Example:

 

Inverter rating 3kw. Daily household usage 10kw.

Is there any cause for concern installing a undersized inverter that can be hooked up in parallel to another 3kw later down the line and so on.

 

Regardless of what the required consumption is will a grid tied inverter supply rated output (taking into account sunlight exposure etc) not the line?

 

Thanks in advance

NN

 

 

You say your daily household usage is 10kW. Is that 10kW instantaneous, ie. the peak combined usage by your house at any one time, or 10kWh usage for a 24 hour period?

If your peak combined usage is 10kW, it will overload a 3kW inverter, and either trip the inverter, or bypass it feeding from grid.

If your total daily usage is 10kWh, then providing you don't peak more than 3kW (possibly double for very very short period) the inverter will handle it.

The 3kw limit is almost certainly what the inverter can deliver from the batteries. It clearly won't power everything in your house, but can it power enough to get you through a load shed?

My average useage is about 13kw/h. The INVERTER part of my hybrid system can deliver a steady 20 amps, thus 4.6 KW/h.

But that is only when load shedding is happening. Most days, given enough sunshine, my system delivers most of the power my home requires - about 97%. When there's load shedding, loads that I deemed non-essential are dropped, and I am "reduced" to a load that does not exceed the steady 20 amps that the inverter can deliver from the batteries. But that's not a big inconvenience. Initially it mean dropping the pool pump, the element in our 2nd geyser (main geyser is on a heat pump) and the electric oven. So we still had our security system, all the lights, the garage door, all the plug points... Of course we could plug something really silly in and trip the system or flatten the battery very rapidly, but that's for us to control.

I can't speak to the matter of having inverters in parallel.

 

OK, some confusion of terminology here.

Firstly as already pointed out, is that kW do not equal kWh. (We should have a sticky for this).

Kilowatts are a rate of energy usage which we call power, kilowatt-hours reflect the amount energy used over a time period.

@Natal_Nic, your inverter is rated at 3kW, but your usage in a day is 10kWh, not 10kW.

For example, 10kWh could be used  either using a constant 1kW of power for 10 hours or a constant 10kW of power for one hour in your daily usage.

Whether an inverter can handle your peak demand depends on you usage pattern. You have not supplied the correct information for anyone to answer that question.

Secondly, @Bobster, the term "grid-tied inverter", is being confused with "hybrid inverter".  An hybrid inverter combines and "off-grid inverter" with "grid-tie" capabilities. It is positioned as a series device that passes grid current through it.

A grid-tie inverter, which was asked about, has no batteries.

A grid-tie inverter is a parallel device, it adds to the grid supply, the grid supply is not supervised by it.

If there is sufficient solar yield, a grid-tie inverter will pump its 3kW  worth of power into the grid all the time. If your loads constantly demand more than 3kW the shortfall will be made up by the grid, and nothing will trip (in normal operation).

Likewise if the loads are less than 3kW the excess generation will flow back into the grid.

Now @Natal_Nic, when you generate excess power to your usage you are exporting power just like a power station does.

Exporting power can create regulatory and supply point issues depending on your meter ( a pre-paid will trip) and national/local restrictions.

On 2020/01/24 at 3:45 PM, phil.g00 said:

Secondly, @Bobster, the term "grid-tied inverter", is being confused with "hybrid inverter".  An hybrid inverter combines and "off-grid inverter" with "grid-tie" capabilities. It is positioned as a series device that passes grid current through it.

A grid-tie inverter, which was asked about, has no batteries.

A grid-tie inverter is a parallel device, it adds to the grid supply, the grid supply is not supervised by it.

Thanks for that clarification, @phil.g00, I'd thought a grid-tie system was a hybrid without the batteries (which is how I ran mine early on). If it's parallel and just supplementing grid feed then that's quite a different system.

Thanks for the feedback.

 

Let me try explain further. The figures used in my first post were purely used as an example.

 

I own 2 swimming academys. 

 

Pool one has x2 heat pumps with a combined KW rating of 26kw. I understand this is not KWH.

 

Pool two has x1 9.5kw unit.

 

Im looking for an option where I can install (Start the solar journey) grid tied inverters with modular capabilities. So basically start small then grow when wallet replenishes. 

To have a hybrid system with batteries is financially not possible now or in the near future.

I see I should try get hold of peak usage figures as, understandably, this is quite important. Would a smart meter such a a Carlo Gavazzi work? Or any recommendations?

Both sites have very high solar yields through out the year.

 

Thanks in advance 

 

 

3 hours ago, Natal_Nic said:

Pool one has x2 heat pumps with a combined KW rating of 26kw. I understand this is not KWH.

