Hi folks, mine's a simple question...

Had a 3000VA Mecer inverter with MPPT charger since 2015.  Attached are 12, 105 a/h batteries.  These are wired in series to provide 24 volts.  There are also 4 PV panels

The inverter was configured to allow maximum charge voltage as 27.6V, the DC cut off as 23.8V.  The intention was to manage the batteries conservatively

Nevertheless, with a 300 watt load (4 x LED lamps, TV, amplifier), after dark, I am getting 40 mins tops from the batteries before the inverter shuts down.  I have measured each battery individually and all are very close in charge state

So I want to go the lithium ion route

Have seen a 2000 watt/hour 26 volt battery for about R18k.

I figured that with a 300 watt load for 2.5 hours, I'd need 750 watts and this battery would be adequate

So the questions are:   Is my calculation of the battery realistic, and (probably more important) where can I buy this or similar battery at a better price, if this is possible

Thank you

PS:  I am in Cape Town

Edited March 21, 20196 yr by chrisc

12 minutes ago, chrisc said:

Is my calculation of the battery realistic

Yeah, it looks fine, you're just using the wrong units. 300W multiplied by two hours is 600Wh (watt-hour), which I assume you then added a bit to (750Wh) for efficiency and margin reasons.

14 minutes ago, chrisc said:

where can I buy this or similar battery at a better price

Reigning price is around 7.5k per KWh. So the best price you can expect would be around 15k. 24V batteries are not that popular or widespread, so I'm not sure you'd be able to do much better than that price. You can talk to BlueNova and FreedomWon, they make 24V batteries. You can also try SolarMD.

All 3 suppliers are pretty useless.  Blue Nova only have 48V,  Freedomwon rattled off someone's mobile phone number who operates in Jhb and SolarMD will not sell me anything, since I am not a registered solar installer

I contacted a fellow called James Dalrymple who lives in Kommetjie.  He will sort me out, plus the diagram that Cape Town Council want

Its almost like a closed shop.  I was an alarm installer for 36 years and found this attitude from several suppliers.  One would think they are awash with sales to turn away customers.   I know that some private customers can ask difficult questions due to lack of knowledge, but then they can refer this person to a third party technical person instead of simply saying that we won't deal with you

In my message, I said that I'd like to use 300 watts for 2.5 hours.  This figures to 750 watt/hours

Load shedding makes people grumpy I am sure.

9 minutes ago, DeepBass9 said:

Load shedding makes people grumpy I am sure.

Yup. I'm not even in sales and I had 8 people contacting me this week to ask what they should do...

On Facebook you see the usual pattern: Lots of new people suddenly installing systems, and in the comments lots of people asking "What is the price for this" (cause nobody ever advertises a price... it seems to be a marketing method of getting hold of people's contact details), and you sit there reading the comments realising that if a price is actually given the only result could be 1) despondence, followed shortly by 2) anger.

And some of those Facebook outfits are advertising non-approved inverters in Cape Town... and delete your comments when you point it out. I feel so sorry for their customers. Some of those doing it has been in the business long enough to know better too...

Having the same experience, I held out a bit too long and struggling to get people that are really interested in our business.

Maybe next week? Now stock levels are so low can't get hold of things so easily.