Lt.Dan
Solar Wizard
I agree. I have a mini split in my office and when it shifts to run a defrost cycle it scares the crap out of me sometimes. Not because it's loud, but because the office will be dead silent and the shift is very abrupt lol
Cinergi's 28 kWh / 4 kW Solar / 10 kW inverter RV build
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curiouscarbon
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interesting! thanks for sharing.
never had much experience with heat pumps in buildings, good to know to be aware of
I personally don't think I have ... this winter I'm in AZ so it's dry and cold temps are short-lived so I don't know that I've had defrost cycles. I recall having them the winter before but I only remember noticing it due to hearing the compressor going at 100% .... and I stepped outside to see what was going on, surprised to feel warm air coming out, and realized it was a defrost cycle.
I'm familiar with the whoosh and related noise that comes when the reversing valve flips. This noise happens a few seconds later as the compressor ramps up and it's almost like someone's playing a horn or instrument inside of my idu.
I guess I will see what cooling performance is like in the spring. It may be I need to adjust my charge.
Thanks to @Repro and the post here, I configured my system for ESS. There are disadvantages (e.g. I can't connect to 120v single-phase, which includes my generator), but I'm hanging out here in AZ for a while and my solar is unable to keep up with my loads, largely due to shading.
Previously, I had the Victron set to connect to shore below 50% SoC, which engaged the charging up to a set voltage (can't do a set SoC) which ended up being around 65% SoC ... and the solar would fill in the gaps. This kinda accomplishes the goal, but the SoC at which the charging from shore stopped wasn't accurate (60-70% SoC) and it wouldn't happen at the best time of the day so that I'd reach 100% SoC for balancing purposes, etc. etc... it's just not particularly elegant.
Enter Victron ESS. I thought I couldn't use this feature because I wasn't using Victron batteries -- but that's false. While there are a couple of limitations by using my own batteries, they're not important (I don't even remember what those limitations are). The configuration says "don't let the batteries go below 50%; if they do, use shore power to provide energy for the AC loads. Don't charge the batteries. The PV will charge the batteries. If the batteries aren't hitting 100%, change the threshold up 5% every day until you hit 100% from PV charging" ... so basically this becomes a "self consumption" system whereby it (optionally) gets the batteries to 100% every day so they have a chance to balance but also reserves enough for a blackout scenario. The numbers are fairly configurable. This configuration can also feed the grid with excess power if you're able to do so (I don't). The downside, as I said, is that this requires "switch as group" to be turned on which means my shore connection must be 240v. Fine for now. If I need to turn off ESS, I have to cause a couple of blackouts inside as the inverters need to be rebooted. It's a fair amount of configuration - not just a simple switch. Not something I'd want to do frequently.
Observing the system is interesting ... it constantly draws a (configurable) small amount of power from the grid at all times - it basically stays connected so that it can handle surges via the grid instead of the inverters, which provides a better experience than the inverters can while on battery alone. It's also how power can be sent back into the grid, if so configured. I have seen small amounts of power feed back into the grid during large transitions of power usage (e.g. air conditioning turning off), where the AC input reads -150 watts or so for a couple of seconds. From what I've read, that's not really an issue except in rare locations where the power company's meters will shut down if they detect backfeeding.
So, my system is dynamically learning where to set the floor of the SoC so that it reaches 100% (can be due to weather changes or load changes, etc). I'm now drawing the bare minimum from shore to stay above 50% and still have enough for blackouts. It's a "self-consumption" system, and would be a really cool setup (Tesla Powerwall style) for a solar/battery/grid-connect system, providing backup capabilities and dumping excess power into the grid. It works with DC-coupled and/or AC-coupled solar.
That was fun to learn and see in action! My stats are always here: https://vrm.victronenergy.com/installation/76892/share/d5bbdd04
Previously, I had the Victron set to connect to shore below 50% SoC, which engaged the charging up to a set voltage (can't do a set SoC) which ended up being around 65% SoC ... and the solar would fill in the gaps. This kinda accomplishes the goal, but the SoC at which the charging from shore stopped wasn't accurate (60-70% SoC) and it wouldn't happen at the best time of the day so that I'd reach 100% SoC for balancing purposes, etc. etc... it's just not particularly elegant.
