Energy Matters Forums

[offgridQLD]

My wife and I have purchased some land with a two year old off grid home. Get the keys next wednesday

Rough System basics.

6.6kw PV consisting of 24 x 275w panels. Fixed array roughly 12 deg tilt and facing roughly +40 deg from true north. About 51 deg magnetic north east.

selectronics PS1 inverter charger 6000w continuous.

Exide 4rp1330 4v cells x 12 - 48v 1330ah /c 100

Kubota J108 9kva 3cyl diesel generator

The system being only two years old looks to be in near new condition. Though I can already see some design faults in the system layout but should be easy to sort out. Things like inverter and batteries housed in the same building (need a dividing wall). Some shading on very back string of panels during the very late afternoon. I will most likely see other things that need sorting once we get the keys and I can go over the system in detail. I am usually fussy about most things but will live with the system for a short while and iron everything out.

Future plans for the home are a home workshop - shed to be built near the home. After not being able to swing a cat in my double garage I use now this is what I am most excited about

I need to able to run my modest size lathe, mill , cold saw, Tig welder among other things. Most inductive loads from motors are 1000w motors or less other than my air compressor thats 2400w though I might just convert that to a ICE engine. Will be a little bit of suck it and see regarding starting loads of all the motors. Also my small tig welder taking PF into account needs roughly 5kva when running at max. The workshop isn't being used all the time so I will base my use around available energy at the time.

My plan is to run a independent PV system for the workshop and give the homes system (batteries) an easy life. Although final plans - decisions haven't been made yet. Rough plan in my head was:

2kw of Chinese panels 8kwhr day average on tracking mount. $3000
12x 125ah sla's - 48v 500ah= 2.4 kwhr to use a day with only- 90% doc (hopefully last long with very shallow discharge)$2400
Taiwanese inverter charger 11kw inverter changer $3500
Generator (share the homes kubota 9kva with the house)
Miscellaneous hardware $2000

this will give me a relatively inexpensive $12,000 DIY workshop system.

I was thinking the property could take advantage of pumped hydro to supplement the relatively small battery bank on the workshop system. There is around 1 acre of flat land at the top of a hill Around 6 acres very very steep heading down the mountain for around 250m. There is a medium size spring fed dam up the top. Also a high annual rain fall of around 2000mm. Perhaps even two 20,000 ltr tanks. One fills off the shed then feeds to the bottom tank down the hill. workshop will be roughly 120m2 roof area or use the dam.

I will keep you all posted when I get the keys and move in.

Some pics of the property and system

Batteries and inverter charger. Hmm, wouldn't want to close the door on that inverter cabinet HOT! Battery banks need boxing in and venting to avoid potential corrosion of inverter.


Kubota 9kva diesel generator. Plan is to avoid using this although why buy diesel when you have 6.6kw of pv? I will have to look at how they have programed the controlling of it through selectroncs inverter. I have a suspicion they were just breaking into the conservative 90% doc some days and kicking it in (they had some inefficient appliances and kids with their own plasma tvs LOL otherwise I don't see it being used by us. Time will tell.


6.6kw of pv on roof. I don't think that little stink pipe gives any shading but will check that out. The roof behind does start to shade the top string after 4:30ish. If the tracking system for the shed works well they might even come off the roof and go on trackers.


Satellite view of the house and flat one acre of land with proposed 12x10m workshop outline. Yet to make a final decision on that, you can see the spring fed dam top right. Huge drop off to the left and views down the valley.


Kurt

[offgridQLD]

Pic of view down the hill from house. around 70 - 85m drop in height over 200 - 250m distance down the hill.Potential pumped hydro from 20,000lt rainwater tank off shed or water from spring fed dam behind the proposed shed. The house has 40,000l of water two 20,000ltr tanks. Would take some creative thinking regarding how to get a 20,000ltr tank down the bottom of the valley. Perhaps hire a Chinook helicopter LOL I think there is a fire trail down there some were.


Pic of spring fed dam at top of hill


Kurt.

[Gordon-Loomberah]

Some shading on very back string of panels during the very late afternoon.

Judging by the aerial photo, I reckon that roof shadow might be moving over the back string of panels by 2 or 3pm in summer at least. It's only got to shade a thin line across the row to wipe out their output completely.

