question

martinvetter avatar image
martinvetter asked

Add battery UPS with solar to existing grid/generator connected installation (transfer switch) in southern Africa

I appreciate all answers or pointers to relevant topics in this forum! I don’t have an electrical background, so pardon the very basic questions and layman’s terms:

We’ve got a 3 phase domestic installation in southern Africa. It is serving as back office for an NGO school project as well as volunteer housing. It is connected to the grid, with regular occurring power cuts of multiple hours. We’ve got an automatic transfer switch to a 3 phase 5.5KVA Generator for everything except water heaters. It’s a quite old but rugged military genset. While the switchover is automatic, we start the genset manually, once the grid is gone. As soon as the grid is back, it is switched back and the genset is idling until we switch it off manually. We do not want an automatic starting and stopping of the generator, since it needs some “love and attention” once in a while.

In a modernisation of the electrical installation some time ago, we already prepared one circuit in the house carrying all important loads (total 500W…1000W, occasional 1500W). Now, with some money available we want to add uninterrupted power supply to this one circuit. The goal is have time before the genset has to be started, possibly not at all during a normal duration power cut of a couple hours in low load situations.

The first idea was to get a MultiPlus and a couple batteries. On a second thought we would like to extend the system adding some solar (only a couple hundred watts), since most power consumption is occurring during daytime/office hours. *Very* simply speaking it seems that installing 100W solar is cheaper than installing 100W additional battery capacity. Also considering that it is not the end of the world, if power on this uninterrupted supply is running low on a clouded day, since the genset can be started. Solar would also help and could be extended, if longer duration power cuts become normal.

My questions are about what is takes to control the system as described above. Is a grid/generator connected UPS system with solar supplement, containing a MultiPlus, BlueSolar Solar Charge controller (or EasySolar), batteries and solar panels a self regulating system? Or is there any other control unit necessary (battery monitor, CCGX)? We want to keep the system robust and low in cost.

The batteries should always be charged for the time the grid fails.

Solar should always be used. For charging of the batteries and supply to the AC consumers, with grid/generator available or not.

What prevents the inverter from feeding solar/battery power backwards to the generator (one phase only), trying to run it like a motor, if the grid is gone, generator is connected/running, batteries are charged, solar is generating a lot of power and there is low/no consumption in the house? What keeps the battery from being discharged to feed the AC consumers when the grid is available?

Can all this be achieved just by voltage settings in the Charger/Inverter and Solar charge controller or are additional components needed?

Multiplus-IIGeneratorsolargridups
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1 Answer
Dave van Dongen avatar image
Dave van Dongen answered ·

I think the easiest way to realise this system, is to build a ESS. (https://www.victronenergy.com/live/ess:design-installation-manual) For this you will need a Venus device. A CCGX or the cheaper version without a screen: Venus GX.
I think technically you could do it without the Venus device and just program a non-ESS mode in the MultiPlus. Sounds you need Hub 1, Policy 2: "Keep batteries charged". (https://www.victronenergy.com/live/assistants:self_consumption_hub-1)

You ask: "What prevents the inverter from feeding solar/battery power backwards to the generator (one phase only), trying to run it like a motor, if the grid is gone, generator is connected/running, batteries are charged, solar is generating a lot of power and there is low/no consumption in the house? What keeps the battery from being discharged to feed the AC consumers when the grid is available?"
Basically the MultiPlus regulates all this. You can fine-tune the programming in the MultiPlus with the Victron victron usb (mk3) dongle. After programming you don't need other devices.

Adding solar is a great idea! :-)

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