Excess power?

[Milo]

Hello, please excuse me if my question is daft, but I would very much appreciate an answer. Having connected my batteries to the charge controller and inverter, how do I utilize the excess power produced by the panels (power not used for charging) there is a DC output on the controller for the excess power but if I connect that to the inverter as well as the batteries obviously I have a problem. Is it the case that I need to add a blocking diode of suitable size between the batteries and inverter, I have a battery monitor that places a shunt on the battery-inverter line, will this do the same job or am I barking at the wrong tree altogether? Thank you kindly for reading.

[Sunking]

Simple, you can't. What you have is a Diversion Load Connector. So when the batteries are full, the panels are connected to something like a resistance heater to heat water or just burn off the power as waste heat and dumped outside. They are intended to be used on wind mills to keep a load on the turbine so it does not over speed and destroy itself. That is the beauty of off grid battery systems, they are very inefficient and waste of valuable resources. You can never utilize all the power. Most of it is wasted and lost forever.

[dkpro1]

hhhmmmm ?

Simple, you can't. What you have is a Diversion Load Connector. So when the batteries are full, the panels are connected to something like a resistance heater to heat water or just burn off the power as waste heat and dumped outside. They are intended to be used on wind mills to keep a load on the turbine so it does not over speed and destroy itself. That is the beauty of off grid battery systems, they are very inefficient and waste of valuable resources. You can never utilize all the power. Most of it is wasted and lost forever.

More untruth from the king .....if your off grid is set up right you don't waste power at all

[dkpro1]

More untruth from the king .....if your off grid is set up right you don't waste power at all

only loss is battery internal res. and inver. loss

[Sunking]

More untruth from the king .....if your off grid is set up right you don't waste power at all

BS you loose 20% just from charge/discharge efficiency in the batteries.. 30% minimum alone is lost in any PWM controller system, and another 3 to 10% in wiring. Another 10% minimum in inverter losses. So you had better learn WTH you are talking about because you just stepped in a pile of your stupidity. At very best with a MPPT system, efficiency can only go to 67 to 70% from panel to utilization. So you have no idea WTF you are talking about.

Now do you wanna talk about all the energy never generated and utilized by the panels they would have otherwise if the batteries were not in Absord or Float mode, or used in Grid Tie application which is what the OP asked? Because all that is energy lost.

[dkpro1]

off grid

BS you loose 20% just from charge/discharge efficiency in the batteries.. 30% minimum alone is lost in any PWM controller system, and another 3 to 10% in wiring. Another 10% minimum in inverter losses. So you had better learn WTH you are talking about because you just stepped in a pile of your stupidity. At very best with a MPPT system, efficiency can only go to 67 to 70% from panel to utilization. So you have no idea WTF you are talking about.

Now do you wanna talk about all the energy never generated and utilized by the panels they would have otherwise if the batteries were not in Absord or Float mode, or used in Grid Tie application which is what the OP asked? Because all that is energy lost.

King have you even lived a day off grid ?

[russ]

King have you even lived a day off grid ?

Please get real - you keep trying to paint a losing proposition as something great.

Off grid is fine when there is no choice but it is a loser otherwise.

[sdold]

More untruth from the king .....if your off grid is set up right you don't waste power at all

If a system is designed to provide year round power, wouldn't there be plenty of times in the summer when there is excess power at the panels that is not used once the batteries are charged?

[Bucho]

Please get real - you keep trying to paint a losing proposition as something great.

Off grid is fine when there is no choice but it is a loser otherwise.

Seems like there's some real question dodging going on around here. I'd like to hear dkpro1 try and defend his claim of an efficient off grid system instead of dodging by questioning Sunking's experience.

I'd also like to hear Sunking's experience with off grid solar.

[Sunking]

I'd also like to hear Sunking's experience with off grid solar.

