Solar PV battery options

reklamos · 20-08-2021 01:53PM

https://www.boards.ie/discussion/comment/117780561#Comment_117780561

Oh wow must have missed that. For 1230 I would get one, not that I need it but would be fun DIY project.

bullit_dodger · 20-08-2021 04:12PM

Even though I've 8.4Kw enroute in a forthcoming installation, for that price, its in the area of cheap enough for it being a fun project to get operational. You'd even be saving yourself a few quid after payback. Lot to love....even at 1800 though. Just got to have the courage.

To be fair, I know I'd be having a bit of a sweat hovering over the "Checkout now" button as 1500-2000 of my hard earned wonga toddles off to some crowd in China, but I'm pretty sure I'll go do something even in the 1-2 Kwhr range in a few months. It's kind of neat.

DrPhil any chance of some updated stats? how's the build been working out for you? Capacity? Charge/discharge limits, etc. I guess everything good according to what the specs were?

bullit_dodger · 21-08-2021 09:57PM

One thing that I'd like to find out from people is what their battery strategy is. Esp for people with around 10Kwhr in storage. Course in middle of December it's a bit of a "no brainer"....you charge your battery up from the night rate and you use that during the day to offset the day price.

In months like October, or say March it's not probably so simple (and I say that with no actual experience only gut feeling). If you charge up the battery from the night rate, you might be missing out on surplus PV generated and storable during the day which you could use in the evening, but then if you don't charge it and it's a cloudy day.....

I guess another strategy is to partially charge it and "back both horses" and as the weeks roll forward through March, April you reduce your % charge. Then there is the matter of, do you charge it at 00:00 or do you wait until 07:00?

I'm not interested in eeking every last penny here, but I am pretty curious as to what people are doing strategy wise as it's an interesting problem. Be great to hear what people are doing with their systems.

DrPhilG · 21-08-2021 10:18PM

Sorry I'm behind time, somehow got unsubscribed from the thread.

I'm currently just letting it rip. Wouldn't be arsed climbing into the attic every other day to fine tune the charging.

October or thereabouts, I'll set the system to not discharge overnight. November through to February I'll charge at least part of the way overnight to discharge during the day.

championc · 21-08-2021 10:33PM

From when the clocks went forward to when the clocks go back, I plan to leave the system to it's own devices, to charge the batteries during the day from PV and certainly "hope" to get to at least midnight at night.

So during the winter part of the year, I will possibly charge to 50% most nights. If we get a good day, I'll get to 100% and on a poor day, I should hopefully still get close to midnight

graememk · 22-08-2021 10:06AM

Been thinking of that myself.

I have full control over my inverter, so that opens up a lot of opportunities. I currently have setup a ui in Node Red that I can select the SOC of what i want to charge to overnight (currently i have it set at below 20%, thus no charge) and how far i want to discharge overnight.

So if tomorrow is going to be a bad day I don't discharge on night rate, Normally I wouldn't say to discharge on night rate but, in May and June, id be rocking into the next day at 70% SoC some days!

I have started to use the new energy tab in home assistant and that can use forcast.solar to predict today and tomorrow Production (for free). I would have loved if it saved the prediction in home assistant so you could see how accurate it was, but it doesn't do that currently.

Thinking of polling the forecast.solar api directly in node red.

Looking out over august, I'm averaging about 12-13kwh on day rate of usage, looking back to July skews it higher as EV charging of solar is being counted in the usage stats.

Could work with something like < 10, charge (or try to maintain) to 50%, <5 charge to 90%.

I have loads that can be put on during the winter that can get rid of a few kwh's very quickly too, and they have to run during the day (rolling barley/maize)

SD_DRACULA · 22-08-2021 11:16AM

Forecast.Solar is borderline useless for Ireland.

