Bypass Advice with WaterFurnace Series 7 Geothermal

[AlyGreen]

Looking for bypass setup advice, is what I need possible?

Disconnect & Bypass setup:
1. 200A fusable disconnect by electric meter
2. Grid bypass, AC power direct to load panel (inverter maintenance)
2. Generator bypass, AC power direct to load panel (grid down)
3. Inverter to load panel, normal setup (controlling solar, battery, grid, generator power sources)

Homeowner doing reasearch on the best solar array, inverter and battery combination for our home.

Planning a solar roof mount array (approx. 19kW) with either a Sol-Ark 15K-2P or EG4-18KPV inverter. Over time want to integrate with 2 or 3 EG4-14.3KWh ProPower Wallmount batteries or something similar that will fit into the garage wall space available.

The biggest design challenge is our allowing existing ground source WaterFurnace Series 7 geothermal system to work with 15kW of backup resistive strip heat during a grid down, (geothermal compressor down) emergency situation. Power being supplied via the existing 20kW whole home generator.

With the Sol-Ark or EG4-18KPV, the built-in inverter bypass (for grid & generator) would not work if the inverter is down (switched off, updating or needing repair) leaving us without heat if the grid is down. A manual generator bypass would allow powering the 15kW resistive strip heat directly from the generator to the load panel. This generator bypass would have to cut out the inverter from controlling the bypass function.

Additionally, the Sol-Ark inverter's max 12kW output on battery or 15kW output on battery + PV would be overloaded, causing a trip if powering 15KW resistive heat. Even if it was possible (using parallel 15kW inverters) the battery size would need to be massive for the sustained draw. With one inverter, the only practical way to do this, I think is the generator to manually bypass the inverter.

Can a setup be wired this way?

Thanks for the advice.

Alastair

 

[pvgirl]

Grid bypass can be done with a 200amp manual transfer switch, that is wired to allow selection of the source of power for the main load panel, from either the inverter output, or the grid. If you have an existing ATS with your generator this could be used to provide generator bypass.

One other way to do generator bypass is to install a breaker and interlock kit to the load panel that will allow either the main breaker to be on and power is supplied by the transfer switch, or with interlock the main breaker is off and the new breaker which is connected to the generator is providing power to the load panel. This could even be a new load panel between the transfer switch and the existing load panel, if there is not room for a new breaker, or the ability to add a main breaker if you don't have one. A 2nd manual 200amp transfer switch could also be used, but will take up a lot of space.

 

[AlyGreen]

Hi @pvgirl ,

Thank you for the reply. The existing whole home generator does have an existing ATS.

I was thinking of removing the ATS and allowing the inverter to control the generator via a 2 wire start, allowing for low SOC battery conditioning if solar or grid supply is not available. Right now the ATS is the first point of ground (interconnect) from the grid and our load panel is a sub-panel. Would keeping the ATS work while also allowing a 2 wire startup?

Forgive my electrical ignorance, reading about this is not the same as fully understanding the wiring possibilities as an electrician would.

Alastair

 

[pvgirl]

You could disconnect the wiring for the automatic transfer and just use the ATS with the manual override, and manually start the generator in the rare case you need to use the generator, and the inverter is offline. This would avoid having the generator auto start when the grid goes out, and allow the inverter and battery to provide backup power. Primary operation of the generator would be by the 2 wire start, and the inverters generator input. Output of the generator would be split to feed both the inverter and the ATS(now manual). When disconnecting the ATS wiring you will need to make sure there is still a 120volt power feed to the generator for the battery charger and any cold weather heaters that may be installed.

 

[millsan1]

I have a series 5 with 10 KW resistive.

I have 18 KPV, 60 kwh, and 32 400 watt panels.

For my heating, I did a wood boiler. The reality is that solar plus batteries will not hold electric heat for long, unless you massively oversize it.

As PVgirl said, I have it wired so I can go back to grid alone, completely bypassing 18 KPV, using a manual transfer switch. If you download the 18 KPV manual, look up the whole house backup with feeder or supply tap drawings, they show it.

I am about an hour from you in PA, you can come look at my setup if you want.

 

[xjaw4]

Is your generator liquid or air cooled?

I'm going to guess it is a LP/NG model vs diesel.

If you are running on generator backup you're better off using the same back up fuel (propane, natural gas or diesel) to generate heat directly rather than using 3x - 6x as much fuel to run a generator to produce electricity to run an electric resistance heater. Possibilities could be ventless radiant heaters or a tankless gas water heater circulating water to a water to air coil in place of the heat strips.
If the generator is running anyway there are opportunities to capture the heat off the engine coolant loop, motor oil and/or exhaust for heating your home and hot water.

