Converting older off-grid system to grid-tie w/ battery backup

ScottS · June 2009

So we're in the process of purchasing a house with an existing off-grid system that we'd like to connect to the grid. We'd like to retain as much as possible of the existing system but we'll obviously need a lot of new components (grid-tie inverter, etc). The system was originally put in place in the mid 80's with some later upgrades (batteries replaced in 1998 after 15 years of prior use)

I don't have full specs yet, but here's what I know of the current system:

18 2 V Surette lead-acid batteries wired as 3 parallel 12 V batteries with a total capacity of 3500 amp-hours
4 Kyocera panels (combined rating of 835W) linked to battery pack w/ Trace Engineering charge controller
Batteries are connected directly to a 12v fuse box and via a Trace Engineering inverter to a 120v fuse box. The inverter's continuous output rating is 1500W
The entire house is wired for 120V AC and 12V DC with most lighting, the washing machine, refrigerator, and well pump on DC power, .
The inverter also has battery charging capabilities but is not currently used in that capacity.
500W Sencenbaugh windmill with its own metered charge controller linked into the batteries.
70W bicycle generator hooked into the battery pack (I'm not so concerned about this one)
There are also one propane and one gasoline powered generators currently used for running large loads directly or for backup battery charging.

In order to get a mortgage on the property we've got to hook it up to the grid, but I'd rather not lose the solar/battery system that's already in place, so I'm hoping that a grid-tied arrangement is possible. However there are several things here that will make this not fit well with most grid-tied designs I've seen:

DC loads/fuse box: most grid-tied systems are AC only, but with the well, refrigerator, and lighting on DC I need to retain DC capability. Can I run DC loads directly off the batteries (via the DC fuse box) in a grid-tied arrangement?
12V system: Most of the grid-tied inverters that support battery charge/discharge are 24 or 48V. Are there any grid tie inverters that can handle 12V battery backup? Is there any other way to hook the PV/battery setup into a grid-tie inverter?
additional non-solar energy sources. How does the wind generator with its separate charge controller link into a grid-tied PV system?
PV upgrades. Will I be able to hook newer PV panels into the system with the existing older panels so we can have more than 835W of power generation.

Cariboocoot · June 2009

Re: Converting older off-grid system to grid-tie w/ battery backup

You've probably already realized there's a lot of stuff that would need changing out in order to grid-tie this system. If the current set-up is working fine, why change it? It might be better to keep the existing off-grid system as a 'back up' and wire in a grid service separately, at least for now. You wouldn't actually have to have anything plugged into the grid, except perhaps the AC input of the inverter for when the sun goes down and takes the batteries with it. This should satisfy the conditions of mortgage approval, but check with the authorities before doing. Just because you have to have utility electric doesn't mean you have to use it!:D

mike95490 · June 2009

Re: Converting older off-grid system to grid-tie w/ battery backup

just what Cariboocoot said - you have a mess. Too small to use any GT system, you would have to basically buy a whole new system.

What is your cost to get utility power to the house ? I was quoted $7K per pole, one pole every 100' or so. At $28K I gave up, and resigned to off grid, and lugging batteries every 10 years

icarus · June 2009

Re: Converting older off-grid system to grid-tie w/ battery backup

My guess it that you may also run into some permitting/inspection issues is the house has always been off grid. Hybrid house wiring systems can get into some pretty complicated code issues regarding mixed voltages, proper wiring, especially on the dc side etc.

Perhaps you should have a conversation with the mortgage lender. If this is a full time house, if it can be demonstrated by the current owner that the house is 100% livable then perhaps you can get an exception. You might have to pay a bit more in interest rate or closing points for a "non-conforming" loan,, but maybe it is worth it.

If it is a recreational property,, perhaps using a lender that specializes in similar properties would be a help.

I know from lots of past experience that loan brokers can only follow a script,, just like tech support folks. Anything unusual and they say, "No it can't be done" Most of the time I have figured a way around it.

As Mike and Marc suggest, you've got a bit of a hodge-podge system that won't integrate very well. The big question is,,, how many$$$ to bring in the grid?

Good luck,

Tony

Solar Guppy · June 2009

Re: Converting older off-grid system to grid-tie w/ battery backup

I suspect when you get a quote for the grid connection, the option to purchase the property will no longer be an option and with it any concern for the Hodge-Podge of RE equipment it contains

It a very common issue for people selling/buying offgrid property, the normal mortgage market wants nothing to do with them. Its pay cash or other higher cost means of financing. Even worse now with the financial melt down, no one wants to loan on a property that can't easily be resold if the owner defaults on a loan, to a bank this property isn't collateral.

niel · June 2009

Re: Converting older off-grid system to grid-tie w/ battery backup

outback has 12 inverter chargers that would work in this application, but i'm wondering 2 things.
1 you can't buy a house with a mortgage unless it has utility power? that's just crazy to be forced to have utility power as that condition of sale.
2 if the seller wants to get rid of it that badly then can't get that stuff done?

