Retrofitting old off grid panels to grid tie

Retrofitting off grid to Grid Tie

I have a off grid retirement house which I built over 25 years ago. I started with 4 - 40 watt panels and have periodically added more panels, and now have about 1.5 KW. About 2 years ago we got grid power. I connected to the grid, but continued to remain off-grid, using the grid as backup (mechanical transfer switch). I am now faced with the problem of replacing my degrading battery bank (ten years old). I am reluctant to spend the money on batteries when the cost of the grid power is so cheep. (7 cents a Kw) So I would like to grid tie my existing system. My power company does net metering, so I would like to use them as my storage batteries. I like to think of it as “ cloud batteries”. I have been unable, however to find any GT inverters that will utilize my existing panels. The quality micro inverters all seem to require 60 cell panels. And the string inverters require DC inputs of over 100 volts. I don’t have enough panels of the same ratings to achieve this series connection voltage. The biggest string I have is 5 Kyocera 120 watt panels at 18 volts – 90 volts series connected. The remainder of the panels are, 18-24 volts of varying types and wattage’s.
The only GT inverters I found that would adapt to my panels were the China micro inverters. In the frustration of not finding a quality inverter, I did actually try one of these, but it only lasted 4 months until it quit working.

So my question is:
Are there any quality inverters (good warranties) out there that will allow me to retrofit my existing panels to grid tie??

PS-- My utility (CFE Mexico) did approve my China micro inverter and it generated 500+ kilowatts before it died.

Comments

  • bill von novak
    bill von novak Solar Expert Posts: 891 ✭✭✭✭
    Re: Retrofitting old off grid panels to grid tie

    1) Figure out what the highest voltage you can get from your panels in some reasonable arrangement of strings. If it's 12V nominal (i.e. 36 cell panels) you're going to have a lot of trouble. If you can get at least 24V nominal (72 cell strings) you have a few options. 48V nominal is even better.

    2) If you can get 48V you can use one specific grid tie inverter - it's a (now fairly ancient) Trace product called the Sun Tie. It accepts 48V nominal. Make sure you get one of the retrofitted ones - the early ones were awful.

    3) If you can get 24V or more you can use a charge controller to charge a 24V battery bank then use a hybrid inverter like an Outback GTFX3624 to sell power back to the grid. You'd be looking at $2000 all told for the charge controller and the inverter, plus wiring and protection. The batteries do not need to be in great shape to run this since they will spend most of their time at float.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Retrofitting old off grid panels to grid tie

    Look at the amount of money you will save for power... Say you get 5 kWH per day from your system in sunny weather, at $0.07 per kWH, that is $0.35 per day of savings (assuming the utility does not hit you with grid tied charges).

    If you could save ~$120 per year--Is spending any money on GT power worth it?

    I would suggest spending on conservation (insulation, low power appliances and lighting) for the "green" part of the equation.

    And I would figure out what solar panels are still good and can be configured into a charging system--And get a few Golf Cart type batteries and a small inverter/backup AC battery charger (if needed) for emergency/backup power.

    Do you have any indications about how reliable the utility power will be?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • animatt
    animatt Solar Expert Posts: 295 ✭✭✭
    Re: Retrofitting old off grid panels to grid tie

    where are you located in mexico?

    I ask because i am not sure how easy it is to get permission to grid tie.

    I did an off grid house in mexico which worked fine the limited time I had it.

    Now looking to start a new project. Initially will be a small offgrid system but hopefully will have grid power soon after. mexico like any other government puts on a good show talking all "green". But how friendly are they to solar systems is something I am curious about.

    I have a feeling they could care less about the green unless they thought they could get some out of your wallet.( well not necessarily green it could be red, blue or pink coming out of the wallet as well).

    You can respond in a PM if you like.

    matthew