Since I'm prone to cluttering up actual threads about it...

Discussion thread for off-grid energy systems.

My office is purely standalone, and is on a 48V/225Ah lead acid bank right now, with about 5kW of panel hung off various charge controllers, and I have a 2kVA pure sine wave inverter that does a very good job of powering all the things.

To address a point from the other thread, though, I disagree that lead acid is "7x cheaper" than lithium battery banks anymore - at least if you're going with LFP/LiFePO4 (lithium iron phosphate). A good deep cycle lead acid battery, designed for off-grid renewable use, isn't nearly as cheap as one might hope.

A ~20kWh nominal bank of Trojan Solar batteries (8x SPRE 06 415) is around $4000. I know, I have a set in a solar trailer around the hill.

Meanwhile, a 15kWh nominal bank of LFP 4U batteries (https://signaturesolar.com/eg4-ll-lithium-battery-48v-100ahd or so), is around $5500 (with a 3U rack for them).

In terms of practical capacity, the two banks are roughly equal - lead shouldn't be deeply discharged on a regular basis, though you can do it on occasion for a deep cycle battery without any real harm. However, you also won't get the nominal capacity out of the bank under heavier use - as you beat lead harder, you get less amp-hours out of it, and so the 415Ah at the 100 hour rate (discharge the battery over 4 days) turns into far less at more useful rates.

https://assets.ctfassets.net/nh2mdhlonj7m/5i2peNrNeLJO58mHprrXc7/86ef16e5e252fcc5f9ec782ba9396d82/SPRE_06_415_DS.pdf

At the 20 hour rate, you only get 377Ah out - so about 18kWh, and as I've learned with a bank of these in a solar trailer, they sag enough under load that you're lucky to get that out - flooded just don't like high C-rate discharge, and will hit low voltage cutoff at somewhat less than rated, if you're not out to abuse them.

So the two banks, in my book, are roughly comparable. But, the lithium bank will supply an awful lot more current in the deal - and doesn't suffer the same cold weather capacity losses. I intend to keep my bank inside, and avoid letting it get too cold in the first place.

Almost all my compute comes from this office, and a slightly more cycle-happy bank would let me do a good bit more compute work as well. :)

Anyway. Off-grid energy. Discuss.

May I ask what yoiu would advise for a UK solar choice?
Annually we use 7,000kWh, with 4,500kWh for home and 2,500kWh for EVs. That's down from 9,500kWh total use in 2017
We went down the local government group purchase route for solar. 20x 400W panels and 10kWh battery. £20K-ish with 8-12 years ROI.
I'm a qualified electrical and electronic engineer, so can close out a lot of the BS. The solar implementation from the LA selected provider did not start well. Luckily, we got our deposit back. Say no more :(
Any advice welcome.
KR. W

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5.3KW of solar here, .9KW on East facing roof gets feed in tarrif. (very generous and based on generation rather than what is actually fed onto grid.3.4KW on West facing roof. currently no batteries. Some excess generation goes into a thermal store water tank rather than onto grid. There is a problem with the thermostat which stops more going there but that should be fixed soon. Combined gas and electric bill for last month was £61 with one computer (Ryzen 7) crunching all night. Probably going to get about 3-400W on shed being built in garden with batteries and inverter which will still be cheaper than paying an electrician to put in mains satisfying all the legal bits which could keep a cheap laptop charged and crunching most of the year.

May I ask what yoiu would advise for a UK solar choice?

If you can legally do the work yourself, do it yourself. I did my own grid tie solar for the house (large ground mount arrays, mostly east-west facing panels for longer solar day), and did it for under $1.50/W when installers want $4/W out here. A neighbor then iterated on that and did his for closer to $1/W.

The grid tie bit has to be done by a qualified electrician these days. but if competent there is quite a bit you can do yourself. After 11 years the inverter for the older panels failed and I was advised by the person whose company did the installation of the 1.92 KW on the East facing side of the roof to buy a replacement and do it myself. A job that took half and hour and would have only taken ten minutes had I all the right tools. The companies I looked at to do it were all going to charge North of £150 quid on top of the cost of the new inverter for ten minutes work or less. (The bit of the job that took 90% of the time was removing the bolts holding the bracket for the old inverter!

Edit: If competent you could get the qualified electrician to put in the wire from the consumer unit. (The thing with all the trip switches on it) to the mains isolator switch next to the inverter and then do the rest yourself. Not many of us in UK have the space for a large ground array hence most of us with our own solar have it on the roof.

