Solar Panel Production Advice

Go with PTC values ensuring your equipment has some additional capacity (even if it is just short-term overload capacity), just in case (which it should have due to standard inverter cable and connector sizes, etc).

Thanks Jack,

GAs to all

http://www.gridtiesolarelectric.com/grid-tie-solar-products/grid-tie-solar-systems/3-2kw-grid-tie-solar-system/

http://www.gridtiesolarelectric.com/grid-tie-solar-brochures-downloads/

You should size your inverter based on 180 watts per panel.

You should, however, expect PTC stated results.

I remember that you are very entrepreneurial the solar farm was not your only project.

Why did it fail ? How is developing your other projects ?

Hi Nick Name,

I found out we are not so free here in America, that you can only do what others of greater power will let you do. The utilities have a monopoly and as much as they say they are "Green" and promote "going solar" , the truth is they don't want us in the boat. Competition is subtly blocked with impossible rules and regulations. We passed a law saying they have to accept solar producers, they get their old CEOs appointed to the leadership of the Public Utilities Commission, (Which helps set rules and regulations). The Federal govt. makes rules that utilities have to accept all small green energy producers and these rules are ignored. We applied for interconnection to the Grid and were rejected because of congestion, and everyone buys this argument. The laws we passed say the utilities were supposed to accept all green energy producers and use that energy to replace existing energy producers that are not green, ( we get a lot of electricity from out of state ). There would be no congestion if our energy replaced some of the other energy comming from out of state. After all if the energy being used in the city is say 10 megawatts and the grid is supplying 10 megawatts and we add 1 more megawatt to the grid it would not be used unless production was reduced someplace else.

I talked to an Engineer of theirs and he was shocked that I would suggest they reduce some of their out of state energy purchases, his reply was that they have a contract and would not stop buying from coal plants at .04 cents a KWH. They offer to pay us .10 cents a KWH, and our break even point is .12 cents, they know this, they built some pilot solar farms and their cost was .15 cents KWH. In the mean time the consumers are getting charged .30 KWH because we gave them permission on account of the extra expences they would have to pay for green energy.

In the end the utilities are raking in the money for green energy expence but are not buying green energy.

Sorry about the rant. This has been a very expensive lesson learned, almost broke us. So we wait for a friend who is suing the Public Utilities Commission for not compliance with federal regulations (PURPA). If she wins we have a chance again.

Other projects are on hold cause of lack of funds.

Thanks for asking, Spacecannon

Generally you should size inverters at about 15% over the DC rating of the panels. There are a lot of nuances, especially when any scale is involved. However, a typical residential system is limited to 10 KW max AC output, and when it's 240 single phase, you will be using one Fronius 10KW, or two af almost any other brand, because they do not offer the configuration you need. There are many good reasons to use two inverters, like two SMA 5000's.

We would (in most places, but not all) shoot for around 11,500 watts of panels (modern poly or mono), probably deployed in four strings. The reason that this is optimal is that inverter efficiencies tend to increase the closer you get to maximum output. In addition, while inverters are rated at point of production maximum AC output, PV is rated at DC (both STC or PTC) at panel location. The two primary factors that indicate the level of PV production that is both desirable and advisable in regards to design and warranty inverter coverage are

1) the inverter efficiency itself. A 96% efficient inverter requires about 104% of DC current to produce an equivalent maximum AC output, which in this case is the maximum inverter output, (almost always the inverter nameplate rating) So, it takes 10,500 watts of DC input to get 10 KW of AC output, in the absolute best case scenario.

2) There is a statistically minor segment of production time that will occur in that peak PV panel STC output time (this is also true of PTC output) Nonetheless, as we have discussed in previous posts, if you want to maximize production efficiency and potential, you will design your circuits and conductors to minimize voltage losses. Typically, you would try to locate the inverter adjacent to your distribution panel, which not coincedentlly, is almost always adjacent to your utility meter. The primary way that people do this is by reducing conductor resistance (use wire ampacity) and increasing voltage. Your opportunity to adjust voltage is limited by equipment and configuration, but nonetheless, will require additional output to supply, at the inverter) the watts to induce inverter nameplate rated output. We build 11,200 to 11,600 STC PV arrays supplying 10KW nameplate rated inverters frequently.

Finally, I'm guessing many of us are puzzled. How is it that you only have 18 of these panels left over for a 1MW array, which would have 5550 of them.

PFR,

Thank you GA. The 18 were for proof of concept, the farm was never completed.

Note: I have a VOC of 93.92 v and I have a guy telling me thats too high a voltage for Enphase, I have no idea what he is talking about. Any ideas, he goes on to talk about different string configurations.

Thanks all, spacecannon