newbie solar considerations

[glstrich6]

Hello, I am new to the forum and looking for guidance on a solar system. Let me start with some background. I live in southern Portugal, there is lots of sun (4,6 hrs/day according to this) so my expectation was that installing solar in addition to existing grid access would be a no-brainer. Walked into a dealership and got quote for a 6kW (likely oversized) system with lithium batteries /without batteries for 16k€ / 11k€ respectively. Based on my back-of-the-envelope math it would take ~30 years to get the investment back (assumptions below).
My initial reaction was to forget the idea and continue using the grid. Portugal has a high share of renewables in the grid and the prices are ok compared to other EU countries. After a few days, I am hoping that DYI might get me to a more economically viable approach (say break-even in 10-15 years), which brings me to this forum.

I am not going off grid, so I don't need to rely on solar. I would like to start with a small(-ish) system, which would allow me to run a few devices (water heater, washing machine, electric oven) on solar during the day. I would like the system to work seamlessly with the grid: use solar as long it is available, otherwise use the grid. Feeding / selling energy into the grid is not important. I would like to have the option to add batteries and/or an electric vehicle in the future.
So my thinking is to start with a reasonable size hybrid inverter (4kW? so I am able to expand in future), a few panels (2-4 x 430W) and a small battery (if at all). I would "stretch" the use of solar over the day by allowing the water heater to run in the morning and running the washing machine in the afternoon.

How does that sound? Can you recommend a specific configuration?
How does a small battery vs. no battery impact the usable output?
Thanks for your help!
Gleb


(assumption: 3000 kWh yearly electricity use (15-20€ cent per grid kWh, 4€ cent/kWh earning for electricity supplied to the grid, 35% of electricity supplied in no battery configuration, 80% w. battery configuration)

 

[Bluedog225]

Welcome,

I love Portugal. I think you will save a lot with diy. From what I’ve seen, Portugal seems great for solar.

Others will be along with specific recommendations. Not sending power back to the grid will make this simpler.

Heating water with solar electric can be done but solar thermal is much more efficient. Similarly, running an electric stove can be done but uses a lot of juice.

If you translate all your needs/wants into watts, it is easier to gauge your project.

Starting with a small system and getting some experience is a great way to go.

There may be some restrictions on grid tie in Portugal (or some fees). Locals will know.

To get a general idea of how this would work, the Will Prowse YouTube videos are pretty good. Though I don’t recall if he has any grid tie info. Still a great overview.

One last thing, it’s best (least expensive) to make a plan before you buy stuff. Lots of new people buy individual components then find out they are not suitable.

All the best.

 

[Bluedog225]

Bump for the op.

 

[glstrich6]

I have a tendency to "no battery" and starting small. It looks like I a system up to 700W can be attached directly to the house circuit through a normal socket. The components are available for as little as 400€, which make amortization easy.
Say I want to start with 2x430W panels - does it make sense to get a 700W inverter or can I run them with a 3kW inverter, allowing for future addition of more panels?

 

[Bluedog225]

Not sure why this isn’t getting input from the people with more experience than me.

But, no. You don’t simply attach to the socket. I believe it’s a very bad idea. It back feeds the system.

Hoping someone will jump in here about a transfer switch.

 

[Hedges]

What do you pay per kWh to buy from the grid?

Grid tie PV may allow you to earn credit on your bill for backfeed, may even pay cash.
Zero-export (current transformer around wires from meter) is a way to operate possibly without involving the utility company although they may notice.

Some hybrids support zero export, and some are batteries optional. Batteries are the most expensive part, convenient to start small or none. Provide PV only or PV + battery backup for critical loads like communication. Backfeed to the house to shave consumption.

But only if your rates are high. It will cost $0.03 to $0.10/kWh to make your own power.

 

[SeaGal]

Not sure why this isn’t getting input from the people with more experience than me.

Just spotted this thread..

From my experience in UK, with much less sun but probably higher energy prices, is that payback is more like 4 years for DIY solution. I started (briefly) with no battery (due to supply issues) 2 years ago, but have battery for last 18 months and bigger inverter more recently.

