Inherited a Residential System with New Home

[dmharvey79]

Hello all. I purchased a home last fall and the previous owner (electrical engineer and general contractor) installed a smaller system a couple of years ago. I am totally new to the solar power scene, but generally handy with projects, and I'm thinking about building upon what the previous owner started. My goal is to establish enough power generation and storage to run our fridge, roughly 20 LED lights in our kitchen/living room area, and a couple of standard outlets 'indefinitely'...so maybe one or two existing circuits (with usage managed accordingly while relying on this solar power of course). I figure this is a good starting point and maybe I can expand the system to cover more of the house in the future...probably the well pump and a couple more existing circuits with LED lights and a couple of common household items plugged into outlets. Our home is on 10 wooded acres surrounded by over 3000 wood acres, about 50 miles west of DC, and I'm looking for this system to be something we can use in the event that we have a very long-term outage. For short-term weather outages we'll be using a dual-fuel emergency generator to power around 50% of the house.

Here is what I know about the existing system, based on my limited knowledge and a recent chat with the previous owner...five 100 watt panels tied to a power inverter in a clearing towards the end of our driveway, located about 500' from our house and main panel. Below is what the previous owner said when I emailed him for some additional details, and I'll include notes in parentheses for context.

"The solar panels I put in were more of an experiment to see what I could get per $$. But you are correct, they have grid tie inverters that backfeed into the lighting circuit that runs along the driveway. The circuit is tied through and each light is switched/photocelled (several light poles with outlets installed along the 200 yard long driveway) so there's not a break anywhere and continuous neutral. You will see the tie through when you pop open the LBs at each pole. It's 12 gauge wire from about halfway down the driveway to limit loss and I designed it to handle a full 1,500 watt load at 2% loss. That circuit actually runs from the panel, up through the master bath at the outlet next to the toilet then out. That was an extra circuit I had during the remodel so I just used it vs having to rewire."

I plan to poke around the forum as I get up to speed on solar power and various options for our system, but initial thoughts and suggestions are more than welcome. Thanks and I really look forward to working on this project as my schedule allows. Here are a few pictures...

 

[svetz]

Welcome to the forums!

What a beautiful location! I didn't see a specific question, but if you're looking for ideas on different ways of doing things you might peruse this thread (the OP has some unique issues) or if you want to look at some examples to get explanations for calculations see the FAQs.

 

[dmharvey79]

Thanks much and I'll be sure to take a look at that thread. No specific questions at this point, just trying to sort of assess the infrastructure I have in place and identify the best options or approaches to consider moving forward.

One general question I have at this point is...should I push power generated by my panels up the line along my driveway, with my battery bank and converter located near the panel (in my attached garage, so I have some control over temps)? If so, would 24v at 50a be the right range to shoot for power from the solar panels to garage...based on the previous owner's comment that the line along our driveway was designed for a 1500 watt load at 2% loss? I assume this would require me to adjust how that line is installed now and I'm sure I'm missing other things to consider as well. If I kept the existing voltage, which I also assume is necessary to to power light poles along the driveway I'd be limited to around 13.5a on that line, correct?

Thanks again and back to learning / researching for now.

 

[svetz]

Usually the answer to that question is $, which is usually based on voltage.

Here's why: watts = volts x amps, so the higher the volts the lower the amps for a set wattage. The lower the amps, the thinner (less expensive) gauge wire you can use.

I don't think I have a clear picture as the 12 gauge wire in his response doesn't make much sense to me with 24V@50 amps. Take a look at the wire calculator to the right... You can plug in different voltages and currents knowing the 2% loss and 600' are constant. So for example if the voltage was 375 then 1500 W would be (1500/375=) 4 amps. That works with 12 gauge wire, but pretty high volts. If you could post a diagram showing where all the parts are currently and where the 600' distance is we might be able to make more sense of it. He might have doubled on the wire or something too, that doubles the number of amps the wire can safely carry.

 

[dmharvey79]

Thanks! Here is a basic layout of what is here now.

- Five ground-mounted 100 watt solar panels tied to an inverter and plugged into the second to last outlet on that line, about 500' from the house.
- I put small circles on the imagery to roughly show where outlets are installed along that line.
- That line along the driveway is tied into the main panel as the previous owner described. Currently no battery storage anywhere.

