Comment by jacknews
10 hours ago
Good read.
"Since that time, I’ve learned that small heaters (like coffee makers or kettles) can be kryptonite to an inverter, and that this is common folk knowledge among solar installers."
Is there any more on this? It can understand inductive loads maybe challenging inverters but resistive loads should be easy? Is it an issue of cheap inverter design, or something more fundamental?
From a quick Google that kinda makes sense, it’s just the strong, _sustained_ power draw that gives them issues. So I’d say fundamental AND inverter design — imagine pushing 2kW continuously through an inverter.
It’s funny, power use can be really unintuitive. Try convincing someone that using the big air conditioner for heating is more efficient than using that little plug-in bar heater. Or yeah, a power board with 8 tiny wattage wall-warts isn’t using a lot of power.
I could probably run my big fridge overnight off my portable battery generator, but it wouldn’t run my small electric kettle without putting it into a special mode and for nowhere near as long.
That doesn't make sense to me. On a cheap RV inverter maybe, but on solar for a house? The inverters should be rated to continuously output whatever the panel is generating. It shouldn't care whether the 2kW is going back on the grid or into your water kettle, it should be doing that all day every day.
Typical hybrid inverters have an output rating around half the theoretical max input of the panels. This is due to theoretical max of panel input being very rare or even impossible in normal earth conditions, the presence of an attached battery to soak up part of the input, and the general cost benefit trade off of solar equipment (more throughput means more heat, means bigger heatsinks, means heavier and more expensive).
You can definitely get equipment that can do symmetrical input/output, but if you actually model out the supply and demand curves on the system it's not usually going to be worth the extra up front expense since peak input is a small portion of the day and that extra hardware will mostly sit idle.
For that matter people often design systems where peak input can't even be accepted by the inverter and the extra power is just wasted, because it's more valuable to have a steady input over a long period than to maximize the daily peak.
6 replies →
> and that this is common folk knowledge among solar installers.
I think it's partially that people want to spend less money and undersize their inverter setup. The average end user non technical consumer (maybe a person buying an off grid PV system from an installer) may not fully understand what 1500W really is, and that something as boring as a $35 tiny space heater that sits on the floor can be a 1500W load.
People will be really surprised if you tell them that their tiny floor space heater uses the same amount of energy as charging twenty high performance laptops simultaneously.
It takes just a few high wattage single item electrical things to totally screw up the electrical load budget of a site, if somebody has something like a single 8000W rated inverter.
If you want to use electric space heaters and kettles and hairy dryers and hair curlers and such, along with the other regular daily load items of a house, you're looking at a setup with multiple 6000-8000W inverters in parallel with each other and synchronizing their output waveforms. Not many people want to spend the sort of money that'll get them 3 x 8000W inverters in parallel with each other all properly installed in an electrical room next to the PV stuff, breaker panels, etc.
Surely in British solar installations the inverters must be big enough to handle kettles ?
Assuming the heating element has a positive temperature coefficient (which seems likely), there will be inrush current greater than the operating current.
As an extreme example, a tungsten filament in a lightbulb would rise to 1500C (2700F) which with even a small temperature coefficient can mean inrush current 10x higher than the operating current.