"Conventional" solar inverters + DMPPT

[Olivier Santiano]

Hello

After reading some of your conclusions : storage is expensive, panels are "cheap", an idea came to myself, would like to share it here with you:

It seems that most actual PV setups (grid-tied or not) are made of one (or more) strings of serial PV panels (in a range from 150-400V) connected

to dedicated (expensive) solar inverters (or MPPT chargers). 

The characteristics of the vast majority of the Solar inverters (for "small setup" <6kW) are: DC Input ~100-500V under 8~15A (depends on power rating) on average.

Would it be feasible to make a (affordable) "Solar Doubler" to connect two or more strings of panels (in the current I & A rating of the solar inverter), but in parallel 

with a small "switching device" kind of DSSR20 but 500V DC rated to disable one or more strings when the sun power exceeds the inverter capacity ?

[PV1a]-[...]-[PV8a] --[solarDoubler1]

|                                                 |

[PV1b]-[...]-[PV8b] --[solarDoubler2]

|                                                 |

[PV1c]-[...]-[PV8c] --[solarDoubler3]

 \                                              /

  \                                            /

  [Inverter rated for 8 PV in serie]

This is the principle of your DMPPT, but applied to some "standard" existing setup.

It would allow to existing PV setup to improve their "bad weather" production, without reinvesting in an expensive inverter/charger when it cover their needs.

Does it make sense ?

Thank you 

Olivier

[Dacian Todea]

Oliver,

You are referring to grid tie system in your example and not sure why you will want to disconnect panels. Most grid tie inverts accept a fairly large over spec PV array so there is no need to make any disconnection.

Also when you are grid connected you can export all excess energy and in most cases you get some sort of credit for that.

A typical 60 cell panel can produce 1 to 1.5kWh in a sunny day and as low as 75 to 100Wh in an overcast day so to make a significant impact in those extremely cloudy days you need quite some multiple.

PV panels cost amortization is around $0.02/kWh and best LiFePO4 is about 10x more at $0.2/kWh the inverters are much more closer to PV panels in therms of cost amortization than battery so oversizing PV array to save on inverter.

Reducing the battery size need to about half by increasing the PV array 3x can make some economic sense but it will not work with grid tie inverters as they are not as expensive in therms of cost amortization.