Solar Panel Questions

[ncowan]

okay, I have a few questions about solar. I've always had this dream of having solar panels on my house, all hooked into my house electric, grid-tied, just so I wouldn't have to pay for electricity. However, that seems too unrealistic, financially speaking. To go completely off solar, I would need a system that could generate 600+ kilowatts a month. So I got a kill-a-watt and figured out how much my tv, computer, other electronics use. So the new plan is to get a couple of solar panels wholesale on my roof then bring the wiring into the house, probably my living room, have batteries set- up somehow in there, and have an outlet where I could plug all my electronics into. So that's the plan, now the questions:

1. Do inverters have AC outlet plugs coming out of them? I can't seem to figure this one out or do they need to be wired with an AC plug coming out of them in order for me to plug in 120-volt appliances.

2. When you do a solar setup, the inverter is plugged into the battery, correct? Every time I see diagrams, it's like the inverter and battery are not directly connected like you would use one or the other, not both. Then how do you use the battery?

3. What is with voltage. Do I need 12v or 24v or 48v? I think I read that the voltage has to do with how far the electricity has to travel. For my needs it would be from the living room roof, right down into the living room, so not that far, so should I go by 12v when buying parts?

4. Some batteries need venting, these batteries will be indoors and I think I read the gel batteries, or is it deep-cycle or both don't need venting. So they would be okay indoors? Eventually, I may have a lean-to greenhouse attached to the living room and I could keep the batteries outdoors in the winter in there, with wires coming inside the house but for summer the heat might destroy the batteries, right?

5. Could I really plug some solar panel system directly into an AC outlet in my house and have it lower my energy bill? That's what these plug-and-play systems supposedly do but if that were the case then wouldn't everyone do it because getting solar hardwired is much more expensive.

 

[sunshine_eggo]

1. Do inverters have AC outlet plugs coming out of them? I can't seem to figure this one out or do they need to be wired with an AC plug coming out of them in order for me to plug in 120-volt appliances.

Some provide 15A 110V sockets, some provide 20A sockets, some provide 30A "RV" type sockets. Some have terminals you attach wires to. Some have both.

2. When you do a solar setup, the inverter is plugged into the battery, correct? Every time I see diagrams, it's like the inverter and battery are not directly connected like you would use one or the other, not both. Then how do you use the battery?

The battery is the only source of power for the inverter, so it is always connected if you want to use the inverter. If you want to use 12V, you need to attach those to the battery as well.

3. What is with voltage. Do I need 12v or 24v or 48v? I think I read that the voltage has to do with how far the electricity has to travel. For my needs it would be from the living room roof, right down into the living room, so not that far, so should I go by 12v when buying parts?

Depends on how much power you want to go in and out and other considerations:

0-2000W - 12V
2000-4000W - 24V
>4000W - 48V

This is mostly about keeping the DC currents manageable. Higher system voltages also benefit from reduced solar charging current, e.g., a 50A MPPT charger can only put 600W into 12V, 1200W into 24V and 2400W into 48V, so you can get more charging power potential for the same $ in MPPT.

You consider wire length at every junction. PV to charger, charger to battery, battery to inverter.

4. Some batteries need venting, these batteries will be indoors and I think I read the gel batteries, or is it deep-cycle or both don't need venting. So they would be okay indoors? Eventually, I may have a lean-to greenhouse attached to the living room and I could keep the batteries outdoors in the winter in there, with wires coming inside the house but for summer the heat might destroy the batteries, right?

GEL and AGM are less likely to vent, but they can still vent. The official recommendation is to ensure they are ventilated safely. Personally, I have a 10kWh FLA bank in my office. I'm just careful about how I use it to minimize venting.

5. Could I really plug some solar panel system directly into an AC outlet in my house and have it lower my energy bill? That's what these plug-and-play systems supposedly do but if that were the case then wouldn't everyone do it because getting solar hardwired is much more expensive.

There are some "grid-tie" inverters ($125 for 1000W) that can do exactly that. They need to be powered by a suitable amount of solar panels at the correct voltage. Why doesn't everyone do it? They are likely not legal in any jurisdiction in North America, but if you never actually reverse the flow back to the power company, they'll never know. Some of them are "zero export" in that they make sure that the power never flows back to the power company, but they will use the solar to reduce what you use from the power company.

Example:

Amazon.com

Personally, I have a smaller 1000W unit that I power with a battery for a very specific reason at random times, but due to the battery voltage (too low for MPPT operation), it never feeds back more than about 350W, and I don't think there's a time that my house has ever used less than 350W.

 

[MisterSandals]

I would need a system that could generate 600+ kilowatts a month.

First, not to nitpick but you should know the correct terms. watts and kW are rates. Watt hours and kWh are amounts.

Lets do some quick math:

So for 600kWh in a month:
600kWh / 30 days = 20kWh / day

Average solar hours are 5h per day (there are websites that will give you a local number for each month):
20kWh / 5h = 4kW of solar panels.

Using 300W panels, that is 4000 / 300 = over 13 panels running at 100% efficiency. Probably closer to 18 panels in the real world.
You would need to store power for most of the 19hrs that the suns not producing:
20kWh x (19/24) = ~16kWh of battery capacity.

That would be about 32x 100Ah lead acid batteries.
Using 280Ah LiFePO4 batteries (4 cells each, 280Ah x 12.8V= 3584Wh): 16000Wh / 3584Wh = 4.5 batteries (~$3000 if you build yourself)

So you're looking at $10k with an inverter and the fixings... minimum, doing it all yourself and being a frugal buyer.

 

[chrisski]

5. Could I really plug some solar panel system directly into an AC outlet in my house and have it lower my energy bill? That's what these plug-and-play systems supposedly do but if that were the case then wouldn't everyone do it because getting solar hardwired is much more expensive

The amount of power these push in using 600 kwh a month is insignificant Compared to the price. A lot of these have portable panels, and this is with its own problems of blowing away.

As mentioned probably can’t do it in your jurisdiction not so much as the greedy POCOs won’t let you but more towards its dangerous. In outages, these could power the lines when someone is trying to fix it for one.

So you're looking at $10k with an inverter and the fixings... minimum, doing it all yourself and being a frugal buyer.

I’d put the cost at around 20k. 2 x 16s 280 ah 48 volt batteries and mounts for panels wiring. I’m also betting some months are 1 megawatt hours plus, and others are 300 kwh.