Circular reasoning (Rolfe's solar energy system)

[QLeo]

Here, the issue is winter. Ask @QLeo about that. You can store enough solar in summer to keep you going, powering the night from yesterday's solar, and over the week you're fine. But in winter when day after day there's nowhere near enough, how do you store excess summer solar and use it then? How many MG4 batteries would you need?

QLeo has a wind turbine and a diesel generator, though I believe he's driving Goth Leo to the nearest charger and bringing back grid-derived electricity that way to run the house from VtL, rather than burn diesel. Storing excess summer solar for winter isn't yet practical.

However, I have no idea what it's like in winter in Australia. Is there still enough to run the house load, spread out over a week or so? You won't get enough to charge a car though, surely.

Yeah, we don't have a diesel generator, just a little petrol one, but until Goth Leo came on the scene, we'd need it perhaps a couple of times a week in winter. Goth Leo does make things easier as we can risk discharging the house battery deeper, then spend plenty of time on Leo's power to get them back up to a decent SOC rather than run a noisy generator.
As you say, long term battery storage at domestic levels is not really possible.
But Aus is much better off than we are for solar, possibly through the year. Even southern Tasmania is 18 degrees closer to the equator than we are, and we get most of our household power from solar for 8.5 months of the year.
But off-grid and feed-in systems are very different things, and priorities are very different. A case in point; someone in the electrical industry visited the other day and asked if we have panels on adjustable mounts. No, because I doubt they'd survive our winter gales. He then asked why the panels were at such a steep angle. It's because we're not seeking to maximise summer input, as one might if wishing to maximise feed-in tariffs. Instead, we want to squeeze more out of those shoulder seasons, so, if they're "optimised" at all, it's for those short times of the year.
Incidentally, and for a change, the person I was chatting with understood immediately why the house battery is a set of huge forklift 2V lead-acid cells - they can take the unpredictable charge regimes of an off-grid environment much better than lithium. But that may also be less of an issue in Aus, where sunlight may well be more certain than the far north west of Scotland.
Oops - got carried away - hope you didn't read this far...

 

[Rolfe]

Of course I read that far. It's extremely interesting (and not even long).

I'm not bothering to worry about the health of my home battery, on the principle that it's LFP and can probably take it. Also that battery prices are coming down so much that a replacement in some years time might not actually be all that expensive. (I have similar thoughts about my bike's battery, although I do try to look after it.)

In what way do you think lithium batteries are vulnerable to being messed around in an unpredictable way?

 

[T1 Terry]

I can see why you want to off grid!!!

Can you have a separate battery isolated from the grid for your own personal use?
One of those MG4 batteries would be fine.

That's the plan, but leave it in the MG4 and use it via V2L. The practice run will be with the motorhome and the 51 on the trailer. We have a 600Ah @ 12V sodium ion house battery.

I'll be setting up a method of charging the MG4 51 battery once the house battery is full via the solar on the roof, then turning on the V2L if the house battery drops below 30% SOC and turns off at 80% SOC .....

Well, that's the plan, the science is still lacking, but I'm confident any ideas I come up with will be shot full of holes as soon as I post them here and on the electric vehicle forums

For some reason, my V2L adapter plug I bought with the "fits every plug type in the world" output, doesn't trigger the load side and sees it as a charging plug .... so maybe there is a solution tied up in the fix to get the adapter to work ......

Other jobs to get finished before I pull the adapter to bits for a peek inside .... like finishing wiring up the control box (my own designed and built BMS), and the new Victron 5000 VA inverter/charger.

[ Edit moderator: 5000kva -> 5000 VA ]

T1 Terry

 

[decrep]

That's the plan, but leave it in the MG4 and use it via V2L. The practice run will be with the motorhome and the 51 on the trailer. We have a 600Ah @ 12v sodium ion house battery.

I'll be setting up a method of charging the MG4 51 battery once the house battery is full via the solar on the roof, then turning on the V2L if the house battery drops below 30% SOC and turns off at 80% SOC .....