Re the larger loads in your proposed workshop, I've found that a 3kW Latronics inverter (9kW surge) will easily start the 2400W induction motor on our drop saw, and the same size motor on the metal cut-off saw. The surge power often goes over 5 or 6kW for a second or 2 for both.

My pumped hydro is of similar head and distance your your proposed system- no way could I get a 20000l tank up the hill, so I have 13500 and 10500l up there, but dragging the 63mm poly around on that slope is a bit of a challenge- waiting for a time when I have a suitable number of able bodies around to attempt the big pull.

[offgridQLD]

Judging by the aerial photo, I reckon that roof shadow might be moving over the back string of panels by 2 or 3pm in summer at least. It's only got to shade a thin line across the row to wipe out their output completely.

I think you might be correct on the earlier shading times. Short term I guess I could move the top 6 panels down to the bottom of the roof just below the stink pipe.I think there is enough room before the gutter. (I am visiting the house on Sunday to do final inspection so will brink a tape measure).

Amazing that who ever installed it didn't put two and two together and work out there would be shading in the afternoon. I guess they just wanted it to look attractive in one block.

Given the panels point north east they would tend to catch more early morning sun I guess to make up some what for the afternoon shading. Given the size of the pv array some losses can be absorbed but it would still bug me that potential power is going to wast.

Good idea regarding a number of smaller tanks linked together. Not as cost effective but a lot easier to manage size weight wise.

Regarding running out your pipe any way of using a tractor and fabricating a spindle? Thats if you have access to one or hire something for a few hrs. I guess the pipe isn't rolled onto a drum ?

Speaking of lifting heavy things. My wife always gets roped into helping with lifting moving jobs that I am trying to tackle on my own . I broke down this week and purchased a 1 ton engine crane and some lifting straps boy it makes life easier and safer with less arguing lol

Kurt

[Gordon-Loomberah]

Good idea regarding a number of smaller tanks linked together. Not as cost effective but a lot easier to manage size weight wise.

That depends on how much you are paying for your tanks I got mine at the monthly auction in town where 2nds are auctioned off- $800 for a 13500l is way cheaper per litre than new 22500l tanks sell for.

Regarding running out your pipe any way of using a tractor and fabricating a spindle? Thats if you have access to one or hire something for a few hrs. I guess the pipe isn't rolled onto a drum ?

The poly was just in a roll, but I have made a spindle for it that mounts on the box trailer. Its not the sort of slope anyone in their right mind would drive a tractor up or down though parts of it are around 40degrees! it really has to be done on foot.

[offgridQLD]

Question regarding inverter standby mode.

The selectronics PS1 inverter has a standby mode where it will pulse the AC output looking for a load. In standby mode the inverter only consumes 15w.When it's active and in ON mode, it consumes 65w. Glancing over the user manual it states the Auto search sensitivity range is 5-40w.

65w x 24hrs is 1.5kwh ! It's a lot of waste. What I am trying to get my head around regarding standby mode is if the inverter is in standby mode and senses a load of between 5- 40w (user adjustable) it will trigger the inverter to go into ON mode. The thing that's confusing me is can the inverter supply any AC power during standby mode? Let's say I want it to power the auto garage door opener 3w load and a few other small loads, say, sub 20w load total.

I have the feeling the inverter has to see zero AC load for the inverter for to go into standby mode. I could be wrong?

I inspected the property today and the inverter was showing 30w load on the LCD control panel. I take it that 30w is the load from garage door opener, dishwasher, electric blinds and perhaps sensor lights all using around 1-5w each totaling 30w. I wondering if they will prevent the inverter from ever going into standby ?

Perhaps I will just have to accept the 1.5kwh that's used each day just to run the inverter in On mode.

Another interesting observation after recording the KWh meters of the inverter and generator 40 days ago when we 1st inspected the property and making note of them today i have some consumption data for the last 40 days.They vacated the house yesterday.

Taking the totals and dividing them by 40 i get..
1.17 kwh day from generator
8.21 kwh day from inverter

What I want to avoid is that 1.17kwh day from the inverter. My guess is the generator is set to come on at 90% Doc or around 6-7kwh from the batteries. I have a feeling they are just tipping into the triggering point each day and then the generator has a minimum run time.

I hope to adjust my consumption (particularly overnight consumption) to avoid this.

I didn't get to do much poking around today as the weather was nasty. I will go over the system in detail next weekend.

