Impress your friends by using correct units and abbreviations

[Hedges]

A graph here indicates Volt-var is control of the EE expression "Reactive" power, inductive and capacitive.

What is Volt-VAr and how does it work?

This article looks at the operation of Volt-VAr settings on a Solar PV system and the impact on customer export. My rough calculations suggest that I am incurring a 1% loss on energy production.

www.linkedin.com

 

[wattmatters]

A graph here indicates Volt-var is control of the EE expression "Reactive" power, inductive and capacitive.

What is Volt-VAr and how does it work?

This article looks at the operation of Volt-VAr settings on a Solar PV system and the impact on customer export. My rough calculations suggest that I am incurring a 1% loss on energy production.

www.linkedin.com

Yeah, that item is a couple of years old - the grid quality standards for inverters have been normalised across the NEM and the level of grid-tied rooftop PV has increased substantially since then. In fact it has doubled in the past two years, approaching 30 GW of installed PV capacity.

As to losses, note that an inverter might have some small production/export losses when volt-var mode is operational, but it is producing infinitely more energy than an inverter which has shut down because the gird voltage has gone past the upper limit.

My inverter was beginning to shut down many times a day. It no longer does. IOW the small sacrifice of having it supply a higher proportion of reactive power is actually resulting in more energy production.

It's good for the grid and it's good for me.

Here's how much reactive power my system is showing per phase, and the per phase voltage. Charts are for yesterday my time (21 Nov 2022).

Phase 1 has my hot water diverter, which you can see keeps voltages down until it completes the heating cycle and the thermostat switch opens. Then voltages climbs quickly.

Phase 2 only supplies our ducted AC, while phase 3 supplies the rest of the home via the off-grid inverter (which will cut over to off-grid solar/battery mode when battery is full and there is enough spare off-grid solar PV.



This chart shows the same day with all three phase voltages (red, white , blue dots) and the net real power flow across all phases (negative = export). The two horizontal purple lines mark 253 V and 258 V, which are the set points for volt-watt and volt-var modes to kick in.

I used to have grid voltage exceed 258 V frequently.




If I go back and show the voltage plot for the months before and after invoking the volt-var settings, it's easy to see the impact on my peak daily voltages (line at 258 V). In that period prior to the change I had constant instances of the inverter shutting down completely. Never since.

 

[Dutchman]

The following are common units and their abbreviations. Note that unit abbreviations are case-sensitive. While some units can be understood when written incorrectly, some have a completely different meaning if the wrong case is used. Avoid any possible confusion or ambiguity and use the correct case.

A - amps, a unit of electric current. Named after André-Marie Ampère.
V - volts, a unit of electric potential. Named after Alessandro Volta.
W - watts, a unit of power. Named after James Watt.
Ω - ohms, a unit of electrical resistance. Named after Georg Ohm.
h - hours
k - kilo (SI prefix for 1000)
K - Kelvin, a unit of temperature. Named after William Thomson, 1st Baron Kelvin. Not really relevant in solar discussions.
m - milli (SI prefix for 1/1000)
M - mega (SI prefix for 1000000)

Current is measured in amps - A
A battery's voltage is measured in volts - V
A battery's current capacity is measured in amp hours - Ah
A battery's energy capacity is measured in watt hours - Wh. Wh is simply Ah x V. Many times it is shortened to kilowatt hours - kWh. Example: 5120Wh or 5.1kWh.
An inverter is measured in watts - W. Many times a value is shortened. 4000W can be written as 4kW. Really large systems could be in megawatts (MW) or even gigawatts (GW). Small electronics might be measured in milliwatts (mW).
A wire's resistance is measured in ohms - Ω. Many times the resistance is very small such as 0.002Ω commonly written as 2mΩ (two milliohms).

--------------------------

AC vs A/C - AC is alternating current. A/C is air conditioning

--------------------------

While not a unit, one common abbreviation that should be written correctly is for Lithium Iron Phosphate batteries. The correct written form is LiFePO₄ though most people find LiFePO4 is much simpler to type. LFP is a shorthand abbreviation understood in the context of this forum when discussing batteries.

Incorrect abbreviations would include LiFePO (lithium iron phosphorus oxide), LiFePo (lithium iron polonium), LiFePo4 (lithium iron tetra-polonium), LiFeP04 (using a zero instead of a capital O), LiFe (lithium iron), LifePo4 (wrong case on the F and O).

Note that there is a lithium-ion polymer battery typically written as LiPo. That is not at all the same as LiFePO₄. You do not want to confuse the two types. Though both of those types are specific examples of the more general lithium-ion (Li-ion) batteries.

Thank you for this! As a EE it drives me nuts when "experts" on the Forums and Amazon give advice and it's so obvious they are speaking out of their arse.

 

[morganco]

Thank You! Posts like this are always appreciated by folks like me who are "newbies"! I will print this out and put it in my "solar system noteboook"!

You did forget one that comes up more and more...........NEC referred to "National Electrical Code" on another website. I was being lectured on another website about putting 12v solar system components on a sheet of plywood (they suggested it must be on cement board or drywall).

In my house, there is 220V AC wire stapled inside a wall to 2X4's and OSB. I know little about the NEC; but like anything .gov it seems to get a little out of control.

 

[12VoltInstalls]

lectured on another website about putting 12v solar system components on a sheet of plywood (they suggested it must be on cement board or drywall)

The funny thing is “cement board” from a couple of major manufacturers is noted as not being a fire proof surface.

And drywall is so good at holding weight?

