Back of napkin calc:
4 each 320w mono-crystalline solar panels wired in parallel to minimize shadowing loss from the mast etc. = 1280w total PV array. Each panel is individually current protected with a solar rated circuit breaker. As is the combined PV input to the Midnight Sun controller and the output from the controller is current protected to the battery bank. The battery bank output is current protected with Class-T high ampere fast acting fuse to the 3500w pure sine wave 12vdc-120vac inverter providing the 120vac hotel load.
The Midnight Solar MPPT Classic 150 solar controller produces 89 amps/hour of smart battery bank charging current if only between 0900 and 1500 hours each day in Panama (9° Latitude) (6 hrs x 89Ah = 534Ah@14.4vdc) into our eight (8) each model 8D lead-acid batteries = 2000Ah bank (requires only a 25-30% depth of discharge each day for extended deep-cycle battery life)
If we were to run the genset (using our IOTA 90A charger) for 6 hours we would burn over 5 gallons of diesel costing about $4.50/gallon x 5 gallons = $22.50/day x 30 days = $675/month.
The solar system out of pocket costs were about $3,800 not counting my labor for installation in Panama. The expensive part was air freight to source the best equipment (way less off the shelf in the USA) but the good news is it will be fully paid back in just 6 months while cruising back to home port this Spring. Then it is near FREE SOLAR ENERGY for the rest of the remaining 25 year solar panel life. Yes it is going to rain or be overcast more than 35% of the time in the northern latitudes but even then we expect to harvest between 225 to 300Ah@14.4vdc of solar energy a day. No matter how bad you want to paint the use of solar picture in 2014 - SOLAR REMAINS A BIG 25 YEAR WINNER!
Here is what we previously said - http://greygooseadventures.blogspot.com/2013/06/add-solar-or-not-year-of-solar-on-mv.html
Here we go again repeating information.... I hope you really get it - its a no brainer once you wrap your mind around it... FREE ENERGY FROM THE SUN - JUST MAKE THE INVESTMENT, GET THE RETURN ON INVESTMENT AND ENJOY THE FREE ENERGY FOR MANY YEARS AHEAD...
1. DUE DILIGENCE - before taking the plunge means taking the time to see what is actually out there and asking the right questions.
Ref: http://mvvikingstar.blogspot.com/2013/10/yearly-energy-usage-for-full-time.html
Yearly energy usage for a full time cruising boat - Viking Stars Energy report for the past 12 months.
It seems I get energetic in October. Today I was updating the cost spreadsheet, plugging in readings from the Hour meters and started wondering - Hum. How much energy did we use this last year? Well, looking over Viking Stars blog I have asked this question a cople of times before:
For the 12 months ending Oct 2012: mvVikingStar.blogspot.com/../update-to-viking-stars-energy-use-per
For the 12 months ending Oct 2012: mvVikingStar.blogspot.com/../update-to-viking-stars-energy-use-per
12 months ending Jan of 2011: mvVikingStar.blogspot.com/../viking-star-average-energy-usage
OK, so I have not been that consistent, nor fixed with October. But who knows, maybe with two in a row a trend is starting!
How much energy do we use in a year?
Lets review. Kristi and I use energy, just like most any person it the world does. But as we live in a very small house, do not have a car, and we use noticeably less energy than the average American. We are full time cruisers and spend from the end of February to the beginning of November 'Out There'. During those 8+ or so months we are fully dependent upon ourselves for energy production as well as, depending on how 'Far Out' we get, water production. During the core of the winter months we tend to come in and rent a transient slip, to get easy access to coffee shops and less-muddy trails.
Our source for Energy is primarily Diesel fuel, with a little Propane and Gasoline thrown in. And with that we move ourselves, heat our space and water, cook our food, generate our electricity, even make our drinking water as needed. And for the last couple of years we have supplement our electrical needs with two Solar panels (mvVikingStar.blogspot.com/search/label/Solar) When in port we try to use the shore power cord as much as possible because, truth be told, shore based energy is dramatically less expensive then on-board generation.
Over the past 12 months energy consumption on Viking Star has been:
- 500 Gallons (320g for the Mains, 50 in the Gen/WM, and 120 for the Hurricane heater, maybe 10 more for the Dickenson)
- 8 Gallons of Gasoline for the dinghy outboard motor
- 15 Gallons of Propane for the stove and BBQ
- 4,900KWh of Electricity while in port.
Running these all through conversions into a common energy measurement ( BTUs) the above comes to 88 Million BTUs for the two of us. A massive reduction from the prior years 116 MBTUs, continuing the downward trend from 140 MBTUs the year before that. What changed?
