Stop current backflow to power company in solar grid tie

Thread Starter

TDave00

Joined Feb 22, 2019
5
I'm itching to play with solar before we build our own home, plus I'd like to take advantage of the 30% tax credit before it runs out. We're leasing now so I don't want to move circuits into a sub panel and install an inverter, etc. I was thinking of going the route of solar panels with microinverters IF there's a way I could make sure I'm only supplementing the grid in my home - not pushing excess electricity back through the meter. It's more cost, but I'd also be willing to go with a solar charge controller, batteries, plus an inverter, if that system would work better in this scenario.

The solution I'm looking for would monitor loads from the panel and then only supply enough power to cover those loads (less 100-200w to make sure I'm always drawing power through the meter). I know a solution like this exists with the Schneider SW & XW inverters, but it involves me moving circuits into a sub panel, and I'd rather not go this route in this home. Any ideas?
 

mvas

Joined Jun 19, 2017
538
So, what happens when your home load is small and the sun is strong and your batteries are full?
You lose all of that energy = very inefficient.
Batteries need to be replaced every 5 - 6 years = very expensive
Batteries are only 80% efficient.
How much do you pay per kilowatt-hour of electricity?
How much sunshine in your state?
In many places normal Grid-Tie is difficult to cost justify,
but then adding batteries and also wasting Kilowatts, makes things worse ...

"Solar Grid Tie Zero Export" may be the terminology for this.
 

Thread Starter

TDave00

Joined Feb 22, 2019
5
So, what happens when your home load is small and the sun is strong and your batteries are full?
You lose all of that energy = very inefficient.
Batteries need to be replaced every 5 - 6 years = very expensive
Batteries are only 80% efficient.
How much do you pay per kilowatt-hour of electricity?
How much sunshine in your state?
In many places normal Grid-Tie is difficult to cost justify,
but then adding batteries and also wasting Kilowatts, makes things worse ...

"Solar Grid Tie Zero Export" may be the terminology for this.
We use approximately 50-60kwh per day, and at this home I'm only planning to start with about 12 300 watt panels. I doubt in that situation we'd be producing more than the loads and batteries are consuming. For now though I'd need the ability to dial it back if we are producing more than we consume. (Once we build a house I can set the Schneider Inverter between the loads and the meter so that it ensures we don't feed the grid.) The ultimate goal would be to go off grid, and I can with the Schneider inverter, but I like the ability to have the grid supplement what we lack until we understand the battery capacity and/or possible extra inverter we might need.

Lithium battery packs from salvaged electric vehicles are being used with great success in solar systems. By reducing the charge/discharge rate by 20%, I've heard estimates that those packs could last 10 to 20 years. Implementing a DIY battery solution like that for say a couple grand makes battery storage a reasonable cost and the payoff short.
 

djsfantasi

Joined Apr 11, 2010
7,919
Why don’t you want excess power to flow back into the grid? I’m not into solar, but here if you feed excess power into the grid, the electric company pays you! Add this into your cost equation and your investment is offset by the payments from the utility.

I may be wrong, but that’s my understanding.
 

iONic

Joined Nov 16, 2007
1,654
I second djsfantasi's opinion. If your lease does not include obtaining excess credit from the power company it may be difficult for the investment to ever pay off.
 

Thread Starter

TDave00

Joined Feb 22, 2019
5
Why don’t you want excess power to flow back into the grid? I’m not into solar, but here if you feed excess power into the grid, the electric company pays you! Add this into your cost equation and your investment is offset by the payments from the utility.

I may be wrong, but that’s my understanding.
If net metering was available here I would go that route, but it's not (in the traditional sense). It just makes no sense to pay .11-.12/kwh and sell back for half, or less than half of that. And, without a net meter contract these smart meters don't roll backwards if you backfeed, they charge what you're feeding in as consumption, so I would be paying for excess energy I produce.

A system like I'm referring to can be disassembled and disconnected from the grid very easily. It requires no "net metering" agreement/contract, no extra equipment and/or costs or interaction from the Power Company. This type of system just uses as much of the PV power as possible and relies on the grid to make up the difference, but also with the option of adding battery storage later to utilize 100% of your PV production. It's a modular system that can be built over time while also realizing real energy cost saving as you build.
 

Thread Starter

TDave00

Joined Feb 22, 2019
5
It seems that Enphase also offers a solution using their microinverters. They call it Customer Self Supply. Their micro-inverters can be scaled up and down by monitoring loads and incoming power to create zero grid export.
 

dendad

Joined Feb 20, 2016
3,939
If you want long life batteries, have a look at Nichol Iron. They are not the best battery in many ways except one, having a very long life and almost unkillable by over charging or discharging. If I had the money, that is the battery type I would go with.
 

oz93666

Joined Sep 7, 2010
737
We use approximately 50-60kwh per day, and at this home I'm only planning to start with about 12 300 watt panels. I've heard estimates that those packs could last 10 to 20 years. Implementing a DIY battery solution like that for say a couple grand makes battery storage a reasonable cost and the payoff short.
You can absolutely forget about payoff time when using battery storage , it will never arrive (unless you have ridiculously high grid electric price)... and no battery will last 10 years if used regularly ... (I have 6kw of panels and have been recycling laptop batteries for a while).

You have a very high consumption , where is that going?? If air conditioning the most cost effective plan is to use solar to take some of that load.
 
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