question

The multiple MPPT unit sizes you suggested should work fine with a 12v system - they will just do their own thing independent of each other since there is no ability to sync them yet (but it's coming).

If you went 24v you could downsize your MPPT units & use thinner cable all round.

The only downside will be that only 2x12v panels in series may mean later wake up time in the morning & earlier shut down time in the evening (since PV voltage needs to be above battery voltage by 5V to wake up).

Regarding monitoring, I would just get the Smart Solar version's of the MPPT which have inbuilt Bluetooth. Otherwise yes you need a separate MPPT display for each unit or a Venus device.

As you did not identify what type of vessel I presume a monohull but this may not be accurate given that you want solar on the deck. We have a sailing catamaran so also 'limited' real-estate but not so limited as a monohull . There are differences between our technologies (rigid vs flexible) so I provide the following with the intention that some of the 'input' may be of assistance.

We had 3 x flexible (all same size and voltage) but one developed a fault. Once down and 'integrated' into the hull/deck this is not a trivial matter. In doing the assessment for a replacement (cost, performance, etc.) we soon saw differentiators and easily elected for 'performance' (noting that we had the real-estate) and selected 3 x 63 volt hard panels feeding into a single Blue Solar MPPT 150-60Tr. The 'flexible' units did not give the same 'value-for-money' which was the reason for getting solar in the first place and it was important to stay with one technology on the same voltage into only 1 x MPPT.

The higher the voltage the better and 63 volt panels means less transmission loss in the cabling back to the MPPT which means more power to battery and also allows for much thinner cabling (vs same loss) as Mark indicates above (weight and cost). I believe that you should be conservative in your sizing and to be very conservative in your wire sizing (bigger rather than smaller). You want to harvest as much solar energy as possible not to just loose it in heat (cable size/resistance). It is important to have the MPPT adjacent to the battery bank for cable sizing and temperature etc. We were charging a 12 volt AGM/900 AH bank. From a voltage perspective 63 volts does not pose an electrical hazard on the vessel and as I understand it anything less than, say 120V, is not considered hazardous in this way.

We made lots of calculations of 'solar angle etc' and actually have 'skewed' panels but in the end it has shown that the sailing configuration easily skews/destroys all this planning (for better and for worse).

Wiring. Each panel has its own circuit breaker next to the MPPT, so we can 'isolate' that panel easily to make an assessment on each panels performance (using Victron Connect app) noting that this was only in the beginning and have never bothered for the last year. Two reasons for this; the 'details' are interesting for a while but in the end it is; long term performance statistics that matter more.

Performance at various latitudes (similar to seasonal change) altered the yield somewhat but not so much as our sailing angle/tack to the sun on the day. Getting high performance panels meant that even then we were getting some energy. My KPI (key performance indicator) was 'is the solar contributing significantly or not to the management of my battery bank? The system performed fantastically with hours and hours of 'float' experienced daily. AGM needs hours of float to 'fully' charge and this was achieved. There are a few exceptions times, and mostly related to longer periods of poor weather and high sailing demand (lots of heavy winch work) where we had no or little float time. The qualitative statements I make were achieved in latitudes around Townsville (AU) in the north all the way down to southern Tasmania (Feb-Apr) in south.

Cable runs/voltage drop (loss). Our boat has some long cable runs with large loads (motors) on the ends (bilge, sewerage pump-out, electric toilets, anchor windlass and two x 57 electric sail winches (24 V - 300A jobs). In the end it was the peak power and voltage drops that convinced us to modify our setup and actually today we are installing a new primary house system of 24 V 200AH LiFePo4 (smart)). There are many reasons but the existing cabling can stay (economics) and we will have less voltage drop (efficiency) to all those consumers (actually 25.6 V not 12.2) as we find that particularly our fridges and freezers etc need as high a voltage as possible. The new capacity is currently 2 x 200 AH (400 AH @ 24 V (actually around 25.6 V) and a relatively 'huge' current capacity when compared to AGM.

Note that we deliberately wanted our AGM to stay within 100% - 60% DoD (life) and no higher than 70 Amp current draw for any longish period (say more than 2 minutes) (also life of battery). To that end I believe we are conservative and looking at the statistics with 900AH and normally > 90% DoD we are 'over' sized for our 12 V loads. We 'watch' our switches and turn off when not in use.

Looking back it has not been a simple or predictable learning curve. Initially I wanted absolute and infinite detail but in the end with data that varies significantly from minute to minute and day to day (solar yield on a sailing vessel) then I've moved to overall performance vs vessel consumer (Load) budget which is was what really matters for my decisions.

Monitoring and data. All parameters, including alarms, are logged by the MPPT for up to 30 days. Connected via BT these are able to be viewed (graph) or downloaded (BT) to MACBook for analysis and integration into a comprehensive solar log (spreadsheet). We have done this since 2016.

Recommend you be VERY clear on what you want to achieve operationally. This is then likely to make it much easier to determine what you need (technology) from a single screen, vs messing around etc.). If it is a 'pretty' picture you want then you can get this in a number of ways but will require some 'tech' to integrate this. I can get both with the above configuration (noting that I only have one technology and voltage for my all 3 x panels - deliberately.

We elected not to include wind generation as their performance over time did not yield value for money. Noting that we have the real estate for the 1kW solar and made the assessment at the same time as looking for the replacement solar 'solution'. It would be even less desirable as a retrofit now.