Well, that's the plan, the science is still lacking, but I'm confident any ideas I come up with will be shot full of holes as soon as I post them here and on the electric vehicle forums

For some reason, my V2L adapter plug I bought with the "fits every plug type in the world" output, doesn't trigger the load side and sees it as a charging plug .... so maybe there is a solution tied up in the fix to get the adapter to work ......

Other jobs to get finished before I pull the adapter to bits for a peek inside .... like finishing wiring up the control box (my own designed and built BMS) and the new Victron 5000kva inverter/charger

T1 Terry

I wish you well Terry, seems like a must have bit of technology once you get it working. But 5000kva?? are you powering the whole suburb?

 

[T1 Terry]

Yeah, we don't have a diesel generator, just a little petrol one, but until Goth Leo came on the scene, we'd need it perhaps a couple of times a week in winter. Goth Leo does make things easier as we can risk discharging the house battery deeper, then spend plenty of time on Leo's power to get them back up to a decent SOC rather than run a noisy generator.
As you say, long term battery storage at domestic levels is not really possible.
But Aus is much better off than we are for solar, possibly through the year. Even southern Tasmania is 18 degrees closer to the equator than we are, and we get most of our household power from solar for 8.5 months of the year.
But off-grid and feed-in systems are very different things, and priorities are very different. A case in point; someone in the electrical industry visited the other day and asked if we have panels on adjustable mounts. No, because I doubt they'd survive our winter gales. He then asked why the panels were at such a steep angle. It's because we're not seeking to maximise summer input, as one might if wishing to maximise feed-in tariffs. Instead, we want to squeeze more out of those shoulder seasons, so, if they're "optimised" at all, it's for those short times of the year.
Incidentally, and for a change, the person I was chatting with understood immediately why the house battery is a set of huge forklift 2v lead-acid cells - they can take the unpredictable charge regimes of an off-grid environment much better than lithium. But that may also be less of an issue in Aus, where sunlight may well be more certain than the far north west of Scotland.
Oops - got carried away - hope you didn't read this far...

The brother in law lives in Tassie on the side of the Huon Valley, you can see the ocean at the very bottom tip of Tassie looking out his windows ..... well, when the clouds don't block it out ... it is Tassie after all

He lives completely off grid, about 5 kms straight up hill from the closest grid supply, and he is the type to shun any of that sort of "easy living" thing anyway

He built himself a 4 panel solar array, end to end along a length of water pipe, that is bearing mounted each end with the lower end adjustable up or down to suit the seasons.

The solar tracking is performed using an old tyre and wheel in a garbage can, with the vertical rod attached to a horizontal bar welded to the pivoting water pipe bar with the 4 solar panels attached.

When the sun comes up and supplies power from the panels, a tap/solenoid is turned on to slowly feed water into the garbage can and this floats the tyre and rotates the panels to track the sun.
Solar tracking is done with a plate with a 6" hole in the centre, mounted a set distance above another flat plate the same size ...... when the sun shining through the hole forms a circle that fits neat on the lower plate, the optimum solar is achieved ..... adjustment of the water flow sets the tilt speed throughout the day ..... at the end of the day, the supply solenoid turns off and the drain solenoid turns on and waters his vegie garden .......

Being on the most southern tip of Tasmania, the winds up that hill are tremendous ...... but a wind turbine isn't part of his plan yet .... gets enough from his solar and if needed, he turns on a tap to drain the spring trickle fed dam up the top of the hill into a Pelton wheel (like a wheel made out of teaspoons) attached to an old car alternator, and he tops the old telephone lead acid battery up with that ...... a true mountain man hillbilly

T1 Terry

 

[T1 Terry]

I wish you well Terry, seems like a must have bit of technology once you get it working. But 5000kva?? are you powering the whole suburb?

