Estimating the Capacity of Solar Panel/Battery System

[Solchar]

I've had this complete off-grid system for over 4 years but never got to really set it up until now due to a house move. I have 4 x 6v L10 400AH batteries, a 60A 24v MPPT Charger and 4 x 290W 12v panels plus 2 x 250W 12v panels (1700W) all rated at about 8A max output at max capacity. The plan was to series 3 groups of two panels and parallel the three pairs to make a 24v panel system. The NW area I live in (Portland OR) can maybe deliver 4-6 hrs of sun (45 LAT - 37 deg) but that is iffy for this past couple years. 4 hrs per day is a safe number. What I need to know is what house load this system can safely handle in terms of KW?

My home uses about 2.5 KW in a 24 hr period worst case. I realize that this system as it is won't handle the whole house load so my second question would be what would I need in terms of panels, maybe another battery bank and upgrade the Charger capacity to cover the whole electrical load?

I would like to see the math for figuring this all out? Thanks. David

[Mike90250]

If the batteries have been sitting idle for more than a year, they are toast or close to end of life.

The system apparently was not "designed" it was obtained, and now the design has to happen to make it work.
4-6 hours sun is not likely, but you have to go with winter sun hours, or go dark. try http://pvwatts.nrel.gov shows Dec is
the worse sun month

4 x 290W 12v panels plus 2 x 250W 12v panels (1700W) all rated at about 8A

Seems to be very likely inaccurate, 250w+ panels are often 30V, never saw a 12V one. 250W @ 12 V = 20A

So a bit more info is needed before we can give you a better answer.

[Wy_White_Wolf]

4 hours is a big stretch for Portland Oregon area. You can't use the yearly average number for off-grid systems. 2 hours would be closer to reality for your winter low. So about 3 KWH is the most it could supply in the winter.

WWW

[Sunking]

Here you go. Get ready for a dose of reality. After you read it, all your green dreams will be smashed to pieces. With less than 2 Sun Hours in winter you are doomed.

[SunEagle]

Here you go. Get ready for a dose of reality. After you read it, all your green dreams will be smashed to pieces. With less than 2 Sun Hour sin winter you are doomed.

Well maybe not doomed but certainly the batteries will get drained without getting a full charge from the solar panels.

[Sunking]

Well maybe not doomed but certainly the batteries will get drained without getting a full charge from the solar panels.

His batteries are 4 years old. Even if he did keep them charged up are now due for replacement. Portland Oregon is no place for Solar. It is as bad as Gloomy Doomy Seattle.

November = 1.7 Sun Hours
December = 1.5 sun hours
January = 1.9 Sun Hours
February = 2.7 Sun Hours.

[SunEagle]

His batteries are 4 years old. Even if he did keep them charged up are now due for replacement. Portland Oregon is no place for Solar. It is as bad as Gloomy Doomy Seattle.

November = 1.7 Sun Hours
December = 1.5 sun hours
January = 1.9 Sun Hours
February = 2.7 Sun Hours.

You are correct about the batteries. They are way past their half life.

As for solar, I also agree that Oregon is not a prime place. For that matter it is not even a secondary place that I would pick. Yet I just read an article that the State is building a 56MW array called the "Gala Sunpower" out near Prineville (which is at least East of Portland) and close to the ones being built by Apple and Facebook for their Data Centers. Seems like a crazy place to harvest solar energy but someone has run the numbers an I guess they work out with some type of ROI.

[littleharbor]

The eastern part of the state is vastly different than the costal west. there are deserts just like Nevada, Utah
and Washington state.

[Sunking]

You are correct about the batteries. They are way past their half life.

As for solar, I also agree that Oregon is not a prime place. For that matter it is not even a secondary place that I would pick. Yet I just read an article that the State is building a 56MW array called the "Gala Sunpower" out near Prineville (which is at least East of Portland) and close to the ones being built by Apple and Facebook for their Data Centers. Seems like a crazy place to harvest solar energy but someone has run the numbers an I guess they work out with some type of ROI.

Makes perfect sense for them. They are using tax payer money just like Walmart. It is all a PR campaign to claim they are Green Mafia paid for by Tax Payers.

[Sunking]

The eastern part of the state is vastly different than the costal west. there are deserts just like Nevada, Utah
and Washington state.

True but Washington and Oregon have unlimited dirt cheap hydro power. If it were not for Washington's Oregon's excess capacity, Northern California would be dark. Southern CA depends on AZ and NV to keep the lights on.

[littleharbor]

True but Washington and Oregon have unlimited dirt cheap hydro power. If it were not for Washington's Oregon's excess capacity, Northern California would be dark. Southern CA depends on AZ and NV to keep the lights on.

This is an off grid system we're talking about here though, sort of.

[Wy_White_Wolf]

True but Washington and Oregon have unlimited dirt cheap hydro power. If it were not for Washington's Oregon's excess capacity, Northern California would be dark. Southern CA depends on AZ and NV to keep the lights on.

Not true about there excess of hydro power. Look at the 500KV powerline running from Colstrip Montana to the northeast to supply them power. Most of No Cals power now is coming from Utah/Wyoming.

[SunEagle]

Not true about there excess of hydro power. Look at the 500KV powerline running from Colstrip Montana to the northeast to supply them power. Most of No Cals power now is coming from Utah/Wyoming.

Hmmm actually CA imports a lot of it's power from the NW according to this article.

[J.P.M.]

Makes perfect sense for them. They are using tax payer money just like Walmart. It is all a PR campaign to claim they are Green Mafia paid for by Tax Payers.

Speaking only about the eastern half of OR, and Prineville in particular to SunEagle's point, by PVWatts, a fixed array will harvest something like 1,500+ kWh/yr. By way of comparison, a San Diego sited array will harvest something like 1,700 kWh/yr. The OR array will ,however, have more seasonal shift, summer/winter, and that won't help much in terms of POCO capacity requirements, but the Prineville situation may be an example of storage measures and capabilities making R.E. measures a bit more viable in the future. Not yet, but someday.

[Wy_White_Wolf]

Hmmm actually CA imports a lot of it's power from the NW according to this article.

Look at the gif map in the chart. Wyoming and Utah are in the Northwest power grid.

"Approximately 122 billion kWh were supplied by the northwest region of the Western Interconnect, consisting of most of Colorado, Idaho, Nevada, Montana, Oregon, Utah, Wyoming, Washington and a small area of northern California."

WWW