Just as an excrcise in futility how would you ...

solar_dave · June 2013

Re: Just as an excrcise in futility how would you ...

NorthGuy wrote: »

You probably can do much better than this.

Power distribution during the day may be important (and somewhat controllable).

If, say, 75% of your loads occur during the day, the power will go directly to loads, which is more efficient and does not need batteries. You can therefore reduce the number of batteries you use. This may lead to troubles on cloudy days, but perhaps most cloudy days are cooler you don't need that much AC on these days. If there's some exceptions to that, you can run a generator.

Also, when planning charging current for batteries, you need to think of AC taking a lot of power during the charging time. So, you will need more charging power than usual, which means more panels than you would normally need.

Agreed and conversely this can lead to reduction in battery bank sizing as well, that seems to be the huge cost item.

ggunn · June 2013

Re: Just as an excrcise in futility how would you ...

solar_dave wrote: »

Agreed and conversely this can lead to reduction in battery bank sizing as well, that seems to be the huge cost item.

It always is.

15 characters

Eric L · June 2013

Re: Just as an excrcise in futility how would you ...

Agreed and conversely this can lead to reduction in battery bank sizing as well, that seems to be the huge cost item.

I probably didn't express this very clearly above, but I think if you start by looking at how much daytime air conditioning you could get with a small battery bank (but still a fairly large array size) and an efficient cooling unit, you might be pleasantly surprised.

It's one of those things where maybe 60% or so of the time that you want the A/C running, including the hottest periods, you can do it very efficiently with the batteries providing little more than voltage regulation and an occasional boost. From there, you can start looking at how much of the remaining run time you'd want to try to provide off-grid, upsizing the battery bank until the cost, size, and hassle factor makes you say "uncle".

solar_dave · June 2013

Re: Just as an excrcise in futility how would you ...

Eric L wrote: »

I probably didn't express this very clearly above, but I think if you start by looking at how much daytime air conditioning you could get with a small battery bank (but still a fairly large array size) and an efficient cooling unit, you might be pleasantly surprised.

It's one of those things where maybe 60% or so of the time that you want the A/C running, including the hottest periods, you can do it very efficiently with the batteries providing little more than voltage regulation and an occasional boost. From there, you can start looking at how much of the remaining run time you'd want to try to provide off-grid, upsizing the battery bank until the cost, size, and hassle factor makes you say "uncle".

I hear ya, At one point I figured to get the kWh needed I would need at least double my current 12.5 kWh array which is grid tied. The net metering which in effect lets me carry kWh forward from Jan all the way to consumption in June sort of spells it out along with the night time purchase on the off peak hours. Then take into account the additional loses in charging a battery to completely unplug you can virtually triple the array size and have a pretty sizable battery bank.. That being said they still is quite a bit of draw during night hours for AC.

Of course before I would even consider it, the data needed to size it needs to be rung out of the current data collection. For something this size I seriously doubt it will make financial sense.

inetdog · June 2013

Re: Just as an excrcise in futility how would you ...

solar_dave wrote: »

Then take into account the additional loses in charging a battery to completely unplug you can virtually triple the array size and have a pretty sizable battery bank.. That being said they still is quite a bit of draw during night hours for AC.
Of course before I would even consider it, the data needed to size it needs to be rung out of the current data collection. For something this size I seriously doubt it will make financial sense.

If you have grid power which is reasonable in cost (<$.50 per kWh) and reliable, then you may want to zero out your net-metering use. But once you add batteries into the equation, either for load shift or PV replacement of POCO, your cost per kWh of the off-grid power usually shoots up above $1.00 per kWh. Sometimes much higher than that.
So going off-grid rather than going zero-net with grid tie does not make economic sense for (almost?) everybody.

solar_dave · June 2013

Re: Just as an excrcise in futility how would you ...

inetdog wrote: »

If you have grid power which is reasonable in cost (<$.50 per kWh) and reliable, then you may want to zero out your net-metering use. But once you add batteries into the equation, either for load shift or PV replacement of POCO, your cost per kWh of the off-grid power usually shoots up above $1.00 per kWh. Sometimes much higher than that.
So going off-grid rather than going zero-net with grid tie does not make economic sense for (almost?) everybody.

As I started out Just as an exercise in futility

YehoshuaAgapao · June 2013

Re: Just as an excrcise in futility how would you ...

solar_dave wrote: »

As I started out Just as an exercise in futility

If you are living in AZ, in a full size older house, with little concern for energy efficiency, I'd budget for 4000KWh per month with the Air conditioner getting at least 2500 of that. That is 133KWh per day.

Mainstream engineers standardize on a 3-day reserve on batteries, but those things are expensive. I think a 24 hour reserve is better (6-12 hours grid-tied), just need a generator skimping like that.

inetdog wrote: »

If you have grid power which is reasonable in cost (<$.50 per kWh) and reliable, then you may want to zero out your net-metering use. But once you add batteries into the equation, either for load shift or PV replacement of POCO, your cost per kWh of the off-grid power usually shoots up above $1.00 per kWh. Sometimes much higher than that.
So going off-grid rather than going zero-net with grid tie does not make economic sense for (almost?) everybody.

I use load shift for combined reason to have use for my expensive batteries and to give them the cycling that they needed as I am using off-grid optimized flooded batteries. If hyperinflation and rolling blackouts caused by the government's incompetent reaction to it waits until after 2016, I won't be bothered by it. Batteries will destroy any hope of positive ROI in the absence of hyperinflation (which hits food & energy the worst).

westbranch · June 2013

Re: Just as an excrcise in futility how would you ...

YehoshuaAgapao wrote: »

The meteorological monsoon typically starts in the first or second week of July.

Ha,,,, it has been Monsooning here for the last 4 weeks and (blub....blub) is continuing for the rest of the week....(splash splash).... just that we do not have the flooding to go with it as yet like Thailand...8)

PS we live in a northern desert area, normally under 10 inches of rain...

Mangas · June 2013

Re: Just as an excrcise in futility how would you ...

I'm running off grid two high efficiency Trane 2.5 ton A/C compressor units and air handlers. Thermostats set at 81 degrees and we are seeing 96 ambient during the day and 80s' at night.

During the hottest summer rain period our genset picks the slack up (runs only 2 hours in the early AM) after two consecutive days of heavy overcast to pick up the batteries a bit.

Works well.

Just as an excrcise in futility how would you ...

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