Another option I can consider is relocating panels and starting from scratch, either roof-mounted (probably preferred) or ground-mounted in the area I circled with red. Both locations seem to get a good amount of sunlight, as does the existing panel site since surrounding trees were cleared a bit since that imagery was taken. Maybe it would just make more sense to move everything closer to the house, even though that line is already installed along the driveway?

I appreciate the responses and I should probably spend some more time researching before I ping you all with too many questions. Just trying to get a basic understanding of my options and things to consider as I learn about the various topics relating to this type of project.

 

[svetz]

What's your ultimate solar goal? I'd say put together an energy budget, and then plan from that. My guess is you'll end up putting 300W panels on the roof and leave the old/small panels to power the driveway lights. If you can afford it, the math shows you save more with the 26% fed tax incentive and net-metering the bigger you go initially.

By budget I mean something like:

Device	Watts	number of hours needed/day	watt-hours/day
fan	120​	6​	=120 x 6 = 720
frig	160​	7​	=160 x 7 = 1120
cell	20​	1​	=20 x 1 = 20

 

[dmharvey79]

Based on the energy budget I put together I'd like to start in the 6000 watt hour range, tied to 2 circuits in our kitchen/living areas, and possibly expand on that a bit in the future to include our well pump and light in some other parts of the house.

 

[svetz]

If you have net-metering, no tiered rates, and outages aren't a concern I'd suggest avoiding batteries as they're still pricey. Although investing up-front in a system that allows you to add batteries later cheaply (rather than AC coupling or folk-lift, something like Sol-Arc) just in case those trying to get rid of net-metering eventually win (see Net Metering under attack, again....).

Next thing to consider is if you want to piece-meal it together or go all at once or perhaps leave room for expansion? Microinverters are the cats meow for easy of scalability and planning, they have a ton of advantages (e.g., no high voltage DC lines, no strings, no worry about temperature coefficients, no worry about organizing into series or parallel, no worries about shading, any single failure doesn't take the whole system down). Historically though they've been pricey for AC coupling, although the Tesla Powerwall, Enphase Ensemble, and other competitors have reversed that.

As to roof or ground mount, I like the roof mounts as I have a flat roof and easy access - so easy to clean them (no snow here, just have to get the pollen and other stuff off periodically) and they're not taking up yard space. Others may have better advice for you based on their experiences.

I'm not sure what type of grid-tied inverter you have at the end of the road, but those types of inverters are current sources, so you don't really have to worry about voltage drop as they jack up the voltage (to some limit) to be able to push the current into the grid. For example, if your house is 240V and there's a 2% voltage drop along the driveway they'd increase their output to ~245V. The main concern on those wires is that the amperage isn't so high it fries the 12 gauge wire. The other concern with a current source is they want to push power even if there's no where for it to go (not as safe as a battery or wall-outlet which are voltage sources and only supply current when needed); that's why grid-tied inverters shutdown when they lose the grid.

To "start" in the 6kWh/d range, the insolation looks to be around 4.5, so 6000 Wh/4.5 h = ~1350 Watt array. You can get more accurate data with PVWatts or SAM. I highly reccommend SAM, takes a bit of learning to get it set up...but once you have your system modeled super easy to do what-if I do this and see how it affects the economics over the life.

Regarding the pump, if it's an old pump you might look into replacing it with a DC pump. They use a lot of power when they run which is easy for a battery to supply, but the startup current can be tough for an inverter - meaning you end up getting a far larger inverter than you'd otherwise need (you also lose power from the inverter efficiency).

Hope that helps some! Sounds like you have a pretty firm grasp on this stuff. But please keep us posted on your progress and of course any questions you come up with!

 

[svetz]

BTW, in the earlier post I totally missed that the grid-tied inverters were at the bottom of the driveway, so you're pushing AC up along the driveway. Assuming a worse case scenario, then five 500W panels on a really cold day with an inverter efficiency of 96% might do 550 x .95 = 523W. At 240V that's 2.1 amps. At 120V it's 4.2 amps. So, plugging that into a calculator that 12 gauge wire is a 1.6% or 6.6% loss depending on voltage. I don't believe either is a safety concern with your current setup.

