25 kW Solar power project in Iowa.

[Redneck in training]

According to the data with the A/C unit it has a "total unit amps" of 30.7 and it is single phase 220-240v

At 240 volts that would be 7369 watts needed to operate the unit.

I would assume that would be for A/C-Heat Pump operation since it takes an additional breaker to run the heat strips. The heat strips are actually optional and the unit can run without them. In fact, the heat strips could be connected to the grid while the A/C-Heat Pump is run from the Solar Power.

As far as roof area, I have an East/West roof - no South facing roof. However, I have 30 acres so finding a place to put a free standing array would not be a problem. I am also capable of DIY.

With this information is it possible to give a more bottom-line type figure for the panels and inverters needed. As far as a frame, I am sure I could build something if need be.

Typical 60 cell panel is 250W DC. The typical efficiency of the system is about 0.85-87. You need 7400W/0.85/250=35. You will need 35 ea 250W panels. Then you have to decide if you want to use single inverter or microinverters. There are pros and cons for each.

Single inverter is generally cheaper, can be placed close to the grid connection. But you have to deal with high DC voltage, there is possibility of arcing etc. Adding panels later on might be also problematic because all panels in the branch has to have the same specs. Shading of one panel affects the whole branch.

Micro Inverters are more expensive but you don't need to deal with high voltages. Wiring is easy because of pre made cable with connectors. You can mix different panels in the array as long as they are compatible with the inverter. Since the inverters are at the array voltage rise between the array and the grid connection is potential issue because the inverters disconect when the voltage rises above 260V AC. In example if you are close to the substation voltage in your place might be at the upper limit (250V) then you have only 10 V cushion for voltage rise between inverters and the AC connection point. In other words the length and gauge of the cable might increase the cost of the system.
Preferably you should buy all the material from one source so the connectors on the panels and microinverters match. You can usually get substantial discount when you buy all the hardware as a package.

Before you start the project make sure that you know what the incentives, regulations and fees are. Do you need a permit? Can you do it all DIY or does the electrical part have to be done by licensed person? What inspections you need? How the metering is handled? etc.

 

[nomad]

The panels were $3.50/W last year. The same panels are about $1.20/W today

I stopped reading the thread till this page in that you say this above.
According to my cost, return, etc calculations here in Turkey, almost like Florida climate, Solar electric power can be economically feasable when the price of solar goes lower than $0.4 per watt in a place where there is already electric grid. Where there is no electric grid, of course, even $3-5 per watt is economically feasable.

Now, your total cost was based on this price of panels, $1.2/W? and this was a few months ago.
Since I am in international business, I get price quotations in different fields in which I done a little works too. 3 months ago, I had searched some solar pv panels for someones and price was about $1-1.5 per watt and this was for assembled pv cells, that's, panels. Now, yesterday, a Chinese pv panel manufacturer sent an email (campaign) saying that special price for Christmas is $0.67 per watt of panel, with mono cyristals, that's, good. If you go for this big volume of pv panel, I believe you can get the price for panels as low as $0.6 or lower per watt.

So, you will reduce your total cost of panels half and portion of pv panel cost in your total cost is about 80%. That means, your total cost will be as low as 60% with this pv panel price, $0.6 per watt. Anyway, panels and their cells are more or less same as long as mono crystal. You need to focus on other components (inverters, regulators, charge controllers, batteries, etc) more as their qualities and prices may change more.

You don't have much knowledge in international business and detailed technical knowledge in this field? My advice is to hire two people temporarily; a person experienced in importing from negotiating to delivery and a technican like electric engineer, they can be retired too. When the project ended, you will have learnt also how to import and some technical details so that you yourself can take care of your own system in the future.

 

[TheGoose]

96 inverters? Whoa...that's a lot of failure points. I'll certainly be watching this thread with interest to see how they hold up. The technology looks very promising.

Yes. Microinverters have special cabling with connectors spaced either portrait or landscape. It makes all connection quick and easy. You can chain up to 17 inverters/branch. Each branch has to have its own 20A breaker. They are grid comutated and produce "pure" sine wave. If the grid voltage drops below 210V or increases over 260V they disconnect from the grid. There is a possibility to use them also off grid. The battery feeds a "master" inverter that makes the microinverters think that the grid is up and running.

We have 96 inverters in 9 branches. Each branch is center connected directly to a breaker and via breaker box to the main cable and grid.

The problem is that nobody (yet) makes a solar-compatable A/C unit. In order to "run" your A/C off your solar panels you will need to connect your whole house to the panels, not just the A/C. I look at A/C and think that it would be one of the better areas to have a dedicated solar appliance since they are used mainly during the sunniest time of year. Having the ability to run just the A/C on solar keeps the equipment and permitting costs down.

According to the data with the A/C unit it has a "total unit amps" of 30.7 and it is single phase 220-240v

At 240 volts that would be 7369 watts needed to operate the unit.

