Does anyone know where I can obtain a 1Kw grid tie inverter designed to work with a battery (36V) with adjustable power output (0 - 1Kw)?
IKw inverters with MPPT for direct connection to solar panels (36V), are now very cheep but I have been unable to find one that can run off a battery with the MPPT disabled and power output adjustable. Preferably I would like to have the power adjustable electronically (eg to balance base load) but for the time being I would settle for one with a manually adjustable output.
I appreciate that some hybrid inverters and presumably ones designed to work with with Tesla power wall, have this feature built in but I am looking for one that can be used as an add on (ie without solar panel input or battery charging facility).
if your only worried about 1kw a the Chinese sunG inverter would work fine 22 - 60v
all you need is PWM. ( with or with out low pass filter) on the dc side the SunG input is designed for ac input and handle the dc pulse of the PWM without problem. the PWM will also limit the current draw from the battery. the sun inverters are built very nice they last long time especially if you run them at <80% of rating
Thanks for the reply. My main concern using a PWM controller (which would be the easiest way of implementing “load balancing”) was the possible interference of the inverters MPPT. There are many different MPPT algorithms out there, some of which use a momentary open circuit voltage measurement. There are grid tie inverters out there that can be switched to “battery mode” (disabling MPPT, with manual control) but there aren’t many of them! I am in communication with a Chinese manufacturer that advertises inverters with a “load limiter” external control but I’m not 100% sure that it would do the job!
that would be the sun GTIL with the limiter I would believe that the only company I know other then one in south africa. . plus also why i mentioned the sunG it thier wind GTI and it MPPT is designed for very erratic power output with very high pulses ( they also can not momentarily disconnect the wind as the the voltage can spike extemely high)
just mentioning - i ve being doing this with the sun G -WDL for while with out issues- you can check out my older version of GTI limiter and diverted. it list the PWM I use they are pretty cheap at ~$5
I think I will go with the SUN-1000G2-LCD from Ningbo Deye Inverter Technology Co., Ltd. It is a 1 Kw grid tie with a proper battery mode which has adjustable power with adjustable current and voltage limits. Cost $210 air freighted to UK + tax on arrival
My SUN-1000G2-LCD has arrived & it seems to work! It has a fiddly and rather small LCD screen but you can set the inverter to battery mode. There are 2 battery modes (which can also be used without a battery) The first has DC current limit & low voltage cut off and the second has AC power limit & DC low voltage cut off. This seems to work fine, the AC power ramps up fairly quickly to what ever you set it to & provided the DC voltage stays above the low limit (which you can also set) the inverter carries on at that power level but you cannot set these values electronically. The max continuous AC power is 950W but this is considerably above 1kW DC. They also do a GTIL version which has a clip on current transformer (with AC voltage to measure load power) and this can be used to use battery power to say, balance your base load.
I’m not actually using a battery at present, so we don’t have a charging circuit. We have built a small, solar powered, hydrogen filling station (200L @ 200 Bar) & I have been using the inverter as a load to test a 1kW fuel cell. The open circuit voltage of the fuel cell is ~48V DC and at full load ~ 30V so it matches the inverter well. There is a slight problem in that it has an electrode conditioning circuit which puts a short circuit on the fuel cell for 100ms every 10s. This trips the inverter low voltage! You can turn the short circuit off but the fuel cell is then less efficient. We have had it running at full power with the short circuit device on but we had to use a blocking diode & a 48V 28F super capacitor but its a bit fiddly & requires care charging & discharging the capacitor!
We are planning to log the FC efficiency under different conditions but we don’t have the data yet. The round trip efficiency (Solar DC - H2 - FC DC) is clearly not good for storage (you’re much better off using batteries) but it has a major advantage for high speed filling of vehicles.
Our H2 is produced via PEM electrolyser we plan to increase storage pressure to 450 Bar for 350B filling.
By the way, does your GTI limiter using a PWM on the DC get smooth control of the AC power output? My attempts at controlling GTI with PWM have produced very erratic power output, presumably because of the hunting due to MPPT.
I haven’t tried your suggestion of the SUN wind inverter yet but I suspect it will suffer from the same problem? I am keen to get a GTI which I can smoothly control the power output electronically. The SUN-1000G2-LCD has very good power control but not electronically.
""There is a slight problem in that it has an electrode conditioning circuit which puts a short circuit on the fuel cell for 100ms every 10s. This trips the inverter low voltage! “”
why not just place a a small 24 volt battery to act as buffer ( or what ever you minimum voltage is for your inverter) - just to fill in that gap in power since you say 30 is your operating voltage 36volt is too high as it be loading off the battery . just isolate the battery with some diodes and use a buck converter to keep the voltage ~ 24 off your fuel cell branch to maintain the battery. if only 100ms every 10s would not need much of a battery the reason I suggest 24 volt battery only so it comes into use to fill in the gap and not powering the inverter under load.
hi Richard-- I retested my GTI limiter purely on GTI limiting with out the diverting . - I used just a basic 500W GTI ( no name cheap solar) the rate at which it limiting is non linear on the top 1/2- gti limiting is a bit jumpy from 100% - 50% (but I suspect if you do a average it would probably appear quite linear decline - ) then after you reach about 50%. then it becomes quite linear as each step down would reduce by 5Wattts till I reached about 30watts then the gti would loose tracking and then pulse send after that… at 30 watt the unit would MPPT lock all the way up to 50% of load then after 50% it can not maintain MPPT lock… I suspect if I change the freq of the PWM pulse ( speed it up) i could get better performance - on my PWM i places a cbb22 cap across the - and + pole to flatten out the step