Off grid office!

[venquessa]

It's sort of a "dream come true" scenario this. My first solar adventure charged my phone 9 out of 12 months of the year. Back then I had ideals of running a 24/7 server on solar and realising how far away my little 50W 12V setup was from that.

Fast forward 5 years and about £2000 and I have this now. Running the entire office! Battery storage, transfer switch the works.



It suddenly feels less "DIY" and less "jury rigged" and more professional. Mostly thanks to me investing into the Victron Multiplus which has made the whole off-grid with grid fall back seamless!

The graph above shows two fairly poor days weather wise, which followed an even worse day. Yet the majority of power came from the inverter.

The transitions need more tuning, but currently under 25.50V for 2 minutes switches over to grid. Should it ever occur the battery charger is enabled for a short boost at 25.5V and float at 25.00V. When the voltage rises above 26.50V again the inverter switches back to ON and disconnects the AC-In entirely.

This gives the battery a small head start in the morning to prevent ping-pong. Seems to be working so far.

A few things are not on this circuit, the main server (35-60W 24/7) and the gaming PC 500W for an hour or two at a time. For those I need to wait for the next upgrade (financing). Going from 330W panels to 1kW panels and I have my eyes on a set of 8 280Ah cells taking storage up to about 8kWh. Then I should be able to run the full office 24/7 with the gaming PC potentially triggering a grid fall back if the total exceeds the 400W sustained from the inverter.... and I can always chain or parallel another multi in there to take that up to 800W say.

 

[venquessa]

A few tuning notes.

Why 25.50V for grid fall back? - I tried 24.00V which should (maybe?) be the bottom end of the pack. However, I do not yet have any "bottom end" balancing. So it resulted in a BMS low voltage disconnect and ... plunged me into darkness. The multiplus cannot function without a DC input.

So I set it to 25.00V and ran with it. No low voltage disconnects. However, the same lower cell that caused the LVC (low voltage cut out) was still low and always low and as 2 to 3 days rolled by the 25.00V transfer point drove it lower and lower.

I figured there was no reason to run the system between 25.00V and 26.00V when it would work just as well from 25.50V to 26.50V, it might work better in current circumstances.

Today I received a 5A flying-capacitor balancer. "Heltec?". I have used their 4 series one before and it's powerful, but wasteful.

I am debating using a "SOnOff SV switch", basically a low voltage dry contact Wifi smart switch, to toggle this balancer based on the cell delta only. If the min-max cell voltage is greater than say, 100mV, then the 5A balancer will engage. This may allow me to lower that 25.50V down to 25.00V or even right down to 24V (3.00V per cell) and maxmimise the bottom end capacity.

The downside of that is it will spoil the top end balance and most like cause the same problem at the top. Cell high voltage disconnects. Again, however, the 5A flying cap balancer engaging above 100mV inbalance will waste a bunch of joules but should do a good job of helping prevent that high cell disconnect.

All theory. First step is to get more data with things as they are. It's working. It's not broken. It doesn't need "fixed", it just needs understood more to guide the next steps and upgrades and which order they occur in.

 

[Decto]

Doing something similar in the UK with an offgrid shed/workshop.

1640W of panels, 1200VA 12V multiplus, 2x 170Ah Renogy batteries with a Fogstar 300Ah arriving this month to hit 8kWh.
Plan to add an extra 700W (4 x 175 Renogy Panels) as that will just fit in remaining space of the shed roof.

Primary use, experiment with Solar, I will be feeding power into a dedicated circuit in the house to run server (unraid) + CCTV + network switches etc. Have been using to run growlights for my veggies, just planted out my 2ft tall tomatoes I started too early!

Need to consider how to optimise solar use but I expect to also be able to run the heat pump dryer as well as that is 1.6kWh per load and ~700W running. Maximum 2 loads per day but ~4 loads per week.

Multiplus switches to mains at 20% currently to max my solar utilisation, not that I have triggered that with 200W of lamps for ~ 14hrs a day.
In winter I expect I'll hold 50% reserve.

Need to work out the optimal mix of loads to most effectively utilise the solar element once everything set up.

Secondary use: backup power for grid outage.
With the expanded panels I expect to cover electric to gas boiler + Fridge freezer + Freezer + phones, tablets, internet + small TV and sat reciever for a few hours in worst case December / Jan, the lowest daylight hours though need to prove out actual solar production.

