Direct Solar to AC Idea

1. Apr 14, 2014

Hello,

I'm in Arizona and was looking to hook up some PV panels directly to the air conditioning unit pump. Is this a reasonable goal?

I figured that I could disconnect the AC unit from grid power and then hook up the solar panels/inverter to the AC unit, but is it possible to have the grid power work hand in hand with the solar cells?

2. Apr 15, 2014

Staff: Mentor

You don't need the aircon except while the sun is high in the sky?

3. Apr 15, 2014

So I was going to put on a solar/grid switch

4. Apr 15, 2014

Staff: Mentor

Check with your local power utility company. They have rules and standard circuits for hooking up your local power generation to the grid. They are very important rules regarding everybody's safety, and it's illegal to connect your power generation to the grid without having your installation inspected and approved by the local power utility company.

This is very commonly done, so they will have useful resources to help you figure out how to connect up to the grid.

5. Apr 15, 2014

psparky

How big do solar panels have to be to deliver at least 5 KVA of power? How much would they cost?

6. Apr 15, 2014

mjhilger

Costs? That is the question with solar! The technology exists, but right now, unless have no access to the grid it is not cost effective to use solar. By the way, even a direct tie would need batteries to cover for the clouds that might pass overhead. And tracking frame and hardware / wiring I'm probably way off on costs on the low end.
Quick search yields:
Solar panels - about $2/watt -> 5000 watts about$10,000
Inverter to convert to AC - I found one on sale 7000 watts -> $1,500 Batteries - Lets say only 2 quality boat or golf cart batteired ->$ 200
Tracking frame, hardware,misc wiring-> $800 -------- total-------------------------------------------------------$12,500

Here is the rub, electricity on the grid in my area is around $0.09 per kilowatt hour so$12,500 = 138,889 kilowatt hours; divide that by 5 (for the 5000 watts of power of the solar sys)
and we get 27,778 hours before we break even. That assumes one time costs covers everything no maintenance or repairs etc.

I love solar and have several panels (10W - 100W) for remote use where grid is not available to run radio, charge lights, etc. And I would love to spend the money to install a system to take me completely off the grid.
However, being realistic the costs is just too expensive at the moment.
In my humble opinion.

7. Apr 15, 2014

psparky

Ok...about what I thought. Not worth the money in this case.

One thing is for sure, when someone does invent a way to "harness" the suns energy efficiently enough make steam electric power plants obsolete, they will be a multi-billionare.

8. Apr 15, 2014

Staff: Mentor

There may be worthwhile savings to be made were you to use your solar power to directly drive some roof-space exhaust fans. Getting rid of the hot air trapped there will give you cooler ceilings, easing the demands on your aircon unit. .... assuming you don't already have these, of course.

A Peltier-based aircon unit would be the shot! But I think they are not very efficient. Yet.

9. Apr 15, 2014

I see, I was looking at the wikipedia article relating to cost/watt and it looks like most the cost for solar is auxiliary stuff like good inverters, installation, tracking, etc.

That is a good idea! I could easily put up a DC fan. The attic does get extremely hot during the summers here.

10. Apr 16, 2014

jim hardy

i'm a believer in solar water heating.
It can replace a lot of KWH.

Copper flat plate collectors are very long lived, low maintenance, and simple enough for a handyman to build.

I'm not aware of a practical solar refrigeration system . That'd be a moneymaker in the Sun Belt.

11. Apr 16, 2014

mjhilger

Could the refrigeration cycle that uses propane/electric heat found in most campers not use the heat from the sun in the same way? Like electricity generation, one would need a way to store the heat when the sun is not shining for total solar. But I think it would be easy to to supplement solar with electric heat/gas backup using a microcontroller to monitor the conditions and switch appropriately.

12. Apr 16, 2014

jim hardy

I guess you're speaking of absorption cycle?
That can be done.
I believe you need around 400 degF which is about the limit of solar collectors due to re-radiation, unless you can get selective surface such as black nickel which absorbs visible like a black body but is opaque for infrared.

The chemicals in such systems aren't conducive to home-fabrication. Ammonia precludes copper, and the bromide doesn't look simple either.
http://www.achrnews.com/articles/chemistry-101-for-absorption-chillers
so what's a home handyman to do?

I thought about this a lot when i lived in S Florida.
If one could use solar generated steam to pull high vacuum on a reservoir of water,
and circulate that water through a heat exchanger placed right behind your central A/C filter,
one would have "booster" for his central A/C which would reduce the amount of time his compressor has to run.
Back of the envelope calcs said if you can evaporate 55 gallons of water over course of a day you'll provide a ton of cooling all day long. Typical central unit where i lived was two or three tons but didn't run continuously, so a ton of boost would make a sizable dent in the electric bill.
Water as the working fluid avoids a lot of problems. Google "refrigerant R718"

And it could be a batch process instead of continuous . If you could arrange it so gravity does your pumping - aficionados of low-tech like myself would crave it.

Somebody will come up with a practical rooftop system surely.

Here's some more ideas.

http://users.ntua.gr/rogdemma/A Review for Absorption Refrigeration Technologies.pdf