Biggest change is how we heat during the Winter. Up until last winter we had heated primarily with the Dickinson Diesel stove, a heater we still love for its warm dry heat. But it is NOT the most efficient, only because it tends to be an all-or-nothing heater. These days we rely on the Hurricane hydronic heater to warm the boat up in the morning, and let the electric space heaters take over and carry us throughout the day and into the evening. That is perhaps the biggest change. Solar helped some as well (See below)
Biggest change is how we heat during the Winter. Up until last winter we had heated primarily with the Dickinson Diesel stove, a heater we still love for its warm dry heat. But it is NOT the most efficient, only because it tends to be an all-or-nothing heater. These days we rely on the Hurricane hydronic heater to warm the boat up in the morning, and let the electric space heaters take over and carry us throughout the day and into the evening. That is perhaps the biggest change. Solar helped some as well (See below)
As with prior years calculations any rental car usage is not tracked; if we add say an extra 50 gallons of gas for the rental cars and buses we use, that adds another 6-7 MBUTs. Lets 'Round up' our yearly energy usage to 95 MBUTs for the two of us, or a little under 50 MBTUs each in direct energy consumption.
How does this stack up?
Going to be lazy here and just assume the average energy consumption per person has not changed that much from last year to this. Hence am reusing last years 'chart'. Converting the US Average of 98,418KWhs of energy consumption per person into BTUs we still get 336 MBTUs per-person.
336 MBTUs vs. 50 MBTUs. Yes, living the Small Life on Viking Star we use less then 1/6th the amount of energy an average US citizen does.
One Sixth...
In fact, we even use less energy than the average world-wide citizen does (at 72 MBTUs).
Living the Small Life on a Boat can be very very energy efficient, even if it is a 50 year old boat..
How much does it cost?
Doing a rough translation of the fuel used above (ala, using $4/gal for Diesel, etc.) I come to a yearly cost of around $2,500. Add in a couple hundred for Rental Car fuel, and we are at a yearly energy cost of around $2,700 .
Which points out a big truth about Energy on boats: We may use little, but what we use costs a LOT. Hence the real strong focus on energy savings, LED lighting, efficent refridguration, Solar / Wind generation.
So, how does this compare to the direct energy costs you see in a year? Electricity, Oil, Natural gas, Auto Gasoline, etc...
A note on the Solar Panels ROI
I added up the number of AHs produced over the past 12 months and it came to around 31,500Ahs of electricity produced. This translates into over 260 hours of time we did NOT need to run the generator. To date we have offset almost 45% of the cost of the solar installation by not running the generator, well on the way to achieving ROI in 4 years.
Energy. As a cruising boat, we know we use a lot more than others. Between space heating, movement, computers, refrigerator and freezer, we are kind of an energy pig. But I think looking at the lifestyle, it is clear we are comparatively but a wee-little one.
More to follow...
Solar Panels on the Boat - Modeling and Performance
One of the challenges I had while deciding about installing solar panels on Viking Star was getting an idea of what to expect. Asking around got a WIDE range of answers, from: “All I need”, to “Charges the batteries by 11am!”, to “Will not work at all in the rainy PNW”, to even “What a monumental waste of money solar is”. Needless to say - no consensus. More troubling was, without exception, none of the "inputs" were based on ACTUAL data. Even those who claimed ‘All I need’ were not able to tell me what their needs were – rendering their input useless to me.
I just could not go down a path blind. I needed SOME idea on what to expect. And so the old engineer in me emerged. Solar system output is really a factor of four things:
- Expected solar radiation from the sun (time of year, location, and cloud cover)
- Size and efficiency of panels and system
- Orientation of panels relative to the Sun
- Placement of the panels relative to obstructions (shading)
Solar Radiation: I located a local shore-based installation who had been tracking their results and who would send me their actual energy produced data. Using this I was able to extract the solar radiation per month in this location covering not only seasonal variations (Summer vs.Winter), but also average cloud cover over a year period.
Size and Efficiency of panels and System: This is easy. Viking Star has two 240w panels so a 480w system. Completing the system is the MPPT controller I selected which has a conversion efficiency of 95%. Need to throw in some additional losses for the wiring voltage drop.
Orientation relative to the Sun: Here is a point where installations on a boat differ greatly from shore-based ones. While most shore installations are pointed due south and tilted towards the Sun (often at a compromise angle between peak output for summer vs. winter) panels of a boat are often placed flat. (or some very small angle). Mounting flat is easiest. While using a more complex mounting system and being able to point the panels towards the Sun can give significant output gains – it also requires adjustments throughout the day as the Sun moves and as the boat swings around anchor. (Shore-based installations do not need to deal with this swinging - hence they often just use fixed tilt mounts pointing due south) I chose to mount Viking Star’s panels flat for two reasons: The panels are rather large - a tiltable mounting system would have to be very robust to securely handle them. Plus I am just lazy. I do not see myself climbing out several times a day ‘repositioning’ the panels as we swing around the anchor…
How much do we lose by mounting flat? That depends on the time of year, as well as the latitude of the boat. The actual formula is:
Loss% = 1 - SIN(90 – Latitude + Solar Declination + Panel Tilt)
(Yes, those Celestial navigation skills come into play!). Putting this all together we get for 48 North:
Sun Declination (Degrees)
|
Solar Elevation Angle (at 48N)
|
Loss due to
Flat Panels
| |
Jan
|
-22
|
20
|
66%
|
Feb
|
-13
|
29
|
52%
|
Mar
|
-3
|
39
|
37%
|
Apr
|
10
|
52
|
21%
|
May
|
18
|
60
|
13%
|
Jun
|
23
|
65
|
9%
|
Jul
|
21
|
63
|
11%
|
Aug
|
14
|
56
|
17%
|
Sep
|
3
|
45
|
29%
|
Oct
|
-8
|
34
|
44%
|
Nov
|
-18
|
24
|
59%
|
Dec
|
-23
|
19
|
67%
|
During peak cruising months (April – September) the loss is relatively small – 10-20%. But this quickly increases as we get into winter where 60-70% of the potential output is ’lost’ due to mounting the panels flat. Combined with the much shorter days means during the winter we can expect little output from the solar system. Happily those are also the months we tend to be in port with shore power readily available.