Ahhh... make that a 5kva inverter ..... and it will power the whole motorhome, HVAC, hot water, fridge freezer and possibly the MG4 51 charger ..... if I can't figure out how to direct DC charge from the solar ... depends how much trickery will be involved in getting the 400- 500vdc open circuit solar rigged up to converter 2 x 200vdc to 250vdc solar arrays in parallel to one x 400vdc to 500vdc in series .....

T1 Terry

 

[Archev]

The brother in law lives in Tassie on the side of the Huon Valley, you can see the ocean at the very bottom tip of Tassie looking out his windows ..... well, when the clouds don't block it out ... it is Tassie after all

He lives completely off grid, about 5 kms straight up hill from the closest grid supply, and he is the type to shun any of that sort of "easy living" thing anyway

He built himself a 4 panel solar array, end to end along a length of water pipe, that is bearing mounted each end with the lower end adjustable up or down to suit the seasons.

The solar tracking is performed using an old tyre and wheel in a garbage can, with the vertical rod attached to a horizontal bar welded to the pivoting water pipe bar with the 4 solar panels attached.

When the sun comes up and supplies power from the panels, a tap/solenoid is turned on to slowly feed water into the garbage can and this floats the tyre and rotates the panels to track the sun.
Solar tracking is done with a plate with a 6" hole in the centre, mounted a set distance above another flat plate the same size ...... when the sun shining through the hole forms a circle that fits neat on the lower plate, the optimum solar is achieved ..... adjustment of the water flow sets the tilt speed throughout the day ..... at the end of the day, the supply solenoid turns off and the drain solenoid turns on and waters his vegie garden .......

Being on the most southern tip of Tasmania, the winds up that hill are tremendous ...... but a wind turbine isn't part of his plan yet .... gets enough from his solar and if needed, he turns on a tap to drain the spring trickle fed dam up the top of the hill into a Pelton wheel (like a wheel made out of teaspoons) attached to an old car alternator, and he tops the old telephone lead acid battery up with that ...... a true mountain man hillbilly

T1 Terry

Love it. Nirvana always needs a persistent, inventive approach.

 

[QLeo]

Of course I read that far. It's extremely interesting (and not even long).

I'm not bothering to worry about the health of my home battery, on the principle that it's LFP and can probably take it. Also that battery prices are coming down so much that a replacement in some years time might not actually be all that expensive. (I have similar thoughts about my bike's battery, although I do try to look after it.)

In what way do you think lithium batteries are vulnerable to being messed around in an unpredictable way?

As I said, on-grid requirements are a very different kettle of fish, and you will almost certainly find your LFP lasting a long time.
I tried to choose my words carefully re the choice of lead-acids - I think you may be thinking of output whereas our concerns are very much input. If the battery needs charged, lithiums typically like a specific type of charge, which is why our cars have charging circuits very much part of the battery packs. When you're off grid, you don''t know how strongly the wind will blow for how long, how much sun you'll have (potentially, on good days, 10 hours in summer and 2 in winter) so the battery needs to cope with that variation. These aren't good ways of giving a battery the type of charge it's designed for. But as an adjunct when you're on-grid, it's ideal.
Oh, another aspect of being so far north is not just that daylight is precious in winter, but the strength of the sun is pathetic. To see this, draw two concentric circles to represent the earth and the atmosphere. Put "the sun" in the lower half (or top is you're in the south) and see how much atmosphere the sun needs to penetrate to get to us.

 

[Everest]

A case in point; someone in the electrical industry visited the other day and asked if we have panels on adjustable mounts. No, because I doubt they'd survive our winter gales.

Also, now that 450W panels are only £50 each then, if you have the space, it doesn't make financial sense to invest in tracking systems, IMHO. Just deploy more panels. Then you have better output in cloudy conditions when tracking systems don't gain much.

He then asked why the panels were at such a steep angle. It's because we're not seeking to maximise summer input, as one might if wishing to maximise feed-in tariffs. Instead, we want to squeeze more out of those shoulder seasons, so, if they're "optimised" at all, it's for those short times of the year.

Absolutely, we have some of our panels at very steep angle for Winter production too.

