Eliminating the battery bank for a AC hybrid solar system with a classic 150

[new2PV]

Could I connect a 2500 watt 48 volt dc power supply to my inverter and parallel with the classic 150 battery terminals.  When a cloud goes by my inverter would be fed from the grid, but when the sun is out the classic output would feed my inverter. I would adjust the voltage lower on the power supply lower than the classic output by a few volts so current would flow out of the classic into the inverter, but I am not sure if it would share the current between sources properly.  Also, r I am not sure if the classic is OK with a 200mv p-p ripple voltage at the battery terminal output. The power supply has no charging profile just constant voltage.

http://www.jameco.com/1/1/45926-rsp-2400-48-2400w-single-output-power-supply-output-48-volts-50-amps.html

[TomW]

new2PV;

I can't help but ask. Where do you get these ideas? What, exactly, are you trying to achieve?

To be blunt and not to discourage you: None of them seem to be sensible or efficient to me.

I get trying different stuff and pushing the envelope but perhaps you could get better workable ideas if you told us what you are working towards? Lots of smart folks on this forum that probably have tried a lot of different stuff and may have an answer to a specific need.

Just curious.

Tom

[new2PV]

Tom,  I am trying to save the costs of purchasing a large battery bank right now.  I want to use the power from solar during the day Ie running my 2500 watt ac unit, when its sunny for example.  However if a clould goes by it would drop out, or it might not even have the capacity to start the compressor, even with the sun out.  Its true there will be a 8% loss in the inverter and about another 10% loss  costing more power to run the system as described.  Question is would it work in theory?

Basically I want for now a grid interactive system, something like the same principle these ac units use.

http://www.hotspotenergy.com/solar-air-conditioner/

[TomW]

new2PV;

I suspect most quality inverters probably have this built in.

My twin Outbacks will charge the batteries and bypass the grid around  the inverter based on setpoints you can program in.

They are technically "inverter / chargers", however.

I think what you propose is technically feasible but unless you include some kind of grid charger control the charger you propose will eventually kill your batteries from chronic overcharge.

A grid driven charger should be OK, same as paralleling other charge sources like turbines, hydro or whatever.

Sadly, the only real cure for an undersized system is to properly size it.

Good luck with it.

Tom

[new2PV]

Ok, Tom you got me on the right track a Grid-assisted system is what I want , and I will need a magnum inverter mspae series for it to work looks like.  Back to the drawing board looks like. I will have to sell my inverters.

[zoneblue]

You dont need a battery. Its call grid tie. Are you trying to avoid "offical" grid interactive arrangement?

A true hybrid system uses (a battery and)  an inverter such as The Outback Radian, or SMA  Sunny Island. Look into the capabilites of those inverters to understand the flexibility that they give you.

Another topology is AC coupling. Take a grid tie inverter, feed that into the AC input of the Sunny Island, allowing it to charge batterys and suplply loads fairly fluidly.

However that all costs money, and unlikely to be cost effective per se, if such is your objective.

Theres only two ways to make money with solar.

1. Grid tie with a freindly power provider. Basically you are using the grid as a battery., and the way to cost this out is if the grid is a cheaper battery than a chemical one. Usually this means getting decent buy back rates, esp lucrative feed in tarifs, and/or nice time of day tarifs by controlling when you sell, and/or low daily line charges.

2. A well designed DIY off grid system that is cheap enough to offset high initial grid connection charges, and/or real high grid per unit charges.

[Halfcrazy]

If I understand correctly you want a grid tied system with no batteries.

The Inverter and charge controller use the battery as a sort of capacitor so without it there will be tons of ripple on the DC lines and I suspect the battery capacitors in the inverter will die a fast painful death but I am not an engineer so I may be wrong.

That power supply is almost 500 bucks and you can buy a string of 6 volt golf cart batteries at cosco for under 800 so I would be tempted to go the battery route

[mike90045]

.....

Theres only two ways to make money with solar.

1. Grid tie with a freindly power provider. Basically you are using the grid as a battery., and the way to cost this out is if the grid is a cheaper battery than a chemical one. Usually this means getting decent buy back rates, esp lucrative feed in tarifs, and/or nice time of day tarifs by controlling when you sell, and/or low daily line charges.

2. A well designed DIY off grid system that is cheap enough to offset high initial grid connection charges, and/or real high grid per unit charges.

Way #2 can never work, battery replacement costs every 7 years prevents break-even.    Only straight Grid-Tie w/out batteries can pay you back.

Any 48VDC inverter requires 100ah battery capacity for each 1Kw generated to be an AC ripple buffer, or as Halfcrazy says, you will kill the inverter internal capacitors.  I know my XW inverter has a error code for Cap Overheat.

[zoneblue]

Never say never?

In NZ (and places like Hawaii and CA) grid per kWh rates are approx $0.30. Even a 100m from road install incurs a 30K+ connect charge. Our system is cost effective, and ive proven it, using discounted cashflow modelling. You can find those spreadsheets in my posting record either here or at NAWs.

Remember i did say well designed. You have to be surgically economical on your gear. I single wrong choice, will have severe effects on the numbers. You also tend to wear/internalise the labor costs. Not easy but CAN be done.

[Westbranch]

and you have to account for equipment bought and found not compatible with your objective 

[new2PV]

I don't want a grid tie I want grid-interactive or grid assist. I don't  want to pay huge connection fees,  double metering, and get taxable income on the income from the utility.  There has to be an affordable solution.

[mike90045]

What you want is called Load Shaving.  The XW line of hybrid inverters can do that, feed your loads without backfeeding the grid.

But there are 2 drawbacks.
1) the inverter is in a mode with fairly high standby loss

2) your utility will quickly know that your power usage has dropped by about 1/3.  Without changing the billing ownership, their auditors will be interested in how do you do that, expect a visit in a couple months.
The batteries in the system will only be 70-80% efficient so you will be spending a fair amount of power recharging them, and some more $ to replace them as needed.

[new2PV]

Thanks , I was looking at the xw6048 system, but I was reading that they are not too reliable, makes me nervous about them that they are made in china.  Even with the cost of the batteries would I still be saving money long term?

[mike90045]

All I can say is that the XW inverters I know of, work great.  There may be issues with the proper set up, from not reading the manual and appendixes fully.

Nearly all electronic gear is built in china.  I had a Morningstar replaced and a Classic replaced, and my original XW is still going fine.

As for batteries, once you add them to a system, your costs never cease.   Water, cables, testing .....

[Halfcrazy]

I have used the XW's and XW+'s for a long time and never had an issue. I personally run my house of a pair of XW+s