Tell me about your solar


#1

I am curious about a few things. How large is your solar system in kw, grid tie, hybrid, off-grid, battery back-up, generator assist? Just curious what people are using. I have yet to get into that game, but it seems to be on the horizon for me.


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#2

The best place to start is getting a handle on your usage and you have started that with Sense. The next stop is to use PVWATTS calculator to enter your address and get an understanding on how much production you will get based on the size, angle and direction (azimuth) of your array. Call your utility company and find out if they offer net metering. Net metering varies from state to state but on average it means that the utility company will pay the same or near price for the electricity you sell as what you purchase. The national average is some where around 11 cents per kWh. A grid-tied system is easiest if you have net metering. There are many who say net metering will never go away. I am not one of those people. Partly because I don’t have it now. In fact 1-in-4 in the US does not have access to net metering.

That brings you to what type of inverter to consider. Micro inverter or string (central inverter). Micro inverters are great for DIY and are efficient. Micro inverters like Enphase are sold independent to the panels, while others like Sunpower are integrated onto the panel. Micro inverters, at this time don’t integrate well with batteries. It can be done with AC coupling but that is expensive. Battery intergration is the one advantage for central inverters. If you go central inverter consider a company like SolarEdge that offer optimizers for each panel. A central inverter is only as good as the weakest panel without them. If a cloud covers a panel, or shade tree, all will affect the output. Calculate that over 25-year warranty of the panels and it adds up. For this reason, I would not consider any system that does not have the ability to optimize each panel. Now that optimizers are available, you have valid choices.

Panels come in monocrystalline or polycrystalline. Mono is more efficient and generally lasts longer. You can tell visually which one you are addressing by the white squares separating the cells. The mono cell is cut from an ingot of silicone. They have not learned how to grow a sqaure ingot yet, thus the white voids on a monocrystaline panel. The warranty are generally better and linear like guaranteeing 97% for the first year with a .5-1% degrade over 25 years. Cheaper panels guarantee only 90% of the sticker out of the box for 10 years typically and 20% over the remaining 15 years. They vary but this gives you something to look at.

Battery storage is coming. Tesla offers a 14kWh system , Powerwall2, for around $6,000. Used EV battery will start to appear in another decade. Then there is vehicle to grid (V2G). Currently those of us who own an electric vehicle (EV), have been against V2G due to the cycling of the battery. The battery will be your weak link with generally only 10 year warranty. Cycling the battery in your EV will shorten its life. That has been the current knowledge, but studies are showing that controlled cycling could minimize this. I just ordered my Tesla Model 3 to go with my Chevy Volt. The Volt uses 10kWh. The Tesla 80kWh. Now we drive less than 10,000 miles per year so I am glad that Tesla is once again considering V2G. For you, just decide if any of that matters to you. If you have net metering now, no need to consider a battery, but it might influence your choice of inverter. Net metering laws are in flux. Your system will last 25 years. I feel strongly that the net metering rules you start with will not be the same through out the life of your system.

Now, this sounds nuts but you need to buy monitoring software for your array. It is generally around $500 and updates around 15-20 minutes. Sense is near real-time so why do you need it? The inverter monitoring will let you know if you lose a panel or inverter/optimizer. I have lost three micro inverters in 8 years. I used to check mine regularly. Now I set it up to tell me when one goes bad.

The Sense solar option works via an additional set of CT clamps so it is flawless. That is well spent $50. Think of solar usage in “thirds”. You use a third, buy a third, and sell a third. This is an approximation but helps see usage. You buy at night and on cloudy days. You use some for you always on as Sense teaches you, and you sell a lot when the sun is shining brightly as you see with the big yellow bubble displayed throughout this forum. Sense does a fantastic job of showing how much solar you actually generate on cloudy days. We generally make enough for our always on and then some on cloudy days.

This brings to another question of whether you have time of use (TOU) charges in your area. TOU and net metering, or the lack there of will determine how you use your solar energy. People with net metering and without TOU generally do not care. Those with TOU and/or without net-metering use the Sense tools to alter some of there usage patterns.

Are you planning a roof mount or ground mount? Roof mounts cost less. Ground mounts generally give you the flexibility of improving your azimuth direction. You generally need the ground mount to be within 300 ft of your power meter to minimize voltage drop. The further the distance the larger the wire. No 2 AWG commonly referred to as mobile home feed will easily let you make 300 ft for less than $100. Roof mounting generally requires an engineering stamp that your rafters can withstand the extra weight. House plans will have this. Older homes may require that cost. Ground mounts require similar engineering approval. Purchased racking will include this. I made my own by recycling ironically galvanized C channel from electrical power towers that were taken down.

