Second newguy from Texas today...

[Mara]

Hi, I already posted twice on the home improvement threads... but maybe can introduce myself here more in general.

I do hardware design (power electronics) for living and these "ecomods" as hobby. My main project is that I have quite respectable size PV array on my backyard that is powering my house "supplemental air conditioning"... The system makes about 1200W of AC power that I use to run two window AC units. Those are enough to keep the house reasonably cool during days when sun shines... It is completely off-grid system, since I didn't want to bother going through all these NEC requirements and get the system approved... so here it goes.

Everything started as a small project, but just kept growing... The system consist of about 1800W (STC rating) of solar panels, Outback MX-60 charge controller, couple 100AH AGM batteries and 1500W sinewave inverter. In addition I have a small PIC18F based microcontroller board that measures the battery voltage and controls the inverter ON and OFF and also control the loads. (In the morning and afternoon only one AC will run, but during the day both AC's have enough power to run.) It is workign nicely and even today close to 100F day we do not run central AC at all!

How this started? Two years ago our electric bill just got so high that we decided to do something... The bill was "only $200", but I never though paying over $200 per month for electricity! So that's how it started. Now, at the current state our month of June bill was less than $80... Less than half what it used to be.

By the way, during winter months our house is heated with natural gas. That bill was also getting high... and to help that we use portable AC with heater (heat pump) function in the bedroom. That reduced our peak gas bills to well below $100 per month as well.

I'm not saving everywhere, though. I do drive Explorer with V8 engine and I don't get much more than 13MPG in city driving...

[SVOboy]

Would you mind if I asked how much your solar set up cost? Sounds like an interesting project.

Welcome to ecomodder!

[Mara]

Originally Posted by SVOboy

Would you mind if I asked how much your solar set up cost? Sounds like an interesting project.

Welcome to ecomodder!

So far I have spent almost $9K... excluding AC units cost and other miscellaneous hardware (bolts, nuts etc...).

Some pics of my setup can be found from this thread.

[SVOboy]

Interesting. I'm not a home owner, but when I am (if I am), this is likely to be first on my list.

[Cd]

Welcome to the site !
It's a small world. I used to live a few blocks away from Texas Stadium.

[dremd]

Nice!

You should try and spray some water on your condensers; I'll bet you can get some more cooling out of your system like that. Or if you were more ambitions you could do a geothermal heat exchanger and maybe cool your house near full time on solar.

[cfg83]

Mara -

Welcome to EM! In LA, the great thing about replacing your AC load with PV is that you are also helping others by "giving back" your juice while the grid is suffering peak-load. The fewer ACs that are running, the less chance of a power outage.

I have since lost it, but there was a website that was packaging "Conventional AC + PV" power systems. It was taking advantage of the California PV incentive programs to sell you AC systems with PV sized for the AC. This sounds like your strategy, i.e. take out the Big-Kahuna AC load.

Question: I have a window mounted 1.5 ton AC unit (18000 BTUs) for our 900+ sqft home :

http://ecomodder.com/forum/showthrea...html#post30552
http://ecomodder.com/forum/showthrea...html#post37988

In your opinion, how many KW of PV would I need to offset that?

CarloSW2

[Mara]

cfg83:

It depends little bit how efficient your AC is... but with EER=10 rating 18000BTU unit consumes 1800W. At hot day expect little bit higher.

My rough estimate is that the PV array STC rating should be about 1.5x of your AC load power consumption. If your location is not very hot, then maybe little less. You'll also need some battery bank to "ride through" some little clouds.

Before I started buying inverters etc... I was looking for DC operated air conditioners. Some are available for trucks, but none I found suitable for household use. (And the pricing was very expensive.) The benefit of DC operated unit is that there is no need for DC/AC inverter that eats about 10% of the power! Also the DC operated AC units claim to be very efficient according to this. You should get better than EER=15! (Don't know at what conditions they have tested...)

[Mara]

Originally Posted by dremd

Nice!

You should try and spray some water on your condensers; I'll bet you can get some more cooling out of your system like that. Or if you were more ambitions you could do a geothermal heat exchanger and maybe cool your house near full time on solar.

Yes, the water on coil helps significantly. There was another post in "Saving@Home" forum where I discovered the mystery rubber plugs on my window AC units... and the purpose of those is to hold the condensed water and the fan blades splash it to the condenser coil. When I plugged the holes I saw almost 10% power consumption decrease! This agrees with my measurements with central AC unit which current consumption I measured using clamp on AC current meter with Cool-n-save system operation and not.

[cfg83]

Mara -

Originally Posted by Mara

cfg83:

It depends little bit how efficient your AC is... but with EER=10 rating 18000BTU unit consumes 1800W. At hot day expect little bit higher.

You got it, 9.7 EER.

My rough estimate is that the PV array STC rating should be about 1.5x of your AC load power consumption. If your location is not very hot, then maybe little less. You'll also need some battery bank to "ride through" some little clouds.

I'm not worried about battery backup because we (eventually) get the ocean breeze. If I can eliminate peak-load, I am a happy camper.

Before I started buying inverters etc... I was looking for DC operated air conditioners. Some are available for trucks, but none I found suitable for household use. (And the pricing was very expensive.) The benefit of DC operated unit is that there is no need for DC/AC inverter that eats about 10% of the power! Also the DC operated AC units claim to be very efficient according to this. You should get better than EER=15! (Don't know at what conditions they have tested...)

Hmmmm, the 2500 Watt/8525 BTU truck version is decent for a one-room summer "panic room".

Overall, I had a similar experience when I researched solar A/C. There were two products that I seriously looked at. I researched the SolCool Millenia :

SolCool - Solar Air Conditioners


Even though it would replace my 1.5 ton A/C, I can't justify $5K (not to mention it seems like it is never ready for public consumption).

Second, I have been tempted by the Solacool swamp cooler :

Solacool solar powered cooling


But, it's a higher maintenance proposition (evaporative pads), so I haven't been anxious to give it a try.

PS - Thanks to your thread, I think I Googled a website that sizes solar panels to categories of A/C usage (yet *another* option) :

Solar Powered Air Conditioning At Incredible Prices !

CarloSW2