Edit: I suspect that building regulations restrict what you can and can not do yourself here even with an off grid system. A friend, about 8 miles away has about8KW of solar plus a 500W turbine to charge batteries. I believe that since his two daughters left home, he has only started up the backup generator to make sure it is still working!

All the grid cares about is what invertor is connected in case you send nasty stuff onto the grid. Get a decent grid tied invertor you know they'll like, do ALL the work yourself, then have them check it's ok before you actually do the final connection. You only need them to check so they can pay you. Otherwise you won't get money when the meter runs backwards, or would you? If you have a non-smart meter, the old ones with a spinning disk, they just run backwards, they "pay" you the same amount as you buy the electricity off them, but smart meters don't, they can buy it for less than they sell it to you for:

"Despite smart meters’ many benefits, there can be downsides for solar homeowners. With analogue meters, the default is 1:1 net metering. You produce excess energy, it reduces the amount of energy measured on your bill by the same amount (the meter spins backwards). With “smart meters” utilities can measure and value your solar production any way the regulators let them. In many situations, when the changeover to smart meters take place — the new meters are not initially set up to properly measure flow going out from the house." - from https://www.solarunitedneighbors.org/news/smart-meters-what-every-solar-homeowner-should-know/

If your not grid connected, do what you like, it's your property.

As for batteries, in the UK a 130Ah 12V lead acid deep cycle is £70, probably less in bulk, I've never bought more than a few at a time.

The link Solarsyonyk posted: https://signaturesolar.com/eg4-ll-lithium-battery-48v-100ahd is quoted on the site as $331.84 per kWh = £261.36 per kWh in UK money. The lead acid batteries I listed above are 1.56kWh for £70 = £44.87 per kWh (5.82 times more expensive for Lithium). I had this discussion with an Aussie before, and over there Lead is much more expensive, because apparently a lot is made in the UK and it's clearly heavy to ship! But in the UK I'm obviously better using Lead Acid. Several times better. And deep cycle will discharge completely to 0% 220 times and still be 80% effective. Lithium is probably similar. Anyway you don't fully discharge because the invertors are clever.

A lead-acid battery with zero charge is one at zero volts, and the life will be substantially below the typical ~200 cycles at 80% discharge (typical lowest survivable discharge is typically about 80% for a flooded cell lead acid battery).
I just wish that battery manufacturers would be a bit clearer in their advertising blub when it comes to number of cycles "expected" - cell temperature (not ambient temperature), charge rate, discharge rate, charge cut-off voltage, discharge cut-off voltage, rest time between charge and discharge, rest time between discharge and charge (and many more factors) play a big role.

You only need them to check so they can pay you.

Quite a lot of electrical work I can do myself. Before I damaged a knee in 2009 I would have even felt confident working at roof heights but I would not have been competent to install panels there and make sure the roof didn't leak afterwards. Internally, the electrical side of things is a doddle. Much easier than the taking up of floorboards and taking the wires through walls and making it all look presentable afterwards.

May I ask what yoiu would advise for a UK solar choice?
Annually we use 7,000kWh, with 4,500kWh for home and 2,500kWh for EVs. That's down from 9,500kWh total use in 2017
We went down the local government group purchase route for solar. 20x 400W panels and 10kWh battery. £20K-ish with 8-12 years ROI.
I'm a qualified electrical and electronic engineer, so can close out a lot of the BS. The solar implementation from the LA selected provider did not start well. Luckily, we got our deposit back. Say no more :(
Any advice welcome.
KR. W

I also went the local group scheme and have been v happy with the install & service. I got other quotes and it saved ~£2K on the costs. This was a couple of years ago now. A friend in the village had an install this year and costs have gone up noticeably for equivalent system under the same scheme (and installer).

A lead-acid battery with zero charge is one at zero volts, and the life will be substantially below the typical ~200 cycles at 80% discharge (typical lowest survivable discharge is typically about 80% for a flooded cell lead acid battery).
I just wish that battery manufacturers would be a bit clearer in their advertising blub when it comes to number of cycles "expected" - cell temperature (not ambient temperature), charge rate, discharge rate, charge cut-off voltage, discharge cut-off voltage, rest time between charge and discharge, rest time between discharge and charge (and many more factors) play a big role.