If you do choose to DIY, you still will need a certified electrician, and the engineering drawings for your roof load or ground mounts as mentioned above. You will have to file with your state utilities commission. That sounds complicated but is easier than you think. You have to file with your utility company to get a new bidirectional meter. Hope this helps get started in your research.


#3

Thanks for taking the time to put this detail into this response. Much appreciated.


#4

Monitoring is why you need to have micro-inverters (unless a string inverter provides a similar function) of each panel. For a string inverter, unless you lose the whole string (sometimes you do, sometimes not, because of bypass diodes), you can’t tell that a panel is bad. If your micro-inverters does not have software to allow you to view individual panel monitoring, if you have a problem, you will never know (in most cases).

Let me give you 2 examples from my SunPower with AC panels (essentially a panel with their own microinverter).

Case 1: A bad panel puts out power till it reaches 50 watts and stays at that point til the power drops below 50 watts. They never picked it up, but I did because I noticed 1 panel not putting out a lot of power when all the others adjacent to it were.

Case 2: A bad panel is some how sending data back to the monitor box (via data on the AC lines - kind of like a powerline sends internet over AC lines) such that every time it exceeds 30 watts, it jams up the entire monitoring, such that no panel can report. The power was in fact being generated and credited with my net metering (It uses a Solar-log power meter to measure the actual total PV power generated), but the monitoring was essentially disabled for all the panels. Covering that one panel with cardboard allowed the monitoring for all the other panels to work.

While properly written software of a solar company could have recognized the failures before me, apparently, they don’t. So you must be somewhat vigilant in terms of checking your arrays for proper operation at times.

And I might point out that when a micro-inverter panel goes bad, it doesn’t take down the rest of the array. This means that even if the solar company goes out of business years down the road, the rest of the array will still operate even with some failures.


#5

Excited to watch this thread, despite being a lowly apartment dweller who can’t have solar :cry:


#6

The best thing you can do is keep your eye on “community solar”. This one requires no government subsidies but it does require interaction. There will be a whole suite of choices for people who live in apartments and condos from leasing, to ownership of your own panels in a large array that doesn’t even need to be close to your dwelling. Imagine acres of solar panels with yours existing the 20th row for example. In this example, your solar usage can go with you even when you move. Stay on your government representatives to offer you community solar.

On a bit of a tangent but related. What about apartment and condo dwellers who do not have access to a charger for an electric vehicle (EV). No worries in 5-10 years you will be able to exit your vehicle and send it to a remote charging area on its own, then have it return to your designated parking spot. An apartment complex could group several fairly inexpensive Level 2 chargers in a convenient electrical supply area and have cars charge in that area. Most likely this will be wireless charging. The basics for this capability exists today and can be added to say a Chevy Volt or LEAF for under $1,800. Now the car only needs the ability to center itself. A highway full of autonomous EVs? We are probably 10-20 years out on that one. Ownership of solar and EVs for apartment dwellers? Inside of 5 years. And the manager can see it all with a Sense monitor!


#7

Great write up.

11 cents?!? I wish but then again everything is expensive in CA.

TOU: In CA it’s a ‘thing’ but when you do the actual math it doesn’t amount to too much. PGE charges 7.5 cents/kWh more between 3-8 pm and pays that much more for solar. Assume you had a toaster that used 1kW every hour and waited until after peak time but still used it for 5 hours you’d have saved $7.50 at the end of a month (peak rates only M-F). The best way to save is to just use less.


#8

Agree with you on that one… The thing I’ve discovered in CA/PG&E-land is that generation (the actual price you pay for energy) is just a relatively small piece of the full price per kWh. Distribution and generation add up to more than the actual generation costs with a typical rate schedule. But Net Metering WITH SOLAR plus TOU can make a big difference in my mind. The biggest savings is that Net Metering takes all the kWh charges for the energy you produce on your own, off the top, as long as you are not producing a surplus (then you only get the wholesale price back). TOU helps even more, if you do time-shiftable things like EV-charging, by giving you peak credit for your solar production, while letting you charge at a cheaper rate. Once again, this benefit is dependent on not overproducing, generating more than you use during a TOU period. As long as you are offsetting your own usage with solar, and not pumping to the grid on a monthly and TOU basis, you’ll do OK with solar in PG&E territory.

Chart below gives basic Non-TOU vs TOU tariffs, but does NOT include the tiering costs… That’s a whole different table and level of explanation.