Combining this loss table with the observed Solar Radiation derived from the shore based installation's production data, I came up with the following modeled output for our system:
Ah/Day
(480w system)
|
Normalized (100W system)
| |
Jan
|
11
|
2
|
Feb
|
38
|
8
|
Mar
|
66
|
14
|
Apr
|
110
|
23
|
May
|
149
|
31
|
Jun
|
153
|
32
|
Jul
|
161
|
33
|
Aug
|
142
|
30
|
Sep
|
99
|
21
|
Oct
|
50
|
10
|
Nov
|
17
|
4
|
Dec
|
16
|
3
|
And here you can see the actual results so far:
We have been tracking ahead of the predicted performance, but then this summer was one for the records books (literally). Side note: Those BIG dips to 50 or below the 1st month are the result of not attaching the remote voltage sensor to the MPPT controller. See more here: http://mvvikingstar.blogspot.com/2012/06/controller-alternator-interaction.html
An easier way (the Shortcut)
If you too want to model output of solar panels you can follow the steps above (and I can send you .xls files with all the formulas, though you will need to locate someone near your cruising grounds that has reliable data from which you can start the assessment). OR, you can just go to this site (which of course I found AFTER going through all the above): http://gisatnrel.nrel.gov/PVWatts_Viewer/index.htmlIt not only has a large database of solar radiation throughout the world, but will also do the tilt (orientation) adjustments for you! On the map click the location you are interested in, and then select the ‘Send to PVWatts’ button. That will transfer the Solar Radiation data for your selected location into the Tilt calculator where you can enter your system size as well as tilt angle. A few notes:
- PVWatts will not work for systems under 1,000w in size. A workaround for this is to multiply your expected system size by 10 and enter that . For example: Viking Star’s 480w system is entered as 4.8 kW (4,800 watts) in the program.
- ‘DC to AC Derate Factor’ is the efficiency of the rest of the system. I found using 0.85 worked well to account for the MPPT controller efficiency and voltage drop across wires.
- ‘Array Tilt’ - Enter 0 if the panels are flat or leave it with the default latitude for a good approximation if you plan to tilt the panels. You can get even better results by changing the mounting to 1-axis or 2-axis tracking (depending on your mounting system - and desire to reposition things throughout the day), but I did not play with those.
- Press the Calculate button to get predicted results throughout the year.
- Looking at the AC Energy (kWh) column, divide these numbers by 4 to back out the 10x we did in step one and make a rough conversion into Ah per day. (for a 12v system. If you have a 24v system, divide by 8 for a ruff idea of 24v AH's)
This web page predicts 162Ah / day expected output from Viking Star's system in June. A bit more than the 153Ah I modeled, but our actuals aboard Viking Star seem to be running ahead of modeled results.
The final issue is shading. Here you need to get creative and try to minimize it. The MPPT controller, combined with built-in bypass diodes in the panels will help a LOT with shading, but still shading will reduce output dramatically During the peak summer months I noticed about a 30Ah reduction per day if we were docked pointing North as opposed to South, this I expect was due to the shadow from our mast when docked pointing north. Just one more ‘consideration’ when pulling into dock now. . .
BTW: There is a good argument for using a separate a MPPT controller for each panel installed on a boat, to help work around this partial shading situation. Given that MPPT controllers are becoming more and more common, and the prices are dropping, doing so would be a good consideration for future installations. But if you do use a single controller, like on Viking Star, make sure to wire the panels in SERIES to maximize output during partially shaded conditions. And note this is a dramatic departure from what was recommended a few years ago (Parallel). It is due to both the usage of the MPPT controller and increased presence of zoning / internal bypass diodes on modern large panels. If connected parallel - a shaded panel will drop out entry while if a modern panel is connected in series the partly shaded panel will lose the shaded segments, but the unshaded segments will continue to contribute (due to internal panel zoning and by-pass diodes).
Overall we are happy with the system. It accomplished it's key goal: reduction of generator time. It is only this last month we needed to start using the Generator, and that was just for covering the drying cycle during laundry. Though as expected - as we are heading into the latter part of October we are finding we need to put time on the generator, varying from day to day.
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