Saturday at home, installing an inverter

[IMHO]

I am playing with another idea currently. I saw I can not afford an off grid system. Too many batteries and the price kills it. So what if one goes grid tied without batteries? This will be purely to bring the Eskom account down and not for load shedding. (Which seems to be a thing of the past in any case) For that and other power outages, I will use my UPS system for mission critical equipment.

When my panels produce nothing or a bit, I will use Eskom. (At night and rainy days)

So, when the sun shines, I use my panels free electricity. When there is a shortfall, I draw from Eskom. When I produce too much, I dump it somehow useful as we can not feed back to the grid. I estimate about 36 panels @250 watt. Still a huge expense but I figure it will pay for itself in 5 years.

First point of departure, I will have to get one of those smart meters to monitor my total consumption for a month, to see when I use how much power.

But is the idea possible? Say it is a cloudy day and my panels produce 2600 watt. Can one draw the balance (6000 watt) you need from the grid? Or is it a case of all or nothing?

What is all the equipment you need in such a setup called? What worries me the most, is how do you draw the shortfall from Eskom and marry it to your own. How do you dumb the excess by sending it somewhere else?

[Justloadit]

It is called a grid tied system, simply put is that the inverter is synchronised to the mains, and increases the voltage ever so slightly, so that the solar system provides as much power as the solar system can give and the balance is then provided by ESKOM. The only problem with this system is that the energy is only available when there is sun, and it may be when you really do not need this energy.

[IMHO]

Video as promised.

For some reason the forum says it is an illegal file and will not show preview.

Here is the direct link.

https://www.youtube.com/watch?v=Sib9...ature=youtu.be

[IMHO]

Here is the demo on the working and ammeter. I see that for a split second the amps is going into 30 amp. How long should it be over 30 amp to blow the fuse?

https://youtu.be/_uC_iKuyNpo

[AndyD]

As Justloadit said, you'll produce most of your power around the middle of the day when you're probably not going to be able to use it. It works in Europe because the power company offers a 'feed in tariff' (FIT) so they pay you for power you put into the grid when you're not using it and this offsets the cost of the power you take out of the grid at another time when you do need it.

There are inverters already available the can take multiple inputs and prioritise their use, look at the Victron Multiplus range for example,even the cheaper Axpert that I installed can do this in a limited fashion. You can connect PV panels, wind turbine, batteries and Eskom power and it will use you PV and wind power to supply the load and if there's insufficient power available from those it will make up the deficit using Eskom power. If there's surplus power coming from the PV and/or the wind turbine it can use this power to charge batteries if they're installed.

Without a feed in tariff I doubt it will be financially viable for a domestic premises to install PV and inverter without batteries, most of the power produced will not be used efficiently if it's used at all.

[tec0]

Video as promised.

For some reason the forum says it is an illegal file and will not show preview.

Here is the direct link.

https://www.youtube.com/watch?v=Sib9...ature=youtu.be

Love your UPS hack, excellent and your question is a damn good one. I spoke to a guy from Battery Centre and he told me my charger was killing my batteries now they are selling a charger that can charge deep cycle battery and it will cost me about R1250 for it. Now thing is with your normal UPS and i think you knew this already so sorry for repeating it. There is no real why to stop it from charging your battery because by design it just stupidly charge the battery to death "had a few UPS's" and if you check the voltages on them you will see that even when the battery hits 14 volts it just continue to charge.

I have no clue how you will get around that yet.... That said YOU DID THE HACK! and not many can say that

excellent post

[daveob]

Here is the demo on the working and ammeter. I see that for a split second the amps is going into 30 amp. How long should it be over 30 amp to blow the fuse?

Hi IMHO

Hope you don't mind me chipping in here.

Video looks good. Well Done.

Had a look at the last few posts here and you seem to be rightly concerned about overcharging the batteries.

I see that you have 2 main possibilities here :

option 1 :
control the charging by the UPS.

You would need to identify the circuitry that charges the batteries.

Then monitor the battery voltage and when it reaches the required level, say 14V or whatever the ideal voltage is, then disable the charging from the UPS.

Battery voltage can be easily monitored using a micro processor ( like an atmega328 IC chip ). The IC runs using 5V which can be supplied by the battery using a linear voltage regulator, and then connect the battery to an analog input pin using a voltage divider.