#9

As they say, “As California goes, so goes the country and the world.” IMO, TOU will take off more so in the future when solar production increases. I personally think that net metering will exist only for those who have four-hour storage and give control of their storage to the utility company. Now that is a huge armchair call. Time will tell. I am only talking about four-hour storage mind you, just enough to do ones part to eliminate the duck curve or peak load if you will. Peak load is where the real cost is. On that thought, I would be very curious kevin1 and willowdog on your thoughts about directing a new user on what type of inverter to choose? As discussed above, I only want a string inverter that is equipped with optimizers. I am pretty set on that, but am open to micro inverters that are built in or stand alone. Micro inverters are what I have currently. It is really hard to look into the future and know how utilites adapt toward battery storage. AC coupling is expensive and AFAIK, the only way to add storage to a micro inverter. I am for the first time really starting to consider V2G whether it be my only storage or combined with a powerwall. Keep in mind I only get wholesale pricing of 4.5 cents for what I put back on the grid and have no TOU. I had planned on getting a standard battery in the Model 3 but went ahead and got the extended battery with the forced premium package in order to take advantage of the credits. Tesla doesn’t support V2G at this time, but if I used a software controlled 10kWh daily combined with my 10kWh of daily driving, I don’t think I would shorten the life. Again 4.5 cents/kWh just makes you mad. But for the good of this thread, penny for your thoughts on inverters and storage.


#10

Hey Kevin,

Not sure I understand. During the summer I do produce excess that I ‘use’ during the winter. The $7.50 I mentioned was specifically generating excess during peak time and then using it later in the day; like not charging an EV from 3-8pm; that said PGE has a separate EV plan. I settle up with PGE annually and always hope to pay them a little as you’re correct, wholesale prices I’d get back are really low. I generate about 10kW max (summer) from 3-8pm and I can shift very little to outside this window so I do get some savings but it’s not much in the grand scheme of things. It looks better on paper.

Bruce


#11

Love the info on optimizes and micro inverters. I am in the research phase right now. I am soon building an extra garage on my property for a tractor and to store some ATVS, etc and it would be nice to get the fuel out of my main garage. I have been looking at doing a hybrid solution and grab some batteries as well. I have a generator for my critical loads right now, but with something like a Schneider Conext XW+ I can do dc coupling and charge my batteries with solar, and augment with generator if needed. I want to explore all options before I dive it. I like to make educated decisions, so keep the info coming. I do appreciate it. Even if it is along the lines of, ‘this is what I did and this is what I should have done’. Or this is what I did wrong. I am hearing pros and cons to micro inverters, so I want real life feedback.


#12

@markhovis73,
Not sure about which panel/inverter technology I would select, but if I had solar and 1 or more EVs (which I do), and no NEMS/TOU, I would initially try to figure out how to charge 1 car slowly during the day to use up every joule of generated energy coming from solar, probably using a smart charger. And if that was impossible, then I probably would look at battery solutions to make sure every joule I generated stayed with me. But that’s kind of based on my understanding of PG&E tariff structure.


#13

Sorry Bruce,
I was basing my comments on comparisons between the traditional tiered PG&E NEMS E-1 plan and my EV-A non-tiered TOU plan. With the EV-A TOU plan, there’s a 22c per kWh differential between Summer peak and Summer off-peak. And Summer off-peak is 11c/kWh cheaper than E-1 even before tiering. That’s a significant difference when you talk about a 50KWh charging cycle every few days. It’s hard to calculate exact numbers, but my Dec. true-up used to run about $5K prior to TOU and now runs about $2K. Much easier to pay.


#14

I am in this scenario and I do use a smart charger to slow charge. I would highly recommend this approach. Such units can be had for a couple hundred dollars more than a standard charger. For the first five years of my installation, I was paid an additional .15 cents from an aggregator NC Green, meaning my solar power was worth double, so I had five years of operating like you and selling as much solar generation as possible. That has radically flipped now with only being paid wholesale for my energy.

I feel that one would want to have access to battery storage in the future. Jason mentioned the use of a generator. I feel that EVs can take this role in the future with V2G. It is a fine line in not shortening the life of your EV battery. That is the worst thing one could do. It all depends on how it is being used thus my question about the choice of inverters. I am still on a waiting list for the Tesla Powerwall 2. I talked to Tesla directly and told them that I was using micro inverters and that I was willing to replace one of my branch circuits with a central inverter if that was possible. Their response was to sit tight they were working on a solution.

So in planning a new array, IMO, it still comes down to whether you think net metering will outlive your array thus impacting whether you add a stand-alone battery or V2G hence affecting your choice of inverter.


#15

We bought our house with the system already installed, so I can’t speak to the design or decision process.

We’ve got an 18-panel PV system with a 5.2kW inverter. The inverter feeds a breaker on a subpanel which also has a generator input plug (L15-30, I think - it’s a locking, 4-wire plug for 240V). The subpanel is connected to a 100A breaker on the main panel.

