Hi,
I currently have 6x400w panels into each string of my 5kw inverter. All 12 panels face south east. I'd like to put more panels on a west facing garage roof if I can do this cheaply (ie, without buying a new inverter). Can this be done?
Can I simply put the first 12 panels in one string and the new ones in the other? Can I tag 4 new panels onto each existing string somehow, using optimisers?
Thanks in advance.
You could add to it, but you will be restricted by the inverters limits. 5kw max. So adding panels would help in lower generation months but during the Summer you will not see much benefit.
Presumably you have a GE 5kW hybrid inverter. Gen1 or Gen2?
Either way there are a number of parameters that have to be checked to ensure they do not exceed allowed limits.
1/ Max DC power = 6500 W
2/ Max DC voltage = 600 V
3/ MPPT voltage range = 120-550 V
4/ Max input current per string = 11.0 A
With 12 x 400W on 1 string, you certainly need to check the Voc does not exceed 600 V under worst case conditions (usually -10.0 C temperature).
You will need the data sheet for your exact model of solar panels.
If all the limits pass the test, then your inverter may have capacity for extra panels that provide up to 1700 W peak on your other roof, but do not take my word for it. 6500 - 4800 = 1700 W.
Normally the prospective installer carries out all the check calculations to ensure the inverter will not be overloaded.
1700 W peak would typically only be 4 x 425W panels on the 2nd string, which may have issues with the startup voltage of the inverter string (Gen1=100V, Gen2=150V). Again the panel data sheet is required for the relevant figures.
For panels on different aspects, you normally need an optimiser on every panel in order to cater for the changing shading/output over the course of the day. This would work out pretty expensive to retrofit on your existing panels as well as any new panels.
Simonturner1 as others have said, ensure the existing panels do not cause an overvoltage condition if you connect as a single string. You need to look at the Voc value, adjusted by the temp coeff for a 35C difference. You may have to lose one or two panels from that string.
Put the 8 new panels on a second string, along with the one or two from the other array. You only need optimisers on the one or two that are not facing in the same direction.
You will be limited to a 5kW output and the inverter will regulate the power if more is available - oversizing arrays is common practice... You get the benefits if a longer generating day and produce more when it's not super-sunny.
Just to clarify, the 6500 W max DC power can only occur when the battery is not full, so the total power of charging the battery (Gen1=max 2600W, Gen2=max 3600W) PLUS the a/c output (max 5000 W) EQUALS the DC input from the solar panels. For example battery charging at 2000 W, at the same time as a/c output at 4500 W, total 6500 W.
Once the battery is full/taking no charge, the DC input will be automatically limited to keep within the a/c output rating of your inverter. The inverter does this by adjusting the MPPT trackers on each string to a non-optimal point, in order to limit the DC power input. The excess power remains in the solar panels in the form of a bit of extra heat, so the panel efficiency drops off from say 20% to 15%.
With more panels you may end up with some power clipping by the inverter on the best Summer solar days, but you will gain with higher output in Winter than you currently get.
Simon_C thanks Simon. My inverter is gen2. I guess I'll just need to monitor the peak power produced in summer time from the existing panels before making any decisions. I hoped that, seeing as the sun cannot shine on both panels directly at any one time then I couldn't overload it (so long as each string is well within limits of the max).
My main goal is to increase winter charge times. I currently lose the sun on the existing panels at around 2pm. At the same time my new panels would start to produce at this time of year. With the sun higher in the sky at summer solstice I very well may have decent output from all panels at the same time around 2pm and, as you say, overloading beyond 6500w may occur.
Thanks everyone for your input.
Simonturner1 you're right that the different array azimuths mean that the peak for each array will occur at a different time of day so the combined peak is longer and lower.
Provided that the string voltage is within limits you can't "overload" the inverter, it will simply limit the output power using its MPPT algorithm. This is completely normal and no cause for concern. I'd crack on if I were you!