Lou Schneider
Site Team
- Joined
- Mar 14, 2005
- Posts
- 13,303
I was looking into installing grid-tied solar on the outbuilding on my sister's property I will be using as a shop next summer. It currently has 120/240 50 amp utility service. At PG&E's current rates of 24 cents per kilowatt-hour I expect the running the lights, some power tools and an air conditioner or two will cost a couple of hundred dollars a month. CA only pays $0.2 cents per kWh for power sent back into the grid so it doesn't make sense to invest in a grid-tied system that uses the grid for storage or sends excess power into the grid for essentially nothing. So I'm re-thinking things.
For a grid-tied system you have to install utility approved solar panels and inverters (think new and expensive, even after disappearing tax credits). I can build a stand-alone system using surplus used panels (going rate is $50 or less for 200-250 watt panels), a standalone inverter like what is used in an RV ($200-$300 for 3 Kw) and inexpensive LiFePo4 batteries ($300 each or less for 12volt, 100 amp-hours). Besides being less expensive, this also allows the system to supply power during utility outages. A grid tied system simply shuts down until utility power is restored.
The grid power will be a backup source for when the solar and batteries aren't enough to meet demand via an RV style generator transfer switch selecting either the grid or the solar inverter. It will connect to solar power whenever the inverter is active, then default back to the grid when the inverter is turned off or shuts down when the batteries are exhausted. At no time will the solar system cross-connect to the grid.
Yes, there will be times when I'm not there and the system is sitting idle. But at current PG&E rates I estimate the payback time to be only a few dozen months of active usage, not the 20+ years for a utility approved grid intertie system. And I'll have emergency power as a side benefit.
For a grid-tied system you have to install utility approved solar panels and inverters (think new and expensive, even after disappearing tax credits). I can build a stand-alone system using surplus used panels (going rate is $50 or less for 200-250 watt panels), a standalone inverter like what is used in an RV ($200-$300 for 3 Kw) and inexpensive LiFePo4 batteries ($300 each or less for 12volt, 100 amp-hours). Besides being less expensive, this also allows the system to supply power during utility outages. A grid tied system simply shuts down until utility power is restored.
The grid power will be a backup source for when the solar and batteries aren't enough to meet demand via an RV style generator transfer switch selecting either the grid or the solar inverter. It will connect to solar power whenever the inverter is active, then default back to the grid when the inverter is turned off or shuts down when the batteries are exhausted. At no time will the solar system cross-connect to the grid.
Yes, there will be times when I'm not there and the system is sitting idle. But at current PG&E rates I estimate the payback time to be only a few dozen months of active usage, not the 20+ years for a utility approved grid intertie system. And I'll have emergency power as a side benefit.