Micro-inverters on solar panels

I wonder if micro-inverters on solar panels could change the solar setup of RV's. The (MPPT) controller could be left out and the converter could charge the batteries. The wiring should be a lot easier and cheaper and some appliances can run on 110V (during daylight hours).

Are there any qualified people who can spell out the pros and cons or if it is at all possible!

Comments

  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Micro-inverters on solar panels

    i think you are going in the wrong direction with your thoughts as inverters like those are for straight utility grid tie connections and not for battery charging. controllers are the regulation circuits for battery charging.
    on thinking further i see where it is your thoughts are going with this as you just want a standard inverter producing ac to plug your onboard charger into, but it doesn't work like that as those standard inverters would need the controller and battery to operate and micro inverters need the grid. what you need is a controller from the pvs through fusing where applicable and straight to the batteries needing charged. no ac involved which would be adding more steps to the charging process anyway and thus less efficiency.
  • BB.BB. Super Moderators, Administrators Posts: 29,489 admin
    Re: Micro-inverters on solar panels

    Unfortinatually, it is not possible to do what you have asked for several reasons:
    • Grid Tied Inverters (including micro-inverters) are designed to only operate with clean voltage and frequency from the utility. If either fall of out specifications, the inverters shut down to prevent damage/injury to linemen, etc.
    • Power directly from a solar panel to an appliance (direct DC or from an AC Grid Tied inverter) is difficult at best to make work in a few limited cases. GT inverters and solar panels do not have any signification energy storage--so variations in sunlight, shading, bird flying by, etc. would result in variable amount of electric power available... To power a TV, washing machine, either the panels would have to be very large (2-5x larger than the load) or you would need an energy storage element (typically a battery bank) to carry through appliance operations when the sun/solar power is insufficient.
    Regarding using any inverter directly connected to a solar panel without a battery is not usually going to work... Normal off-grid inverters accept a limited range of voltage (typically 10.5-15.0 volts for a "12 volt" inverter) and solar panel output for "12 volt panels" range from zero to 22 volts or so.

    You can do a variant of a connection--Basically you get the correct type Off-Grid inverter setup to run your AC appliances. The, you connect your solar panels and Grid Tied Micro Inverters to the AC output of the Off-Grid inverter...

    The Off-Grid inverter will set the 120 VAC and 60 Hz and supply AC power when the sun is down, share power when the GT inverters and loads are running, and if there is excess AC power from the GT inverters, actually push power back through the Off-Grid inverter and charge the battery bank (back-driving the inverter).

    There is an issue--The Off Grid Inverter is not designed charge a battery using this method--And you can end up damaging the battery bank from over charging... So, you would need to add one (or two--for back) some sort of battery charger/charge limit system for your micro-power system.

    Anyway, it is possible, and a few people have experimented with doing this (and at least one Wind Power company even advertised a setup like this for their product).

    There is also a product called the "Sunny Island System" that has components to build such an AC network--but this is probably too large/expensive for a typical RV system.

    But, for the most part, you will be on your own to configure/design the system.

    The typical solar panel to charge controller to battery bank to AC inverter to AC load with backup AC power / Genset is still usually the most cost effective small off-grid system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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