Pic of inverter display at 10:30am today. Was very overcast with heavy rain.Good to see the batteries at 100% as the house is empty.




Kurt

[Gordon-Loomberah]

What I am trying to get my head around regarding standby mode is if the inverter is in standby mode and senses a load of between 5- 40w (user adjustable) it will trigger the inverter to go into ON mode.

Correct. However, not all loads will bring the inverter out of standby. My 1100W Bosch angle grinder certainly doesn't. I think there was something else that didn't bring it on either, perhaps the Davey pump that doesn't get much use. In any case, I have the inverter set to be on all the time anyway, since the laptop running the weather station software (and PV solar/wind/load data logging, but not ATM due to lightning damage to the logger) is always on.

The thing that's confusing me is can the inverter supply any AC power during standby mode? Let's say I want it to power the auto garage door opener 3w load and a few other small loads, say, sub 20w load total.

None at all, unless it is triggered to ON. The pulses, probably about 330V peak, are only ~once/second (depends on the particular inverter), which wont run anything. Some modern fridges are confused when the power is not on all the time, so depending on what you are running, that 65W continuous may be unavoidable. It shouldn't really be a problem with 6.6kW of PV available though. Pumped stored hydro power should easily cover it, and most of the need for generator use too!

I have the feeling the inverter has to see zero AC load for the inverter for to go into standby mode. I could be wrong?

It is probably just a bit below the set turn on wattage for a certain time. The loads you mention could well be keeping it on, depending on what it is set to of course.

That PV array is certainly underutilised in a major way! A couple of hours sun each day is all that is needed to meet the demand. An array half that size could meet most of the demand in that location, even less with trackers.
I'd be inclined to allow a bit greater DOD to minimise the generator use.

[offgridQLD]

Thanks for that info. I will just let the inverter run 24-7. I have a few small loads that are handy to have switched on. I think I will just set some timers on things like the dishwasher and garage door opener.

That PV array is certainly underutilised in a major way! A couple of hours sun each day is all that is needed to meet the demand. An array half that size could meet most of the demand in that location, even less with trackers.
I'd be inclined to allow a bit greater DOD to minimise the generator use.

I 100% agree with that. I know we have been having some bad weather this last month for solar but even my modest 1.5kw grid fed system has been putting out some ok numbers especially if you multiply them by 4 for 6.6kw.

The other thing with the 90% DOD trigger point for the generator. You would have to hit that consumption number 6-7kwh from say sundown to sun-up 5pm-7am the next morning as the batteries would be full at the end of each day. That's 14 hours to consume 6kwh, and 8 of that you're asleep.The home has LPG oven, cooktop and hot water. So not sure what they were doing overnight to use so much generator.

I get the feeling that it will be different once we move in, as we have extremely efficient appliances and relatively savvy energy-use habits, as I don't mind keeping the shallow depth of charge if it means extending the battery life.

Kurt

[Gordon-Loomberah]

The other thing with the 90% DOD trigger point for the generator...

Is that what is set in a controller? Given the daily use figure you mentioned earlier, it is hard to imagine most of that is used overnight!

<speculation mode = on> I'd suspect the generator is set to start at a certain voltage, and that may well happen towards the end of the night during a fridge compressor or pump start, or similar brief large loading.</speculation>
What is controlling the generator start? If it is voltage, and you have an adjustable time delay IE, below 50V for x seconds, then increasing that time may eliminate much of the generator use.

[offgridQLD]

I need to look into the settings. I haven't gone into the secondary menu on the inverter yet to see what trigger point they are using. I'm not even 100% sure if it is 10% DOC as that is just what I remember from the first inspection - the owner mentioned something about 10% and the generator starting.

If it's voltage based trigger, then yes that's good thinking, the refrigerator or potentially a water pressure pump when someone flushes the toilet late at night or more likely has a very early morning shower before the sun is on the panels. I think it's a double wattage hit, when the house water pressure pump comes on as it most likely shortly after the water drains to waste, it kicks in a 2nd pump to remove the greywater to a dispersion trench from in the septic water tank, effectively double handling-pumping the water. Potentially the two pumps could be on at the same time during a shower. I will have to look into the wattage of both pumps.

All will be revealed when I get a chance to monitor the system and dive into the setting this coming weekend.

Kurt.