The subpanel has the critical services on it (furnace, refrigerator, TV :slight_smile:), and has a linked pair of breakers that switch its feed from the main panel to the generator. This allows us to completely disconnect from the grid in the event of a power outage and use both generator and solar to run those critical services.

It’s a pretty elegant setup, if you ask me. But I certainly didn’t design it!


#16

My System
I have 39 panels of Sunpower 345 watt AC panels (The AC panels are just their 345 watt panels with their microinverter). My panels average about 13 megawatts-hours per year, which means about 916 watts-hours per day per panel average in the Boston, MA metropolitan area.

This 13 megawatts provides enough power (with extra) to supply my entire household including running about 60% of the miles of my Chevrolet Volt.

3 of my panels face south, 18 east, and 18 west. Surprisingly to me, each panel pretty much averages the same total power each day. My system is grid tied, which is generally best at this time. Batteries (or other storage methods) are a solution for the future. With a panel transfer switch, I can change to a 8000 watt generator, although there was only 1 time in 30 years that I would have required it and that was for a transformer outage of 4 days.

Because their microinverter maxes out at 320 watts, that is the maximum I can ever get out of one panel. The time any panel stays above 320 watts is relatively short, so it doesn’t cost a lot of generated watts. This is also what studies that Enphase has said for their 250 watt microinverters, that using panels up to 300 watts does not lose a lot of potential watts. Using 345 watt panels instead of smaller ones maximizes my total generation under 320 watts despite losing some power between 320 and 345 watts. Also, it gives more headroom for panel degradation over time.

Single-Point-Of-Failures
I had looked at power optimizers, essentially microinverters that standardize the DC voltage for the panels, then feeds the DC voltage to a string inverter. While this eliminates any individual panel causing a problem for other panels from a string system, it still requires a central (string) inverter to do the conversion to AC. This central inverter is a single point of failure (SPOF) in the system, so if that fails (and their lifetimes are typically 10 years), you lose the whole system. This is why I suggest people use microinverters. Solar companies hate them (power optimizers too), because any failure in them requires a roof visit, and a lot more work. But from the consumer point-of-view, they are much better.

Grid-Tie
Grid tie helps even out usage locally, so that means less power flowing through transformers when everyone’s AC’s are blasting in the summer. This means that their equipment lasts longer for the utilities (not that you’ll ever see that money back), and helps lower their peak loads. Nevertheless, the utilities still must be able to handle the base load for the night time and during area wide inclement weather.

If you want to have backup power for outages, you need either batteries or a generator along with a manual or automatic transfer switch. Batteries will need to be charged by the AC power, and convert the power back to AC when utilized.

Off Grid
If you go totally off grid, you may find a need for as much as 2 weeks of backup power for bad weather, so that’s a lot of batteries or generator fuel.

Reroofing
If you intend on replacing your shingles on your roof before solar installation, and are in an area that ice dams occur (and even if they don’t), I highly suggest you put a premium full ice and water shield like Grace’s on your entire roof (normally they only do the lower 6 feet and valleys in the roof). This sticky rubber membrane will prevent leaks in your roof from almost any penetration like roof nails or Solar support structures, as it tends to reseal around the penetration, eliminating leak potentials.


#17

6.38KW system with string optimizer and SolarEdge inverter here. Just a couple observations:

You can’t really have a generator and solar running at the same time (not without some complicated wiring setups). Your inverter bumps up the voltage to push the power into your electrical panel. If you have a generator in the same panel, it’s doing the same thing. They end up fighting each other and somethings gotta give and you’re going to let your smoke out.

Net metering at retail rates CANNOT last. You might get grandfathered in, so you might get it forever, but the utility companies can’t buy power from you at 11 cents and sell it back to you at 11 cents for everyone. As solar power grows, the end of net metering approached.


#18

Thanks for the details. In the scenario I described, the grid and the generator are AC inputs. Generator only used to augment battery if grid down and solar production is low or if grid down and batteries need to be charged. It’s like a tertiary or quaternary power source.


#19

I always wanted to use quaternary in a sentence. Thanks everyone for helping me reach a life goal.


#20

3.4kw due to roof limitations. Canadian Solar panels, solaredge inverter & panel optomizers. Grid tied net metering. Ultility FirstEnergy asks that system not exceed 90% of previous years usage. No battery backup. We also have Nissan Leaf with level2 charging. Our electric bill has gone from about $100/month to between $2 and $21 per month. This includes charging the leaf and driving about 800 miles month. Installed net cost after rebate was $7,800