Hi, I can get the RCT 8kw for R18000. 2 mppt inputs. Should I buy 2 Solarwize inverters and put them in series for 10kw, or this one? 

 

Thanks

Edited June 6, 20224 yr by GJ Cronje

All depends on your power needs and also your battery capacity. So usually you try to size an inverter and a battery on a 1:1 basis. So 10kW of inverter power to 10kWh of battery power. In this case your choice might be dictated by the battery size at your disposal. However, I myself have the 8kW RCT in my own residence and the power output is below my peak loads so I am comfortable with my user requirement. However, your peak requirements may be higher than mine. 

The parallel of two 5kW machines onto a single phase is also possible but comes with some fundamentals that the batteries have to be shared by the two inverters and common to both. So you cannot have two seperate 5 kWh batteries. You need 10kWh Batteries ie. 2 X 5.1kWh batteries in parallel. The inverters basically need to have the same voltage otherwise you will have faults and errors in the operation. 

From a redundancy perspective 2 is better than one but the quality level of the 8kW MAX is really good and I would not hesitate to say they just don't Sommer fail anytime soon. This is not the former Axpert inverters from the past littered with clones and fakes. There are no clones to speak of in the High Solar Charge Controller models. The main reason is that the PV DC voltage is lethal. You don't just toy around with 500V DC to make a cheapie. If the model fails usually someone might be badly hurt. 

I guess both options are viable, but the RCT 8kW will be cheaper to install and to acquire. 

 

Thanks alot Steve. Sorry I meant the onverters in series for 10kw. But yes, the batteries will be 2 similar packs with 2 bms's. Do you think I should build one 10kw pack with one bms? I need to consider which will be the best. 

28 minutes ago, Steve87 said:

All depends on your power needs and also your battery capacity. So usually you try to size an inverter and a battery on a 1:1 basis. So 10kW of inverter power to 10kWh of battery power. In this case your choice might be dictated by the battery size at your disposal. However, I myself have the 8kW RCT in my own residence and the power output is below my peak loads so I am comfortable with my user requirement. However, your peak requirements may be higher than mine. 

The parallel of two 5kW machines onto a single phase is also possible but comes with some fundamentals that the batteries have to be shared by the two inverters and common to both. So you cannot have two seperate 5 kWh batteries. You need 10kWh Batteries ie. 2 X 5.1kWh batteries in parallel. The inverters basically need to have the same voltage otherwise you will have faults and errors in the operation. 

From a redundancy perspective 2 is better than one but the quality level of the 8kW MAX is really good and I would not hesitate to say they just don't Sommer fail anytime soon. This is not the former Axpert inverters from the past littered with clones and fakes. There are no clones to speak of in the High Solar Charge Controller models. The main reason is that the PV DC voltage is lethal. You don't just toy around with 500V DC to make a cheapie. If the model fails usually someone might be badly hurt. 

I guess both options are viable, but the RCT 8kW will be cheaper to install and to acquire. 

 

Thanks

Yes they are wired in series but I guess in the Mandarin conversion to English in the Manuals they refer to it as Parallel. As long as the concept is understood I guess who cares what it's called 🤣

8 hours ago, Steve87 said:

Yes they are wired in series

? How do you wire inverters in series? That makes no sense to me. Unless you need split phase perhaps.

@Coulombmore of an observation than a descriptive rule. The official world of Solar people know it to be parallel and so do I. I worked with a Sparky once & he made me see it differently. When you look at the wiring in the pic it runs parallel but look at the individual connections they are in series 🤣

Hence it's more of a depends which way you look at it. But the picture clears up all the confusion.

2 hours ago, Steve87 said:

@Coulombmore of an observation than a descriptive rule. The official world of Solar people know it to be parallel and so do I. I worked with a Sparky once & he made me see it differently. When you look at the wiring in the pic it runs parallel but look at the individual connections they are in series 🤣

Hence it's more of a depends which way you look at it. But the picture clears up all the confusion.

😂 Thanks for clarifying this. 

 

Ok I will look at the RCT 8kw,  and what do you think of the battery, one 10kw pack or 2 x 5kw packs. One 10kw pack will connect two 3.2v cells in parallel and then all in series, with one bms wire on the each parallel pack. I don't like this, but is saves me money by getting only one bms. Will this be a problem, if you maybe know😁

Many ways to do it. Do you have access to LFP cells ? Or will you buy a commercial battery on the market?

6 hours ago, Steve87 said:

When you look at the wiring in the pic it runs parallel but look at the individual connections they are in series 🤣

? Only the communications connectors are in series, although it's a closed loop, which is not a normal series connection.

The "business end" is definitely in parallel, and that's what counts.

3 hours ago, GJ Cronje said:

I don't like this, but is saves me money by getting only one bms.

"Buddy pairs" (pairs of cells in parallel, with the pairs connected in series) are not uncommon. I run them myself.

There is no problem with this, although it's worth making an effort to properly connect the cells so that they share the current equally. For pairs of cells, you use the "diagonal takeoff" approach. This is usually the obvious way to connect them, except perhaps at the ends of rows.

The cells should be at similar states of charge before connection, and they should be of the same age.

I always try to run in series and not double up. Yes you save on a BMS, but the savings can be all wasted if you cannot see the individual cell voltage. Lets just say I like to be able to keep an eye on all the cells.