diy solar

diy solar

generator connected to grid tie inverter.

sut12345

New Member
Joined
Mar 31, 2022
Messages
5
hi ,
can someone help with this problem/idea iv got.

i would like to connect a generator up to a grid tie inverter, to work with the grid mains income.
dont want it to work as a back up so happy for it to turn off when no grid power.
dont want solar panels connected to it.
just a generator connected to a grid tie inverter to supplement my house electrical supply.
is there an inverter out there for this ?

i have a 5kv diesel generator.
was looking at a string inverter with pv input up to 500vdc
then using a bridge rectifier to change ac from generator to 330vdc and feed it in through the pv connection.

would the 330vdc from generator need to be a smooth dc.
or could it just be a full wave rectified input. not sure if this would make the inverter turn on and off as voltage would drop to zero in between each wave.

thanks
for any input.
 
Most, if not all, MPPT string inverters have a clause in the manual saying something along the lines of "do not connect any source other than solar panels to the PV input"!! Obviously there is a reason for this, try it at your peril, the Magic Smoke may exit.

There are plenty of GTIs which can take DC input from batteries or whatever, but these do tend to be limited to 48V max. So you would need a fairly high-power buck converter to get your rectified mains to a usable level (they do exist).

But!

I'm intrigued, what is your fuel source that makes your diesel genset cheaper to run than using grid power? We have a source of used cooking oil from a family restaurant, but they would rather sell it to the local farmers to run their Kubota "Iron Buffalos" on (filter and mix 50-50 with pump diesel).
 
Thanks for the info.

ive got about 600 ltr of used oil from my factory.
which i get for nothing.
needs filtering but have been testing it on the 5kw generator and it seems, at least in the short term to run
without any problems.

going to do a long run test on it soon to see for sure.

if it works ok then looking at how to put it into my home to generate electricity.
electric price here has just doubled in price over night.

have looked at generator synchronisation with mains but cant find any equipment off the shelf that does it.
and not sure of how to set it up so that if grid power goes off the generator will also go off.
as the generator will power any relay connected to the mains and keep it on.

then there would be a few linesmen somewhere that wont be happy.

might look at a battery bank connected to an inverter and use the generator to charge batteries.

thanks
 
You can't connect the generator directly to the mains.
The mains will always win that battle. (And fry the generator)
Not to mention that it would be very dangerous for the power company workers.

might look at a battery bank connected to an inverter and use the generator to charge batteries.
This is the correct way.
Or install a transfer switch, and select between mains or generator.
 
Or install a transfer switch, and select between mains or generator.
This has potential to cause damage to either the generator or inverter, not sure which is more robust. If the demand is less than the inverter is producing, it's going to try to put that excess power back into the "grid" which is now the backup generator. I'm not sure how the generator would fail, but they aren't designed to have power coming in.
 
This has potential to cause damage to either the generator or inverter, not sure which is more robust. If the demand is less than the inverter is producing, it's going to try to put that excess power back into the "grid" which is now the backup generator. I'm not sure how the generator would fail, but they aren't designed to have power coming in.
No
The transfer switch keeps them separated.
That's the purpose of a transfer switch.
And, this scenario doesn't have an inverter.
 
He doesn't have an inverter.
He was thinking of it being one of the possibilities.
 
I just re read the question.
Basically, he has a generator and a supply of free fuel.
And wanted to try to sell electricity to the power company.
So.......
My suggestions don't match the goal.