ScottS · June 2009

Re: Converting older off-grid system to grid-tie w/ battery backup

icarus wrote: »

My guess it that you may also run into some permitting/inspection issues is the house has always been off grid. Hybrid house wiring systems can get into some pretty complicated code issues regarding mixed voltages, proper wiring, especially on the dc side etc.

As Mike and Marc suggest, you've got a bit of a hodge-podge system that won't integrate very well. The big question is,,, how many$$$ to bring in the grid?

Good luck,

Tony

Actually the incoming service connection isn't the biggest difficulty. The house is on a street with existing electrical service, and I'm pretty sure it's close enough not to need any additional poles -- there's already a phone line into the house from the on-street pole. The original owners lived off-grid because they wanted to, not because on-grid electrical wasn't available or was less expensive.

I suppose I could even just pull the existing 120V AC fuse box off the battery inverter and have it hooked into the incoming service -- or more likely take the incoming connections into the AC fuse box and have them routed into new circuits on the grid-connected service panel. The end result here would be a grid-only AC distribution and an off-grid DC-only distribution. This would be a lower up-front cost, and I wouldn't have to deal with grid-tie issues, but with a new-to-the-grid house there will still be lots of code issues lurking.

I'd rather find a way to tie it all in, but I'm not sure that's possible with the existing equipment there.

ScottS · June 2009

Re: Converting older off-grid system to grid-tie w/ battery backup

niel wrote: »

outback has 12 inverter chargers that would work in this application, but i'm wondering 2 things.
1 you can't buy a house with a mortgage unless it has utility power? that's just crazy to be forced to have utility power as that condition of sale.
2 if the seller wants to get rid of it that badly then can't get that stuff done?

Banks want to be able to sell the property easily in the event that people default (well selling "easily" is a relative term in this market!). I've been told by more than one source (including my current mortgage broker) that off-grid is fine _if_ it's in an area where off-grid homes are common, but you have to produce recent comparable home sales to prove it. If you're in an area where all of the other homes are on-grid the bank is afraid that they'll have difficulty selling the property.

The length on the market and price drops with the house we're looking at sort of proves the bank's point here. The sellers lived in the house off-grid for 20 years or so, but they've already moved out. They never had a mortgage on it, as they built it themselves over time. But in this case they dropped the price sufficiently to make the sale rather than put more money into it.

In the short term the cheapest option would probably be to just put in an on-grid service and hook it up to the existing 120V circuits assuming 1) we can hook the existing 120V circuits into the new service without hitting massive inspection/code problems; 2) we can leave the existing PV/battery system as-is for supplying the current 12V loads.

We could even dismantle the whole system and replace the 12V loads w/ new 120V loads/circuits, but it would be a shame to throw it all out.

Ideally I'd like to take the reusable parts of the existing infrastructure (PV/batteries/wind power), expand the PV arrays for a somewhat larger system and hook it into a grid-tie arrangement. But from the comments so far this may not be feasible. On the other hand if I can find a 12V grid-tie inverter then it may be possible to work this system in and keep the 12V loads on the batteries as they are now.

Looking at the Outback site I see some 12V off-grid models (FX2012T and VFX2812) but all of the grid-interactive inverters are 24 and 48V only. So 12V inverters and charge controllers are around, but I'm not seeing anything that's designed for actual grid-tie operation in this range. The other problem seems to be that a lot of the 12V equipment is sized for smaller installations (like what's in this house now) -- so significant expansion would require higher voltage battery packs anyway -- but that, too, would impact the current 12V wiring/appliance infrastructure.

BB. · June 2009

Re: Converting older off-grid system to grid-tie w/ battery backup

My only suggestion is "...don't fall in love with the property." Approach this as an "investment" property.

Depending on the quality level of the electrical work done--it could be very expensive to bring up to code. Get an unbiased opinion on what needs to be done and how much it will cost (and include all of the other normal structural/code issues too). And codes change over time--In our area, if you spend more than XX% of the homes work on a "remodel"; you are stuck with bringing the rest of it up to (near) current code too (fire alarms, emergency bedroom exits, etc.).

Look at what the next door homes (with power) currently cost. Ask if the original owners will carry some sort of mortgage, etc.