While a grid-tied inverter will make up the voltage loss, the higher the voltage drop the hotter the wire gets. AFAIK NEC doesn't actually care about voltage drop, but local inspectors might not like anything over 5%. YMMV.

For 1500W at 600' at 120V this calculator recommends 3 AWG for a 3% loss and 4 AWG for a 5% loss.

With only five 100 W panels, the maximum DC voltage is probably under 100V, so smart of the previous owner to use the higher voltage by having the inverters close to the panels. If you end up putting another ten similar panels (e.g., 1500W) and put them all in series you might get up to around 270V. So not much savings in moving the inverters to the house if they're operating at 240V.

 

[BubbaDX]

I have no input on your solar, but I really like the lighted driveway. I might do that myself. My driveway is about 1/4 mile long and when I have company coming over it would be nice to light up the driveway for them.

 

[dmharvey79]

Just a quick follow-up on what is currently installed after I got a chance to go check things out closer.


Panels:

• 2x RICH, RS-P100 (polycrystalline) (https://richsolar.com/products/100-watt-solar-panel-poly)
• 3x Mighty Max, MLS-100WM (monocrystalline) (https://www.mightymaxbattery.com/p3...mono-off-grid-battery-charger-for-trucks.html)

Inverters:

• 2x SoyoSource, 500w-GTI48 micro inverters (one tied to each of brand panel above) (https://www.amazon.com/-/es/Red-Tie-Inverter-Solar-PV/dp/B075FNGG3C)

Micro inverters are plugged into an outlet on line that runs along the driveway. Everything seems to be in good working order, as best I can tell.

Thanks for the compliments on the lights along the driveway. They are hooked to a Kasa switch and set to turn on for a couple of hours at sunset each evening. The previous owner completely remodeled the home before we purchased and he added a lot of cool little things like that in the process...Kasa switches on various things, hardwired POE cameras around the property, mesh access points covering about 5 acres of the property, etc. He was also very into energy conservation and installed a mini-split system for HVAC, which we really like so far. Based on everything he did I'm wondering if he went with a DC well pump, since the pump was replaced as part of the remodel. I kind of feel obligated to run with this solar thing after all of his efforts, haha.

 

[dmharvey79]

Thinking about just bumping up panels to 5 of each and calling it a day for this existing setup. Then focus on more of an off-grid / backup setup closer to the house...starting with something to power a portion of the kitchen / living room and maybe a similar setup to power the well pump and possibly the water heater. I assume this will be the best general approach to reach my overall goals.

 

[dmharvey79]

Here is a response I got from the previous owner. Any thoughts?

Since those are grid tie inverters your best bet is to get a good rack of batteries and an active inverter at a disconnect in front of the panel as those grid ties only work when they see power on the line. That way when you are down without power you can power the entire house off the batteries and generator depending on your power needs. To do it legally and right I'd yank the meter from the socket so you can install a double throw switch and select your source. Check out some of the 220volt inverter/chargers online. You can easily run a house off this with this guy as the mini split is a soft start. https://www.amazon.com/Inverter-Charger-120Vac-Output-Listed/dp/B07MVNL2RD
The only thing I'd do is to get a soft start controller for the well pump as it's like 60+ amps inrush when it first kicks in then drops to 15/20amps. That inrush might not play well with the inverter with lots of other loads on.

I might have a pallet of very high end SLA batteries I can get my hands on for you for 1/10th of what they cost new. They came from a UPS unit with life critical ratings that sat on a shelf and since it's a hospital install they are swapped every 2 years. They are less than 2 years old from what I know. Those together in a parallel 48 volt strings could yield you multi day power with no maintenance needed.

 

[svetz]

...Any thoughts?...

• AC Coupling, Incrementally Adding AC Batteries
• SLAs aren't as bad as FLAs, but make sure you know about them particularly DoD and Temp effects (see Battery FAQ)
• Think about a DC pump if you want it to run when the grid is down, less inverter no conversion losses
• Take a look at the lower power appliances to reduce battery costs for grid outages.
• Is it lunch time yet? I wonder if my wife left the downstairs fan on? What's the best PCM? Do you need Al in the mix, or just ions? .....

 

[Shwetaa]

Thanks for all the information. It is a very helpful thread!