Which inverters can be used with this system?

lazza · November 2011

HI Forum

My question today is regarding a Grid-Interactive system. In this post please ignore any financial logic that you may have- I know that such as system that I am proposing is unecessarily expensive, but it's a potential solution we wish to be able to offer for people who wish to reduce their contracted kW hours and an experimental system. Maybe we could imagine a scenario in that the €/kWh triples or quadruples in price, out go fixed charges and you pay for only what you use (ie we see the end of unjust

"line rental" from Endesa etc)

The system would be a PV/Wind system that uses the grid as the support AC power for a battery bank (instead of a normal diesel/gasoline generator). This would be similar to a "battery back-up system" except for the fact that the batteries are used as first choice power supply, until their voltage drops below a certain level, and then the grid will kick-in to supply power to the house and charge the batteries. The concept is to use the minimum minimum amount of electricity from the grid (if at all). I hope this is clear.

My question is: Which Inverters on the market can supply this option?? As it's a slightly odd way round, I'd be very grateful if someone could list all the products that may meet with my requirements,

Thanks as ever

Larry

mike95490 · November 2011

Re: Which inverters can be used with this system?

Xantrex, SMA and Outback, all have "Hybrid" inverter systems.

Xantrex has the XW series, with 4 different models, with integral transfer switches.

I'm sure SMA & Outback (I own XW6048) work in similar manners.

But, they are limited in output, the largest Xantrex is 6Kw, and Outback has an 8Kw model just out. They can be "ganged" to get higher output, but that's more expense. And you will need an expensive & large battery bank to continue running while power is off. You could run lights for a couple days, a refrigerator for 1 day, and air conditioning for a couple hours. You can't run your "whole house" but will have to only power selective loads.

attached, full size NiMh battery bank for 6kw inverter
(800ha, 48v)

mike95490 · November 2011

Re: Which inverters can be used with this system?

This would be similar to a "battery back-up system" except for the fact that the batteries are used as first choice power supply, until their voltage drops below a certain level, and then the grid will kick-in to supply power to the house and charge the batteries. The concept is to use the minimum minimum amount of electricity from the grid (if at all). I hope this is clear.

Clearly expensive. If you have grid power, it's price has to go up 10x, to where it's affordable to use it to charge batteries.

Cariboocoot · November 2011

Re: Which inverters can be used with this system?

Hey guys he did say to ignore the (lack of) financial logic. :roll:

Six Radians @ 8 kW each equals the 48 kW of a typical house service here.
Battery bank as needed to supply a days' usage. Multiple charge controllers and arrays.
Yes, it could be done.

topper · November 2011

Re: Which inverters can be used with this system?

Mike. I looked at your thumbnail pic of your batt bank. What brank of batteries are those?? At what kind of cost??

ggunn · November 2011

Re: Which inverters can be used with this system?

I know the OP said to ignore financials, but to the rest of us I would submit the question of why he would want to do this. I once had a potential customer approach me with a similar idea (he wanted to run off-grid with PV and only use the grid as a backup when he ran out of battery power), but when we ran the financials up the flagpole, including considerations of how long his batteries would last when he is cycling them every day, he decided not to salute the results.

Cariboocoot · November 2011

Re: Which inverters can be used with this system?

ggunn wrote: »

I know the OP said to ignore financials, but to the rest of us I would submit the question of why he would want to do this. I once had a potential customer approach me with a similar idea (he wanted to run off-grid with PV and only use the grid as a backup when he ran out of battery power), but when we ran the financials up the flagpole, including considerations of how long his batteries would last when he is cycling them every day, he decided not to salute the results.

The only situation I can think of is if you live where the grid power is unreliable or unstable, even though inexpensive. Then it might be worth the expense to maintain steady, quality power in the home.

Or else the client has "Greenitis" and is willing to spend ridiculous amounts to prove he/she is more ecologically-minded than the neighbour.

lazza · November 2011

Re: Which inverters can be used with this system?

HI Thanks for your replies.

So I take it only SMA, Outback and Xantrex would do the job for this particular set up? Anyone aware of any other manufacturers?

The trouble is, net-metering is not permitted yet in spain and the FiT is inaccessible for individuals due to the excessive bureaucratic requirements and costs.

Thus, although not financially sensible (unless there are some serious shifts in costs in the near future)- for the ideologically minded who wants to be self-sufficient, this is an alternative, and just something I promised to investigate.

Will inform you if it ever takes shape

Cheers
Larry

Cariboocoot · November 2011

Re: Which inverters can be used with this system?

lazza wrote: »

HI Thanks for your replies.