I tried to choose my words carefully re the choice of lead-acids - I think you may be thinking of output whereas our concerns are very much input. If the battery needs charged, lithiums typically like a specific type of charge, which is why our cars have charging circuits very much part of the battery packs. When you're off grid, you don''t know how strongly the wind will blow for how long, how much sun you'll have (potentially, on good days, 10 hours in summer and 2 in winter) so the battery needs to cope with that variation. These aren't good ways of giving a battery the type of charge it's designed for. But as an adjunct when you're on-grid, it's ideal.

Genuinely interested in exactly what you are referring to, charge-wise, by using LA over LFP.

Obviously LA will be better for very low temperature charging if your batteries are not stored in a warm environment. But LFP's can safely and regularly charge up to 0.5C charge rate and 1C is not an issue up to around 70-80% SOC if temperature is in the 20 to 30 degree C range.

I have no experience of LA batteries being used for home storage, but from what I had read (on the Internet, so it must be true ) was that they couldn't charge up to 1C, can only be discharged to 50% SOC and didn't have the same longevity as LFP's?

What size inverters are you running and what charge rates?

 

[QLeo]

Also, now that 450W panels are only £50 each then, if you have the space, it doesn't make financial sense to invest in tracking systems, IMHO. Just deploy more panels. Then you have better output in cloudy conditions when tracking systems don't gain much.


Absolutely, we have some of our panels at very steep angle for Winter production too.


Genuinely interested in exactly what you are referring to, charge-wise, by using LA over LFP.

Obviously LA will be better for very low temperature charging if your batteries are not stored in a warm environment. But LFP's can safely and regularly charge up to 0.5C charge rate and 1C is not an issue up to around 70-80% SOC if temperature is in the 20 to 30 degree C range.

I have no experience of LA batteries being used for home storage, but from what I had read (on the Internet, so it must be true ) was that they couldn't charge up to 1C, can only be discharged to 50% SOC and didn't have the same longevity as LFP's?

What size inverters are you running and what charge rates?

Well yes, panels are getting cheaper, but the last pair of 400W we bought, they wanted (and got) £300 for delivery to where we are.
Re the lead-acid versus lithium issue I've been describing, I know there are all kinds of "ideal" discussions, mostly by people either who have never tried this, or who are on-grid and talking about home storage rather than offgrid living, but 17 years of off-grid experience have taught us, often the hard, expensive way, that there are practical but perhaps not academically idealised ways of doing things. Again, in the discussion I was referring to with the person from the battery company, he immediately understood the issues, which was gratifying. I have written up a few things on my blog from time to time, though not addressing this particular issue.
Re the question about charge rates, that's exactly the point I was making. When you are dependent on environmental, weather conditions for charging, all discussion about charge rates goes out of the window, so I can't answer the question. There are time when you;re grateful for 2 amps coming in. And the info re discharge rates is true for car batteries but not for deep cycle or forklift batteries, and longevity is not an issue.
In summary: there are theoretical ways of doing things, and practical ways of doing things, and they don't always align perfectly. For example, the theory won't take into account a line of hills to the south that block winter sunlight until 11:30 am, or wind chargers that burn out in 100mph gales.
Apologies if this comes across as mildly frustrated, but I've been asked to answer some doozies over the years, including, as close to a low point "How much do you make from feeding this into the grid?" What part of "off-grid" was unclear? And again, not sure if the MG4 forum is the place for this discussion, but I would say to folk wanting to try these things do what you think is best for your circumstances/budget/requirements/wishes. By all means see what I've done, but I'll not be the first to say this is how it should be done.

 

[Everest]

I have written up a few things on my blog from time to time, though not addressing this particular issue.

Would like to read that - can you post a link, or pm it? Thanks.

"How much do you make from feeding this into the grid?" What part of "off-grid" was unclear?

FOFL

 

[QLeo]

Would like to read that - can you post a link, or pm it? Thanks.