-Bill

Solar Guppy · June 2009

Re: Converting older off-grid system to grid-tie w/ battery backup

So the sellers moved out and left the RE stuff ... pretty much looks like there is almost no value there

No way the house meets code and would have to be gutted to remove things like the in wall 12V stuff and redo all the AC to be code compliant split phase 120/240

You must really want the home ... from a distance and this market there would be MUCH better opportunity's to be had. Find a good bank repo and with the saving put in a brand new grid-tie system with the savings. Buy one that needs all this work in today market is financial suicide

Having to get a loan and having to meet restrictions like grid-power, meeting building code and inspections not only protects the bank, but from potential purchases from buying into something they shouldn't.

ScottS · June 2009

Re: Converting older off-grid system to grid-tie w/ battery backup

Solar Guppy wrote: »

So the sellers moved out and left the RE stuff ... pretty much looks like there is almost no value there

No way the house meets code and would have to be gutted to remove things like the in wall 12V stuff and redo all the AC to be code compliant split phase 120/240

You must really want the home ... from a distance and this market there would be MUCH better opportunity's to be had. Find a good bank repo and with the saving put in a brand new grid-tie system with the savings. Buy one that needs all this work in today market is financial suicide

Having to get a loan and having to meet restrictions like grid-power, meeting building code and inspections not only protects the bank, but from potential purchases from buying into something they shouldn't.

Well the inspections aren't done yet, and at this point I'm gathering information on what would be needed. Once the inspections are done and I've got a clear idea of exactly what is needed to get the systems in order we'll be able to determine whether it makes more sense to continue down this path or back out, as we're stil in the due diligence period here.

That was largely the point of this thread -- to help me figure out whether the existing infrastructure would help in getting grid-tie system in place or whether I'd be starting over with an on-grid installation. For a next step I'll have to take it up with a local inspector and a local electrician as to exactly what I'll need to do (and at what cost) to meet the relevant code requirements. Until then I'm well aware that this could go either way.

niel · June 2009

Re: Converting older off-grid system to grid-tie w/ battery backup

they used to have some at 12v, but i suppose the demand was too low for such inverters and they decided to drop it. the 12v operations can still be done from a higher voltage battery bank via a converter or converters depending on how large of a current requirement is needed at 12v. the wind turbine is a different problem, but maybe you could also split the 12v operations from the higher operations with solar.
do yourself a favor and see if the pvs are outputting what they should be for the short circuit current test. do this individually if you can. i also would like to know what model they are if you had not said as otherwise i'll take a look back and see if you posted that just for my curiosity. ok they are kyocera, but which model to work out to that odd 835w for 4 of them?
is the wind turbine operating properly too?
are all of these uncertainties worth it to you as i'm sure it's going to cost you more than you think so the bank might be right this time?

Dave Angelini · June 2009

Re: Converting older off-grid system to grid-tie w/ battery backup

I did an upgrade to code on a similar property. It was not going to be grid connected but it had all the trappings of old hippy era 12volt RV/yachties. As others have posted forget the 12V wiring and abandon it. Use only AC in the house and have a panel capable of split AC. Any DC wiring you keep inside the structure must be in metal conduit, over current protected, and inspectable. The inspection part can only have light shed on it by your building department or someone who knows them!!!!

I would counter Bill's take and say that you have to really love the place to want to take on a project like this. Financing as others have said will be a nightmare and it may be best to have the system removed before appraisal. Good Luck!

ScottS · June 2009

Re: Converting older off-grid system to grid-tie w/ battery backup

Dave Sparks wrote: »

I did an upgrade to code on a similar property. It was not going to be grid connected but it had all the trappings of old hippy era 12volt RV/yachties. As others have posted forget the 12V wiring and abandon it. Use only AC in the house and have a panel capable of split AC. Any DC wiring you keep inside the structure must be in metal conduit, over current protected, and inspectable. The inspection part can only have light shed on it by your building department or someone who knows them!!!!

I would counter Bill's take and say that you have to really love the place to want to take on a project like this. Financing as others have said will be a nightmare and it may be best to have the system removed before appraisal. Good Luck!

Oh I'm becoming more aware of the difficulties by the day. I'm more than willing to walk away if this proves completely impractical, but we've gone far enough here that I'm withholding final judgement until we get the home inspection, electrician's estimates, and a firm answer from the town's building/electrical inspector as to what exactly they'll require in terms of the 12V stuff (rip it out vs. disconnect in-place vs. leave it in-use as long as it's not tied into the grid anywhere).

If the current system can be left as-is (and off-grid), then we can bring in the new service and gradually replace 12V components with 120V equivalents (on new wiring). When the 12V legacy system needs new batteries -- that's when we'd finally pull out the old infrastructure and expand the PV grid-tie infrastructure (if this goes in with the on-grid equipment)

Converting older off-grid system to grid-tie w/ battery backup

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