Enter Victron ESS. I thought I couldn't use this feature because I wasn't using Victron batteries -- but that's false. While there are a couple of limitations by using my own batteries, they're not important (I don't even remember what those limitations are). The configuration says "don't let the batteries go below 50%; if they do, use shore power to provide energy for the AC loads. Don't charge the batteries. The PV will charge the batteries. If the batteries aren't hitting 100%, change the threshold up 5% every day until you hit 100% from PV charging" ... so basically this becomes a "self consumption" system whereby it (optionally) gets the batteries to 100% every day so they have a chance to balance but also reserves enough for a blackout scenario. The numbers are fairly configurable. This configuration can also feed the grid with excess power if you're able to do so (I don't). The downside, as I said, is that this requires "switch as group" to be turned on which means my shore connection must be 240v. Fine for now. If I need to turn off ESS, I have to cause a couple of blackouts inside as the inverters need to be rebooted. It's a fair amount of configuration - not just a simple switch. Not something I'd want to do frequently.
Observing the system is interesting ... it constantly draws a (configurable) small amount of power from the grid at all times - it basically stays connected so that it can handle surges via the grid instead of the inverters, which provides a better experience than the inverters can while on battery alone. It's also how power can be sent back into the grid, if so configured. I have seen small amounts of power feed back into the grid during large transitions of power usage (e.g. air conditioning turning off), where the AC input reads -150 watts or so for a couple of seconds. From what I've read, that's not really an issue except in rare locations where the power company's meters will shut down if they detect backfeeding.
So, my system is dynamically learning where to set the floor of the SoC so that it reaches 100% (can be due to weather changes or load changes, etc). I'm now drawing the bare minimum from shore to stay above 50% and still have enough for blackouts. It's a "self-consumption" system, and would be a really cool setup (Tesla Powerwall style) for a solar/battery/grid-connect system, providing backup capabilities and dumping excess power into the grid. It works with DC-coupled and/or AC-coupled solar.
That was fun to learn and see in action! My stats are always here: https://vrm.victronenergy.com/installation/76892/share/d5bbdd04
DerpsyDoodler
Solar Addict
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I dont understand what you mean by you couldnt get a full charge to the batteries from the grid. That sounds wonky. i have a 24v system. I configure my charge voltage to x and configure the end of charge absorb current to y. So when charge current drops to y current at x voltage, the inverter knows the batteries are full. My inverter is a Samlex Evo 4024. How is it that your super premium and expensive victron can't grid charge your batteries to 100%? Is there something I'm missing?
I didn't WANT to fully charge the batteries from the grid, because then they'd be too full for PV later and I'd end up wasting PV. I want to rely as little on the grid as possible, and I can only do that if the system is configured to provide the bare minimum from grid and let PV do the rest. That's the idea behind "self consumption"
Repro
Solar Enthusiast
Nice job!
I really like the Victron Inverter/Chargers. They are so flexible and allow for really complex configurations to meet your needs. The only downfall is the configuration learning curve is a little steep at first. Once you know what you want to do and where to find it, it is very fast and easy. My one gripe with Victron is that in most cases, you need to use up to three different Victron applications to make different changes to your config. I wish they would consolidate this.
Victron Energy has made strides to their "Online" VRM (Victron Remote Management). Since Jan 2022, they have added Firmware updates and uploading/downloading of configuration files, temperature monitoring and more. They are slowly adding more features to their truly awesome online monitoring.
Glad you were able to get your system to do what you wanted.
DerpsyDoodler
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I see. I have my system configured to only switch to grid when batteries are at a low (nearly empty) voltage. The rest of the time solar does its job. Inverter operates in "online mode" (thisis what samlex calls it), meaning even when shore power is detected it will continue to use battery until the unit hits a configured low voltage warning. then it switches to grid for pass-through and charging. Solar always does its thing regardless. When batteries hit configured full charge, inverter switches back to inverting, and solar mppts enter float thereby covering as much of the loads as solar can. Same concept as your "self consumption" with the notion that my batteries will cycle to nearly full on grid, but will never draw from grid unless the batteries get too low. Solar always does its thing independently, and grid is used only to charge the batteries to full fast and cover loads while charging. Solar continues charging in tandem.
Do you have enough solar to charge while your A/Cs run?