So I take it only SMA, Outback and Xantrex would do the job for this particular set up? Anyone aware of any other manufacturers?

The trouble is, net-metering is not permitted yet in spain and the FiT is inaccessible for individuals due to the excessive bureaucratic requirements and costs.

Thus, although not financially sensible (unless there are some serious shifts in costs in the near future)- for the ideologically minded who wants to be self-sufficient, this is an alternative, and just something I promised to investigate.

Will inform you if it ever takes shape

Cheers
Larry

Technically, if selling to the grid is never going to happen, then any off-grid inverter will work; allowing power available from the grid to be connected and recharge the batteries/run loads as needed. In essence the grid just becomes a kind of 'generator' for an off-grid system.

However if such a design is put and place and then grid-tie becomes feasible in the future you end up starting all over. That potentiality narrows the choices to the hybrid GT inverter brands mentioned. There may be others available in Europe or even in the U.S., but they are not well-known to forum members here.

ggunn · November 2011

Re: Which inverters can be used with this system?

Cariboocoot wrote: »

Technically, if selling to the grid is never going to happen, then any off-grid inverter will work; allowing power available from the grid to be connected and recharge the batteries/run loads as needed. In essence the grid just becomes a kind of 'generator' for an off-grid system.

You could just build an off-grid system and buy a separate battery charger you can use to store off some juice from the grid when you need it. Put a shunt on the battery bank that both the CC and charger feed through so that the CC knows what the battery SOC is.

Cariboocoot · November 2011

Re: Which inverters can be used with this system?

ggunn wrote: »

You could just build an off-grid system and buy a separate battery charger you can use to store off some juice from the grid when you need it. Put a shunt on the battery bank that both the CC and charger feed through so that the CC knows what the battery SOC is.

Yes indeed.
You know what? More than once that same design recommendation has come up on this forum for people who live in areas with really poor quality utility service.
Great minds think alike.

mike95490 · November 2011

Re: Which inverters can be used with this system?

topper wrote: »

Mike. I looked at your thumbnail pic of your batt bank. What brank of batteries are those?? At what kind of cost??

That's a new bank of NiFe that's not been wired up yet. 1.2V per cell, 48V bank, 850 ah capacity. Cost is 4x that of lead acid, but I was figuring in 10 years, a replacement bank of lead acid may not be available. NiFe is supposed to last 50+ years. Maybe electrolyte replacement every 10-15 years.

stephendv · November 2011

Re: Which inverters can be used with this system?

Larry, since you have the grid available the system could turn out to be cheaper than if you were off-grid. Firstly, the system you're describing is not "grid interactive" because you're not selling any power back to the grid - you could call it an off-grid setup with grid support (yes, slightly contradictory but I think most on this board will understand it

)
It's necessary to make that distinction because it means you can use a much wider range of inverters because they don't need to sell power back to the grid.

To get a handle on costs, you'd need to know what your average daily consumption is in kWh/day and also what your peak and average power draw are in kW. Now, the nice thing about having the grid available is that you can size the solar system to only provide enough power for May-October and use the grid to make up the shortfall in the winter months. If you were purely off-grid you could end up sizing the panels to supply all the power year round, which means you end up throwing away excess power in summer when the system produces double what you need.

Another advantage of the grid is that you don't need that much battery backup. Off-gridders will typically install 3 days worth of battery backup - which is very expensive. Since you have the grid, you can get away with installing just 1 day of backup.

And finally, some inverters have a grid boost or gen boost function which can add to the power supplied by the grid. This means you can contract a smaller supply from Endesa, e.g. 3kW, then install a 3kW inverter - and you'll have 6kW peak power available.

In addition to the inverter brands already mentioned (note that the 3kW outbacks do NOT support grid boost), there are also the Victron Multiplus range and Studer range both of which support grid boost.

lazza · November 2011

Re: Which inverters can be used with this system?

Hi, yes thanks Stephendy- it's "grid support" rather than "grid-interactive"

Do you (or anyone in the forum) know therefore if I could use the grid instead of a generator in "generator support" mode for pretty much all makes and models? for example Victron??

I see you live in Spain... how do you see the coming years? do you think they will introduce net-metering finally?

cheers
Larry

stephendv · November 2011

Re: Which inverters can be used with this system?

Yep you can use grid instead of gen without issue.

Don't know much about when/if net-metering will be introduced. What about plain old grid tie? 0.29 Euro/kWh as far as I remember. You could get an installer to fill out all the required red tape.

lazza · November 2011

Re: Which inverters can be used with this system?