I know it's a prediction but you can't really base any automation off of it, it always way over-estimates:

And they are off by as much 10kwhs consistently.

i.e. No way in hell I'll be hitting 23kwhs today

reklamos · 22-08-2021 11:46AM

I find https://www.yr.no/ is good in forecasting. The detailed view gives hourly cloud cover. I'll be doing automation with nodered to automate charging based on that forecast.

graememk · 22-08-2021 12:22PM

https://www.boards.ie/discussion/comment/117787982#Comment_117787982

Mines been "close enough" from a casual observation, pulled each array back from 4.3 to 4 kwp and its a close enough value. Although Im only on the lookout for good/bad/meh day.

https://www.boards.ie/discussion/comment/117788076#Comment_117788076

Met eireann have an api based on the norway met software - and they all share data so you're prob pulling from met.ie servers, they have an hourly solar radiation forcast but getting that into a meaningful value is another issue. It distinguishes from a dark cloudy day vs a bright cloudy day.

https://data.gov.ie/dataset/met-eireann-weather-forecast-api

bullit_dodger · 22-08-2021 03:13PM

hmmm, that's interesting graememk. Hadn't thought about that. So I guess one optimization which, to be fair, has questionable return on investment (time) but an interesting project for geeks like me , is to setup a scheduled task on a rasberry PI or a PC you have on 24x7 and fire off an API call at (say) 6am to met.ie for the hourly forecast for that days weather.

metwdb-openaccess.ichec.ie/metno-wdb2ts/locationforecast?lat=53.3;long=-6.25

This example above returns an xml file for roughly center of Dublin (yes, that minus is correct for the longitude - bloody Norwegians! :-) It has the hourly forecasts for clouds etc and also an interesting xml object called.....

While it would be great if that was the forecasted sunlight on the ground, I think it's just the energy falling on a m2, with clear skies worked out against the angle of incident of the sun on the surface at this location due to time of day and of course, time of year. Still with the "% cloud info" and this "globalradiation" value, you could work out the amount of hours of sunlight and the expected amount of sunlight you would be getting and generate a simple scale like you suggest.

Basically a sort of "expected hours production" during the day. If it's <4 then you completely charge your battery to 100% before 8am. If it's 4-6 you go to 50% charge, and greater than 6 hrs production you let the battery charge 100% from PV.

The above numbers are just some random thoughts, you'd have to tune it a little, in fact, if you system had log files for daily production you could get it to auto-tune based on historical data. To be fair now - you'd probably only eek out another 10-15% cost savings , but the engineer in me likes to tinker :-)

garo · 22-08-2021 05:27PM

Eh? What do Norwegians have to do with it? It is convention to take Westerly longitudes and Southern latitudes as -ve. Saves you having to suffix N/S E/W.

garo · 22-08-2021 05:32PM

BTW if you take full irradiation - it's around 1100-1200 for Ireland - the 283.6 is pretty useful. Basically your panel will produce ~25% of what it would have otherwise. Combine that with this spreadsheet: https://aces.nmsu.edu/pubs/_circulars/CR674/welcome.html and you are in business.

bullit_dodger · 22-08-2021 05:40PM

https://www.boards.ie/discussion/comment/117789802#Comment_117789802

The application interface (API) system that Met Eireann uses is based on the one that the Norwegian met office developed so that's why I mentioned Norway - but no your right garo, I was in error. While I was aware that northern locations were positive, I had it reversed for the longitudes. I thought that longitudes east of the prime meridian were supposed to be negative.

graememk · 22-08-2021 06:19PM

https://www.boards.ie/discussion/comment/117789100#Comment_117789100

Ive been watching the global radiation value on and off for the last 6 months. Its what actually hits the ground. - have a look into node red, make working with JSON and xml super easy.

I have something like that running, counts the number of "good hours" currently set at 150, (I wrote it in the winter) and at a glance I can see oh its gonna be good (sunny) tomorrow. Tomorrows rating is "10" , 0 is 6am UTC.

Ironically, I am looking like I'm going to beat the forcast.solar prediction (16kwh) today (currently sitting on track to hit 19).. thanks to the mist lifting at half 4! pulled my battery from 35% to 78%. 21kwh predicted for tomorrow

DrPhilG · 22-08-2021 08:13PM

29.3kWh for me, with nearly 15kWh into the battery.

bullit_dodger · 22-08-2021 09:43PM

That "radiation value" in the xml is pretty neat from Met Eireann graememk. Even if it's (loosely) accurate and gives general trends for the day, it will be pretty useful for building some decision making algorithms. For example, I plotted the solar radiation for me here in south Dublin city for the next 60 hours from the Met Eireann data.

Looks like tomorrow is good, but right now Tuesday will slightly surpass it. Be interesting to compare with real life data captured from people in Dublin on Weds to see how the forecast now maps to reality.

