Grid Tie Inverter running off batteries!!!

[MattieG]

Hi All

Ok my question is pretty simple!

I have a 300W small grid tie inverter (power jack) and I want to run it constantly (22hours maybe) all day and all night off a big battery bank instead of a solar panel.

Do these devices run off batteries at all, I cant really see any difference.
Ive ran it for a few hours off batteries to test and it seems fine.

I can understand if it its on 24 hours a day it may well burn out but does anyone have any other views on this?

Thanks
Mattie

[Sunking]

Why do you want to do this? You are throwing money away.

[MattieG]

Hi Derek

Basically I live in rented accomodation so I cant get my system MCS certified as its up on scaffold etc.

Basically I can generate alot ofpower per day and store it in batteries but only when the sun is out. I want to leave the 300W grid tie inverter on all the time running from the batteries so I can run the fridge for 24hours and a few other low power gadgets. This should save me 30p a day I reckon. I will also use the battery bank for PC and small heater etc.

I cant think of any other way of getting round this problem apart from buying a 24v inverter to run the fridge off batteries. Any advice etc is appreciated

Mattie

[Sunking]

Basically I live in rented accomodation so I cant get my system MCS certified as its up on scaffold etc.

Well there is so many things wrong with your assumptions I do not quite know where to start.

I assume you are in England? OK first if you do not have your certification tells me you do not have Net Metering. Net Metering is a special meter that measure both power you buy and sell back to the utility. Utility companies are pretty smart with the new meters out today to defeat what you are trying to do, operate an illegal connection. More than likely the meter you have will show what you generate as used from them. That means you will be paying the electric company for the power you generate. Gotcha!

Basically I can generate alot of power per day and store it in batteries but only when the sun is out. I want to leave the 300W grid tie inverter on all the time running from the batteries so I can run the fridge for 24hours and a few other low power gadgets. This should save me 30p a day I reckon. I will also use the battery bank for PC and small heater etc.

OK time to face the math quiz and reality check. Assuming you could do this, the most power a 300 watt inverter can convert in a 24 hour period is 300 watts x 24 hours = 7.2 Kwh. Here in the USA the average price of a Kwh is 11.2 cents. So 7.2 Kwh x $.112 = $0.81. So what is 30 P? Is that 30 pounds sterling? I do not know what the electric company charges you for a Kwh, but I am certain it is not 4.16 pounds sterling.

I cant think of any other way of getting round this problem apart from buying a 24v inverter to run the fridge off batteries. Any advice etc is appreciated

You cannot figure out a way to do it, because it cannot be done. Well it can if money is no object to you. To operate a battery system will cost you 10 to 30 times more than just buying it from your electric company, and that has to be paid up front in 5 year increments. After 5 years you get to replace the very expensive batteries. Speaking of batteries, we are not talking about a car battery sitting in a corner. We are talking 1000 pounds of lead and acid taking up the space of a dinning room table in your apartment.

[Sunking]

Ok here is a scenario based on a few assumptions mostly your location and guessing it is England. So you want your 300 watt inverter to run full power for 24 hours right? Well that is 300 watts x 24 hours = 7.2Kwh. OK to do that with a battery system we have to account for the high losses in a battery system. So that means your solar panels must generate 10.8 Kwh in a day

Ok to do that year round we must use your winter insolation of December and January. In gloomy doomy foggy England your winter insolation is 1.3 hours. So you must have a solar panel of 10,800 watt-hours / 1.3 hours = 8300 watts Here in the USA solar panels sell for about $3 per watt, so that is around $24,000 just for the panels in the USA. I understand solar panels are higher in UK. Any idea of how big and massive a 8300 watt solar panel array is? Bet it is bigger than your apartment.

But the fun has just started. I assume your 300 watt inverter operates on 12 volts. That would mean you would need 8300 watts / 12 volts = 691 Amps of charge controller. There is no such thing as a 700 amp charge controller. The largest consumer grade is 80 amps @ $600 a unit so you would need 9 units to a tune of $5400. But here is the kicker, the cable required to handle such current would require a pair of 750 MCM cable about the size of your wrist. The cable sells for around $12 per foot, and takes very special and expensive tools to terminate not to mention a gorilla to work with it. So just for the charge controllers and cable you are looking at around $6000 to $7000

As for the batteries well you will need to have 40 Kwh of storage. Roughly 1100 pounds of lead at a cost of $140 per Kwh so 40 Kwh x $140 = $5600

So just for parts and materials listed you are looking at around at $30,000 USD to generate less than a dollars worth of electricity per day. Using US prices and based on 5 year battery life means you will be paying $30,000 / 13,176 Kwh = $2.28 per Kwh. You can buy it from the electric company here for $0.112 Kwh. Is that a great deal or what?