My 2p worth is:-

I would like to start with a small(-ish) system, which would allow me to run a few devices (water heater, washing machine, electric oven) on solar during the day. I would like the system to work seamlessly with the grid: use solar as long it is available, otherwise use the grid. Feeding / selling energy into the grid is not important. I would like to have the option to add batteries and/or an electric vehicle in the future.

You say 'smallish', but those devices are high energy ones, heating things. Work out what the max instantaneous power you need is. In my case I started with a 3.6kW inverter, but now have a 6kW one (Solis S5-EH1P-6K). The 3.6kW worked fine, but couldn't power 2 heating devices (e.g. kettle and microwave, or oven and air-fryer) at the same time. The price difference between the two inverters was only about 100GBP so, with hindsight, should have been a no-brainer to go for the bigger one).

As for panels, you will need a minimum to generate enough voltage for the inverter to start up (120V in case of my Solis). Hence 4 panels will be marginal, so I'd aim for a min of 6 to start with, you can always add more later.

As for battery - it's easy to retrofit a battery pack or packs or build DIY pack as I did, provided you go with an inverter that uses the more common industry standard low voltage (48V-60V) system, rather than high-voltage ones which tend to be proprietary.

In the UK we have things called clouds... not sure whether you get them in Portugal ... but the battery is great for time-shifting the clouds out of the way - so you can (say) run a washing load and not worry about drawing from the grid when a cloud comes across. Also (obviously) a battery will be great for powering the house, cooking etc, after the sun has set. Typical estimates (in the UK) are that a battery will increase your solar usage from about 50% to 90% powering from the sun, rather than grid. If you have enough battery to power the house overnight, then with the sun you get in Portugal you should be self-sufficient for a lot of the year.

HTH.

 

[Hedges]

(assumption: 3000 kWh yearly electricity use (15-20€ cent per grid kWh, 4€ cent/kWh earning for electricity supplied to the grid, 35% of electricity supplied in no battery configuration, 80% w. battery configuration)

3000 x 0.2 = 600/year utility bill. Just 50/month? Do you use other energy sources like gas, coal, etc. or is weather mild enough you don't need heat? Even if you do, without good net metering rates you can't store summer production for winter.

At least in the US, DIY GT PV makes power for $0.03/kWh and turnkey installed $0.10/kWh, amortized over 20 years. (In Australia, they get it installed for what we pay in parts alone.) I would expect your costs to be similar to ours.

Your 0.04 credit for backfeed means no loss but no gain for DIY power you don't immediately use or store on-site. 60% loss if turnkey installed.
If you use a battery, assume 20% energy loss round trip so $0.03 --> $0.04 or $0.10 --> $0.12
Also, battery costs between $0.05 and $0.50/kWh over its cycle life. Minimal financial benefit.

I think solar is a poor investment for you, unless you use the power for A/C at the moment it is produced. In that case GT PV could be beneficial.

Build a small backup system if you like so communications gear stays up during power outages.

If you want to save money, create a Pareto chart of expenditures, consider which of the highest expenses you can tackle.
(Biggest bang for the buck may be eating healthier? And that likely doesn't show up on the chart yet.)



Consider what other investment, or enjoyment, you can put your time and money into.

 

[SeaGal]

Consider what other investment, or enjoyment, you can put your time and money into.

Oh gosh... I didn't realise there are more enjoyable things than DIY Solar!

 

[Hedges]

https://www.youtube.com/user/colinfurze/videos

 

[glstrich6]

thanks for all the helpful comments. Really appreciate different perspectives and critical feedback.

Consider what other investment, or enjoyment, you can put your time and money into.

agreed this is not going to be the best ROI nor the most meaningful contribution to the budget but I guess that's not the point. The point is to capture some of the sun energy as long as it is economically viable, get first hand experience with solar and enjoy the process. I am calculating a 8 year payback period, which is good enough for me.

In my case I started with a 3.6kW inverter, but now have a 6kW one (Solis S5-EH1P-6K). The 3.6kW worked fine, but couldn't power 2 heating devices (e.g. kettle and microwave, or oven and air-fryer) at the same time. The price difference between the two inverters was only about 100GBP so, with hindsight, should have been a no-brainer to go for the bigger one).