The battery in my car would probably survive 200 cycles to 20%. My deep cycle leisure batteries would survive to 0% 200 times. Even my car battery would take 0% about 20 times - I know this for sure, because I have a stupid Renault which likes to run the battery flat overnight for no reason whatsoever. I've finally got into the habit of always disconnecting it.

Quite a lot of electrical work I can do myself.

I do all of it, I would never pay someone to do something that simple. I even moved my own gas main (sssh! That's illegal apparently!)

Before I damaged a knee in 2009

I have a damaged knee, ankle, thigh which play up randomly. If I'm going to go up a roof, or even go hillwalking, I put on velcro straps, they work wonders keeping the joints aligned. If it's too bad for even that, can you get a replacement? If they can do a hip, surely they can do a simpler knee which bends less directions?

I would have even felt confident working at roof heights but I would not have been competent to install panels there and make sure the roof didn't leak afterwards. Internally, the electrical side of things is a doddle. Much easier than the taking up of floorboards and taking the wires through walls and making it all look presentable afterwards.

I find it amazing most people think electrical work is difficult. Even the tradesman across the street came to ask me how to fit a three way lightswitch! Even after I explained how they work, he didn't understand and took my word for what to put where.

I also went the local group scheme and have been v happy with the install & service. I got other quotes and it saved ~£2K on the costs. This was a couple of years ago now. A friend in the village had an install this year and costs have gone up noticeably for equivalent system under the same scheme (and installer).

I tried twice to get a "free installation". The first time the company backed out due to terrible timing. The government dropped the subsidy rate just as they were about to install it. The second time he took an hour going through details, then finally admitted they used a bank loan in my name to buy the panels. When I told him I had a black credit score he got very angry. How was I supposed to know he was going to borrow money in my name? I called him some very rude things and told him to leave.

If they can do a hip, surely they can do a simpler knee which bends less directions?

A ball and socket joint like the hip is actually simpler to replace. They have about a quarter of the failure rate of knee replacements. I will get one at some point when consultant and physio deem it bad enough to go on the waiting list. There are people in a far worse state than I am not on the list yet but I don't want to risk my knee giving way because I turn on it in the wrong way when on a roof!

A ball and socket joint like the hip is actually simpler to replace. They have about a quarter of the failure rate of knee replacements. I will get one at some point when consultant and physio deem it bad enough to go on the waiting list. There are people in a far worse state than I am not on the list yet

You can always go private, if you have the cash. The NHS is a piece of excrement.

but I don't want to risk my knee giving way because I turn on it in the wrong way when on a roof!

Grab the nearest neighbour and tell him what to do.

You can always go private, if you have the cash. The NHS is a piece of excrement.

I worked in the NHS for over 30 years. I have also had extensive contact with the private sector. If anything were to go wrong during an operation I would be a lot safer in an NHS hospital.

A ball and socket joint like the hip is actually simpler to replace. They have about a quarter of the failure rate of knee replacements. I will get one at some point when consultant and physio deem it bad enough to go on the waiting list.

They have made a lot of progress in hip replacements in recent years. A few decades ago an acquaintance of mine had a hip replaced and he spent a week in the hospital doing recovery. Then many weeks in residential physical rehab.

When I had my hip replaced a few years ago, the surgeon told me it would be a one-day outpatient procedure, but because I was so old, they would keep me overnight. He normally did half a dozen to a dozen operations in a day, so they do not take very long. They had me walk the day of the surgery. On the next day they decided to keep me overnight because my blood pressure was 70/40. I asked them why I was not fainting, but they did not know. It is a common (but rare) after effect of the anesthetics used. They took me offf my b.p. meds for a couble of days..\

IIRC, there was not much of a waiting list. The operation was done about a month after the decision to do it. Partly delay in getting clearance from my insurance company.

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If you have a non-smart meter, the old ones with a spinning disk, they just run backwards, they "pay" you the same amount as you buy the electricity off them

Not all of them run backwards. A lot run forwards in both directions, to solve the problem of "people putting the meter in upside down a week a month to reduce their bill." The smart meters also typically have separate registers to count "net energy through" and "total energy through," and if they split and you're not listed as a solar install, your power company may come sniffing around.

As for batteries, in the UK a 130Ah 12V lead acid deep cycle is £70, probably less in bulk, I've never bought more than a few at a time.

Yeah, but that's not a long lived battery, is it? What's the datasheet say?