7kWh usable at a pinch gets me three days backup on pure battery though extended to 6 days with expected worst case solar production at half of panel capacity per full day. As a backup I also have a 1.2Kw inverter generator which can recharge batteries at 50A ~ 700W + losses through the multiplus. Data I have for my area is average of 1kWh per 1kWh panels on average in Dec / Jan, however the low days are ~0.5kWh per 1kWh panels. So 2-3 hours runtime should give a decent boost on the really dark days.

Also picked up 2 very cheap LifePo4 GOLABS R300 (300Wh, 300W max) power stations on Black Friday which I can recharge from the solar, need to finish my DC/DC converter for optimal charge rate battery to battery using the MPPT input. I suspect these were cheap as they have now ceased trading so I expect clearing stock. I had heard a rumor at the time so was an informed risk. Keeping an eye out for a cheap compatible panel top dedicate to these.

Longer term would like a large array on the house roof ~8-10kWh, though currently have some restrictions likely to delay this a couple of years.

 

[venquessa]

We are in very similar situations, although you are way ahead on panel power!

I used to use a "propogator" in the garage to bring on red peppers and a few early veg. Starting in February in the tent in the garage with a 100W LED lamp and a 250W heater on a smart switch to keep it above 17*C at night. That then resulted in the need for a humidifier as the 250W heater dries the air out.

The reason I stopped this, was, after bringing the plants indoors, in a window with the 100W LED light in additon, did produce me quite a harvest of red bell peppers. (Hydroponic). The issue was they cost about £5 per pepper when you totalled up all the electricity!

When the price of 'leccy shut up last summer I stopped all the hydro ponics.

Maybe another time. When I have more solar!

After phoning around about a dozen different places and finally finding a solar installer who is willing to come out and chat about my options for a roof install. The finance for the natural gas heating upgrade clears soon, so a roof-top solar array would be a good option to replace it.

I put it to them, that if I have roof-top solar, then at very least I can trigger my off-grid battery charger. However there may be better options depending on their recommendations to make it "Notifyable" for permenant hardwire connection. That said, I realise if I connect an 800W multiplus to my consumer unit it will very likely just trip out and go AC in only. I'd need 3-4kW to make that practical.

Part of me still thinks keeping the off-grid system completely isolated in the garage and not interconnected to the main roof top solar has advantages. Especially as I don't think the initial roof-top solar budget will extend to a hybrid house battery install.

 

[venquessa]

You mentioned the dryer. My garage also contains my laundry equipment. I have pondered it. The washing machine peaks at around 1.8kW for 20 minutes or so when the heater is on at the start of the wash. The dryer uses 2kW cyclic. The VE 24/800 will not handle that. However, the washing machine spends a large amount of time only pulling pulses of motor load at 180-300W.

Obviously right now with only 2.4kWh storage and an 800W inverter it would be quite painful to watch it try and run the wash cycle. I mean it might work. The Multi is configured to switch to pass-thru mode if the load is over 600W and switch back to inverter when it comes down below 400W. So if the battery manages to survive the load spike for the few milliseconds it will take the transfer switch to close it might work. However, it is also likely the transfer switch is not fast enough and the inverter trips out and resets.

I was pondering when I upgrade the battery to 2 or 3 times that size, I can always buy a cheap 4kW inverter with the intent to run just the washing machine from it. No need for the full top-notch spec like the VE Multiplus, just a cheap £300 4kW inverter which hopefully we put out 2kW without tripping.

 

[StuartV]

The washing machine peaks at around 1.8kW for 20 minutes or so when the heater is on at the start of the wash.

Yes, I learnt the hard way about that!

Bought a 1Kw inverter as I had checked the washing machine usage more than halfway through the cycle! Thought "ooh, only uses 350watts, a 1kw inverter will do"! Got the inverter, panels & battery, Saturday came (laundry day), put the WM on, tripped the inverter! Upgraded to a 3Kw AIO, no problems since! Phew!

 

[Decto]

We are in very similar situations, although you are way ahead on panel power!

