Offgrid solar and inverters

[aramis720]

Does anyone have recommendations for a good inverter for a 500 kW offgrid solar battery backup system running on 24 volts? I'm seeing recommendations for 2,500 watt expensive inverters (easily $1,500 or more) but my feeling is that this should be doable at far less cost. What about Go Power or some other type of pure sine wave inverter?

[OpenD]

Do you mean 500 watt? (Not 500 kW) Automotive and RV supply places have them.

[kalakoa]

Selection is more limited at 24V; these are 1000W, but other capacities are available.

If "cheap chinese" is acceptable, Power Bright is "stocked and shipped (free)" by Amazon.

http://www.amazon.com/Power-Bright-APS10...B002EA006S

For a bit more quality, look at Samlex, beware the shipping cost (or find another vendor).

http://www.amazon.com/gp/product/B00AYH6EL8/

[Hotzcatz]

Some of the new PV systems produce 110v directly from the little inverters on each panel. Enphase makes them, I think is their name. The inverters that is, they fit on a variety of different panels.

---

"I like yard sales," he said. "All true survivalists like yard sales."
Kurt Wilson

[unknownjulie]

So, does this mean that the solar panel has a wire that goes to a battery and then the battery has a wire that goes to the inverter- that you can plug stuff into? What is "inverted"? I thought electricity was a row of electrons running along a wire. Does it make it somehow go upside down? Thanks. I know I'm pretty clueless about this.

[kalakoa]

Inverters convert DC power (solar panels, batteries) into AC (grid, generator).

Not strictly necessary; you can always use all-DC lighting and appliances.

The per-panel inverters are nifty, but they're a grid-tie thing.

[MarkP]

The inverter makes the electrons go back and forth (alternating current, AC) instead of just from negative to positive (direct current, DC). On an off-grid installation the output of the panels would go to a charge controller. The output of the charge controller would go to the batteries. The charge controller babysits the batteries, feeding them just the right amount of DC electricity from the panels so they charge right and don't overcharge. You could in theory hook the panels directly up to the batteries but there are many problems with that and no one with a clue does so.

The inverter takes DC power (usually 12, 24, or 48 volts, although 36 volts is not unheard of) from the batteries and converts it to 120 volts AC. Because both the inverter and the charge controller are hooked up to the same points on the battery bank, depending on battery charge and sunlight, sometimes the power is just flowing straight from the charge controller into the inverter without going into and out of the batteries. This is often a good thing because the batteries are not 100% efficient. You shove the electrons in at 14.5 volts and take the same electrons out at 12.5 volts, close to a 20% loss right there. I run the washing machine in the morning when the sun is on the panels and there is plenty of time left in the day to top the batteries off after having been drawn down. Most charge controllers have lights that show the state of charge ob the batteries and what charge mode the controller is in. When flashing that means that the batteries are topped off and the controller is feeding them only a part of the power that is available from the panels. Save up your laundry and run the washer then to use the PV power that would otherwise be wasted.

[unknownjulie]

Thank you Mark. So the simplest way to do this is to have solar panels and have them go directly to an inverter- that has a plug on it to plug things into it. When the sun does not shine, then you have no power, but on a sunny day, you could use it. (I have Helco electric already) Do you need a "charge controller" if you have a wire that goes directly from the solar panel to the inverter? This doesn't sound all that expensive if you did it this way and had a few household things plugged into that plug that didnt' need to run at night. Washing machine is a good example, or vacuum cleaner- whatever... Are there solar panels that are made for those of us that do not know anything? Is it an actual wire, or is it a cord that goes from the solar panel to the inverter? thanks!

[kalakoa]

I believe 60V systems might actually be more common than 36V.

A direct-drive inverter only works in a grid-tie configuration; as the PV harvest fluctuates, there's no way for the inverter to add/drop load to match the available power. Something has to buffer the difference, even if it's a very small buffer.

Counterexample: modern DC fridges (Steca, others) that are designed to be connected directly to a solar panel have variable-speed compressors with a controller that spins them up or down based on the input power.

A simple system would consist of: solar panel(s) - disconnect breaker - charge controller - battery - inverter, all wired to each other serially (and in that order).

[unknownjulie]

kalakoa, I know you are trying to give me information, and thankyou, but I don't understand any of it. I would like a solar panel that has a cord, that plugs into the inverter (that I buy on amazon)- that has places on it for me to plug electrical appliances into. Does this exist? Why not?