Yeah that's pretty much the configuration I had before, and then I switched it to stop at a certain voltage so I wouldn't get to 100%, and then I discovered ESS mode would work for me.
Yes, I produce 2800-3200 watts (23kWh/day in June in New England) while the A/C typically uses < 1000. It's just these damn trees at the park that are really killing me right now. Here in AZ I often need heat overnight, too (mini-split in heat mode .. which uses a lot more energy than cooling). Normally I can be 100% self-sufficient on solar alone even with A/C.
Hedges
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Any chance of storing heat in a thermal mass? Oh, RV? bit of trouble hauling around a ton of bricks.
For stationary applications, would be nice to dump hot side of A/C into thermal storage. Or at least PV resistance heating to thermal storage.
I'd like to do that for peak rate times (4:00 to 9:00 PM in my area.)
DerpsyDoodler
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That clarifies what I was missing. Nice setup. How long can you run A/C on battery alone?
If the average high is under 90F and I don't have to run A/C after dark, Probably 2 days (0 sun). But even with crappy solar production (which reduces heat load), I never run the generator. And I'm pretty inefficient (2 inverters with something like 100 watts of standby and my base DC loads are relatively high for some reason (haven't investigated yet). The only time I fired up the generator was in the badlands where it was over 100F daytime and over 80F nighttime so the A/C was constantly running. I was consuming something like 40kWh/day (20ish from solar, 20ish from generator). Granted, I was low on refrigerant but still.
Haha yeah no bricks. More battery? lol
A friend of mine has a home that stores thermal heat off-peak. I bet the round-trip efficiency of a battery is better .. wonder what the energy cost comparison (battery vs. thermal) looks like.
If I had 4kW of panels, I think I'd be 99.9% solar powered. with 3.2, there are situations where it's not enough - but I have to say, the system is performing better than I originally hoped for! I wanted a "no-compromise" setup especially since I work full-time in the RV.
My initial target was also 3kw of PV. However, looking at my layout options, I could just barely squeeze 4kw of PV onto the roof. Which based on my insulation and AC efficiency, should be pretty much 100% of my needs in summer, which includes a condenser dryer and induction cooktop. Even with the occasional cloudy day or two. Winter is another matter, though if I can work out a panel tilt method, It should be fine in most moderate climates.
I'd be OK in the winter with flat panels if I didn't use electricity for heat or A/C; typically I don't need A/C in winter in AZ (probably would in FL), but I definitely need heat .. and I use my heat pump for that. 4kW would probably still not be enough, flat, for my heat pump needs in AZ winters. I actually have 400 watts (2 200 watt panels) of ground-deployed angled panels in addition to my 3200w rooftop panels right now - which I did because of all the shading I'm getting.
CharlesK
New Member
@cinergi Question: Is the "DC Power" on your vrm a new addition? Does it report current 12VDC usage (RV lights, water pump, etc., etc.)?
Or was it always there, and I never noticed?
It's always been there
but it's horribly inaccurate. It's supposed to be the DC usage yes but the method used to derive that number is inaccurate especially while inverting or charging (so pretty much always!). It's not measured by as shunt; I've asked them to make it so that value can be measured by a shunt AND included in the power usage graphs. Right now the graphs don't reflect DC usage (something like 2 kWh per day).CharlesK
New Member
Thanks. I did remember you mentioning the inaccuracy of DC usage some time ago. But, I could not remember the details. Thanks for the explanation.It's always been there
I am still working on my coach remodel. My electrical plan includes a BMV-712 shunt and a Cerbo GX. I believe that will give me the readings and history for DC usage. Maybe?
Thanks. I did remember you mentioning the inaccuracy of DC usage some time ago. But, I could not remember the details. Thanks for the explanation.
I am still working on my coach remodel. My electrical plan includes a BMV-712 shunt and a Cerbo GX. I believe that will give me the readings and history for DC usage. Maybe?
Nope. The shunt is used for SoC and overall amperage calculations. In order to figure out the DC-only loads, the inverters "measure" (poorly) their DC inputs and subtract it from the shunt's value... thus the inaccurate value.
And the kWh graphs are AC-only.
It's still amazing stuff. I do wish I could see/graph/measure my DC side ... I was off-inverter for a while and my DC load consumption was shocking... I need to figure out where it's all going.