I'd done some sums and realised how little energy was generated in winter so went for a deal on 4 x 410W full size panels with a bit of space to expand onto the rest of the roof though roof not enough for 6 big panels I would have liked. Unfortunately the smaller fill in panels will actually cost almost the same as the large ones.... but they do have a long life I guess.

I actually start my seeds in the airing cupboard under LED striplights, then then only move out to the shed once it's warmer and they outgrow the space. The shed is insulated with 100mm rockwool in the 70mm joists and internally boarded so actually doesn't take a lot of heat to keep warm. 200W of lights keeps it ~8C warmer than external ground temperature so generally keeps the frost off and even on the coldest nights doesn't freeze. I run the lights overnight rather than daytime to generate heat in the coldest hours, then phase to normal daylight hours as the frosts subside.
I am planning a 'warm box' in there where the lights will heat a smaller sub space with additonal 50mm celotex insulation and I'm hopefull less lighting will generate enough heat in a smaller space (4ft W, 2ft D, 3ft H) for some dwarf tomatoes, microgreens and salad leaves. If not, then I'll move it into the built in garage which tends to stay a little warmer and still power for the solar as much as I can.

I'm planning to run a subgrid for the multiplus with some limited load I can add to or remove depending on time of year. When I do go full solar, possibly next year then I'll likely still keep it as an independant backup subgrid. I think a larger battery helps manage the loads as most consumption is out of peak generation hours.

The multiplus will feedback power into the grid at a limit you set so if you've 'notified'. You can set a limit and it will just add a continous 100+ W etc as a backfeed when enabled which will either power your local consumption or feed back into the main grid of your consumption is lower. I'm running as off grid so I'm not using this feature in case I inadvertently backfeed to the grid.

I've tested with a 1.2KW heater and the switchover limit at 1KW and the Multi switches seamlessly so no concerns on the mains pass through.
Only concern I have is effeciency as when it switches to pass through the inverter is still inverting so I expect there are losses rather than straight pass through (changeover). I do need to check how this works and if there are losses with a couple of Kill A Watt meters.

The server, CCTV switches are ~ 120W so nearly 3Kwh /day and I can scale back over the coldest months so if I add this to a few dryer cycles and a few adhoc loads I can likely get my utilisation reasonably high to at least offset some of the cost over the next few years.

I'm all for the larger battery, I see a number of days when my solar generation peaks at mid day when my batteries are full, though if I have a few poor generation days it gets close to mains cutover and partial charge so I'm expecting a larger battery will give me some more buffer with my usage pattern allowing me to capture more on the good days and defer to the poor days. Panels are cheaper than batteries, but only good if you can use the power when you're generating!

A big inverter may be an option, but if it's only supporting the washer, there may be more beneficial upgrades for the cash. I expect just switch over at 600W so the you use grid for the short heating cycles and run the rest of the cycle on self generated power.

 

[Hedges]

You mentioned the dryer. My garage also contains my laundry equipment. I have pondered it. The washing machine peaks at around 1.8kW for 20 minutes or so when the heater is on at the start of the wash. The dryer uses 2kW cyclic. The VE 24/800 will not handle that. However, the washing machine spends a large amount of time only pulling pulses of motor load at 180-300W.

In the US we can easily wire our 240V dryers for 120V, cutting peak heating element current to 1/4 as much.

You would have to change wires inside, not just change power cord connection. But if you put a 220V to 110V step-down transformer wired to the heating element it should work similarly.

A diode in series with heating element (cheap way to power some US appliances from UK voltages) is less likely to be satisfactory.

High wattage dimmer is another possibility, but like diode is going to be more stressing on inverter.

Transformer is the best option. Reduces watts, just takes longer.

Or, does your washer have a no-heat option? Does dryer have high and low wattage settings? Does dryer have two elements in parallel, which you could rewire in series?

 

[45North]

Poor sun in the UK, no surprise there. I'm in Canada, we had 3m of snowfall here this winter.

 

[venquessa]

In the US we can easily wire our 240V dryers for 120V, cutting peak heating element current to 1/4 as much.

You would have to change wires inside, not just change power cord connection. But if you put a 220V to 110V step-down transformer wired to the heating element it should work similarly.

A diode in series with heating element (cheap way to power some US appliances from UK voltages) is less likely to be satisfactory.

High wattage dimmer is another possibility, but like diode is going to be more stressing on inverter.

