Please check my assumptions and logic
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Dannyo
Registered Users Posts: 10 ✭
I tried to upload my excel spreadsheet and it wouldn't work. Then I tried to upload an image of it via Microsoft Word and it exceeded the max limit (89.5kb versus 19.5kb). So let me try this method.
There is no house or electricity on our waterfront lot. We are building a boat house next month with a storage room. I want to install a solar panel to run a few things: ceiling fan, 2 lights, 1 motion flood light, radio, weather monitoring, water pump, and boat lift. We only visit the lake every 23 weeks, and only for a day or two. The water pump and boat lift will be DC, therefore they will not go through the inverter. During the winter, we wouldn't use the water pump or the boat lift. He are my assumptions:
Batteries 2
Battery amp hours 105
Battery > 50%
Battery availability 105 hours
True Sine Inverter  output watts 600
Inverter > 50%
Inverter availability 300 (versus 247 if everything running simulataneously)
Panel wattage 130 Kyocera 130GT
Panel amps 7.39
Panel voltage 17.6
Charge Controller amps 10 (versus 7.39 from panel)
Panel wattage 130
panel wattage @ 85% 111 watts
wattage w/ inverter loss @ 6% 104 watts
wattage w/ particulate loss @ 7% 97 watts
wattage w/ nonoptimal tilt @ 3% 94 watts
sun hours 5.1 avg
watts generated per day 478
watts generated per week 14,336
amp hours generated per day 27
Amp hours used per week 194, but only 135 in winter (no pump or boat lift)
Watt hours used per week 2,329, but only 1,619 in winter
Kyocera 130 watt GT $610.00
Samlex 600 Watt Sine Wave Inverter $244.00
Morningstar 10 amp, 12v, low voltage disconnect $50.00
Batteries Marine 2 deep cycle, 105 amp hrs $200.00 with core charges
Mounting hardware, wiring, connectors $60.00 (just a guess)
Total System Cost $1,164.00
There is no house or electricity on our waterfront lot. We are building a boat house next month with a storage room. I want to install a solar panel to run a few things: ceiling fan, 2 lights, 1 motion flood light, radio, weather monitoring, water pump, and boat lift. We only visit the lake every 23 weeks, and only for a day or two. The water pump and boat lift will be DC, therefore they will not go through the inverter. During the winter, we wouldn't use the water pump or the boat lift. He are my assumptions:
Batteries 2
Battery amp hours 105
Battery > 50%
Battery availability 105 hours
True Sine Inverter  output watts 600
Inverter > 50%
Inverter availability 300 (versus 247 if everything running simulataneously)
Panel wattage 130 Kyocera 130GT
Panel amps 7.39
Panel voltage 17.6
Charge Controller amps 10 (versus 7.39 from panel)
Panel wattage 130
panel wattage @ 85% 111 watts
wattage w/ inverter loss @ 6% 104 watts
wattage w/ particulate loss @ 7% 97 watts
wattage w/ nonoptimal tilt @ 3% 94 watts
sun hours 5.1 avg
watts generated per day 478
watts generated per week 14,336
amp hours generated per day 27
Amp hours used per week 194, but only 135 in winter (no pump or boat lift)
Watt hours used per week 2,329, but only 1,619 in winter
Kyocera 130 watt GT $610.00
Samlex 600 Watt Sine Wave Inverter $244.00
Morningstar 10 amp, 12v, low voltage disconnect $50.00
Batteries Marine 2 deep cycle, 105 amp hrs $200.00 with core charges
Mounting hardware, wiring, connectors $60.00 (just a guess)
Total System Cost $1,164.00
Comments

Re: Please check my assumptions and logic
dan,
i'm not sure that'll quite work the way you think it will. you may need to go over the loads you will use and for how long to come up with the watthours of power needed to be used in say the weekend or 2 days. the usable power from the batteries over that 2 day period will be 105x12=1,260 watthours. over 2 days that will be an average hourly draw of 1,260/48=26.25 watts. is that enough for your needs? the battery capacity would be enough to run your inverter at 600w for 2 hours!
also note that you may need more pv to charge those 2 batteries as a good rule of thumb is to have between 5% and 13% rates of charge to the batteries. 210ah x .05 = 10.5 amps minimumly from pv and could go as high as 27.3 amps at 13%. seeing as how it will have the opportunity to charge over several weeks then you could stay on the low side of the charge rates and you may even get away with that 1 pv as we also say 3% as an absolute minimum with no loads on and given enough time to charge the batteries. 7.39a/210ah=3.5%. for more batteries employed, more current to charge them must also be employed.
also note that if you think you'll get 478 watthours (not watts) a day from that pv the weekly figure at best would be 7x that or 3,346wh and let's face it it will be cloudy or rainy on some of those days further reducing the net wh you will reap from the pv. 
