solar power back to meter

[jchealey]

I am having some solar panels installed and need to get the power back to the meter. I have a well junction box that is closer to the panels. Can I run the power to that juction box which goes back to the main panel?

It means a difference of 150 feet vs 300 ft.

thanks

Jerry

[HayZee518]

Will you be running DC to the box and then to the inverter before the main? What size wire is there now? What are you talking about for amps feeding into the inverter?

[jchealey]

The inverter will be at the panels. Running number 8 or 6 to the pump. Highest amprege will be 32 amps if every watt is producing. I was thinking of putting a 30 amp breaker going back to the panel. that will limit the amp flowing through the 10 gauge wire.

[HayZee518]

I plugged in some values into my voltage drop calculator and at a load of 32 amps at 120 volts I come up with a #1 wire. This is for a distance of 300 feet.
As you know, as voltage goes up, amps goes down by 1/2. Conversely as voltage goes down amps goes up!
Copper carries a resistance constant per foot which enters into the calculation.
What I'm envisioning is how you are going to run the complete circuit - #1 photocell, #2 conductors to the house, #3 Primary disconnect, #4 Voltage regulator/Charger circuit, #5 Secondary disconnect, #6 Batteries, #7 Inverter for 120 volts AC, #8 Disconnect for the AC, #9 Feed to transfer switch or breaker, #10 Panelbox connection.

[jchealey]

No batteries in the system, instead a meter that runs backwards. You lost me on the rest of the numbers. I am not sure what you are trying to point out. But, maybe the questions is: How do I feed the pump to still work and feed back to the meter at the same time? I don't know the answer to that.

[HayZee518]

No batteries in the system?? What happens when the sun goes down?? --> no power!!
Usually a wind generator or photo-voltaic array feeds batteries to store the energy. Also the photocell array's voltage is not constant - it keeps going up and down according to the sun's strength - or a passing cloud, henceforth your output will go up and down.
I don't think you can use the same line to feed the pump AND backfeed DC to the house. The AC to the pump, the wires will be a certain size as you said #6 or #8. #6 will carry 65 amps and #8 - 40 amps, but because it's DC,and considering distance the wire size will be BIG if you want the same current available from the source to the load. Take a look at the wire size in your car off the battery to the starter - must be around a #1 or 1/0 and this is for a short four foot distance!

[HayZee518]

[jchealey]

No batteries because, I will sell electric to the power company when the sun is out and buy it back when the sun goes down at the lower rate.

The inverter will be at the panels so the transmission will be AC. This hook up will be only for about 7 months while we remodel parts of the house. But I still want it to be safe.

[HayZee518]

Legally I don't think you can tap on after the meter and make it run backwards. Your input to the system has to be greater than what you're taking in for it to make any difference on paybacks.
Say your total house load is 48Kw. You'd need at least 48Kw to equal the house load and cancel out the power. 49Kw to feed power back into the system.
32 amps @ 12 volts = 384 watts, 32 amps @ 24 volts = 768 watts

32 amps @ 120 volts = 3840 watts

Check with your power company before undertaking this task.

[HayZee518]

Check this out:

http://www.sierrasolar.com/articles/sellpower.htm

[LazyPup]

jchealy

Back in the late 70's and early 80's the government started expressing incentives for alternative energy sources. One of the incentives they created was to pass a bill requiring Electrical Utility Companies to buy back any excess energy produced by a consumer, however, before you spend a lot of time and money setting up a photovoltaic system with aspirations of selling back excess power you better read the fine print very carefully.

The idea might have some feasibility if you were receiving an equal credit but in reality that is far from the truth.

While it is true that the power company is required to buy back excess energy, they are only required to pay for it if it is produced in increments of 1KW/HR and the amount they pay you is equal to their wholesale cost of buying power off the grid. In turn they are allowed to charge you a premium for providing the additional metering equipment. When you cut to the bottom line you will pay approximately 10% more for the power you purchase from the Utility while you will be compensated for your power back to them at their wholesale cost, which is about 60% to 70% of the retail cost of power.

In addition, in order to create a photovoltaic array capable of producing 1 KW/HR it needs to be approximately 1 acre in size. You are then confronted with an additional 5% to 10% loss of power to internal resistance and hysterisys currents in the inverter and metering equipment.

A much more cost effective method of using photovoltaics is to install an AC to DC inverter such as used in campers and motor homes along with a battery bank, then convert the general lighting of your house to low voltage DC lamps. In this manner during the day your photovoltaics can charge your battery bank and you use the stored energy to produce your general lighting needs, thus greatly reducing your consumption from the Electrical Utility provider. The AC to DC inverter remains available to provide the necessary low voltage DC to your lighting system in the event that enviromental conditions limit your photovoltaic production below your demand. In this configuration you will have much less equipment to maintain and you will receive a true watt for watt compenstation for what you produce.

[jchealey]

I am based in CA and I don't know if the rules are different for how they buy back the electricity. Our neighbor installed panels last year in the same type of system. The utility buys his extra and then sells him electricity when the sun is down at the lower rate. You can buy two different meters that turn backwards. One pays at a higher rate if you plan on using little of your production during noon and 5PM. The neighbor uses that system and has had a electric bill, since instalation, never over $4 per month. At that rate, the system will pay for itself in about 4-6 years. Total life of the system is rated at 25 years.

As to your wiring, I agree we will have to ask PG&E. I just can't get to the side of the house where the main panel is without cutting through many water lines and a few power lines. After remodel, I can drop the distance by 60 feet when we install a new main panel. I also will only have to worry about one water line in that area. I am just trying to get by for about 6 months so we will see what the power company says. The solar guy that I hired for part of the work thinks it may be ok but also feels that it is up to the county and PG&E.

You should see the size of the concrete ballast they require to hold the panel down in case of wind. Amazing, about 9 yards for panels 15 feet by 48 feet.

Maybe I will add batteries in the future and tell PG&E to go away.