Good morning all,

I have a query on a technical aspect of a large scale system.

We are in Zimbabwe with 18 hour daily power outages and are going to have to put in solar in order to continue to operate in this environment. Our operation currently draws from a 500kva transformer at night and we run a 550va genset in the day. We are therefore looking at going to solar in the day to reduce the demand for diesel which is not easily available.

The initial inquiry that I have got is recommending running a 250-300kw array with the generator running behind it as the 'battery bank', generator manufacturers and solar installers recommend a minimum continuous runload of 50% on a genset to avoid glazing which will ultimately destroy the generator. This means that the fuel required drops but nit that significantly and you are still running up maintenance costs etc.

My question is(and I have been told it is not workable) can I not include a battery bank that say gives me a 1 hour cover on the load should clouds come over etc and wen they reach a defined DOD the genset automatically kicks in and takes up the load before the batteries deplete?

This for me would be a best case situation as we would remove the unnecessary run time on the genset and not have to overspend on batteries.

I realise that this is probably a pipe dream but thought I would throw it out there nonetheless.

Thanks

Doug

1 hour ago, Dougiedanger said:

My question is(and I have been told it is not workable) can I not include a battery bank that say gives me a 1 hour cover on the load should clouds come over etc and wen they reach a defined DOD the genset automatically kicks in and takes up the load before the batteries deplete?

Start here 🙂

That paper covers many of the issues you raised. Things have moved on a bit since then, but that paper still gives a good overview of what is achievable without even adding PV modules. You can of course also add PV which will extend the amount of time you can remain on battery.

In practice you might only run the generator at night, but with a Victron setup you can charge the batteries with any remaining power, thereby loading the generator to a more or less constant load. Then you can coast through the "na-nag" as we say in Afrikaans (the after-night, aka early hours of the morning) on battery and either have a short generator-run at breakfast time, or wait for the sun.

3 hours ago, plonkster said:

Start here 🙂

That paper covers many of the issues you raised. Things have moved on a bit since then, but that paper still gives a good overview of what is achievable without even adding PV modules. You can of course also add PV which will extend the amount of time you can remain on battery.

In practice you might only run the generator at night, but with a Victron setup you can charge the batteries with any remaining power, thereby loading the generator to a more or less constant load. Then you can coast through the "na-nag" as we say in Afrikaans (the after-night, aka early hours of the morning) on battery and either have a short generator-run at breakfast time, or wait for the sun.

Thanks so much, I have gone back to the original guy and he is coming round and seems to think he can come up with a solution so I will wait with bated breath. I tell you this loadshedding is a real mission!

That's a fair bit of power you're using, what type of business are you in. Is there a different way to save some power without so much solar/generator use?

7 minutes ago, seant said:

That's a fair bit of power you're using, what type of business are you in. Is there a different way to save some power without so much solar/generator use?

It is a poultry abattoir, refrigeration that has the biggest draw on the supply, my one motor is 160kw. We already maximise the 6-7 hours of power we get at night for production but that is not enough.

2 minutes ago, Dougiedanger said:

It is a poultry abattoir, refrigeration that has the biggest draw on the supply, my one motor is 160kw. We already maximise the 6-7 hours of power we get at night for production but that is not enough.

In that case I think you definitely want to AC-tie your PV. At those power levels I think it makes more sense.

You are however talking of a pretty significant investment in batteries. To run a 100kW from batteries, at a nominal 50V or so (to make the math easy), that's 2000 ampere, and if we assume that an LFP bank wants to be discharged at C/2 or less, that means you need a good 4000Ah storage, or 200kWh of storage. And it will be empty after just two hours.

But it can be done. You're also going to need a serious inverter. The theoretical limit for a Victron system is 60kW per phase, 180kw total power, either 12  x 15KVA Quattros (4 per phase), or 18 x 10kva Quattro (6 per phase).

There is such a system at Jao camp in Botswana.