New System Questions

[thundercowpoke]

As for what is taking 100kwh/day. This is an average. In the spring/fall usage can be as low as 60kwh but in the winter and summer it can go as high as 140kwh. I blame the inefficient heating and cooling unit. If I owned this place it would have been replaced and the windows and insulation would have been upgraded. Why I expect at least a 40% reduction maybe more at the new place.
What I would like to do is offset our usage when it is possible. If I only generate pv power 3 to 6 hours a day so be it. We will be on the end of the line and our neighbors we out of power for a month during the last bad ice storm. Why we will have the generator.
The solar system makes no financial sense, just want to do it because I like to mess with stuff like that.

[Sunking]

As for what is taking 100kwh/day. This is an average. In the spring/fall usage can be as low as 60kwh but in the winter and summer it can go as high as 140kwh. I blame the inefficient heating and cooling unit. If I owned this place it would have been replaced and the windows and insulation would have been upgraded. Why I expect at least a 40% reduction maybe more at the new place.
What I would like to do is offset our usage when it is possible. If I only generate pv power 3 to 6 hours a day so be it. We will be on the end of the line and our neighbors we out of power for a month during the last bad ice storm. Why we will have the generator.
The solar system makes no financial sense, just want to do it because I like to mess with stuff like that.

You are talking over $250,000 initially, and replacing over $100,000 worth of batteries every 5 years.

140 Kwh per day for heat with free NG. That is the funniest thing I have ever heard of. Not even Warren Buffet or Bill Gates come close to your usage. You are talking something like a Walmart or Grocery Store useage. Or come to think of it growing ganja in a green house with artificial lighting.

[littleharbor]

BIG greenhouse.

[thundercowpoke]

The usage is for an electric heating and cooling unit. I expect the reduction in usage to be attributed to getting rid of that unit and the electric stove and oven. No gas at the current house.

I am not going off grid at all.

Was really just asking for advice on components.

Wasn't planning on much of a battery in the first place and now looks like I may not need it at all. Starting with a system that could generate 10kwh/day but will probably average 6 to 8 on a good day. Possibly doubling the system the next year. Plan to add more as I go. No delusions of replacing all of my power but would claim success at 15%. Pricing everything out I might spend $10K on the first phase.

[jflorey2]

I am in the process of setting up a new array. The location is northeast Oklahoma and it will be a grid tie system with a limited battery bank and a generator. This is a new building site and the best estimate I can make of how much power we will use is from my current usage, @100kWh/day, since I will be taking all my appliances minus the electric stove and oven and inefficient heating and cooling unit. I am not trying to go completely off grid but I would like to be able to have power when the grid is down. I plan to increase my array over time starting small and building from there. What I have so far is 8, 320W 24V mono panels. My next purchase will be the charge controller and inverter. This is where I am having trouble deciding on what to get. I know this information is probably on this forum but I haven't got months to sift through it all. Does anyone have any suggestions on what brands are the best?

Here's my suggestion:

First, inverter. I have had good luck with the Outback Radian. They come in 8kW "chunks." So determine your load first; if your average load is under 8kW and your peaks don't exceed about 10kW you'll need one. If it is over that you'll have to add another in parallel.

Radians will also do generator support which will be important for you.

Next, batteries. You have a very unusual requirement (high power but low energy) since all you want to do is live until the generator kicks in, which could be from ten seconds to a few minutes. (From personal experience, having ten minutes or so to go outside and see why the genny isn't starting is pretty important.) So I'm going to have some unusual suggestions:

1) Small LiFePO4 batteries. These have very high peak power outputs, and thus you will be able to size the battery bank smaller than you otherwise would. Outback recommends a minimum of 350 amp-hours for lead-acid batteries, since their inverters can draw 170 amps continuously and up to ~400 amps transiently. That is a "C" rate of C/2 continuously which is hard on a typical lead-acid, but not that hard on a LiFePO4. CALB batteries (which are not great batteries BTW; they're about the cheapest you'd want to consider) can go to 2C discharge rates, reducing the size of the battery you'd need by a factor of 4.

2) Starter batteries. Normally the advice with these is simple - never, ever use them for off grid power. They are NOT designed to store energy or be discharged deeply, and will fail almost instantly in typical off-grid applications. They are good for one thing and one thing only - providing about a minute of very high power to crank a cold engine. They then expect to be pampered for a while, and sit in a constant float charge on an alternator. So in most cases, no good. However, in this case, that's precisely what you need - a short period of very high power followed by days/weeks of float charging. Again, these can allow you to reduce the size of the bank you need. They are not as good as LiFePO4 in terms of internal resistance so you will see a lot more voltage sag for a given ah rating.

The standard choice will be flooded lead-acid; you'll need at LEAST 400 amp-hours for each Radian. Rolls makes a 428ah battery that would work for a single inverter.

Charge controller is less important since you won't be relying much on solar. The Midnite line of charge controllers is a good one.

[thundercowpoke]

Thanks!

I have been looking at the outback and the Schneider lines. I would like to buy one big enough to handle up to 24 320 watt 24v panels. That is probably as big as the array will ever be.

[Mike90250]

..........Charge controller is less important since you won't be relying much on solar. The Midnite line of charge controllers is a good one.