Depending on what you decide for a solar inverter you might be able to downsize the generator. If the solar inverter can handle the surge loads then the generator only needs to be able to make up the energy deficit vs what solar was able to provide to keep the battery topped up during an outage.

 

[pvgirl]

Is your generator liquid or air cooled?

I'm going to guess it is a LP/NG model vs diesel.

If you are running on generator backup you're better off using the same back up fuel (propane, natural gas or diesel) to generate heat directly rather than using 3x - 6x as much fuel to run a generator to produce electricity to run an electric resistance heater. Possibilities could be ventless radiant heaters or a tankless gas water heater circulating water to a water to air coil in place of the heat strips.
If the generator is running anyway there are opportunities to capture the heat off the engine coolant loop, motor oil and/or exhaust for heating your home and hot water.

This is good advice in general, but in this case we are talking about about a double failure condition, compressor failure in the heat pump, and the grid is off, which should be a very rare event, and the cost of installing a new backup fuel heat source, that may never be used is hard to justify.

 

[AlyGreen]

You people are amazing! Thank you both @pvgirl and @millsan1 for the great advice.

Pvgirl, using the existing ATS in that way was not an option that I had considered, great thinking.

Millsan1, agreed that batteries would not be viable supplying the 15kW resistive heat for long. I understand the wood boiler backup, our last home had one, but the home we live in now didn't have an existing fireplace or good location for a flue or chimney and we really wanted to go all electric if we could, hence the resistive backup heat option.

Thanks for the system visit offer, that is most generous, I will definitely keep it in mind for the future. Right now we are still in very early planning phase for the solar system having lived with the geothermal now for two years to get a good sense of electrical consumption, so be able to correctly size the solar array to provide all power or close to it.

Over production in summer, under production in winter to balance out overall.

The winter electrical power draw as you know is much higher with a geothermal system so your 32,400W array makes sense. The best we can do with our roof square footage, is about 20kW and is the best panel array location avoiding shade. SSW orientation 192 degrees azimuth (approx. 10% tree shade) but good for prime time solar raditation.

I knew I could force the generator start via the inverter but had been reading differing opinions about whether the inverter passthrough on power out automatically set the bypass to closed or left it open. Some people though the inverter had to have power and be functional to close the bypass and let the grid or generator power through, others thought is would automatically default to the closed position.

Knowing I could not rewire things myself, that was the main reason I was thinking of a manual generator bypass option.

I don't mean to start a conflict discussion, just I don't know the true answer about how an inverter without power behaves not seeing that in either manual. What if the inverter gets smoked (destroyed) will the built-in bypass still function? I would love to use the built-in functionality just trying to understand how redundant the system might be.

Alastair

 

[AlyGreen]

Hi @xjaw4 , yes I agree about propane being a good efficient source of direct heat. I am just using it for emergency backup to power our home right now, when the grid goes down. Our goal has always try to go all electric with the geothermal and now planning for the solar system so the only time we would pull on the propane generator is to top up the SOC low battery bank and in a dual failure situation.

Geothermal compressor failure, no sun, no battery, inverter failure (outage) so I can live with the propane cost in that rare situation. We live in the Appalachian Mountains and were planning on a worst case scenario to figure out the best way to design our system to cover giving us heat in winter or severe weather. Parts or service might not be immediately be available so to cover ourselves were looking for a solution.

Thank you for the ideas, much appreicated.

Alastair

 

[pvgirl]

If you have the land, and local zoning allows you may want to consider ground mounting part of the array to add capacity beyond what will fit on the roof.

 

[AlyGreen]

@pvgirl , we do have 1.25 acres but there is a force stronger than zoning, my wife doesn't want to look at a ground mount out the window!

I did a manual shade survey, which was fun by building the survey tool. Here are the shading percentages and a timelapse sun on roof sequence, south and north facing. Got to love solar projects, such fun to learn about.

 

[AlyGreen]

Hi @pvgirl ,

Have worked with Sol-Ark's excellent tech support this last week and come up with a simpler solution. I photoshopped the Whole Home Generator wiring diagram to show a manual bypass after the ATS. This allows for one bypass to handle both grid and generator.

The Whole Home Generator setup wiring, lands both grid and generator on the GRID terminals. As long as "GEN Connect to Grid Input' is enabled then the Sol-Ark will handle things through the ATS.

Apparently the 15K-2P can detect whether or not the generator or grid are online and only export (grid sell) when the grid is connected. The Sol-Ark does this by pushing a small amount of power upstream first. If voltage increases too much, it will stop attempting to sell via the grid terminals, and not damage the generator.

This is a much simpler and neater solution, using our current ATS install and just one manual bypass, so costing less.

Thought I would pass the knowledge learnt on to you and the forum.

Alastair