Solar Panel direct connections

boisblancboyboisblancboy Posts: 131Solar Expert ✭✭✭✭✭
Is it possible to run, cell chargers stuff that small etc, obviously with the use of an inverter directly connected to a solar panel? Or is it always a good idea to run them off a battery in conjuction with the solar panel?

Comments

  • BB.BB. Posts: 27,329Super Moderators admin
    Re: Solar Panel direct connections

    It could be done--but is not because the solar panels output is proportional to sunlight, and the inverter's input is proportional to its output load.

    You would need to have a much larger than needed solar panel to power a fixed AC load from, for example 9am to 3pm... It would barely run the loads at 9am and 3pm, and be two to four times larger than needed to run the loads between 11am and 1pm.

    So, the general idea is to have a storage device, batteries, that take the opportunity to capture as much sunlight as possible during the day. Then the batteries provide energy, both during the times the sun is not available (night, cloudy days) and to provide energy for peak starting loads (motors, pumps) and short term usage (power tools) that exceed the arrays current energy output (dark, light, high noon, etc.).

    There is a version of inverter that connects directly to solar panels (no batteries). That is a "grid tied" or "utility interactive" inverters... These 100% of the available voltage and current of the solar array is converted by the inverter (using the formula P=I*V*inverter efficiency) into 120/240 VAC 60Hz (or whatever the local utility spec. is).

    At first glance, this looks like what you where asking for... But, in reality, it is not. There is a "battery" in this system, but instead of a DC chemical battery between the solar panels and the inverter, it is the Electric Utility itself, and this battery is an AC 120/240 VAC device--the distributed grid itself. The utility sets the voltage/frequency itself, and the inverter pushes all available energy into the grid (really, you are just another generator and the power is absorbed by the homes, with out solar, around you, or inside your own home/appliances).

    There are other ways of approaching the problem of solar to AC--but the above two ways (grid tie and off-grid with battery) are the two major ones.

    Make sense?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • boisblancboyboisblancboy Posts: 131Solar Expert ✭✭✭✭✭
    Re: Solar Panel direct connections

    Yep that makes perfect sense. I know to be efficent you would want a battery for storage, I just wasnt sure if you could possibly do that. I know it wouldnt be a very efficent way to do this, but I was wondering.

    I have looked that those grid tied inverters. Too bad they are so expensive!
  • BB.BB. Posts: 27,329Super Moderators admin
    Re: Solar Panel direct connections

    Grid Tied inverters are probably the cheapest part of the installation... Rough retail pricing:

    They run, roughly $0.50 to $1.00 per watt.

    Solar panels are $5 to $10 per watt (you may find sales/used down in the $3 per watt range).

    Fixed solar panel mounts, around $1 per watt range.

    Wiring, installation, Engineering and Inspection Sign Offs--$2-$3 per watt

    And, typically, from what little I have seen, if you are "building" a 2kW system or smaller, the prices per watt are at the higher end.

    If you are building a 3kW or larger, the prices tend towards the lower range.

    In the US, there are some government rebates and tax credits (state and local RE breaks very a lot) that can knock of quite a bit on the price of a Grid Tied system (10%-50%), and not many Gov. breaks/credits for off-grid systems.

    Off Grid, larger or smaller, costs a lot--because of the extra hardware (charge controller and inverter) plus the costs and replacement of batteries over time.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • boisblancboyboisblancboy Posts: 131Solar Expert ✭✭✭✭✭
    Re: Solar Panel direct connections

    Yeah typcial with just about anything the larger you go the cheaper it gets.

    You would think with energy prices climbing that the rebates and such would be voiced and become more popular. But with anything its probably going to be last minute when energy reserves become extremely low.
  • BB.BB. Posts: 27,329Super Moderators admin
    Re: Solar Panel direct connections

    Energy prices are currently tanking... And collection of taxes based on a percentage of energy costs, plus those collected on per gallon pricing, are being reduced too.

    So, it is more surprising that there is still money out there to be "given" away based on the downward revenue spiral that "government" is in at the moment.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • boisblancboyboisblancboy Posts: 131Solar Expert ✭✭✭✭✭
    Re: Solar Panel direct connections

    Yeah "currently" the prices are headed down, but we all know that is not going to be the case forever. Its inevitable that they will rise and in the future continue to break all time highs.

    It is nice to have the relief we are getting, but also in the same token since the enconomy is tanking we have less money as a country to spend on even cheaper amenites.

    But you are right, it is kind of amazing that there is still money out there to be given away.
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