If you have the generator, you may not even need solar, as the Grid / Generator / Radian inverter can recharge the batteries,

But I'm concerned about your 100Kwh daily usage. That's huge, and will require a lot of generator runtime, as batteries cannot supply that (for any reasonable cost)
Electric stove and heating gear, should be considered for replacement by propane. Along with a Twin of the generator, as you may as well have common spares, as it sounds like you will be using it a lot. Set the AGS to alternate gensets, even / odd days or something, to split the runtime. And lay in a stock of oil, filters and common spares.
Generators should be laid out so servicing (oil changes) is easy, and not locating the drain plug at a blind wall.
Air Conditioning needs to be looked at as to replacement with an efficient unit, along with insulation of the house.

Midnight, Morningstar and Schneider all make good solar MPPT CC. And Outback.
If you are going with nearly 8Kw array, it's important to design this part carefully,
at 48V, thats going to be 160 Amps. That will need to be split over 3 controllers for about 55A each. Since you are looking at Radian, why not look at the Outback controllers, I think they share a common command / data structure and will be easier to integrate than mixed bag of Mfg's which, when there is a problem, each will blame the other.

And you are going to have to work closely with an EXPERIENCED installer, as this is going to be a VERY LARGE system and any mistakes will be amplified and expensive.

[thundercowpoke]

Thanks Mike.

I did some checking and my parents have a similar sized house and farm close to where my new place will be. All of their cooking and heating is non electric like I am planning. They have more freezers and refrigerators than I will have and an electric clothes dryer that I plan to have on gas. Their average usage is 20 kWh/day. I expect my load to be somewhere close to theirs.

Keeping all the components the same mfr is a good idea.

I thought that I would have a new CC for each step of my plan. I was trying to buy a big enough inverter so I wouldn't need to buy two.

Any thoughts on trackers and optimized?

[Mike90250]

.......Any thoughts on trackers and optimized?

No and None.

Trackers break, cheaper now to get more panels, face some SE, some SW and voila - Virtual Tracking. (when wired right)

Optimizer only needed if you have un-avoidable shade and going grid-tie Building new, you orient your house properly and put the plumbing vents on the non solar PV side or you use a pole or ground mount array.

If you have a way to NOT have 30 roof penetrations , (ground & pole mount) that's always nice.

[thundercowpoke]

We will be grid tie. We are in the wide open no shade until 4:30 this time of year. I plan on fabricating the array not having to worry about tracker weight limitations makes that much easier. If I stack the panels three high my array will be 18' high by 36' long roughly. Probably start 6' off the ground and put power house under it.

[J.P.M.]

Any thoughts on trackers and optimized?

Unless this is for a real hobby with no regard to cost, maint. or hassle, skip tracking until you've got a handle as to what it entails.

According to the Solar Radiation Data Manual from NREL, a south facing array tilted at latitude around Tulsa will intercept about 5.1 kWh/m^2 per day. A single N-S axis tracker tilted at either latitude or latitude -15 degrees will intercept about 6.5 kWh/m^2 per day. a 2 axis tracker will intercept about 6.7 kWh/m^2 per day.

Tracking arrays will probably produce more power over the course of a year, but for the extra expense, maintenance and potential hassle of a tracking system, I'd consider simply consider buying more panels and increasing the size of the array for the same production.

From PVWatts estimates of long term average annual production for arrays in Tulsa: 1 kW of fixed array tilted at lat. will produce about 1,547 kWh/yr. 1kW of single axis tracker will produce about 1,884 kWh/yr. or about 21 % more output. A 2 axis tracker will put out about 2,076 kWh/yr., or about 35 % more than the fixed array.

I'm not sure, but I'd have some hard #'s on construction costs and put a price on the hassle factor for tracking systems before I automatically assumed tracking is the way to go.

[jflorey2]

Any thoughts on trackers and optimized?

Trackers - no. They're not worth the hassle - cost, mounting issues, possibility of malfunction and elimination of many mounting options.
Optimizers - no. Go with short strings and use an MPPT converter and you will get most of the benefits of optimizers.

[thundercowpoke]

Thank you!

It definitely looks like we will do a fixed array and just make it bigger. More panels are cheaper than trackers anyway.

Looking at an outback 8048 with two fm80's. Not sure yet if it will support 3 CCs but if I go to 32 panels I could just run two identical systems. That won't be until I see how the first half works.

[inetdog]

Trackers - no. They're not worth the hassle - cost, mounting issues, possibility of malfunction and elimination of many mounting options.
Optimizers - no. Go with short strings and use an MPPT converter and you will get most of the benefits of optimizers.

Only remotely justifiable if you only have space for one small array of panels (which would fit on one tracker) and cannot put any more panels in place period. In that case getting the most from that limited size array might justify a tracker.
Horizontal (axis running North-South) may make sense for a commercial scale solar farm where you can use a very simple and reliable mechanism to move a balanced weight.
Those work best in low latitudes, of course.

[jflorey2]

Only remotely justifiable if you only have space for one small array of panels (which would fit on one tracker) and cannot put any more panels in place period. In that case getting the most from that limited size array might justify a tracker.

Even then, in most cases you get almost the same benefit from two arrays - one SW, one SE - in the same footprint. (And with the cost of solar running about 70 cents a watt, it's no more expensive.)