Re: Please check my assumptions and logic
Thanks Niel,
I'm new and I don't all of the terminology, but I calculated 478 watts per day as follows: 94 watts per hour (for a 130 watt panel) multiplied by 5.1 average sun hours (found on a website).
As for consumption, I calculated as follows:
Light bulbs, 23 watts, 4 hrs per day, 2 days per week = 208 watthours
Motion Flood lights, 50 watts, 1 hr per day, 7 days per week = 350 wh
Ceiling fan, 75 watts, 5 hrs per day, 2 days per week = 750 wh
Radio, 10 watts, 5 hrs per day, 2 days per week = 100 wh
A/C charger, 1 watt, 24 hrs per day, 7 days per week = 168 wh
Laptop, 85 watts, 1/2 hour per day, 1 day per week = 43 wh
Water pump, 120 watts, 1/2 hour per day, 7 days per week = 420 wh
Boat Lift, 1452 watts, 0.1 hour per day, 2 days per week = 290 wh
Total is 2,329 wh per week, or 851 for a weekend day, or 1,701 for Sat and Sunday.
As you suggested, I will be short by 441 watt hours (12601,701), partially offset by the new energy created on Sat and Sun. An additional battery will add 630 watt hours, and cover the shortfall. Otherwise, my 2 batteries will decline to 33%, which is not ideal.
As you suggested, I have to make sure that the 130 watt PV panel can charge all three batteries. Let's assume 4 hours per day in the summer, which creates 376 watts (94*4). If I divide by 17.6 volts (per the panel specs), I get 21 amp hours per day, then multiply by 12 volts to get 256 watt hours per day. Then multiply by 7 days to get 1,792 watt hours that go back into the batteries. With total weekly consumption of 2,329, then I'm short. However, we only visit the lake every 2 or 3 weeks, therefore I think the PV panel is sufficient to charge up all 3 batteries.
Niel, I've reread your response about the 5% minimum battery charge. I'm still not entirely clear, but it sounds like you don't want to 'trickle' charge these batteries. Are you saying that my proposed panel with 7.39 amps should only be used to charge batteries totaling 148 amp hours or less? 
Re: Please check my assumptions and logic
A quick look, and the first thing I can think of is your loading. With judicious use of cfls for lighting, especially for the motion lights you could reduce your lighting load a bit.
Second, there are some 12vdc ceiling fans that draw between .5 and 1.2 amps which would reduce your fan loads a bit as well.
I don't know it you are pumping from the lake or a well, or what head (pressure) you are pumping to, but you could possibly reduce your water pumping load a bit. ( I use a shurflow 12/24vdc submersible that pumps to 60 psi (more in fact) and draws ~3.5 amps/12vdc to pump 1 gal/min into 60 psi.
I guess my point is, as in all RE, the cheapest energy investment is in conservation (Reducing the load) Then building a Pv system becomes much cheaper and fulfills more of the load(s)
Icarus 
Re: Please check my assumptions and logic
Thanks for responding Icarus,
Yes, some of my load estimations are very conservative. I'll continue to refine it and research various products that use less energy. Thanks for the tips on the fan and Shurflo pump.
I'm not 100% sure about my calculations, the size of the charge controller, the size of the inverter, etc. Nothing has been mentioned yet, so I assume they are ok. I still need to do some more detailed calculations on the panel size in relation to the amp hours of the batteries.
Do I need a breaker box?
The panel will be on top of a metal roof, do I need to run a 30 foot ground wire back to shore? or pound a metal rod into the lake (water is only 2 feet deep there)? 
