How many Watts of Solar is enough?

[Gary Hatt - Publisher BCM]

If you have Solar, how many Watts do you have and what is the length of your bus?  Also is your bus all electric or do you have Propane on board?

[HB of CJ]

Sunlight or shade.  Summer or winter.  Color of your Bus Conversion?  Dunno.  Dynamic.

[Utahclaimjumper]

I have three panels of 100 watts each, they do a great job under "normal" conditions, but it all depends on usage and everyone uses power differently  I will run my generator for one hour each morning under boondocking conditions to replace what was removed during the night (furnace, refer, TV  and other trace users.. After that hour, and in sunlight, the solar will hold its own all day.>>>Dan  (could use one more panel)

[bobofthenorth]

What Dan said.  Anything less than 400W is largely a joke unless you drastically modify your lifestyle from what most people consider "normal".  And you're still going to need a generator for the heavy lifting.

[Iceni John]

The only reason I have eight big grid-tie panels is because ten or twelve won't fit!   I decided I could either laboriously calculate all my electrical loads and then arrive at a notional size of my PV system, or I could instead just carpet the whole darn roof with panels.   I know what's easier.   It's like when folk ask me why I have 220 gallons of water capacity  -  the simple answer is because I don't have space for any more!   I work on the basis that RVers don't usually complain they have too much of anything.   If in doubt, err on the side of excess!

Seriously though (?!), if the sun don't shine I want to have three days of power before my batteries reach 50% SoC.   In practice I would probably use my emergencies-only generator before that point.   I also want enough PV to be able to charge the batteries at the upper end of their recommended 5-13% charge rate, so if the sun is low or weak I can still get a useful charge into them.   I think that for most of the year I will have excess power from the panels, but I can heat water with it or use it to run power tools so it won't go to waste.

I've designed my bus to comfortably support one person for at least a month off-grid, or two people for at least a fortnight.   That includes taking a nice shower every night, cooking, using the loo, etc etc, in other words not deliberately scrimping and saving.   The only anticipated limitations to extended boondocking will be of fresh water and food, not electricity!

John

[Dave5Cs]

Just got the Barn at the ranch 80 new PV panels replacing 75 old ones that slowly went bad also new inverters. Two of the inverters were still usable and 3 panels which were newer are usable.

Don't Know not much about these numbers can I in any way use this on the bus. (It was use on a regular house system where it made electric both ways, to the house and back to the power company). With a Magnum 4024 Hybrid sharing inverter/Smart 120 watt charger which I use now with 4, 6volt deep cyle batteries 232 AH wired in series 24VDC, with a 7KW genny and 50 amp shore with a Auto transfer switch. also have a 20-60 Vanner that handles 12 volt system and 24 V start batteries Group 31's(2).

Each Panel 190 Watts each Total=570 Watts
Voltage 37.8
Current 5.06
open circuit 45.3 Volts
Short circuit 5.56A
Tolerance +5

Inverter is a Sunny-boy 2500

Or should I just use them on my Ranch Trailer?

[Beluga Bus]

I have two 100 watt panels feeding two group 31 batteries. Works well for boondocking and really minimizes generator use depending on how much sun you can get. Would like to add a few more panels to eliminate generator use, but flat panels on a curved roof limits that.

Matt

[windtrader]

Solar is near the top of the discretionary list. Monitoring and calculating the range of typical energy usage during 24 hours. Based on that the house battery pack can be sized and the amount of solar generation estimated. Broad guess is a couple 280-320 watt panels (500 watts usable) should keep the house batteries charged up. We us very little during the day and most consumption is lighting, some short microwave usage, refrig (x24), and hot water. just hoping to eliminate running the generator on most days.

Generator is expected to run the AC when used. not planning on sizing system to run AC off batteries or plan on running multiple days off batteries. If it don't shine and batteries need a charge, that's why the generator is there.