If you have concerns, use 16ga sheetmetal and mount it with #12 screws through 1- or 2” metal pipe or fittings or stacked nuts so there’s 1-1/2” of air space between the sheetmetal and the drywall or combustible surface. Mount the sheetmetal to studs.
You might review with your code office if that needs to be part of your installation and approval is needed.

 

[timselectric]

Truthfully, cement board is a pain to work with.
Especially If you want a nice finished look.
Drywall has a fire rating.

 

[12VoltInstalls]

Drywall has a fire rating.

Exactly.
Mostly because it doesn’t fracture, is structurally compliant to some movement, and is fairly nonconductive/resistant to heat. So drywall behind an airspace and sheetmetal is a pretty stinkin good insurance policy.

 

[Hedges]

Gypsum, Plaster of Paris, undergoes an exothermic chemical reaction with water during manufacturing.
If later exposed to heat, it decomposes, absorbing heat and releasing water.
It is used in fire resistant safes, keeping documents inside cool enough to be undamaged for an hour.
Not recommended for objects subject to rusting (firearms.)

Gypsum Products and Properties as a Building Material for Construction

Gypsum is one of the widely used construction material mainly in interior designing. Properties and products of gypsum to be used as building material in construction works are discussed.

theconstructor.org

How To Build A Fireproof Safe | Home Security Store

What you need is a little creativity. In this article, I’m going to teach you how to build a fireproof safe that is simple yet effective.

homesecuritystore.com

 

[jandjmh]

I’ve seen it called either but energy capacity does seem to be a bit more prevalent.

I’ve seen it called either but energy capacity does seem to be a bit more prevalent.

Watt hours specifies energy capacity. A battery might have an energy capacity of 250 Wh/kg. Power capacity is a completely different measure. The same battery might have a power capacity of 2500 W/kg, if it is capable of 10C discharge.

Power capacity and energy capacity are definitely NOT interchangeable.

 

[timselectric]

I see "power" and "energy" as interchangeable.
When talking about capacity/weight, that would be energy (or power) density.

 

[curiouscarbon]

I see "power" and "energy" as interchangeable.

?

Power -> Watt
Energy -> Joule -> Watts * Time

fundamentally different units. interchanging them seems inadvisable.

some recipes specify mass, others specify volume. interchanging the units can result in an unappetizing cake.

kind regards

 

[morganco]

The funny thing is “cement board” from a couple of major manufacturers is noted as not being a fire proof surface.

And drywall is so good at holding weight?

If you have concerns, use 16ga sheetmetal and mount it with #12 screws through 1- or 2” metal pipe or fittings or stacked nuts so there’s 1-1/2” of air space between the sheetmetal and the drywall or combustible surface. Mount the sheetmetal to studs.
You might review with your code office if that needs to be part of your installation and approval is needed.

lol I actually thought about that. Then my own "sense of logic" (which is not always correct) kicked in and said.......12V low amperage system mounted on a non-conductive surface.......verses mounting it all on wood tied together with a good conductor (steel)....hmmmmmm

If I did it again I would drywall over the sheet of plywood, then mount the components.

Safety is good, but as said in the original post, my house has 220V AC stapled on wood studs.....inside a wall. All to NEC (code). I do not have any concerns about my system except that I feel doing ANYTHING on your own without .gov excessive oversight /rules/having to hire it done by a licensed contractor is a thing of the past.

 

[Supervstech]

lol I actually thought about that. Then my own "sense of logic" (which is not always correct) kicked in and said.......12V low amperage system mounted on a non-conductive surface.......verses mounting it all on wood tied together with a good conductor (steel)....hmmmmmm

If I did it again I would drywall over the sheet of plywood, then mount the components.

Safety is good, but as said in the original post, my house has 220V AC stapled on wood studs.....inside a wall. All to NEC (code). I do not have any concerns about my system except that I feel doing ANYTHING on your own without .gov excessive oversight /rules/having to hire it done by a licensed contractor is a thing of the past.

Big difference between code approved conductors with breakers protecting the wiring from overheating being stapled to wood…

And an appliance with clearances required between combustible surfaces…

 

[Ceefiveceefive]

I've always been taught that the abbreviation for voltage is E, which stands for electromotive force.

I (capital "i") is the abbreviation for current.

 

[Supervstech]

I've always been taught that the abbreviation for voltage is E, which stands for electromotive force.

I (capital "i") is the abbreviation for current.

It depends on what you are writing.
E would be correct in a calculation on an engineering formula...
But for setting up a description for a mechanical build like diy...
V would be correct.

 

[wattmatters]

I've always been taught that the abbreviation for voltage is E, which stands for electromotive force.

The SI symbol for the SI derived unit volt is V.

Electromotive force often uses the symbol

(like the Greek letter epsilon).

 

[morganco]

Big difference between code approved conductors with breakers protecting the wiring from overheating being stapled to wood…

And an appliance with clearances required between combustible surfaces…

Hey, dont want to fight. I know the union and regulatory guys are protecting their space. No problem.

My 12v low amperage system (with multiple fuses, breakers , appropriate conductors, ETC. ) is a very low risk and you all have bigger fish to fry. Dont Tread On Me.

 

[12VoltInstalls]

union and regulatory guys are protecting their space. No problem

ok then ????​

 

[curiouscarbon]

welcome to the forum! ?

 

[brandnewb]

It depends on what you are writing.
E would be correct in a calculation on an engineering formula...
But for setting up a description for a mechanical build like diy...
V would be correct.

lenz's law also uses E for voltage

Lenz's law - Wikipedia

en.wikipedia.org

I learned about that law far too late in a persruit of building a kick ass alternator.
But better late than never.