For these days like tomorrow, it's a no-brainer. You should charge your battery from PV rather than night rate, but what I'm thinking is having automation fire at day 6am every day, and it decides the level of charge to take from night rate before 8am (when it switches to day rate in the winter) and then fill the battery to the appropriate amount.

If it thinks that it's going to be a sunny day, it might only put in 20% from night rate into the battery and leave the other 80% for the PV to fill up. If the day looks cloudy it might charge it up to 70% off night rate and then leave the remaining 30% for the PV to try and fill. I'm sure there'll be some tweaking involved and of course the load from day to day would need to be roughly equal, but I like this. Always nice to have a project on the go :-)

graememk · 22-08-2021 10:05PM

https://www.boards.ie/discussion/comment/117790843#Comment_117790843

From April-Oct its unlikely you'll need any night time charging.

What size solar are you thinking of? - Also something to keep in mind going forwards what inverter are you getting? what can it charge and discharge at (the new Solis can do 5kw) - also can communicate with it via its RS485 modbus port, and i think it can be remotely controlled too. - only drawback is that its the same port that the data logger connects to. - the workaround is to put a relay on the power to the data logger and turn it off whenever your reading data (or ditch it and log everything yourself!)

I'm using emoncms to log all the power data.

Pull the forecast.solar graph and see how it lines up with the met.ie data too.

bullit_dodger · 22-08-2021 10:57PM

System which is enroute (2-3 weeks lead time) is 4.5Kw panels coupled with a 5Kw inverter and 8.2KwHr Givenery battery. Battery charges/discharges at 60a, so assuming a normal voltage around 60V, it'll charge/discharge at 3.6Kw. I'm very much tempted to add 2x extra panels, not so much that I need it but it's cheaper to do it now rather than to get someone to come out and add 2 panels in a year or twos time.

Agreed, I think from Apr-Oct it's mostly an easy answer to the question. You just charge from PV - but even in this time period there are days that are so heavily overcast that I would imagine that getting surplus over base load may be hard to achieve. For those days, you might as well grab a few units off night rate. Great thing about automation is once you have it tuned in, it (should) do all the work for me. Picking the right charge levels everyday. If that's 100% charging from PV, or leaving 40% for some expected production......hopefully it's automatable.

Once I have the installation up and running, I'll no doubt be onto you to tap into your knowledge. Sounds like you have a good setup in play and while it's nice to figure out how to get stuff working, there's a lot to be said about not reinventing the wheel too.

graememk · 22-08-2021 11:44PM

Put as many panels as you can on now, you'll not regret it. Esp if you have to get someone out to do it. I am fortunate to have mine on a steel roof, was v easy to add more panels.

Nominal voltage of the givenergy is 51.2v (16*3.2v, lithium iron) you have a 10kwh pack but it's limited to 8.2, but you use 0-100. So it's more or less the same as what I have, as I only use 20-100.

You'll not get 3.6kw, prob only about 3.

I have separate solar (solis) and storage (sofar) inverters , so won't be able to help you with control. All my monitoring is done via an emontx. Except for the SoC of the battery, that's pulled direct from the storage inverter.

Getting info from the inverter directly will greatly improve any automation.

As for time spent on it, I'm not even counting, it's a hobby and enjoy the puzzle.

I'm gonna be leaning more on the forecast.solar more, and trying to predict where the battery will be at, when night rate kicks in the next day and decide according. - do I try and look further ahead, tomorrow is going to be good, but the next day, that's horrible, no discharge at all tonight, and rock into the bad day with a high charge.

With a smaller array, night time charging will come into effect sooner. (Or at least restricting discharge on night rate)

Jonathan · 23-08-2021 09:13AM

https://www.boards.ie/discussion/comment/117790931#Comment_117790931

I'll be getting PV installed in next few weeks. Getting a Solis 5G which comes with a wifi dongle. I understand that the wifi dongle acts as the modbus master, with the inverter as a slave.

Do you mind me asking, what are you using to interact with the inverter and log the data? RPi + a RS485 hat? Did you roll your own software around libmodbus, pymodbus etc?