Transformer is the best option. Reduces watts, just takes longer.

Or, does your washer have a no-heat option? Does dryer have high and low wattage settings? Does dryer have two elements in parallel, which you could rewire in series?

Interesting. Timely too. Next in the queue for household appliances to replace is the dryer. It's a "Hotpoint/Whirlpool" model which has burnt about 200 houses down and mine has the fault, it also now has a small hole in it's fluff filter, so... it's a fire hazard.

The issue is... if I upgrade it, it's highly likely to be some modern micro-controller controlled thing. The one I have is very simple. It does have a "High/Low" setting, which may be parallel elements. I will have a look at it.

I can fix/replace the filter and I can open the unit up to clean out any lingering fluff from the elements and do my own fire safety check on how it looks inside. (The fire happens due to excess fluff and clothes debris building up around the heating elements, eventually leading to fire.

As it has no "electronic smart brain", it's just a manual spring loaded timer and a door button, it makes adaption to a lower power inverter far more likely to succeed.

There even exists the option, as it's a single device to run it off a 120V inverter if it will run.

Just went down for coffee. I have a little dashboard in the kitchen. 126W for grid usage. I find that annoying. The office is on the inverter, the inverter has the capacity to make that go to 0, but not the wiring and sign off, or transfer switch.

Then the coffee machine kicked in. 1807W. I'm not making that off grid... yet The highest peak load seen in the past year was 7.2kW for a few minutes. 5kW is more common weekly peak. That will probably have been the oven, dishwasher and the drier all at the same time with a busy day in the house. The average is only about 250-300W.

I have upgrade paths with the off-grid single circuit which should additionally run the gaming rig and 24/7 server. However I'm obviously looking for the next target and yes, the laundry stuff being in the garage and "easy" to off-grid without DNO/Electric operator blessing. They are good candidates. They are also nice "load test" loads. Hard, heavy, but short lived. Easy to interrupt or pause if needed or tripped out.

 

[venquessa]

On the growing space. The advice I'd give you, if you are going for heating the space. Don't use an air heater. It results in the need for a humidifier. As I was growing peppers, which are tropical plants, I thought it was a wise idea to take the temp up to 25*C and the humidity up to 80%. Unfortunately I had a simple software bug which stopped the heater triggering over night. The temp fell to 12*C and the humidity hit 100% by 21*C. The result was litres of water condensing out on everthing. The timelapse photos I had of it showed the complete melt down, it was literally raining and forming clouds at one point. Then the humidifier shorted and went into full 100% humidify mode adding to the problem. Luckily, I seen the photos before I opened the tent and disconnected all power before opening it. It was practically flooded, most of the sensors were dead, the humidity sensors never worked again and may need a few hours in the oven to fix.

Instead use a thermal mass, such as a couple of 1 gallon jugs with fishtank heaters in them. They will self regulate and therefore won't need the full environmental control software which I did. It should help regulate the humidity too.

Thanks for the info on the Multiplus. It does sound handy in that mode, if/when I get notified. I was also looking at the "Power assist" mode. I can't quite work out how it achieves that without back-feeding. So I am wary of switching it on, to say, power the washing machine on partial battery/solar.

On scaling up. Right now I am procrastinating on whether to budget panels or batteries first.

I bought one panel. Those panels are still in stock, but running out. I'd feel more comfortable getting 3 matched panels from the same batch or production run.

3 panels however will push the charge current up to 40A on a 100Ah pack. About twice what I'd like it to be on a daily cycle basis. Although that will be "minus loads". So I can even introduce "bleed loads" with smart switches if needed.

It's summer, part of me says that the battery is more important as incoming power is readily available for the next 5-6 months. It may even exceed
loads.

Downside is, if I order the batteries today they will not arrive until August. EDIT: I expect the batteries AND panels will be use in winter. The former bridging the dull days and the later rapidly charging as much as possible on the good days and trickling as much as possible the rest.

It's looking like the panels first, spank the battery a bit for a few months order the cells as soon as I can.

 

[Hedges]

Interesting. Timely too. Next in the queue for household appliances to replace is the dryer. It's a "Hotpoint/Whirlpool" model which has burnt about 200 houses down and mine has the fault, it also now has a small hole in it's fluff filter, so... it's a fire hazard.