FOFL

DM sent

 

[Rolfe]

As I said, on-grid requirements are a very different kettle of fish, and you will almost certainly find your LFP lasting a long time.
I tried to choose my words carefully re the choice of lead-acids - I think you may be thinking of output whereas our concerns are very much input. If the battery needs charged, lithiums typically like a specific type of charge, which is why our cars have charging circuits very much part of the battery packs. When you're off grid, you don''t know how strongly the wind will blow for how long, how much sun you'll have (potentially, on good days, 10 hours in summer and 2 in winter) so the battery needs to cope with that variation. These aren't good ways of giving a battery the type of charge it's designed for. But as an adjunct when you're on-grid, it's ideal.
Oh, another aspect of being so far north is not just that daylight is precious in winter, but the strength of the sun is pathetic. To see this, draw two concentric circles to represent the earth and the atmosphere. Put "the sun" in the lower half (or top is you're in the south) and see how much atmosphere the sun needs to penetrate to get to us.

I charge mine from solar as well as the grid, but realistically much more from the grid. Solar really just to mop up extra generation which would otherwise be clipped. But I do charge and discharge at maximum speed quite a bit.

I know what you mean about the latitude. This year on Ne'erday, I got a princely 314 watt-hours! You're even less well-served.

 

[Rolfe]

So, I got it wrong again last night and woke up to 83% in the battery. But as it happened there was only a short spell of full sun at the relevant time of day so I didn't lose much clipping. I did get 17% into the battery.

My mistake is that I've been trying to do something which turns out to be insanely complicated, if not downright impossible, and that is to heat the water when the battery is already at the SOC I want it for the morning. One setting and the Eddi will draw from the battery instead of the grid, the other setting and the battery will charge while the Eddi heats.

Much better to charge the battery up, then heat the water while the battery is held at 100% by still being on charge, then discharge it to whatever SOC I want it to hold at until clipping starts. That way all the electricity comes from the mains and the battery exports to the mains without being gobbled by other things.

Snagette would come if I'm charging the car, because if the car is still charging after 4 am the battery will be eaten by the car rather than exporting. (This is a point in favour of John's approach to the wiring.) However, I don't charge the car every evening and it's not a major issue.

 

[T1 Terry]

My wife wrote a lot of advice regarding LFP cells/batteries on the ex business website T1 Lithium | Custom-built lithium batteries for RVs and off grid
Many nights and travelling time was spent asking me questions, then turning it into something people could read, I tend to go all techo far too often.

If you build your battery from cells to the capacity you want/need/can afford, control the charging and discharging via cell voltage and not total battery voltage, you can charge as fast as you like. When it's too fast for a group of cells to absorb, the voltage goes up, but drops immediately when the charge rate is reduced to a rate it can absorb.
I have charged at 5C on a few occasions, not very often I can get enough supply current from the multiple charge sources available, but the cells can absorb it for a short period.
I've pulse charged at 10C using an LTO battery as the capacitor, the pulse starts at a 50% cycle rate and the on/off ratio heads in favour of the off part of the cycle as the battery passes the 90% SOC point ......

No, it does not harm the cells, shorten their cycle life or cancel future birthdays, as long as the cells stay below 3.8V when pulse charging and 3.6V when constant current charging. We have systems on the road, 24/7 off grid, approaching their 13th yr of service and showing no signs of reduced capacity yet ......

There is a lot of nonsense on the interweb, and very little hard earned knowledge, I have been doing this since July 2011, learnt the truth the very expensive way, I don't recommend using that path

Just as disclaimer, I still assist customers when they run into problems, but I no longer build or install systems for anyone but close friends and myself, and I even avoid that wherever possible.
my passion now is the learning path for Sodium ion cells/batteries. I have a 600Ah@12V nom. one in our motorhome at the moment, repowering some of my fleet to BEV or PHEV, and getting this 2002 V10 6.8 ltr wallet draining Winnebago (Australia) Explorer upgraded for permanent off road living and using our MG4 51 as the extended battery capacity. The end game is to convert it to PHEV, using the V6 and hybrid transmission for my, given to me, Lexus GS450h .....