The 'facts' as collected from the solar panel combined with a focussed look at the 'consumer load profile' (in detail but then just 'averaged' over a quarter (by season) meant that I have now marginally 'downsized' the main bank (900 AH/12 volt vs 400 AH/24 volt). We want 95% - 60 (or 50)% DoD for the LiPo as the 'planned' usage cycle. The MPPT we matched (upsized) for the higher charging capacity of LiPo and limited by the existing solar array capability. For the AGM technology the 150-60Tr with dongle or new 'smart' version with built-in is well matched in my opinion because of the lower charging currents and longer charge cycles of AGM do not utilise a higher charge capability (bulk period aside). We have gone with all Victron (Venus, 5KvA Multi, VE.Bus BMS, MPPT, etc.). Time will tell how well we have engineered this.

We found that small to medium loads over time have much greater impact on capacity than large loads intermittently (main sailing winches a big exception).

Re DC-DC converter or 12 V AGM bank with charger. Noting that we still have 2 x engine start, 1 x generator start and a dive compressor (12V motor/battery) and we want to retain them in their 12 V 'OEM configuration' for the moment (Warranty, mission safety, maintenance) therefore we elected to keep a small 12V AGM (House 2) for these consumers. There is also much new 12 V LED lighting which is not economical to change along with a couple of instruments (VHF), computer charging etc.

So to keep the 12 volt / 200AH AGM (house 2) charged (with VSR to other 12VDC batt) we have a 12 V charger (also Victron) which is connected as an AC load on the Multi. Our large fridge and seperate freezer work much better (efficiently) on 24 VDC (12-32 volt input).

You make no mention of AC (230 V) on your boat so this may not be relevant but we have quite a few consumers (microwave, aircon, water maker etc.) so distributing AC was much easier and effective than DC-DC. We also considered that over time DC-DC did not give me a level of comfort in properly managing the charging cycle for AGM batteries compared to a smart Victron charger (multi profiles etc.).

Re technology; In summary at the 'system' level I believe we have 'better' efficiency on the charge side with high voltage panels into an MPPT (most can handling up to 70 VDC) as it also is a 'smart' charger in its own right and one 24 V on the distribution side (noting capital equipment purchases aside). All our 'sailing' electronics, except the VHF, are multi-12 or 24 volt so no cost there. All lighting on the boat can only handle (circa) 14 volt.

Effort vs reward. I believe your concern about 'messing around' with BT somewhat depends on whether you want 'instant' answers with no history (< 30 days history) or want to log and built up a comprehensive picture over a longer period. I set up BT with the MPPT once only at the beginning (once each of 2 x iPhone, 1 x iPad and 1 x MacBook) some years ago. Once the pairing was done no more action required - ever (unless you change phone e.g). Not a lot of 'messing around'. I then simply 'tap/boot' the application (Victron Connect) and selected the MPPT or other 'device'. It connects very quickly I look at the last 30 days yield with alarms and / or down load the csv file (to MacBook or PC) and then 'mess around' to my hearts content so that I can get a great overall understanding of how the 'solar' is performing over months or years and also over latitude.

Re 'single' display. You will get a single display (e.g. one x iPhone or Android) from anywhere on the boat but not a single 'graph' simultaneously for all three panels if following the above. Are you looking to 'compare' seperate panel yields at the same 'instance'? We find it is always different and dynamic (moving quickly and sometimes significantly) in any case when on a sailing boat depending on sails up/ down, angle, weather, clouds etc (Ps and we do not heel) so we no longer are interested in that comparison. I found that the overall 'combined' yield was what I now use operationally and even really now it is the battery State of Charge (SOC) and looking at the weather forecast that really is my decision input not the solar yield at the end of a day. The combined solar yield over time has however importantly given me a solid understanding (facts) into how to properly 'size' (total Ah) the new House (LiFePo4) battery bank because my operational configuration over time (years) is not going to change much from what it has been over the last few years (averaged). Therefore perhaps it is a matter of the level of comfort or discomfort you have with your 'current knowledge' of your vessel usage (total consumption over a year or so then averaged by (say) season or general latitude. No guidance there just a hint that what you want now may change when you get it.

Overall battery management. We use a VenusGX but a Colour Control GX or a BMV712 would monitor this easily and give you input for the 'graphic' output as well. I have had mixed results from 'experts' and as I have an electrical / avionics background I was willing and able to enter the debat and suggest you work hard to get a 'trusted' advisor this being one who does not have an interest in the outcome. - in summary every human has their reason for behaving as they do - not necessarily based on facts. If there is anything you disagree with above; good at least you can go ask a pointed question and make your own conclusion. Best of luck and hope this helps a little.

Thank you guys for the advise. Sounds like two 100/50s and a 100/20 will do the job. After reading a bit more about the products I'm inclined to get a VenusGX plus a BMV712. Michael is of course spot on in saying that once the system is bedded in there should be little need in constantly checking individual dials. Battery state is another matter though, so that's where the battery monitor will be handy.

Michael, thanks heaps for your detailed reply. We have a 38' mono, currently based in Melbourne, but hoping to go north soon. "Deck" was just meant generic. We have the panels mounted on a dodger (2x100), bimini (2x250) and 4x160s are rail mounted on a pushpit.