Re: Please check my assumptions and logic
dan,
you are right that i would be reluctant to say 1 130w pv will suffice as it would be close for the 2 batteries you initially propose. if you up the amount of battery capacity to 3 of those batteries the charge needed from the pvs will also need to be increased so that could mean 2 130w pvs. with your current requirement of 1700wh that means the batteries have to hold double that so that you don't exceed 50% depth of discharge or 3400w total capacity. 3400w/12v=283.3 amphours of battery capacity.
as was brought up by icarus, that if you can conserve and use less power that it will make a big difference and if you manage to conserve enough it could make the system you initially proposed work.
the batteries will be in parallel as you stated you won't be there for several weeks at a time to switch the individual batteries for charging. also know that you could add to the 130w pv if the initial pv system isn't enough for you, but when it comes to the batteries you should get the capacity you need now as adding later isn't advisable unless you'll know quickly. if you wish to learn more of the why not add a year later, there are threads on it in the forum as it comes under mixing different batteries or capacities of which you shouldn't do. you don't have to add another of the same pv to add to the pv system as a 90w pv could be added to a 120w pv when operating in parallel as long as the vmp is similar. cross that bridge if and when we get to it. 
Re: Please check my assumptions and logic
Thanks for your suggestions, so here is the system that I'm going with. My estimate is about $750 plus the cost of the mounting hardware, connections, fuses, etc.
Kyocera 85 watt
Samlex 300 Watt Sine Wave Inverter
Sunsaver 6 amp, 12v, with LVD
1 Battery Marine deep cycle, 105 amp hrs
Battery has 630 watt hours of availability (105*50%*12).
Panel amps (5.02) are within the 5% minimum in relation to the battery's 105 amp hours.
Panel Generates 252 wh per day (operating at 63 watt efficiency with 4 sun hours)
A more efficient water pump, fan and other conservation has allowed me to get by with a smaller system. By switching the ceiling fan to DC, I'm able to downsize my inverter to 300 watts with no problem. The smaller PV panel (5 amps) also allows a smaller charge controller.
Consumption is 124 wh per weekday and 480 wh per weekend day. We usually only stay on Saturday, but I assumed the same usage on Sunday (to be conservative). After the weekend, the system will recharge the batteries within 4 days. We typically don't visit every weekend, so the system has 12 days to charge, if needed.
If you see any problems with this logic, then please let me know. Thanks again for your guidance and suggestions.
Danny 
Re: Please check my assumptions and logic
Danny,
A couple of observations.
Before you buy or install anything. (If it isn't too late!)
spend a bit of time reading and learning about the detail of PV systems. To do so would avoid a lot of Ready, Fire, Aim, and thereby reinventing the wheel. Many of us here have made a lot of expensive mistakes over the years and perhaps you can avoid some, (probably not all!) of them.
My initial observation is that loads increase over time, once you realize how nice it is to have power 24/7. As Neil suggests, adding panels later is an easy option, but if your controller is too small you will end up buying twice. Same for inverters. Batteries can be added later but there are significant consiquences to doing so. (See related posts.)
If I was starting over, I would spend the extra for a MPPT controller upfront, and then buy and oversized battery bank, and then add panels as needed.
I would also buy a good charger depending on how you are going to power it. For a small system like this using a small generator the Xantrex TrueCharge 20/40 series works great.
I know that there is considerable discussion on these boards regarding the ratio between panel capacity versus battery capacity. I personally feel the debate is a bit over blown. In a system like yours that will have days to charge between discharge cycles I think having more battery and less panel is a good way to start. (Of course there is really no such thing as too much panel! I always want more!)
You will need a fuse between the panel(s) and the controller, between the battery and the load(s) In a simple system, you wouldn't need a breaker box, but it might be nice to start our with one, instead of auto type fuses.
As to grounding. I live on a lake in the Canadian shield where we have little or no soil. Grounding anything electrical is a challenge. What I have done, and it has worked for years with several lightning strikes over the years to proof it, is run a ground wire at every proper ground location to the lake, and then a dozen feet or so under water. The generator neutrals, the fuse/breaker ground lugs, the panel frames etc.
Enjoy the process, and learn along the way,
Icarus 
Re: Please check my assumptions and logic
Thanks Icarus, I'm not ready to fire yet. I have about a month to learn some more. Thanks again. 
