Full off-grid system

[Colin62]

First off, I'm pretty new to the whole backup power and inverter stuff, but have been doing a lot of reading up and trying to catch up, so I might ask a few dumb questions which seem obvious to everyone else. I've had a look around and not managed to find a thread discussing the specifics of total off-grid solutions. If one exists, could someone let me know and I'll get a mod to move this to there.

I'm planning a build myself a cottage to retire to, at some point in the next few years. I've bought the land already and am happy with what I've got. It's not in the bush, but it is in a secluded area, and getting municipal power is an option, albeit an expensive one. The stand is a keyhole stand with a long driveway (about 70m) and the spot where I'd like to build is a bit away from there too, and so I'm looking at about 200m of cable on top of the municipal connection fee. Rough calculations show that the cable will cost close to R300 000, and given that the power in the area is notoriously unreliable (probably three to four power cuts a week), I'm looking at going fully off-grid, and rather spend the money on a decent system.

Total load is hard to gauge at this stage, I'm renting a five bedroom house with a pool etc, and no optimization of power consumption (due to the electricity being included in my rent), so I'm going off thumbsuck figures for that.

The cottage will be two bedrooms, two adults living there (possibly some guests from time to time). Stove is gas, geysers will be gas or solar and the main source of heat will be a wood burner, and if that's not enough, probably gas too. Essentially I'm not expecting the cottage to cause any issues. The problem is my workshop. I do wood turning, and that uses power - I'm happy to limit my work to when there is enough sunshine to keep me going, but between the lathe and the dust extractor, I'm going to need some capacity.

I'll make a couple more posts for specific queries, so that they're easier to find, rather than forcing everyone to read this great wall of text.


TLDR: I want to go totally off-grid, a two bedroom cottage and a workshop. Capital costs offset by not paying to connect to the grid, running costs offset by not paying Eskom every month.

 

[Colin62]

One system or two?

My first thought was to get two inverters, one for the house and one for the workshop, so that if the workshop dies because I drain too much power, it doesn't affect my domestic bliss.

House would use a 5kW inverter, sufficient solar and enough batteries to mage for a few days of cloudy weather and rain.
Workshop would use a 5kW inverter and solar with enough battery to drive lights at night so that I can work with hand tools and cordless tools.

Giving it more thought, it probably makes sense to link the two inverters for 10kW, combine the batteries and solar panels and just discipline myself to be careful when using the big machinery.

This would give me a better safety margin in total kW drawn in the workshop. The main power users in the workshop are the lathe (2kW running off a VFD, so it's possible to limit the current), the dust extractor (2kW of Chinese power or 1kW of measured power) and a compressor rated at 1.6kW. Those are the three which may run at the same time, but I can wiggle things so that it's only two of the three simultaneously.

 

[ThatGuy_ZA]

Would you consider a small diesel (+-10kW) generator for the wood shop? It could double as a backup supply for the house in the event that demand exceeds supply.

 

[Colin62]

I might want to buy components (while I'm still earning a salary) and store them for a year or two, until I'm ready to use them.

To the best of my knowledge, batteries age even when stored.
Solar panels age, but I suspect that if they're stored they'll be fine.
Inverter will be fine stored, but it's warranty may expire before it's take out the box.

Any guesses as to where the biggest improvements in performance or price may come in the next couple of years? Or do I just stick the money under the mattress and buy it all shiny and new when the time comes?

 

[F1 Fan]

I don't know much about going off grid so can't help you there.

I am interested to know how you got the 300k quote for the cable to your property though?

 

[Colin62]

Would you consider a small diesel (+-10kW) generator for the wood shop? It could double as a backup supply for the house in the event that demand exceeds supply.

I currently own a 5kW petrol generator, and will use that as a last resort if the weather is really terrible for a long time. I'm not sure if the capital cost of a decent generator is justified or if I should rather push the money into more capacity on the solar/battery side.

Two things put me off a generator, the first is the obvious one - noise. The second is that most of the generators around are designed for a very limited duty cycle, and if you're using it daily, even for a few hours a day, they don't last. And of course a decent industrial quality generator, is an order of magnitude higher than a cheapie.

 

[Rocket-Boy]

One system or two?

My first thought was to get two inverters, one for the house and one for the workshop, so that if the workshop dies because I drain too much power, it doesn't affect my domestic bliss.

House would use a 5kW inverter, sufficient solar and enough batteries to mage for a few days of cloudy weather and rain.
Workshop would use a 5kW inverter and solar with enough battery to drive lights at night so that I can work with hand tools and cordless tools.

Giving it more thought, it probably makes sense to link the two inverters for 10kW, combine the batteries and solar panels and just discipline myself to be careful when using the big machinery.

