July 16, 20223 yr Hi all Hoping the more experienced folk here can guide me if possible? I've acquired a Linkqnet 3000VA Inverter (UPS-INV-3KVA-VP-LQ) with the following specs: Peak power: 3000VA RMS power: 3000W AC Voltage: 230V DC Voltage: 24V (Will not operate without batteries) Transfer time: 10ms/20ms AC charge: 25A SCC Type: PWM SCC Voltage: N/A Max PV OV Voltage: 80V DC Max SCC power: 1200W SCC Charge: 50A Max combined charge: 70A Parallel capable: No Communication: USB Direct Bluetooth: No WIFI option: No 3G option: Yes SNMP option: Yes Battery types: Flooded, AGM, GEL, Li-Ion, Custom BMC Support: No Am looking to combine it with two (eventually four) Hubble S-120's & a cell balancer to begin with, to carry my TV/PC/internet/lights through the Stage 2/4 and hopefully Stage 6 load shedding. My question is now in terms of solar panels, what should I be looking and saving my $$$ for in terms of max efficiency in charging the batteries and running small loads off the inverter/solar during the day? Thanks!
July 16, 20223 yr Hi GraigeZA You are very limited in the solar panel area. The limitations are the 80v open circuit voltage and the maximum wattage of 1200w. The best you can do is 4 x 300w solar panels with 2 parallel strings of 2 panels in series. You cannot go any higher as the open circuit voltage is too high. It is a pity you are limited as you can only get about 5amps max at 220vac at best. You can only expect 80% of this with the full sun which is about 4 amps at 220vac. I hope this will help you. Edited July 16, 20223 yr by Peter Topp
July 16, 20223 yr 25 minutes ago, Peter Topp said: Hi GraigeZA You are very limited in the solar panel area. The limitations are the 80v open circuit voltage and the maximum wattage of 1200w. The best you can do is 4 x 300w solar panels with 2 parallel strings of 2 panels in series. You cannot go any higher as the open circuit voltage is too high. It is a pity you are limited as you can only get about 5amps max at 220vac at best. You can only expect 80% of this with the full sun which is about 4 amps at 220vac. I hope this will help you. Luckily the OP can overspec the panels by 20% to compensate for the 20% drop in PV. In order to use more than 4-5 amps during sun periods it is easy to add an external MPPT. Being a 24V system there are many cheaper good MPPTs around. A 20A MPPT would add another 520W of PV power. There are also 100V/40A external MPPTs. Then Victron have some high power MPPTs but they can cost more than this inverter. As said one is limited to 60 cell panels at about Voc around 38V. Also using S-120 batteries means you can use quite a bit of power during the LS sessions up to the inverter maximum. 2 will easily provide 2kwh per session and 1kwh can be recharged in the period the grid is back when no sun. Edited July 16, 20223 yr by Scorp007
July 16, 20223 yr Hi I do believe in overspec of the pv panels however in this case the open circuit voltage is 80v and the 300w panels are on this limit. If you overspec you stand a chance you can damage the inverter and I would not advise anyone to do this. You can overspec the current but this is limited to the number of panels used. Edited July 16, 20223 yr by Peter Topp
July 17, 20223 yr Author Thanks, recommendations on four 300w panels (to be installed in series & parallel) that will keep me under the PV OV 80v limit? EDIT: Would 4 of these suffice? Edited July 17, 20223 yr by CraigZA
July 17, 20223 yr Hi To my knowledge inverter's pv input work best between certain voltages. My best guess for this inverter as I have no manual the pv voltage should be close to 30/32v to work the best. If this is true putting the panels all in parallel would limit your available power. In this case, 2 panels in a series would give you the earliest power output during the day. Edited July 17, 20223 yr by Peter Topp
July 17, 20223 yr Hi P1000 I see you are confused. I had another look. I have had a 3kw inverter with a pwm and after looking at the manual I see they do suggest you can connect in parallel. I do believe you could be correct to install the panels in parallel. My original thinking is that the voltage at its peak will only be about 25v (31.3v-20%) at its peak during the day and by doubling the output to the inverter you could be closer to the 30/32v for most of the day for the best efficiency. Edited July 17, 20223 yr by Peter Topp
July 17, 20223 yr Author Excerpts from the manual here (excuse the quality, the manual almost as small as my iPhone!). Given the above, is the answer to put four of those ARTsolar 280w panels in parallel? Thanks!
July 17, 20223 yr 1 hour ago, Peter Topp said: Hi P1000 I see you are confused. I had another look. I have had a 3kw inverter with a pwm and after looking at the manual I see they do suggest you can connect in parallel. I do believe you could be correct to install the panels in parallel. My original thinking is that the voltage at its peak will only be about 25v (31.3v-20%) at its peak during the day and by doubling the output to the inverter you could be closer to the 30/32v for most of the day for the best efficiency. @P1000 Is spot on that the ideal is to use panels in parallel as you also found in the manual. If say 36V panels of 280V are used the current is around 7.77A. If 2 panels are in series and produce 72V the current to batteries will be pulses of 7.77A. If the 2 panels are in parallel you will get pulses of 15.55A to the battery. Due to this reason an external MPPT will for 2 panels in series provide 72/29X7.77=19.3A to the battery. Thus 38.6A to batteries for the 4 panels @CraigZA has in mind. Actual will depend on the panel voltage/current. Edited July 17, 20223 yr by Scorp007
July 18, 20223 yr 16 hours ago, Peter Topp said: Hi P1000 I see you are confused. I had another look. I have had a 3kw inverter with a pwm and after looking at the manual I see they do suggest you can connect in parallel. I do believe you could be correct to install the panels in parallel. My original thinking is that the voltage at its peak will only be about 25v (31.3v-20%) at its peak during the day and by doubling the output to the inverter you could be closer to the 30/32v for most of the day for the best efficiency. PV panels behave counter-intuitively when it comes to voltage VS insolation. Voltage is much more dependent on temperature than insolation (as long as it is in full light). When it is not in full light, the voltage is usually so low that you cannot really compensate for it, and under the same conditions it also produces so little current that it is not worth thinking about.
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