I would assume that would be for A/C-Heat Pump operation since it takes an additional breaker to run the heat strips. The heat strips are actually optional and the unit can run without them. In fact, the heat strips could be connected to the grid while the A/C-Heat Pump is run from the Solar Power.

As far as roof area, I have an East/West roof - no South facing roof. However, I have 30 acres so finding a place to put a free standing array would not be a problem. I am also capable of DIY.

With this information is it possible to give a more bottom-line type figure for the panels and inverters needed. As far as a frame, I am sure I could build something if need be.

 

[Redneck in training]

I assumed that it will be grid tie system that will offset the cost of running the heat pump. The system should be sized up such a way that it will bring the best return on investment. It all depends on the billing deal you can get from the utility.

 

[Redneck in training]

96 inverters? Whoa...that's a lot of failure points. I'll certainly be watching this thread with interest to see how they hold up. The technology looks very promising.

In fact it is the other way around. The system has very high redundancy. Failure of single cell, panel or inverter will not disable the whole system as it could with panels chained in strings and connected to single inverter.

 

[TheGoose]

No, I understand how micro-inverters work. I understand that they will actually increase power especially under shading conditions as opposed to a single string that could get shaded on one panel and bring the whole line down or one failed module.

Are those MI (micro-inverter) solid state?

 

[Qapla]

I assumed that it will be grid tie system that will offset the cost of running the heat pump...

Actually, no I was thinking of an Off-Grid system for the A/C.

The problem is that nobody (yet) makes a solar-compatible A/C unit. In order to "run" your A/C off your solar panels you will need to connect your whole house to the panels, not just the A/C...

A company called Solar Cool claims to make a solar compatible a/c. Lenox site lists a solar powered unit for commercial use but not residential.

Now, as for not being able to run just the a/c from solar ... why not. Why would you need to connect the whole house to have a package unit running on solar only?

 

[Redneck in training]

Actually, no I was thinking of an Off-Grid system for the A/C.


A company called Solar Cool claims to make a solar compatible a/c. Lenox site lists a solar powered unit for commercial use but not residential.

Now, as for not being able to run just the a/c from solar ... why not. Why would you need to connect the whole house to have a package unit running on solar only?

I am not an expert on PV systems. I just learned a lot building my own system. Therefore don't take what I say as absolute truth. Get second opinion.

Grid tie has several advantages.
1.) Your AC/heat will operate even when there is no sun.
2.) When your system produces more energy than you use you get paid for it.
3.) It is much cheaper and simpler system than system with batteries.
4.) Once you develop the effort to install PV you might just install system that would run your whole house.
5.) If power goes down (in example during hurricane) you might disconnect from grid and use small generator (in example Yamaha pure sine wave inverter) to make the PV inverter(s) think that grid is up and save lot of fuel when the sun is shining.

There are (usually commercial) systems where one inverter is not grid commutated (it can run even when the grid is down) and the rest of the inverters are commutated by it.

 

[TheGoose]

I looked at the solar cool site. They don't make a "solar powered" A/C, rather an A/C that uses a thermal collector to somehow assist in the efficiency of the overall system. Since I'm not really an A/C guy I really don't see how super-heating the refrigerant is going to help with the efficiency, but it has been many years since I studied thermodynamics.

I just wish a company would make a small window-type A/C unit that could be connected directly to solar panels (like a solar well-pump) and provide supplemental cooling.

 

[nomad]

I looked at the solar cool site. They don't make a "solar powered" A/C, rather an A/C that uses a thermal collector to somehow assist in the efficiency of the overall system. Since I'm not really an A/C guy I really don't see how super-heating the refrigerant is going to help with the efficiency, but it has been many years since I studied thermodynamics.

I just wish a company would make a small window-type A/C unit that could be connected directly to solar panels (like a solar well-pump) and provide supplemental cooling.

Of course, there are many Solar A/Cs today, just check youtube and google. Last year, I was about to do a container load business with an Australian small company who produced solar a/c, totally powered by Solar. This business could be done because these solar A/Cs would be installed in the containers in a desert where there is no electric grid line.

Of course, most of solar a/c s today are hybrid systems cause most of a/c users already have electric grid and price of electric through the grid is around 0.1-0.3 usd per watt which is still 1/3 of price per watt by solar (investment return in 3 years today unlike 2 years ago when return was 5-7 years.) Hybrid solar in A/C to increase compressor efficiency or combination of any alternative energy today is a transient period toward totally green energy. In Germany and Italy where people voted no to nuclear energy, nowadays, green energy is becoming more important as price of electric through grid is increasing day by day due to lack of production of electric by classical methods (hydro, thermal coal, natural gas, nuclear.) Especially Germany has put a heavy weight in supporting green energies since last year. So, when the restrictions on non-clean (coal thermal, etc) or dangerous (nuclear) energies increase, electric price through the grid lines too will increase a lot. So, don't expect only decrease of green energy prices, but expect also increase in non-green energy prices too.