New response.
I don't know of a good way to do this.
I would just use the free electricity, for my own uses.
 
hi thanks for the comments.

to be clear, not looking to sell electricity to the power company.

looking at a way to install a generator into my house to work with/at the same time as the grid also supplying the house.
would probably only run the generator at peek times so that i would use a smaller amount of electricity from the grid.
the battery charging is a good idea as it can then continue to feed power into the house after the generator is off.

have seen this where they have built a hydro generator and feed that into an inverter to charge batteries for an off grid system.
they have used the solar pv input on the solar charger to connect the hydro generator.

https://www.victronenergy.com/blog/2019/01/03/diy-ingenuity-hydro-power-mkii-part-i/
https://www.victronenergy.com/blog/2019/01/23/diy-ingenuity-hydro-power-mkii-part-ii/

ideally i would want an inverter that accepts a generator input but not as a back up or off grid system.
that would feed the house along with the grid supply.
option of charging a battery bank also would be good as when there is surplus electric it could go to charge batteries.

thanks
 
Deye makes a grid tied inverter, that will work.
You will still be on either generator or grid. (Not together at the same time) but, while on generator, it will charge a battery bank. This way, you get the most efficient use of the generator.
 
I think feeding rectified AC into a grid-tie inverter is a reasonable approach.
Most GT PV inverters have only a MPPT profile. Some older model Sunny Boy have turbine profiles, which might work better.

One issue to consider is inrush; the inverter input capacitors would look like a short initially to the generator. Inverter waits 5 minutes before exporting, plenty of time for a precharge circuit.

Trukinbear reported his generator costs around $1.00/kWh. That was with a good diesel, but he bought fuel. Maybe you can compete with utility rates if fuel is free. Consider doing it in the winter, with captured heat put to use as well.

ive got about 600 ltr of used oil from my factory.
which i get for nothing.
needs filtering but have been testing it on the 5kw generator and it seems, at least in the short term to run
without any problems.

I read a government study which found burning straight oil caused more coking of the engine than using diesel.
You might want to make diesel out of the oil for long term use without problems.
 
hi hedges,
thanks for the reply.

looking at the specs for an inverter i thought it would be possible.
thinking of something with approx 600vdc pv input to give a good amount above generator voltage spikes.

looking at rigging the generator to produce the amount of amps i want by taking out the AVR and setting the input amps with a variable resistor.
this way when i start it up it can be on zero amps and slowly turn it up to max.
hopefully this will help with the charging caps in the inverter.

thanks
 
Last edited:
Starting up the generator when already connected could fix inrush. Inrush limits could be another way, I think commonly put between grid and SMPS input.


Maybe this one would be good:



PV input to inverter/SCC needs to be floating. Often generators do not have neutral bond (but if you also use generator output for loads, would be a problem.) An isolation transformer could help. Needs to handle continuous draw; may be able to program that to less than inverter/scc max rating.

You already have your generator, but for others maybe an inverter generator would be good - tap into its own DC rail, and it already adjusts generator speed to match load. So long as it isn't so smart as to look at its own AC output, just load/voltage at DC.

Since a GT PV inverter takes in DC and makes AC, its decoupling should be sufficient to take in AC and make out of phase AC. An SCC takes in DC to make DC, doesn't have to follow low-frequency sine wave. So may need additional capacitance to avoid excessive ripple which would wear out or overheat its capacitors.


dont want solar panels connected to it.
just a generator connected to a grid tie inverter to supplement my house electrical supply.

Solar panels will be cheaper than diesel for your generator after just one year of operation. 1/10th the cost over a decade.
Any reason you don't want solar panels?
 
The fuel is free oil from a factory.
I would get solar eventualy but need to sort my roof out/ chimney/
Ridge tiles. So by the time I get the money will be a few years down the line.
Also some people in uk say solar not that good? . Takes 10 years to get build cost back?
So I’d have to look into it a bit.
 
The fuel is free oil from a factory.
I would get solar eventualy but need to sort my roof out/ chimney/
Ridge tiles. So by the time I get the money will be a few years down the line.
Also some people in uk say solar not that good? . Takes 10 years to get build cost back?
So I’d have to look into it a bit.
Most of the solar components, built today. Last over 20 years. A 10 year ROI, isn't terrible. With doing all of the work, myself. And some smart shopping. My ROI is 7 years.
 
Did you ever get anywhere with this? I'd like to be able to do essentially the same thing to test my generator under variable load, and it looks like some modern hybrid inverters can program the maximum generator load...
 
Back
Top