T1 Terry

 

[Rolfe]

Fascinating stuff, Terry. There is a setting on my battery that gives permission for the battery to do a 10% charge or discharge cycle to warm itself up if it gets too cold. I've not seen it activate very much, because the battery is inside the garage. Although having said that, water will freeze in that garage in winter and I have seen -13.5°C on my previous car's dashboard when I went to get it out on a cold morning!

I think I have cracked the problem of harvesting the clipping now, as it's working very well today. I made another mistake last night because I decided that to give time for all the things I wanted to do during the off-peak tariff I would start the battery charging at 23:45 rather than midnight. Unfortunately I hadn't realised that setting the charge to run 23:45-04:00 would actually stop the charge at midnight, because that's another day. Fortunately something made me check as I was going to bed. I saw the battery wasn't charging, figured it out, and changed the settings to two slots, 23:45-00:00 and 00:00 to 04:00. The gap in charging didn't cause any problem, it just made the graph look a bit odd.

When I woke up the battery was being held at 38%. It had discharged to 39% in the slot I had specified, then used another 1% to run the house from 05:30 till dawn an hour later. (Eventually we'll get to the point where the solar can run the house from the end of the off-peak tariff, but we're still only in April.) The morning was a lot cloudier than forecast but it got better just before eleven and the battery started to charge intermittently. It's now (13:40) up at 58%, so I've gained 20% charge even given the cloud, and in the sunny intervals I'm seeing up to 7.8 kw generation.

Even if it had been much duller than forecast and there had been no generation above the clipping threshhold, 38% is plenty to do me through the evening, even if I get ambitious with the cookery. The only thing to remember is that if I want to switch something on when the sun is behind a cloud it's prudent to flip the export setting on the inverter to off while I do it, then flip it back on again once the load has finished. It would have to be terribly dull for the solar not to cover the house base load, and if it's that bad I can just turn the export setting right off and go back to normal working. The battery can power the house, and take any solar there is.

 

[Rolfe]

We're now past the time where clipping is possible. There was a fair bit of cloud around but the battery SOC increased from 38% to 66%, so by 28%. The GivEnergy app is saying 2.84 kWh so that seems about right. When I wanted a coffee the sun was shining so I didn't need to do anything. The kettle just used a bit of what would otherwise have been exported.

It's falling off now. The panels are slightly east-inclined, and another part of the roof tends to shade them in the late afternoon. I noticed clipping is now ceasing about 3.40. It's getting on for time to start cooking, and obviously I'll switch the battery export off when I start. By the time I'm done it probably won't be worth trying to export anything more, so it can stay off and if there is any more excess the battery can have it.

I'm trying to avoid scooping up solar into the battery in the late afternoon, because it's only going to be exported later, and if I let it export in the first instance then I avoid losses within the system. But it's not worth making a fetish of it. Doing things this way does mean I have to keep an eye out and switch off export at the right time to avoid drawing mains power in the evening. I have it set to do it automatically at six, and if there's still excess after that then the battery can have it, such as it is. But if I start to cook before then I have to switch it off at that point. Also, if the weather is very dull I need to keep an eye out for an early start to the solar failing to meet the house demand.

If it's too much like hassle I can just revert to the winter setup, which runs on its own, but I think once I'm used to this setup it will be fairly easy to do.

 

[Everest]

You need to treat yourself to one of these...

https://www.argos.co.uk/product/4821261

Only draws 1kW

 

[Rolfe]

Oh dearie me no. I'm the impatient sort. I did buy a kettle for travel recently, and scoured Amazon to find one that would take 3.5 kW.

 

[johnb80]

You need to treat yourself to one of these...

https://www.argos.co.uk/product/4821261

Only draws 1kW

Jeez, nooooooo, life is too short waiting for those damn things to boil. I have a Franke hot tap so boiling water is constantly available 24/7.