Hi Meggs,
House is on Fraser, no we don't want a generator.
Primary purpose of this setup is to run the fridge & TV, gas fridge has been replaced by the large electric. It easily runs these. Then we start thinking what else can we run that might reduce the gas usage further. These extra batteries came at the right price (free is the right price). Hence the interest in adding these to the system. The comments about the toaster remind me of a saying I heard."Do you want toast? eat bread. You say you don't want bread, well fine."
When I get a chance at work I will give the businesses list above a ring.
from Marty.
FollowupID: 433073

Follow Up By: Member - Jerry C (WA) - Monday, Jun 12, 2006 at 23:47

Monday, Jun 12, 2006 at 23:47
Hi Marty,
In trying to draw out a circuit of your proposal above I can't see that it will work as you propose. If the discharge cycle works as you describe then the diode will be reverse biased (turned off) as soon as the solar panel voltage exceeds the battery voltage, thus no current will flow into battery 2.


FollowupID: 434358

Follow Up By: MartyB - Tuesday, Jun 13, 2006 at 18:00

Tuesday, Jun 13, 2006 at 18:00
Hi Jerry,
The way I figure it is Batt2 will only receive charge after Batt1 is fully charged. Charging will be via the feature of the PL60. Also Batt2 will only supply any current when Batt1 voltage is below Batt2 voltage. During the day the solar voltage will mean Batt1 will be above Batt2 so Batt2 will not receive or provide any current. In bright sun only the fridge will be running so the panels will supply the load plus charge Batt1. When the house is empty Batt1 will fully charge then Batt2 will charge. Batt2 would in effect only be a backup to provide some extra capacity when Batt1 was low. Seems like the only option so far.
from Marty.
FollowupID: 434446

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