[Jerry W Campbell]

I have 1580 watts and the only reason I don't have more is because at the time it's all I could get to fit on the roof. With 1600 amps of AGM's.
I believe what John says is true, you can never have enough charging power. There are lots of partly cloudy days.
Jerry

[belfert]

Just got the Barn at the ranch 80 new PV panels replacing 75 old ones that slowly went bad also new inverters. Two of the inverters were still usable and 3 panels which were newer are usable.

Did the solar panels themselves go bad?  From what I have read it is extremely rare to have the panels themselves go bad.  There are panels still running from the 1970s when solar was just getting started.  It seems sort of silly that today's panels have a 25 year performance warranty, but many only have a 12 year warranty against other failures?  Isn't the panel performing at zero percent of original performance if it fails entirely?

I would like to put four 60 cell panels totaling around 1,000 watts on my bus, but they have to be cheap around $100 per panel to make it worth the effort.  The $750 total cost of the system could buy a lot of diesel for my generator.  I don't use the bus enough to make solar really pay off.  The additional four to six hours a day of not hearing the generator run might be worth it although my generator is pretty quiet.

[Iceni John]

I would like to put four 60 cell panels totaling around 1,000 watts on my bus, but they have to be cheap around $100 per panel to make it worth the effort.  The $750 total cost of the system could buy a lot of diesel for my generator.  I don't use the bus enough to make solar really pay off.  The additional four to six hours a day of not hearing the generator run might be worth it although my generator is pretty quiet.

Unless you get a great deal on used panels, you probably won't find PV for that price!   I paid $0.79 a watt a few years ago for my new Grade B made-in-USA Sharps (they are cosmetic blems with some cells not exactly the same color as others!), and prices have dropped further since then, but you have to buy pallet-loads to get down to $0.50 a watt.   For me, not having to hear a generator was a primary reason to go solar  -  if I'm parked somewhere beautiful I really don't want to hear one droning away for hours, and because I'll be in the desert Southwest most of the time the choice for me was obvious.

John 

[windtrader]

Typical current pricing in the Bay Area. not 50 cents but still very attractive pricing. One consideration of mine is not having panels so wide they hang much beyond the curve of the roof. Best configuration is hidden or barely visible panels.
https://sfbay.craigslist.org/sby/for/d/new-320w-solar-panels-only/6412950964.html
https://sfbay.craigslist.org/sby/for/d/285w-mono-solar-panels-with/6428304967.html
https://sfbay.craigslist.org/nby/ele/d/renesola-250w-pv-solar-panels/6431199743.html

[belfert]

Unless you get a great deal on used panels, you probably won't find PV for that price!   I paid $0.79 a watt a few years ago for my new Grade B made-in-USA Sharps (they are cosmetic blems with some cells not exactly the same color as others!), and prices have dropped further since then, but you have to buy pallet-loads to get down to $0.50 a watt.   For me, not having to hear a generator

I paid 27 cents a watt for twenty 300 watt used panels last March.  I paid 45 cents per watt for twelve 265 watt new panels in October.  Prices for solar panels have gone up quite a bit since March.  I believe back in March I could have found some new 60 cell panels for close to $100 each.  I watch CL for panels locally and the prices some people want is ridiculous.  One guy wanted $10,000 for an old 900 watt array with inverter.

In the southwest USA I regularly see panels on CL for $100 or just over that for new panels.  Unfortunately, I don't live down there, but I will probably be driving through in May.

[windtrader]

Brian,

I agree that prices on panels, particularly those from China have crept up. It seemed a response to the govt. and the trade imbalance with China. Not following but solar credit programs may be changing as well. Either way, for the few panels that'll fit on a bus, it hardly matters. For us in Calif. the asinine 30 cent tax on diesel dents me much more.

[Oonrahnjay]

Brian,

I agree that prices on panels, particularly those from China have crept up. It seemed a response to the govt. and the trade imbalance with China. Not following but solar credit programs may be changing as well. Either way, for the few panels that'll fit on a bus, it hardly matters. For us in Calif. the asinine 30 cent tax on diesel dents me much more. 

     And, just as they planned, China "dumped" enough solar panels to put many of the larger US manufacturers out of business (and drive the European manufacturers out of the market).  Now that there is little competition, they're putting their prices up again.