I like the idea of an oversized inverter for a marginal extra cost. Can I run a 4.6 kW inverter with say 2kW panels in the beginning and expand later?

As for battery - it's easy to retrofit a battery pack or packs or build DIY pack as I did, provided you go with an inverter that uses the more common industry standard low voltage (48V-60V) system, rather than high-voltage ones which tend to be proprietary.

I kind of got comfortable with the idea of using 30-50% for own consumption since the economics of batteries seemed unattractive (high cost, limited lifetime, unsure payback). The retrofit / DIY idea sounds intriguing, could you share more details / point me to some resources?

 

[Hedges]

I like the idea of an oversized inverter for a marginal extra cost. Can I run a 4.6 kW inverter with say 2kW panels in the beginning and expand later?

Pay attention to no-load consumption of inverter, PV production in winter, and battery capacity.

If the inverter only needs to be turned on a limited portion of the day, e.g. to do laundry, that can help.
Some have a standby mode where they wake up periodically to check for loads.
These approaches could let you start out smaller.

Or, pay a premium for higher quality lower no-load consumption inverter.

 

[sumpower]

Pay attention to no-load consumption of inverter, PV production in winter, and battery capacity.

If the inverter only needs to be turned on a limited portion of the day, e.g. to do laundry, that can help.
Some have a standby mode where they wake up periodically to check for loads.
These approaches could let you start out smaller.

Or, pay a premium for higher quality lower no-load consumption inverter.

Just helped a DIY guy, and looking at the specification on his inverters idle consumption told him where his battery usage was mysteriously going. His cheaper, but brand new inverter was using just a bit over 4kw/hour per day just by itself.
No-load inverter consumption seems to be a theme here, but worth repeating!

 

[Hedges]

Victron 5kVA, 96% efficient at full load, 20W no-load, 3.4W sleep.

https://www.victronenergy.com/upload/documents/Datasheet-Inverter-Smart-1600VA-5000VA-EN.pdf

SMA 5750W, 91% efficient at full load, 25W no-load, 4W standby.

https://files.sma.de/downloads/SI6048US-DS-en-28.pdf

https://files.sma.de/downloads/SI4548-6048-US-BE-en-21W.pdf (page 231)

If operated continuously at 100%, the efficiency difference would also be 4 kWh/day!
Most of us don't.


Those two would consume 500Wh to 600Wh per day.
Cost a few grand, but save money on batteries and are good quality.

 

[glstrich6]

Have been checking out inverters based on the input above and found some interesting deals for used equipment. For example a 13 year old SMA SB 4000TL-21 for 200-250€ (datasheet). Power loss in night mode is <1W. To me It seems a good option to get started at low cost. What do the experts think?

Few specific questions:
- My understanding is that to get started I will need panels, mounts, cables (DC,AC) and likely an electrician to connect to the grid. Anything I am missing?
- Voltage range is 125- 750V. Does this mean I can start with as little as 3 460Wp panels with 50V each (parallel)?
- What's the max number of 460Wp panels I can use with this inverter?
- What extra equipment will I need, if I wanted to add batteries at a later point?

thanks!
Gleb

 

[Hedges]

Sunny Boy is grid-tie photovoltaic, not hybrid.
Some newer models can do batteryless backup, don't think this one can.

It is possible (likely) your utility requires new grid stability support features not found on earlier models. That is the case in the US, where 3 or 4 years ago additional features were required. And some years before that, earlier changes. The old models get discontinued and replace with one that complies.

There can be additional features required by code, such as arc-fault. I don't see it listed on that data sheet, but the feature has been around quite a few years in the US.

If you also bought a Sunny island, together with that Sunny Boy you would have a PV/battery backup system (check their list of compatible inverters to be sure.) That's about what mine is. Sunny Boy takes lead-acid or lithium battery, and some (more expensive) brands have communication between their BMS and Sunny Island.