Re: Please check my assumptions and logic
i concur to go bigger if you can. i did indicate that reducing your loads would make the 2 batteries with a 130w pv more workable and you can always add to the numbers of pvs if it isn't so. this also comes in handy for a reserve capacity, just in case, and your lighter loads will allow a longer lifespan on the batteries.
go with a controller that not only will have expandability for more pvs, but will have a float voltage setting along with having it capable of a battery temperature sensor as we always recommend using the battery temp sensor. in the case of mppt controllers it is advisable for you to read up on them before deciding to get one of them as they are usually for larger pv systems than you are going for, but in some cases it is feasable if you wish the extra costs involved and they do help recoup some losses for an average of about 10%.
as to the capacity of the inverter it doesn't hurt to have that extra 300w from the 600w model that gives you the room for future expansion with a slight increase in cost now and not having to sell the smaller one at a cheaper cost to recoup later. 
Re: Please check my assumptions and logic
Ditto to what Neil says: I would add that you can use 2 300 watt inverters on separate circuits in the future if need be. People often use 1 small inverter for smaller loads, but use a bigger one for the larger ones. Inverters are more efficient when they are used closer to their capacity. Once again, the more research you do the better feel yo will have for both your long term as well as short term loads.
Icarus 
Re: Please check my assumptions and logic
Dannyo
I'm curious about your boat lift, you say that it uses 1452 watts and your proposed inverter is a Samlex 600, it seems to me that you might have a problem using the boat lift with that size inverter. Just a thought. Maybe I misread your posts. Anyway the rest of your system will probably work just as you have proposed, with just a few tweeks along the way.
Larry 
Re: Please check my assumptions and logic
larry,
you may have a point as i didn't give it much thought as to whether that was run by ac or dc and i assumed dc.
dan,
this high load is reason enough to go with 2 batteries and not just 1 as 1 battery will not like a load that large even though it's for a short duration.
also the batteries when having loads or charging sources connected to them should be cross connected. that means connect loads or charge sources to the + of say battery 1 and the  of battery 2 or the opposite, but never both to the same battery. interconnect the batteries with as heavy of wire or buss bars as you can, but as big as or preferably larger than the largest wire being used in the entire system including the inverter wires. 
Re: Please check my assumptions and logic
The boat lift motor is 12vdc, so it won't run through the inverter. It only takes a couple of minutes to raise or lower the boat. Niel, thanks for the suggestion about cross connection. I've created various scenarios in an excel spreadsheet, and I've determined that the best system for me is:
Kyocera 85 watt
Samlex 300 Watt Sine Wave Inverter
2 Batteries Marine deep cycle, total of 210 amp hrs
Xantrex C12 charge controller (although somewhat crude, I like the LED's that tell me if the batteries are fully charged)
The Shurflo 2088 water pump is 12vdc, 9 amps, 3.5 gpm at 45 psi, self priming 912'. It won't run through the inverter either.
NAWS recommended the RV mounting feet. They seem quite a bit cheaper ($16.50), and I guess I can build a frame out of metal or wood. I'll have to research the appropriate angle.
Thanks again for your comments. 
Re: Please check my assumptions and logic
ok, but for the 2 batteries you will need a higher input power to achieve a marginal ability to charge 210ah of battery so the 130w pv should minimumly be used to start with and if you later find it not enough pv you can add to that. crewzer likes 1 watt of pv for every ah of battery capacity at 12v so you can see we are far below that with a 130w pv at 7.39amps out. 7.39a/210ah=3.519%. like i said a 513% charge rate is the normal range we recommend and an 85w pv would not charge those 2 batteries. 
Re: Please check my assumptions and logic
Ok, I guess I'll go with the 130w panel, and go to the lake more often. We've come full circle from my original post 
Re: Please check my assumptions and logic
It will charge the two batteries, only slowly. It just falls outside the "ideal" charge design of 513%. If you are happy with the results you will be fine. If not, adding another panel is not that expensive. As I said before, I tend to (contrary to other experts) to discount the 513% rule a bit. I lived for 8 years with 55 watts of panel, ~205 amp/hour batteries, drawing ~10wamp/hours a day. The batteries are still going strong on a secondary system.
Icarus 
Re: Please check my assumptions and logic
My previous post overlapped yours. You'll never regret having "too much" panel capacity!
Icarus
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