This would give me a better safety margin in total kW drawn in the workshop. The main power users in the workshop are the lathe (2kW running off a VFD, so it's possible to limit the current), the dust extractor (2kW of Chinese power or 1kW of measured power) and a compressor rated at 1.6kW. Those are the three which may run at the same time, but I can wiggle things so that it's only two of the three simultaneously.

The workshop equipment will have a big inrush current so that needs to be considered. The Lathe is most likely going to be a 3 phase universal motor converted to single phase through the VFD(Im interested to know what lathe this is, Im a wood turner) That level of motor is also pretty high on battery drain so that will need to be factored in.
The items in your house that you need to worry about are microwaves, hairdryers and similar appliances. It will take some getting used to make sure high drain appliances are not used at the same time.

 

[Rocket-Boy]

Any guesses as to where the biggest improvements in performance or price may come in the next couple of years? Or do I just stick the money under the mattress and buy it all shiny and new when the time comes?

That one is easy, batteries.
You really dont want to be using lead-acid/AGM on a system like this, it needs to be Lithium based. Its more expensive up front but lasts a lot longer and is cheaper in the long run.

 

[Colin62]

I don't know much about going off grid so can't help you there.

I am interested to know how you got the 300k quote for the cable to your property though?

I didn't get an actual quote, and the R300k is the worst case scenario.

Basically as follows:
To allow for less than a 5% voltage drop over the 200m run, at 60A, I'd need a 150 sq mm cable. Looking at ACDC's website, that's over R1600 a metre and that gives yo about R320 000 for the cable.

I know I can get the cable for less by buying 200m, but I've still got the municipal connection fee and the cost of digging a 200m trench for the cable, so I reckon there won't be a lot of change from R300k.

 

[Colin62]

That one is easy, batteries.
You really dont want to be using lead-acid/AGM on a system like this, it needs to be Lithium based. Its more expensive up front but lasts a lot longer and is cheaper in the long run.

That's my feeling too. I'm thinking that buying the panels if I have spare cash now is the safest of the three main components.

 

[Rocket-Boy]

That's my feeling too. I'm thinking that buying the panels if I have spare cash now is the safest of the three main components.

Yup, inverters and panels dont change a lot over time.
Batteries on the other hand are changing constantly and the prices are actually coming down too.

PS, I still want to know what lathe you have

 

[Colin62]

The workshop equipment will have a big inrush current so that needs to be considered. The Lathe is most likely going to be a 3 phase universal motor converted to single phase through the VFD(Im interested to know what lathe this is, Im a wood turner) That level of motor is also pretty high on battery drain so that will need to be factored in.
The items in your house that you need to worry about are microwaves, hairdryers and similar appliances. It will take some getting used to make sure high drain appliances are not used at the same time.

The dust extractor is the main culprit. Pulls about 4kW on startup, and then settles to 1kW. I know that some 5kW inverters can handle up to 10kW for a few seconds , so I'll have to start that first (which is how it works anyway).

The compressor is a pain because you never know when it's going to kick in, but if I'm using it at the same time as the lathe, it's for the vacuum chuck, and I'm only taking small cuts so the lathe itself is just idling. I might have to look at a small vacuum pump though, instead of the venturi system I've got now, and leave the compressor off.

The lathe is a three phase motor driven by a single phase VFD. It's a Vicmarc VL300, and is my pride and joy. I haven't had a chance to measure the power usage while taking a cut, but spinning up a chuck with a medium sized blank on it, it didn't draw more than 400W, and settled on 300W at about 1000rpm, and 350W at 1600rpm. The VFD is fully programmable, so in effect I set the maximum current to just about anything I want, although it would be a pity to lose any of the grunt.

 

[Rocket-Boy]

The dust extractor is the main culprit. Pulls about 4kW on startup, and then settles to 1kW. I know that some 5kW inverters can handle up to 10kW for a few seconds , so I'll have to start that first (which is how it works anyway).

The compressor is a pain because you never know when it's going to kick in, but if I'm using it at the same time as the lathe, it's for the vacuum chuck, and I'm only taking small cuts so the lathe itself is just idling. I might have to look at a small vacuum pump though, instead of the venturi system I've got now, and leave the compressor off.

The lathe is a three phase motor driven by a single phase VFD. It's a Vicmarc VL300, and is my pride and joy. I haven't had a chance to measure the power usage while taking a cut, but spinning up a chuck with a medium sized blank on it, it didn't draw more than 400W, and settled on 300W at about 1000rpm, and 350W at 1600rpm. The VFD is fully programmable, so in effect I set the maximum current to just about anything I want, although it would be a pity to lose any of the grunt.

I just left tears all over my keyboard! VL300 is an amazing lathe, it must have cost a fortune to get from AU to SA.
Im eyeing the Laguna 18-24 when funds permit, tired of turning on a midi lathe now.

Back on topic, those motors are going to be tricky, especially if they need to run together. You will most likely need to team all batteries to support the tools but keep an eye on charge levels.