HI Stephen

I wish it was that simple- Trouble is to get through the FiT procedure it will cost you hundreds if not more Euros (application for connection point, administrative fees, required deposit etc...) and what's more it takes at least a year and there's no guarantee they'll concede the FiT as it's done on a quota basis!! I dont know what the bureaucracy is like up in the north of Spain, but here it is catastrophic.

Hence why we are hoping for net-metering. There is a draft of a new Real Decreto for microgeneration to comply with the European Renewables Energy Directive (2009/28/EC), but it's been put on hold with the elections, and I dont think those most likely to be the new residents at the Moncloa have any intention of supporting Renewable Energy production.

But Hope springs eternal

Larry

stephendv · November 2011

Re: Which inverters can be used with this system?

lazza wrote: »

and what's more it takes at least a year and there's no guarantee they'll concede the FiT as it's done on a quota basis!! I dont know what the bureaucracy is like up in the north of Spain, but here it is catastrophic.

Yep no different here unfortunately; Since I'm off-grid I could apply for the 'subvenciones' for solar - which was also a bit of red tape, but not too much - and it resulted in the government paying 30% of the cost of the install. Which I was quite chuffed about, given that the communities are supposed to be bankrupt...

I've seen some installers selling grid tie kits with the Soladin plug in inverters (600W) and I suspect that they just install them without telling the utility anything. The guy who runs this shop sells them and is quite active on the spanish solar forums: http://www.hmsistemas.es/shop/catalog/soladin-600-p-211.html

With that system, it's not true net metering as you get no credit for the power sold back to the grid - you just give it away. But at the same time you reduce your consumption.

If you want to install solar DIY give me a shout because I have a registered SL so can get the components at near wholesale rates.

lazza · November 2011

Re: Which inverters can be used with this system?

HI Stephen

Yeah we're actually already selling Soladins here as the best half-way option. Small investment, and works well for people who have continuous consumption throughout the day, but it's a long way from self-sufficiency.

I actually have a business here too, but it would be very interesting to compare prices anyhow.

If you dont mind me asking, is your business related to solar?

cheers
Larry

solarvic · November 2011

Re: Which inverters can be used with this system?

What did you mean about having a grid interactive system? I think you described just getting grid power to charge batterys when you didn,t have enough generation by solar and wind. You don,t want to sell to power co. Do I understand you correctly? You could use grid powered battery charger and just about any inverter in that case. I am using a Magnum inverter that has utility pass thru to charge battery, but you can,t send power back to utility. :Dsolarvic:D install in process now but not completed

stephendv · November 2011

Re: Which inverters can be used with this system?

lazza wrote: »

If you dont mind me asking, is your business related to solar?

Nope, completely unrelated business. I spent a long time hunting for the best priced components, as every year our house build was delayed so the goal posts for the solar install kept moving.
The consistently lowest prices for panels came from ibc-solar.com, for sunny island from proinso and batteries from sunlight.gr.

lazza · November 2011

Re: Which inverters can be used with this system?

HI Solarvic

Well not exactly. I am looking at a system that is a small PV-battery-inverter set up, but when voltage is low that it switches to grid mode. In this mode it would need to both power the loads and charge the battery.

So far it only seems that the Xantrex models will specifically accomodate this. I have just read the SMA 5048 manual and it doesnt specify this particular set up. It is possible that you could simply substitute the Generator in AutoGen mode at the AC2 connection for the grid supply. However SMA doesnt mention that you can do this (anyone know if this could be done?)

The reason it would need to be this way is that if the batteries go low it is most probably because the consumption is high and will need the grid directly feeding the loads- simply charging the batteries may not supply the necessary energy for that high-consumption period.

Cheers
Larry

stephendv · November 2011

Re: Which inverters can be used with this system?

You can definitely do this with the Sunny Island, see section 14.2 of the manual, has more than a few pages describing grid connection.

Then capter 19.2.3 External Settings describes the detailed settings for the grid. Note that the sunny island has a built in battery monitor so it makes battery decisions based on the state of charge, not on the voltage. E.g. start grid charging when the batteries are less than 50%, etc.

You can do the same with the Victron multiplus as far as I know.

lazza · November 2011

Re: Which inverters can be used with this system?

Doesnt appear very clear to me- maybe you could send me the manual, or a link of the one you have?

It has grid-support, but this i think is actually the opposite, for when the batteries are supporting the grid and not the other way round.