I thought they drew in room air and exhausted out a duct, so fluff would not come back to heating element. Maybe it does some recirculation?
Just buy a new screen?

The issue is... if I upgrade it, it's highly likely to be some modern micro-controller controlled thing. The one I have is very simple. It does have a "High/Low" setting, which may be parallel elements. I will have a look at it.

I like simple. But there are some other types to consider. Condensing dryers are available with air heat exchanger (blows hot air into house), refrigeration type condensers, and washer/dryer combos use cold water to condense. I bought a Bosch air-cooled condensing dryer because rental condo did not have a vent nor was it practical to make one. Tip on condensing dryers: They have to be level, or water pools and re-evaporates rather than draining to condensate pump. These are marketed as using less energy.

I can fix/replace the filter and I can open the unit up to clean out any lingering fluff from the elements and do my own fire safety check on how it looks inside. (The fire happens due to excess fluff and clothes debris building up around the heating elements, eventually leading to fire.

As it has no "electronic smart brain", it's just a manual spring loaded timer and a door button, it makes adaption to a lower power inverter far more likely to succeed.

And easy to repair. I searched washer timer part number on eBay and found exact replacement.

There even exists the option, as it's a single device to run it off a 120V inverter if it will run.

Our dryers have 120V motor and controls. Just the heating element is 240V, so simple change of power cord wiring lets it run on 15A 120V cord instead of 30A 240V cord (heating element will draw 1/4 the current.)

These used to have 3-prong L1/L2/G plug, but motor and timer used ground wire as return (also connected to chassis). The new way is 4-wire cord L1/L2/N/G. Took me a couple tries to find and change a couple connections inside so no current went through ground; before that it tripped the GFIC (RCD) I was trying to use. I feel better with laundry machines having those protective devices because they are outside on a porch, sometimes we're getting wet when we use them.

I would expect yours to have 220V motor and controls.

Then the coffee machine kicked in. 1807W. I'm not making that off grid... yet The highest peak load seen in the past year was 7.2kW for a few minutes. 5kW is more common weekly peak. That will probably have been the oven, dishwasher and the drier all at the same time with a busy day in the house. The average is only about 250-300W.

I've thought a priority switch, disabling a heavy load like heating element when another large load is enabled.
Some like pumps and thermostats may have convenient control signals. Otherwise, current transformer controlling relay?

 

[venquessa]

I thought they drew in room air and exhausted out a duct, so fluff would not come back to heating element. Maybe it does some recirculation?
Just buy a new screen?

It's a condensing drier, so yes, it recirculates through the condenser and only exhausts dry air and water. It does still raise the humidity in the room and the temp, but not that much. I believe "normal" driers just vent hot moist air, fluff and all and people put the fluff trap in the exhaust duct.

I've thought a priority switch, disabling a heavy load like heating element when another large load is enabled.
Some like pumps and thermostats may have convenient control signals. Otherwise, current transformer controlling relay?

I mean the main thing stopping me is regulatory. The multiplus might only be capable of 400W sustained (the 800VA is thermally limited to 45*C mosfet temp). For off grid I have it set to "fail back" to grid AC if the load hit 600W for 1 second. I have no expectattions of how it would cope when a 1.7Kw coffee maker load joins the party. I don't think the system would hold it for the 1 second before it tripped the AC circuit out.

Grid-tie mode would sort that out completely and I could just pick and choose how much inverter power I want to feed my house with.

I suppose it depends on how good a job I did. I have a solar installer coming out at some point. If he says he can get it to notifyable state for a few hundred quid, he can go for it.

 

[venquessa]

On funky use for equipment.

Portable air conditioner. The best freezer defroster you will ever find. Just put it exahust first into the freezer. It will thaw and dry it in about an hour.

Speaking of the portable air con. There is a load that is poetic to solar power. Again however, it's a 1.2kW inductive load with such a bad start up kick it literally shakes the room. Not a load for a tiny little inverter.

 

[venquessa]

Back on topic.

Grafana

snapshots.raintank.io

A graphana dashboard for "today."

Summary, working exactly as intended, and F'ing epic. Tomorrow is to be better! The front garden need strimed down, the inverter will run the 250W strimmer (weed whacker? what is the international term?).

