I have just installed a 5kw system consisting of 2 2500w Sunny Boy's, 40 Siemens SP 130's mounted on 4 Direct Power Top-of-Pole mounts and I have a few questions. The installation is in the El Dorado Hills area (East of Sacramento Calif.) and the inverters are mounted in a shed under one pole. It gets really hot here. Inverters are 350 ft from House ac sub panel. 8 ga wire used from inverter to house. Electrical installation was done by a licensed electrical contractor who specialzes in solar systems. Solar array is wired with 10 ga wire.

1. I recently read that a cooling fan may be necessary or adviseable in a hot area and /or mounting in a shed. What do you recomend? 1 fan for both inverters? 2 fans - one for each inverter? ac fan or dc fan with power tapped from 1 or 2 panels. DC fan only perates in daylight hrs when needed, AC would need a timer? I fan pulling air into shed, some type of cover over heat sink with air outlet on other side of shed? i.e pull air in and blow over heat sinks and exit hot on other side. Size of fan? Cover over heat sink would be to direct air flow over it and direct air out of shed.

2. When system is on (yesterday) both inverters put out about 2,000w, ac voltage at inverter was 243 volts, ac voltage at house was 234 volts. Voltage drop was 3%. Is 3% ok? Can I add 2 additional 8 ga or larger wires and run from inverter to another ac breaker in house to reduce voltage drop? i.e run 2 pair of wires paralle so I don't have to rip out the first wire. How much power is lost over the life of the system with a 3% drop vs a 1% or 1.5% drop in California with a Time-of-use meter and most loads being used at off peak hrs? Is this the correct way to determine voltage drop?

3. How do I verify that the system is working properly and that all potential losses are minimized?

4. Do solar panels have to be grounded separately with a wire from panel to pole or inverter, or is the physical contact from panel to mount to pole to inverter ok?

Thanks for your help.

Hi,

I just checked with www.homedepot.com for correct pricing of the wire ....


using the wire spreadsheet at http://www.homepower.com/magazine/downloads_solar_power.cfm (pv_wire)size) ... your losses are

700 feet of wire
240 volts
20 amps


IR loss

AWG LOSS in Watts Cost of wire 500ft rolls (2x for 1000 ft)

8 188 51.88 (103.76)
6 118 74.49 (148.98)
4 74 113.68 (227.36)
2 46 178.92 (357.84)

If it was my system I would go with the 2 AWG , which would be $254.08 more
in wire cost to save 142 watts in IR losses. You can get 1000 foot rolls
from electrical supply houses and the cost will be a bit less.

8 Gauge doesn't even meet code , ask your electrician to supply his NEC
calculations which need to be made at low line (213 volts) which bumps up
the current and power losses. The sunnyboy may have problems at high power
since the line impedance will be very high due to the long run to the
service from the inverters and will go offline , thinking there was a grid
failure

[img]images/smiles/icon_smile.gif[/img]

On your Hot shed ... install a pair of vents to allow good air circulation ... keeping the sunnyboys out of the sun is good , but they need air flow to cool properly

On the grounding , NEC requires the panels be earth grounded , so yes there need to be wires from panel to panel to earth ground

On your performance , the sunnyboys are excellent in that they have a good free pc program that you can monitor your inverters , wether thru RS232,RS485 or powerline modem for connection to the PC [img]images/smiles/icon_rolleyes.gif[/img]

I just installed the 2 ga wire. First test shows a 1.1 volt loss (vs the 9 volt loss with 8 ga wire). New wire is MUCH better.

By the way, I ended up installing the gound wires and enclosing all dc wires in conduit myself. Contractor did not want to do it. He said everything was fine as it was.

Thanks,

ol