If you are allowed to use that inverter, cheap enough to be good to start with. You might later replace it with a hybrid rather than buying an expensive separate battery inverter. Some hybrids from China are quite cheap and take cheap batteries.

 

[SeaGal]

I like the idea of an oversized inverter for a marginal extra cost. Can I run a 4.6 kW inverter with say 2kW panels in the beginning and expand later?

Yes, provided you have enough panels for inverter start-up voltage and MPPT tracking in range of panel's output.

I kind of got comfortable with the idea of using 30-50% for own consumption since the economics of batteries seemed unattractive (high cost, limited lifetime, unsure payback). The retrofit / DIY idea sounds intriguing, could you share more details / point me to some resources?

For me the cost was reduced from DIY. But prices have dropped in the last 24 months, so either would have very good payback with UK energy supply rates (mine is about 3 to 4 years). you say "Limited lifetime" - hoping for at least 10 if not 15 years. By then I suspect there will be better technology available and they will have repaid for themselves 3x already.

Regarding 'retrofit' - all I meant was if you buy a hybrid inverter now, then you can add batteries in the future without any additional/wasted expense.

but brand new inverter was using just a bit over 4kw/hour per day just by itself

Did you mean 4kWh per day? My Solis hybrid inverter uses just 30W idle consumption.

Few specific questions:
- My understanding is that to get started I will need panels, mounts, cables (DC,AC) and likely an electrician to connect to the grid. Anything I am missing?

Fuses + isolation switches spring to mind.

- Voltage range is 125- 750V. Does this mean I can start with as little as 3 460Wp panels with 50V each (parallel)?

No. In parallel, current will increase but voltage remains the same. You will need to connect them in series. Even so, 50VoC panels are likely to only generate around 40V under load, depending on luminescence, so you will likely need minimum of 4 panels in series to get enough voltage.

- What's the max number of 460Wp panels I can use with this inverter?

Lookup the max inverter voltage. Then calculate max number of panels which, when you factor in their max voltage (VoC + factor in the temp coefficient), won't exceed the max inverter's voltage. That will give you max number of panels in series. You may be able to parallel panels too if the inverter handles twice the max current of the panels.

- What extra equipment will I need, if I wanted to add batteries at a later point?

Either a hybrid inverter or a separate AC-couple inverter and battery combo.

 

[glstrich6]

Thanks a lot! Looked at newer inverters incl. some hybrid models. Huawei SUN2000 seems well priced. Datasheet lists only one specific battery. How do I know if an inverter can also be used with othe (e.g. DIY) batteries?

 

[SeaGal]

How do I know if an inverter can also be used with othe (e.g. DIY) batteries?

that's because that inverter uses high-voltage battery in range 350-450V (as detailed in the spec sheet).

Most DIY batteries are in the range of 48-60V (16 cells at 3.2V nominal each) - so check for that and check to see what BMS protocols they support. An inverter that supports several different protocols should be suitable.

 

[frasere2]

you spend 500-600Eur/yr on electricity, why bother? If you must have solar, you do NOT need a 6kw system when using only 3000w/yr. Get a small growatt inverter, 6kw is more than you need. Normally I'd say get the 3kw version, but 6kw allows for future expansion and is about 700 Eur. Marginal difference for smaller inverters is not enough to justify buying just the smaller inverter. Buy 4kw of panels at 0.25/watt if you can. Should be doable in Europe. That's 1000eur. Now buy optimizers, 45 each. You will need PV wiring, but you can get that for 1.50eur/m, buy online for cheap. Same for connectors. MC4s are less than a 1Eur online. You didn't describe roof, so can't tell you what racking to use. With 4kw of panels, you will produce 200% of your needs, possibly 300% depending on weather. Even at 4c/kwh from utility, you will almost cover your entire bill (assuming 35% usage of solar, 65% sent to grid). Consider mounting some panels vertically toward the sun to extend time of use during day and during winter months. No batteries, too expensive for 600eur/yr, or add later. Your total equipment cost should be under .8Eur/watt (so less than 3200Eur). Just find a reasonable electrician for install. If you must do it cheaper, use fewer panels.