 

Pool two has x1 9.5kw unit.

Hmm, now I think you've introduced a third issue.

I think a heat pump rating is in terms of its output power.

But a heat pump may have an efficiency of 300% or so, then the electrical input power is far less.

You should know what your electrical power draw is.

In electrical terms, all generation of an under-sized grid-tied inverter will be used and the grid will supply the remainder of the power required.

If you can guarantee that your constant load at daytime exceeds your grid-tied capacity, you will not have export issues.

Every watt you generate will reduce your electrical  bill.

 

13 hours ago, Pietpower said:

f a heat pump is sized correctly it will most likely switch on and off during the day.  When the heat pump is on then you will use all the solar power produced but when off and the inverter is bigger than the remaining load then the solar power produced will ramp down.

No it wont, not automatically anyway.

A grid-tied inverter goes full tilt all day long.

On ‎2020‎/‎01‎/‎24 at 3:45 PM, phil.g00 said:

Likewise if the loads are less than 3kW the excess generation will flow back into the grid.

Now @Natal_Nic, when you generate excess power to your usage you are exporting power just like a power station does.

Exporting power can create regulatory and supply point issues depending on your meter ( a pre-paid will trip) and national/local restrictions.

So to avoid this happening, you need a CT clamp? This is all new to me, but something I'm investigating right now as I have 3kW of solar panels on the roof being used to charge 4kWh of battery use, and the rest of my generation is practically lost. Been thinking of installing a hybrid inverter so the panels can assist in powering the whole house, not just charging batteries and powering my rather modest essential loads (300W on average), but I do not want anything feeding back into the grid, even if it means lost solar efficiency.

Edited January 28, 20205 yr by viceroy

3 minutes ago, viceroy said:

So to avoid this happening, you need a CT clamp? This is all new to me, but something I'm investigating right now as I have 3kW of solar panels on the roof being used to charge 4kWh of battery use, and the rest of my generation is practically lost. Been thinking of installing a hybrid inverter so the panels can assist in powering the whole house, not just charging batteries and powering my rather modest essential loads (300W on average), but I do not want anything feeding back into the grid, even if it means lost solar efficiency.

From what I have gathered on the forum, a CT clamp is not the panacea it seems to be, if you have the wrong type of meter.

The lagging response time when a load switches off, means the temporary power export still causes nuisance trips of the meter.

I don't have one of these type of meters, so I am sure a CT clamp would work OK for me.

If you have any purely resistive heat loads they can be fed by a load diversion DC PWM set up once the batteries are charged. This is what they use to power dump loads with wind generation.

This is probably the best solution in your set up to capture the lost production.

13 hours ago, phil.g00 said:

No it wont, not automatically anyway.

Of course not, it will drip out of your wall plugs!

14 hours ago, phil.g00 said:

A grid-tied inverter goes full tilt all day long.

Some do, but most sold in SA in combination with a "Grid Meter" does not. It increases and decreases the production according to the loads. 

 

6 hours ago, Jaco de Jongh said:

21 hours ago, phil.g00 said:

A grid-tied inverter goes full tilt all day long.

Some do, but most sold in SA in combination with a "Grid Meter" does not. It increases and decreases the production according to the loads. 

All do, but I clearly wasn't specific enough.

I mean't "of themselves" as opposed to combining them with additional control equipment.

On 2020/01/24 at 3:45 PM, phil.g00 said:

Firstly as already pointed out, is that kW do not equal kWh. (We should have a sticky for this).

Yup, my OCD-o-meter also goes a little crazy whenever someone says such a thing.

So how far is your office from your home? Oh, not far... only 50km/h!

🙂

The SI unit of energy is actually the Joule, but it is a bit unwieldy for electrical use, so the Watt-hour is used instead. There is 3600 Joules in a Watt-hour. A joule in turn is a watt-second, so literally one watt wizzing past every second.

On 2020/01/24 at 3:45 PM, phil.g00 said:

A grid-tie inverter, which was asked about, has no batteries.

Again, massive confusion with terms here. Technicially a Hybrid inverter is also a grid-tied inverter, as in all hybrids are grid-tied, but not all grid-tieds are hybrid 🙂

I really have a lot of sympathy for newbies... I do.

2 hours ago, Pietpower said:

It can only keep going full tilt if you can feed back into the grid.  Is this commonplace? 
When you can't feed to the grid or have a load then the pv will throttle down

What do mean by "can't"?

Do you mean "shouldn't"? When you shouldn't you will have to deploy some sort of gateway control in addition to the grid-tied inverter.

Otherwise, it "can" and it will.