It doesnt seem to explain how you program when the grid kicks in and when it kicks out.... any enlightenment much appreciated

Larry

ggunn · November 2011

Re: Which inverters can be used with this system?

lazza wrote: »

Doesnt appear very clear to me- maybe you could send me the manual, or a link of the one you have?

It has grid-support, but this i think is actually the opposite, for when the batteries are supporting the grid and not the other way round.

It doesnt seem to explain how you program when the grid kicks in and when it kicks out.... any enlightenment much appreciated

Larry

The Sunny Island is very flexible and has scads of programming options. One of them is a pair of progammable relays that you can set to respond to a number of parameters, one of which is battery state of charge. You could use one of them as a control circuit to flip a transfer switch to connect the grid to the AC input when the batteries get down to whatever SOC you choose and to disconnect from the grid when SOC reaches whatever level you want.

lazza · November 2011

Re: Which inverters can be used with this system?

ggunn wrote: »

You could use one of them as a control circuit to flip a transfer switch to connect the grid to the AC input when the batteries get down to whatever SOC you choose and to disconnect from the grid when SOC reaches whatever level you want.

The "Transfer Switch"- is this a transfer switch within the Inverter, or a separate device? ...

thanks
Larry

ggunn · November 2011

Re: Which inverters can be used with this system?

lazza wrote: »

The "Transfer Switch"- is this a transfer switch within the Inverter, or a separate device? ...

thanks
Larry

It's a separate device. The relay internal to the Sunny Island won't carry the current. But I have only scratched the surface of the Sunny Island's programming; it has a transfer switch built into it for anti-islanding. It may be possible to program it so that the switch will respond to battery SOC, but I don't know.

I have configured one to start a genset in response to battery SOC, though, by porting the inverter's AC output through a relay to the genset's sensing relay. When the battery voltage gets below the lower setpoint, the relay opens, cutting the power from the sensing circuit. The generator sees the AC voltage go away and starts up. After a time delay to let the genset come up to speed and stabilize when the Sunny Island sees AC on its inputs, it shuts down its inverter, and goes into passthrough mode, feeding the microgrid from the genset and charging the batteries.

When the battery SOC gets to the upper setpoint, the relay closes, showing the genset the AC voltage, which causes it to shut down. The Sunny Island sees its AC input go dark, fires up its inverter, and powers the microgrid from battery power.

The Sunny Boy on the AC output of the Sunny Island keeps running the whole time except maybe for a short timeout when it sees a blip on the AC at switchover.

It seems to me that substituting the transfer switch in place of the genset would be pretty much the same thing, only it would connect the Sunny Island to the grid.

stephendv · November 2011

Re: Which inverters can be used with this system?

Manual here:
http://www.sma.de/en/products/off-grid-inverters/sunny-island-5048/dlf/U0k1MDQ4LVRCLVRFTjExMDM0MA%253D%253D/download.html?type=281&cHash=e19324601d61b8ad9f9c6d4916fd453b

In case the link doesn't work, it's from: http://www.sma.de/en/products/off-grid-inverters/sunny-island-5048.html under "Technical Description" NOT under "Manual"

Page 163 for the specific settings, GdSocEn, GdPwrEn, etc.

stephendv · November 2011

Re: Which inverters can be used with this system?

ggunn wrote: »

It may be possible to program it so that the switch will respond to battery SOC, but I don't know.

It is

There's no need to use the relays, you can just use the internal transfer switch.

ggunn · November 2011

Re: Which inverters can be used with this system?

stephendv wrote: »

It is There's no need to use the relays, you can just use the internal transfer switch.

Very cool, and I am not surprised. The Sunny Island has so much programming capacity that it can be a little daunting.

stephendv · November 2011

Re: Which inverters can be used with this system?

ggunn wrote: »

Very cool, and I am not surprised. The Sunny Island has so much programming capacity that it can be a little daunting.

Too true, it took me ages to get the reverse power setting right - whenever the generator stopped it would briefly backfeed it with a few amps before shutting down.
It's a great bit of kit though, the built in battery monitor is a definite plus for me

lazza · November 2011

Re: Which inverters can be used with this system?

Thanks Stephen

Ah yes, looks like the key here is "41 GdSocEna Activate the grid request based on SOC". So looks like it could be set up in this way. However the Xantrex/Trace manuals I find in general much better explained- not sure how the rest of the forum feels.

Will let you know if such an installation ever comes to light. I suppose if you think of a price per kWh of say 4€/kWh... you can understand the hypothesis and reasoning.

Cheers
Larry

Which inverters can be used with this system?

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