[MattieG]

Hi Guys.. woo thanks for the reply... ill try and give you more info.

Ok I already have 8000 Watts of solar panels and a battery bank 600 Ah at 24V.
I have an outback FM80 controller charging the battery bank at 24V.

I appreciate the lead acid batteries arent cheap and only last 7-10 years but I already have them for free

Due to the size of my garden I currently have 4 x 280W panels pointing to the morning, evening and directly south at the sun. This is not ideal I know but allows me to charge the batteries constantly through the day without going over the maximum 80 amp of the controller. Even on a dull day I can produce 400-500 watts minimum.

Therefore this is enough to pump 300W into the small grid tie and some battery charging. So I wouldnt require the grid tie inverter to run on batteries all day only for 8-10 hours (maybe less).

The inverter runs directly off a 12V panel or from a DC source upto 28V so I can (in theory) connect it directly to my battery bank at a max of 27V.

I know it sounds idiotic but basically its worth a try
When my 8Kw are up and I own a house I will obviously be grid tied etc.

Any thoughts on that guys? Dont forget in the good old uk electricity is

[Psi]

[QUOTE=MattieG;9674]Hi Guys.. woo thanks for the reply... ill try and give you more info.

Ok I already have 8000 Watts of solar panels and a battery bank 600 Ah at 24V.
I have an outback FM80 controller charging the battery bank at 24V.

I appreciate the lead acid batteries arent cheap and only last 7-10 years but I already have them for free

Due to the size of my garden I currently have 4 x 280W panels pointing to the morning, evening and directly south at the sun. This is not ideal I know but allows me to charge the batteries constantly through the day without going over the maximum 80 amp of the controller. Even on a dull day I can produce 400-500 watts minimum.



Therefore this is enough to pump 300W into the small grid tie and some battery charging. So I wouldnt require the grid tie inverter to run on batteries all day only for 8-10 hours (maybe less).

The inverter runs directly off a 12V panel or from a DC source upto 28V so I can (in theory) connect it directly to my battery bank at a max of 27V.

I know it sounds idiotic but basically its worth a try
When my 8Kw are up and I own a house I will obviously be grid tied etc.

Any thoughts on that guys? Dont forget in the good old uk electricity is

[Carlo]

Why not just hook X amount of panels directly to the inverter instead of going through the battery bank?

[pdmoney]

Just curious if you ever got this working for any length of time...besides the costs mentioned, does it function?

[Meph]

Hello. Yes you can do this. Seems like you have the same issue as me. I have a 250w inverter an a 24v bank @300Ah (for free). I dont have a net meter so i can only run the inverter when im useing more power than i create. Basicly im running the inverter when my heatpump is running (they are connected to the same phase). If i generate more power than im using on the same phase its counted as consumption and i have to pay for it!

So yes do it! hopfully you inverter manages is it fan cooled?

Ansered on my iphone in bed. Hope its possible to read

[Mike90250]

Lucky folks to have your inverters sync to the grid without smoke ! Amazing luck.

[Sunking]

Basicly im running the inverter when my heatpump is running (they are connected to the same phase). If i generate more power than im using on the same phase its counted as consumption and i have to pay for it!

Amazing, you have a 120 VAC heat pump, everyone else has 240 VAC heat pump. Is this for a closet?

[Meph]

Lucky folks to have your inverters sync to the grid without smoke ! Amazing luck.

Why are we lucky? and no.. its not inverters. Its GRID-TIE inverters.. Not the same thing... You can never connect a regular inverter to the grid..

[Carlo]

I believe his comment was based on the fact that some people have had problems with the cheap 117 volt non ul-listed devices. Some have commented in the past that they "smoked" when plugged into AC.

[Meph]

Amazing, you have a 120 VAC heat pump, everyone else has 240 VAC heat pump. Is this for a closet?

Where in my reply do i say i have a 120VAC heat pump?? Open your eyes and read it again

The heatpump is for a 180 square meter house i live in...

My heatpump is a 3phase heatpump.. compressor works with 230v one phase and the electric heatpipes in it are 3 phase 12kW (380-400v)..