Well my respomse was on here, it got deleted so let's try again.

dkpro simply does not know what he is talking about plain and simple. If he did he would know the first loss comes in the wiring, of 2 to 10 % burned off as heat. Next comes the charge controllers wiht MPPT being the lowest loss of around 3 to 5%, and with PWM at best 32% is lost and up to 50%. Then we have the batteries, FLA you loose 20% just with the charge/discharge losses. AGM is better at 5 to 10%. Then we finally get to the inverters where we loose at leat 10% and in some cases another 50%/

So at the very best if you could actually utilize every watt hour available which is IMPOSSIBLE, with a MPPT system 66% efficiency is as good as it can theoretically be on paper. With PWM you loose 50% or more. Now here is the real kicker. In real life application you are doing great if you can utilize just 30 to 40% of what is possible, but you CANNOT DO THAT, it is IMPOSSIBLE. A well designed system turns off just after solar noon when the batteries go into Absorb and Float mode. Technically you do not loose the power, it just gets turned off. Contrast that to a GT application and every watt hour is utilized by someone somewhere with only the line and equipment losses of roughly 20% making them 80% efficient.

So as you can see dkpro is just uniformed and does not really know what he is talking about.

[inetdog]

There are two easy to confuse metrics in play here:
One of them is the relative cost per kWh between off-grid and grid tied. I do not think that anyone can argue the economics of an off-grid system when a reliable grid with net metering is available.
The other is the efficiency of the two types of systems defined in terms of exactly how much of the potential power that the panels could produce actually makes it into the form of consumed watts in useful loads (or sell back of course).
When you get into that, you have to also make a subjective evaluation of the relative usefulness of opportunity loads, given that there would be other competing ways of satisfying those loads. We can be generous to the off-grid efficiency by assuming that opportunity loads will be powered directly from panels to inverter with no associated net current into or out of the battery bank, thus removing the charging and discharging efficiency of the batteries from consideration.
For opportunity loads such as water heating, the underlying assumptions are that there is always water that needs to be heated and will not be superheated to the point that increases heat loss from the storage tank, and that there is no more cost effective way of using AC or DC to provide that heat (e.g. heat pumps, etc.) To the extent that either of these conditions are not met, some percentage of the opportunity load must still be considered waste.

There are some suggested guidelines for the discussion, let the battle continue.

[Sunking]

We can be generous to the off-grid efficiency by assuming that opportunity loads will be powered directly from panels to inverter with no associated net current into or out of the battery bank,

You cannot do that until after the batteries have fully charged. Such a supply and load is so dynamic, panel production and use would rarely ever match the load demand.

[inetdog]

Then we have the batteries, FLA you loose 20% just with the charge/discharge losses. AGM is better at 5 to 10%. Then we finally get to the inverters where we loose at leat 10% and in some cases another 50%/

As noted in my post #11, I think that for real time opportunity loads or time shifted loads moved to peak solar hours you can eliminate the battery loss from the equation. For night time loads, on the other hand, the power does have to go into the batteries and come back out again.
The POCO virtual battery has no such losses. Just very small local wiring losses. Now from the POCO's point of view, the exchange is not an even one since they have to make up some distribution losses, but those are on the other side of the meter.

[inetdog]

You cannot do that until after the batteries have fully charged. Such a supply and load is so dynamic, panel production and use would rarely ever match the load demand.

True, so I am being very generous and assuming opportunity loads which are infinitely variable or at least switchable in small steps. The load management systems offered primarily in the UK claim to be able to do that. The extent to which they succeed is an open question for me.

[Sunking]

True, so I am being very generous and assuming opportunity loads which are infinitely variable or at least switchable in small steps. The load management systems offered primarily in the UK claim to be able to do that. The extent to which they succeed is an open question for me.

So tell me how to do that. A human cannot do it. A PLC could if you had a vast assortment of load devices to tune the system, but I can see nothing but chaos of stuff getting switched on/off constantly.

If you have monitored power output over the course of a day, it changes every second. Even with a PLC would be extremely difficult. A off-grid system by its very nature is over designed based on worse case conditions. As I get older and wiser my design philosophy has changed with acquired knowledge. Such as under designing the system and using a genny during the 4 to 5 low Sun Hour months to make up for the shortage works better from economics. Is summer the system generates excess power which is still lost forever, an din winter all the power is utilized and must be supplemented by a genny which is a mandatory item every off-grid system must have to perform maintenance in batteries.