If you look closely you can see the grid voltage vary with the local roof top solar output. I love high res data, I'm a complete junky now.

 

[Decto]

Back on topic.

Grafana

snapshots.raintank.io

A graphana dashboard for "today."

Summary, working exactly as intended, and F'ing epic. Tomorrow is to be better! The front garden need strimed down, the inverter will run the 250W strimmer (weed whacker? what is the international term?).

If you look closely you can see the grid voltage vary with the local roof top solar output. I love high res data, I'm a complete junky now.

Definitely a lot of data you have there, what do you use to host? I keep meaning spend some time setting up some decent data logging but always seem to have lots of other things to do. I have a couple of Pi 3 / Pi 4 that might do the job with SSD for storage.

Grow wise, I was hopefull just to use the radiant heat of the lights. 100 - 200W in a smallish well insulated box should be plenty. I can then used forced ventilation to cool as required. Well at least that's the theory, testing required. I hadn't considered humidity. I was thinking mostly micro greens, salad leaves and perhaps some microdwarf tomatos. Just seeing how they grow in the greenhouse to get an idea on size.

My Fogstar 300Ah arrived today, though still in it's box. Typically the 170Ah Renogy is on offer today at £610 with a voucher on Amazon, had it been that price a month ago I likely would have just ordered one to match the other 2 I have. Still the Fogstar does boost the overall pack size and give me a mix of cell based + Prismatic.

Panel vs battery priority is definitely seasonal. In summer, I feel it's mostly better to have battery to allow generation to be offset as light is plentiful, but in winter you want as many panels as possible for every scrap of light. If you get the panels now, you can usually limit the charge current in the controller. Is there a reason you are looking for matched panels? It's not something I'd though about.

The chart attached is from some data I downloaded from a university which logs 12 months rolling solar generation vs installed capacity in UK. The generation figures were huge so I think they were including all the commercial generation in the UK. Interesting bits for me are that some winter days are shocking with 0.2 - 0.3 kWh per day per kWh installed (perhaps it snowed). However the aggregate rarely drops below below ~ 1kWh. From a trend point of view I was suprised to see it's pretty much only Dec and Jan where power gen is <2kWh per day. Trend lines a little hard to read but trending 3 data points does most of the smoothing, with 5 and 10 not that much better. Of course this could be data over a large area which would mask locally poor weather but it does indicate battery of least 3x the installed PV array really smooths out the generation during the minimum solar season.

My peak array will be 2.35 kWh however as it's split East / West and at a suboptimal incline (match shed pitch) I'd assume best case <= 1.8kWh effective hence a battery of ~8.2kWh should give in the region of 4-5 day smoothing vs base capacity during minimum production. That's the theory at least, I'll have to see how it goes. The house is also east west, so this will give some data before I spend far to much on a house array and supporting battery.

I'm hoping the multiplus will be enough to start my portable AC so I can run guilt free on those hot summer days. I'll have to run an extension to test it for now... base consumtion is fine, just the inductive load when the compressor cycles. Though the multi uses a low frequence toroidal transformer, hence the weight and cost so should be pretty good at inductive loads.

 

[HRTKD]

(weed whacker? what is the international term?)

Weed Eater, Weed Whacker, Trimmer. Whatever works. Weed Eater was a brand name early on, like 30 some years ago.

 

[Hedges]

...the weed hacker incident.

Over the Hedge (2006) clip with quote ...the weed hacker incident. Yarn is the best search for video clips by quote. Find the exact moment in a TV show, movie, or music video you want to share. Easily move forward or backward to get to the perfect clip.

www.getyarn.io

 

[OffGridForGood]

I like to say "Whipper-Snipper"
We converted the ICE trimmer to Battery electric last summer! so much quieter now, grab and go, no fuel no noise no mess!

 

[Decto]

A bit of testing today with the multiplus 1200VA (1000W)

8000 BTU (0.7 ton) freestanding AC runs ~ 700W, no issues when the compressor kicks. Ran for a couple of hours.
Was hoping to run a pair of these, but would be too much unless I get a second inverter.

LG dual inverter tumble drier, 600 - 860W. 2 drying cycles ~ 4.5 hours total.

Solar production was very good today, battery didn't dip below 97% throughout as almost all power was from the panels.