What features do you use lose by ditching the Solis cloud portal? Can you configure any parameters via the cloud portal, or is writing to modbus registers the only avenue for automation?

graememk · 23-08-2021 10:14AM

https://www.boards.ie/discussion/comment/117791908#Comment_117791908

I dont have a solis hybrid, my storage is connected to a Sofar ME3000sp. Im using this https://github.com/cmcgerty/Sofar2mqtt to communicate with it (well my own version of it, ive tweaked the code a bit to give me more information.) - That does the communication over modbus and posts everything to a MQTT broker, It also does control- I do all my management from node red then - and send commands via mqtt.

@reklamos , and @SD_DRACULA have hybrids and have at least dabbled with the RS485 control on the solis hybrids. - you dont even need a rpi hat, you can just use a usb to rs485 adapter with a raspberry pi and some python scripts.

by ditching the wifi dongle, you lose the "cloud" monitoring, (updates every 5 mins or so) and an easy way to see what alarms that the inverter may have had, remotely without digging into the inverter menus.

you can replicate the cloud monitoring by doing it youself locally. I use the emoncms system, running on a raspberrypi, it has its own mqtt broker and you can send it all your different inputs, (import/export, solar, battery charge/discharge) and then make feeds out of each import and store it locally.

So, how deep into this rabbit hole do you want to go?, You'll never make back any of your time but if you enjoy working on this sort of stuff, have a go.

Jonathan · 23-08-2021 10:58AM

https://www.boards.ie/discussion/comment/117792198#Comment_117792198

Thanks. I don't have an problem piecing it all together technically, but time for hacking on this stuff is not plentiful right now, so if the Cloud interface is good enough, I'll probably stick with that for moment. Maybe @SD_DRACULA or @reklamos could confirm if you can change Inverter settings from the Cloud interface, or if it is only for retrospective data analysis? Ideally I'd be changing the battery charge rate or time based on forecast. Inverter will likely be in attic, so I'd rather not have to climb up there every time to tweak.

reklamos · 23-08-2021 11:17AM

https://www.boards.ie/discussion/comment/117791908#Comment_117791908

as @graememk said you do not need RPI. I found the the best solution for me to monitor Solis and battery is with elfin-ee11 RS485. It has web server running and I just pull info from it using modbus TCP. Also I can power it up from Solis wifi port. It will depend on what you want to monitor/automate and what back-end you will use as there are multiple options. I use HomeAssistant(HA) with NodeRed for house automation. But for long term data storage I use Prometheus. You can HA to talk to modbus devices and pull data. I just wrote simple Prometheus exporter with MQTT inside of it.

I do not use Cloud monitoring but to make things working I placed esp8266 with simple relay and tasmota that allows HA/Prometheus to pull data and also send data to Solis cloud. All that is power from Solis itself.

Jonathan · 23-08-2021 11:45AM

https://www.boards.ie/discussion/comment/117792504#Comment_117792504

Thanks for that info. Just to confirm I understand your final sentence; You are still using the Solis wifi stick, but use the tasmota relay to disable it when you need to be the sole Modbus master for talking to the inverter using the elfin-ee11? Can you configure inverter options through the Solis Cloud or is it readonly?

bullit_dodger · 23-08-2021 12:07PM

Took your advice grememk and added the 2x panels now to the order. An extra 380 euro, which is probably half the price over getting someone to come out in 12 months and add them then. That'll bring me to 5.2Kw rated max output - which of course we all know we rarely get, but yeah - smarter to do it now. Anymore and I'll start running out of roof space.

Yeah, I'm super eager to get everything up and running and start "tinkering" with the modelling. Have to see what configurations are available with the Givergy battery via the API assuming they have one? If anyone has some automation done there already, drop a response here or PM me please. Shame I can't nick all your setup - I like the sound of what you've got going there.

graememk · 23-08-2021 01:00PM

https://www.boards.ie/discussion/comment/117792611#Comment_117792611

Solis cloud is read only unfortunately.

reklamos · 23-08-2021 02:22PM

https://www.boards.ie/discussion/comment/117792611#Comment_117792611

Correct I use solis wifi stick and elfin connected to the same port on inverter but power goes through relay. This ensures that only one modbus master is up at a time. This allows me to get 1min resolution for automation and also to push data to he Cloud.

You cannot configure inverter through solis cloud. This would be big security concern. I can control Inverter through home assistant at home and also remotely. For this I just VPN in with my phone.