Designing a 60KW community solution

**DanKegel** · 04-20-2015, 12:02 AM

How many kWh do you expect each house to need?

Can you tolerate running the A/C only when the sun is shining?

What's your budget?

Will you have someone onsite who can fix the tracking system when it breaks?

**miahallen** · 04-20-2015, 07:30 AM

How many kWh do you expect each house to need?
25KWh per day

Can you tolerate running the A/C only when the sun is shining?
No, we will want to run bedroom A/C mini-split units at night.

What's your budget?
I think we will not want to exceed $350K...but could push that figure if there was a strong case to do so.

Will you have someone onsite who can fix the tracking system when it breaks?
Yes.

**russ** · 04-20-2015, 08:13 AM

Add a few more panels and forget tracking. Cheaper and much more reliable.

**miahallen** · 04-20-2015, 09:24 AM

Sounds reasonable to me. I'm more interested in your ideas for storage & CC/inverter/genset...

**Amy@altE** · 04-20-2015, 10:22 AM

I would highly discourage a tracker in your area. Adding the mechanical component is just asking for a maintenance nightmare.

Kyocera panels are salt spray tested and do very well on islands.

You may want to consider a sealed inverter to help resist corrosion. Outback has a new version coming out, the FXR, that gives the configurability and stackability of the Radian, but with a sealed version for the sea air. You can stack up to 10 of them for 30kW. So you could do 2 systems for your 60kW. http://www.outbackpower.com/outback-...ategory_id=444

Note that you do not have 10 sun hours, you have 10 hours of sun. Big difference when calculating solar. For sun hours, you've got about 4.2 in December, that's the number the calculations should go off.

I'll run some numbers and see if the size you are proposing is enough for your loads, stand by.

**Amy@altE** · 04-20-2015, 10:35 AM

25kWh per house x 10 houses = 250kWh a day / 4.2 sun hours / .67 system losses = 88.9kW system needed.

250kWH x /.92 inverter efficency x 3 days autonomy / 50% DoD / 48V = 34,000Ah 48V battery bank.

Definitely can't do within your proposed budget. Double check the daily power requirements of the houses, any chance you can get that lower?

**miahallen** · 04-20-2015, 10:57 AM

Originally posted by Amy@altE

I would highly discourage a tracker in your area. Adding the mechanical component is just asking for a maintenance nightmare.

Kyocera panels are salt spray tested and do very well on islands.

You may want to consider a sealed inverter to help resist corrosion. Outback has a new version coming out, the FXR, that gives the configurability and stackability of the Radian, but with a sealed version for the sea air. You can stack up to 10 of them for 30kW. So you could do 2 systems for your 60kW. http://www.outbackpower.com/outback-...ategory_id=444

Note that you do not have 10 sun hours, you have 10 hours of sun. Big difference when calculating solar. For sun hours, you've got about 4.2 in December, that's the number the calculations should go off.

I'll run some numbers and see if the size you are proposing is enough for your loads, stand by.

Thanks for your thoughts Amy...I am about 70 miles inland from the coast in the jungle...salty air isn't a huge concern, but high humidity is a major factor, so your suggestions are relevant and appreciated.

Sun hours in Belize if I face the array due south at a 17 degree tilt:

Belize.JPG

So I stand corrected, I was looking at incident solar insolation per day...a single 60 cell panel is approx 1.5m2 so each (15% eff) panel should produce approx 7.5x1.5m2x15%= 1.7KWh per day....right?
That should give me approx 400KWh per day from a 240 panel array (getting really rough here) on a sunny winter day....maybe about 40KWh per cloudy winter day.

Amy, thank you for your calculations. I am not planning for 3 days of autonomy, 2 at most. We will have a large diesel gen-set on site for cloudy spells.

Based on my proposed budget, how many KWh per day per household can we afford?

**Amy@altE** · 04-20-2015, 11:06 AM

I don't know where you got those sun hour numbers, but there is no way it is right. Find another source, trust me on this one, your source is wrong.

Belize, Belize - Sunrise, sunset, dawn and dusk times for the whole year

http://www.gaisma.com/en/location/belize.html

Belize, Belize - sunrise, sunset, dawn and dusk times for the whole year in a graph, day length and changes in lengths in a table. Basic information, like local time and the location on a world map, are also featured.

Solar Irradiance Calculator

http://solarelectricityhandbook.com/solar-irradiance.html

250kWH x /.92 inverter efficency x 2 days autonomy / 50% DoD / 48V = 22,600Ah 48V battery bank.

**DanKegel** · 04-20-2015, 11:26 AM

Originally posted by miahallen

I am not planning for 3 days of autonomy, 2 at most. We will have a large diesel gen-set on site for cloudy spells.

If you can fire up the genset after 2-3 hours of clouds rather than 2-3 days, your battery costs will go way way down.
If you can run the genset at night, too, your battery costs will go way way way down.

Think of the solar system as a way to save on fuel costs, not as a way to avoid running the genset.

**miahallen** · 04-20-2015, 11:27 AM

source - http://pveducation.org/pvcdrom/prope...lar-insolation

**J.P.M.** · 04-20-2015, 11:38 AM

Originally posted by miahallen

source - http://pveducation.org/pvcdrom/prope...lar-insolation

And mostly a good starter for solar energy in general. For additional details and a bit more rigor on irradiance and other things, see the references in pveducation site referenced, and Duffie & Beckman.

**Amy@altE** · 04-20-2015, 11:44 AM

But not a good source for insolation.

**J.P.M.** · 04-20-2015, 12:03 PM

xxx

**J.P.M.** · 04-20-2015, 12:06 PM

Maybe, but a good sources of knowledge. Kind of like going to driving school or reading the driver's manual before you get behind the wheel and take a driving test.

Depends on what you're looking for. Those sources can provide background information that will help in making informed decisions about what various sources if irradiance data contain, their strengths, weaknesses, meaning and suitability to that application at hand.

Notice how many folks are ignorant of any knowledge of how, say a TMY is calculated or where its used. Not all irradiance information is created equal, nor is it intended to be. For example, an application may need irradiance (power) data, or insolation (energy) data, or (often) both.

To say "just give me insolation data" without some understanding of what you're getting or even what's needed is, in the opinion of some, ignorant.[/QUOTE]

Designing a 60KW community solution

Designing a 60KW community solution

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