A lead-acid battery with zero charge is one at zero volts, and the life will be substantially below the typical ~200 cycles at 80% discharge (typical lowest survivable discharge is typically about 80% for a flooded cell lead acid battery).

Only 200 cycles at 80% DoD? Weak...

This is the Trojan battery I have in one of my solar trailers.

https://assets.ctfassets.net/nh2mdhlonj7m/5i2peNrNeLJO58mHprrXc7/86ef16e5e252fcc5f9ec782ba9396d82/SPRE_06_415_DS.pdf

Per the datasheet, it's rated at 1200 cycles to 80% DoD (down to 20% state of charge), and 2000 cycles at 50% DoD.

I just wish that battery manufacturers would be a bit clearer in their advertising blub when it comes to number of cycles "expected" - cell temperature (not ambient temperature), charge rate, discharge rate, charge cut-off voltage, discharge cut-off voltage, rest time between charge and discharge, rest time between discharge and charge (and many more factors) play a big role.

If you don't buy batteries from "Cheap manufacturer of the week," you get those datasheets in various forms.

My standing policy is that I won't buy a battery for deep cycle use without a datasheet.

I worked in the NHS for over 30 years. I have also had extensive contact with the private sector. If anything were to go wrong during an operation I would be a lot safer in an NHS hospital.

ROFL! I beg to differ. My sister works in the NHS and she constantly tells me how utterly useless they are, she's constantly correcting mistakes of others. Myself and my father have had a lot of work done on the NHS, they screw up every single time. I've made complaints twice, but they always weasel out of it. Now when I've gone private, and the multiple times my Aunt has gone private, way better customer service, way better quality of work, everything goes according to plan and without months of waiting hoping you'll die and be removed from the list. We'd be better just deleting the NHS and have everyone pay for it. You can get health insurance to avoid the risk of a huge unexpected bill.

My office is purely standalone, and is on a 48V/225Ah lead acid bank right now, with about 5kW of panel hung off various charge controllers, and I have a 2kVA pure sine wave inverter that does a very good job of powering all the things.

What do you do about earth/ground? Domestic properties in the UK have live (240V AC), with neutral and earth tied together (0V). Very stupid really, since you can touch a bare live wire and the actual ground and get a shock. If it was floating, like on a building site with isolating transformers, you couldn't. No current would flow.

So if I didn't have computers, I'd make an off-grid system with no earth at all. But computers like stable stuff without interference, so I guess they would like shielding, their cases connected to the real ground. And multiple computers talking to each other, best if both chassis are the same voltage exactly, so no current flows through the ground wire of a USB cable for example. I did have the earth in my garage come disconnected, I noticed when I felt a bit of electricity when I touched a PSU casing, presumably some induction somewhere. A multimeter told me it was 80V AC with a tiny current. Not harmful to me, but to a microchip?

So I think I'd leave live and neutral floating, and connect "earth" to the real ground with a stake. I guess the batteries can sit floating too.

The reason I thought of this was I was considering powering the 12 GPUs directly from the batteries to save wastage on invertors and PSUs converting from 48V to 240V to 12V. I could use one of the sets of batteries, 0V and 12V, but I couldn't plug other GPUs into 12V and 24V, as they'd end up with different DC grounds and short out. If I only used one battery set, I'd have a massive current going through the battery equalisers. Or I could use a 12V system, but then all the low voltage wires would be thicker and more expensive.

They have made a lot of progress in hip replacements in recent years. A few decades ago an acquaintance of mine had a hip replaced and he spent a week in the hospital doing recovery. Then many weeks in residential physical rehab.

Yes, a friend told me hip replacements are now better than the real thing.

On the next day they decided to keep me overnight because my blood pressure was 70/40. I asked them why I was not fainting, but they did not know. It is a common (but rare) after effect of the anesthetics used. They took me offf my b.p. meds for a couble of days..\

My colleague fainted due to low blood pressure, and discovered it was caused by running marathons regularly, then stopping suddenly, he was told to go back to running and wean off it slowly. Very odd, some kind of physical addiction to exercise!

IIRC, there was not much of a waiting list. The operation was done about a month after the decision to do it. Partly delay in getting clearance from my insurance company.

Try the UK with our wonderful NHS, 50/50 chance you die before the end of the waiting list. My father's been waiting for 6 months for a heart operation. A very urgent one. He was originally told 2 months. He should have gone private, but since he was lied to with the "2 months", he didn't.