The voltage divider ( consists of 2 small R3 resistors and a capacitor ) basically scales the battery voltage down to a level that the IC can read. The IC can measure from 0V to 5VDC. So if your absolute max voltage on the battery under charge will be, lets say 20V to be on the safe side, then we need to scale the voltage down to 25% of the source ( battery ) and feed the scaled down voltage to the IC. The analog input pin of the IC has a 0 to 1023 scale, so is reasonably accurate.

So the IC would see 20V source as 1023 on it's analog scale ( 5V at the IC from the voltage divider ), 15V as 767 ( 3.75V ), 10V as 511 ( 2.5V )

Once you have that working, that same IC can control a transistor, which in turn controls a Solid State Relay, or opto-coupler, or any other device to turn the UPS charging system on or off.

The downside here is that you have no control over the charge rate.
Plus side of having the IC here is that you can also use it to monitor the voltage of the batteries when the UPS has no mains supply, and is discharging.

You may find your UPS will discharge the battery to, lets say ( just for an example ), 10V. But your battery supplier says you should not discharge below 11V to ensure the battery lasts 5 years longer.

So the voltage divider to the IC is used to monitor the battery voltage during discharge, and if it gets to a certain level, say 11.05V, then you disable the SSR or relay that connects the battery to the UPS. Yes, your appliances lose power, but your batteries live to fight another day.


Option 2 :
Disable the charging of the batteries by the UPS and charge them using a separate independent charger that is designed for different charge rates.

There are a number of designs out there that will monitor battery voltage ( as described above ) and use PWM to control the charge and charge rate to the batteries, ranging from full power charge upto certain voltages, then reducing charge rate to a trickle or 'maintenance' charge.

Just my 2c worth.

[daveob]

Actually, having just thought about that, I think it also important to point out that in so many cases, people are spending small fortunes on systems to ensure that they have power when the outage hits - but little or no thought or concern about what happens when the power is restored.

There have been numerous mentions of routers that work erratically. The mains power is all over the place when it comes back on and everyone starts up at the same time. So if you're getting 180VAC into the router transformer that expects 200 - 240VAC, then the 12VDC output may not be 12V and the router starts doing weird things.

Or the TV set and sound system that you paid +R12k for that is subject to wild voltage swings on power up.

Or this pride & joy battery system. What happens when the power comes back on. Does the UPS immediately disconnect the battery and router the mains to the devices plugged into the UPS ? Most likely the case. What effect does voltage changes have on the charging circuit ?

The solution is to install a device that can :
1. prevent the mains power from being supplied down the line.
2. monitor the incoming mains voltage until it is above a set value ( eg. 200VAC ) and below 240VAC.
3. Start a timer ( eg 5 minutes, 15 min, etc )
4. delay the supply of mains power downline until the timer has expired ( unless the override button is pressed )

That way, you get to minimise the startup impact on your equipment.

[tec0]

So basically micro controlling will become the norm here, I was thinking about a Arduino Uno, they can handle a lot of inputs and there are shields available for modification and the program IDE have a look at arduino. There is also a heavily supported library for it so copying and pasting code may well be an option "depending"

I am planning home automation with it... I am sure a Google will give you results on how to make smart chargers and all the rest. There is a ton of stuff on YouTube.

hope it helps a little

[daveob]

So basically micro controlling will become the norm here, I was thinking about a Arduino Uno, they can handle a lot of inputs and there are shields available for modification and the program IDE have a look at arduino. There is also a heavily supported library for it so copying and pasting code may well be an option "depending"

I am planning home automation with it... I am sure a Google will give you results on how to make smart chargers and all the rest. There is a ton of stuff on YouTube.

hope it helps a little

Look at the Mega2560 instead. Has 54 I/O pins instead, and not that much more cost.

Personally I use a Mega2560 for home automation ( 3 x gate control, alarm system, sms to cell on trigger, web based control of gates, alarm, smart sensor control ( eg disable indoor passives in living room area when kids break beams in passageway in the morning, etc ).

Yes, you will find a lot of open source code based on Arduino for charge controllers, etc.

Just remember that boards like the Arduino have a 'per pin' and 'total board' current limit, so outputs are basically limited to an LED or an NPN transistor ( which in turn can drive much bigger loads ).

Once you have an Arduino, you can also use it to program a stand-alone atmega IC ( about R70 for atmega vs R350 for Uno ) so once your code is working, push it on to an atmega and reduce your hardware cost.

ps .. when you make a board for the atmega IC, use an IC saddle ( type of socket that the IC clips into ). If you have a system problem, very easy to remove the IC brains and replace it with the spare that you made.