The other side of this is that you need a plan B, a generator is probably the most practical for that. There will be days when your consumption exceeds your generation and the genny would be good for those times.

 

[Colin62]

I just left tears all over my keyboard! VL300 is an amazing lathe, it must have cost a fortune to get from AU to SA.
Im eyeing the Laguna 18-24 when funds permit, tired of turning on a midi lathe now.

I looked long and hard at both the Laguna 18-24 and the 24-36, but wasn't in the market for anything nearly that expensive. But then lock-down arrived and I had to change my lifestyle completely, and ended up being able to save a fair bit every month. I noticed that I could buy the Vicmarc for a similar price to what I'd pay for the big Laguna, and ummed and ahhed a bit, and then went for it.

If you have the chance to upgrade, I don't think you'll regret it. I'm really happy with my beast.

Given how much noise the dust extractor makes, I wonder if the neighbours will even hear a genny running... Actually in that area they'll think they're just lucky that they're still up while someone else is running their genny.

 

[Rocket-Boy]

I looked long and hard at both the Laguna 18-24 and the 24-36, but wasn't in the market for anything nearly that expensive. But then lock-down arrived and I had to change my lifestyle completely, and ended up being able to save a fair bit every month. I noticed that I could buy the Vicmarc for a similar price to what I'd pay for the big Laguna, and ummed and ahhed a bit, and then went for it.

If you have the chance to upgrade, I don't think you'll regret it. I'm really happy with my beast.

Given how much noise the dust extractor makes, I wonder if the neighbours will even hear a genny running... Actually in that area they'll think they're just lucky that they're still up while someone else is running their genny.

I could talk lathes all day but dont want to derail this thread.
In almost all off-grid setups there needs to be a failsafe for when batteries run low, a genny is the cheapest of the lot. It sure beats having to buy more battery capacity or trying to faff about with wind generation.

I think you are on a good track though, getting off grid with everything going on with Eskom is a great idea.

 

[signates]

Sunsynk 8kw hybrid inverter and 4 hubble 5.5kW batteries.

You could even go with 2 x 8kw sunsynk inverters just to be safe.

Existing 5kw generator can be connected to them and the inverter can switch it on automatically in the event of very low battery or low pv generation.

2 x Sunsynks and 4 hubble AM2 batteries could be had for under R180k

Hubble Am2 5.5kw battery = R26k x 4
8kw sunsynk inverter = R32k x 2

 

[SauRoNZA]

I might want to buy components (while I'm still earning a salary) and store them for a year or two, until I'm ready to use them.

To the best of my knowledge, batteries age even when stored.
Solar panels age, but I suspect that if they're stored they'll be fine.
Inverter will be fine stored, but it's warranty may expire before it's take out the box.

Any guesses as to where the biggest improvements in performance or price may come in the next couple of years? Or do I just stick the money under the mattress and buy it all shiny and new when the time comes?

Surely make more sense to store the money rather than the equipment.

Technology may also change so rather buy as new as possible when the time comes.

Costs are more likely to come down than go up. Or if base cost doesn’t come down you’ll at least get more capacity for your money.

 

[SauRoNZA]

As for splitting or keeping one single system if I was in the same boat I would build one single larger system but then use some smart automations to limit potential overload.

 

[itareanlnotani]

I would second the Sunsynk 8KW

Has more than enough oomph to run the workshop and the house.
I'd lean toward what I'm doing - 24 panels + 8KW inverter + 20KW of battery.

I've gone with 24 x 395W Mono Perc JA Solar panels in 3 x 8 series strings.
Overkill for what I need, but gives me a lot of headroom.

I'm doing mine in stages - panels + inverter first, batteries in a year or two (as i already have 10kw of storage which suffices downstairs).

So far:

Inverter 32k
Panels 48k
Mounting 4k (8 x 6m rails + 96 clips)
Electrical bits n bobs 5k (wire etc)

Storage will be approx 100k for 20k, but not going to do that due to budgetary issues. Will be cheaper when I do add it, assuming the rand stays in the current range.

 

[wingnut771]

I would second the Sunsynk 8KW

Has more than enough oomph to run the workshop and the house.
I'd lean toward what I'm doing - 24 panels + 8KW inverter + 20KW of battery.

I've gone with 24 x 395W Mono Perc JA Solar panels in 3 x 8 series strings.
Overkill for what I need, but gives me a lot of headroom.

I'm doing mine in stages - panels + inverter first, batteries in a year or two (as i already have 10kw of storage which suffices downstairs).

So far:

Inverter 32k
Panels 48k
Mounting 4k (8 x 6m rails + 96 clips)
Electrical bits n bobs 5k (wire etc)

Storage will be approx 100k for 20k, but not going to do that due to budgetary issues. Will be cheaper when I do add it, assuming the rand stays in the current range.

Why 3 strings when there are 2 MPPT's?