Beginner's Brain Freeze

NCTinkerer · August 2015

I am brand new to solar, although I have many years of electronics experience. My son and I recently built a 12x16 shed behind his house for storage use. We thought it might be fun to setup solar instead of trenching in a power line. We are planning for a few dozen watts of LED lighting inside, 2 x 30 watt motion activated LED floods outside and an outlet to charge his electric lawn mower (about a 100 watt charger.) The lights will be used infrequently and the mower will be charged overnight after use then trickle charged afterward.

I've been reading a lot and websurfing like crazy.

When I ran across this forum I thought "These guys are really patient with dumb questions." So here goes. We're considering a Renogy 100 w mono PV panel, a PWM charge controller, a single 12 v deep cycle battery, and a small inverter. I saw one post where a guy said that a modified sine wave inverter would not charge his laptop. Is this a known issue with MSW inverters, that they don't play well with battery chargers?

I'm overloaded by the dozens of brand names of equipment available for wildly varying prices. I figure the cheapest stuff is junk and the most expensive stuff is either overpriced or more complex than we need. Considering the setup I've described, what brand names of charge controllers, batteries, inverters, panels are good values for such a small system? I'm not looking for specifics and don't want to start any arguments. I just want to know which brands have proven themselves over the years as good values.

Thanks for your patience...

inetdog · August 2015

Yes, it is a known issue that an MSW inverter does not play well with most battery chargers. The problems range from overheating and damage to the charger to the charger not working properly (as in some laptop power supplies.)
If a large portion of your expected power consumption is the laptop, you should look into getting a 12VDC input power brick for the laptop and avoiding the losses of a back and forth conversion between AC and DC.

BB. · August 2015

To see what a really good (and not badly priced) TSW 12 volt 300 Watt inverter looks like--The MorningStar model is really nice:

http://www.solar-electric.com/inverters-controllers-accessories/inverters/moin/mosu300wasiw.html

But--I always like to start at the beginning... What your loads (Watts, Watt*Hours per day), voltage, expected usage, etc... Design the battery bank, then design the solar array to both properly recharge the battery ban and the solar array to supply Watt*Hours per day based on location. A Kill-a-Watt type meter is a really nice tool to have around the house.

And welcome to the forum NCT.

-Bill

NCTinkerer · August 2015

Here is the info from my original post. If not specific enough, let me know and I'll try to do better.

NCTinkerer wrote: »

...We are planning for a few dozen watts of LED lighting inside, 2 x 30 watt motion activated LED floods outside and an outlet to charge his electric lawn mower (about a 100 watt charger.) The lights will be used infrequently and the mower will be charged overnight after use then trickle charged afterward.
Thanks for your patience...

NCTinkerer · August 2015

I just ordered a Kill A Watt meter. We have power temporarily connected to the shed with a long extension cord. With the meter between the cord and the shed, I'll soon be able to give a good answer on power requirements.

Roger Thoms · August 2015

I'll second BB's recommendation on the SureSine 300, great inverter. I have one that I used for my temporary power set up when I was installing my new PV system. It is now going to be moved to our "guest house" which is a small out building that is a little far away to trench power to. Sound like a very similar situation to yours.

Roger

inetdog · August 2015

Roger Thoms wrote: »

I'll second BB's recommendation on the SureSine 300, great inverter. I have one that I used for my temporary power set up when I was installing my new PV system. It is now going to be moved to our "guest house" which is a small out building that is a little far away to trench power to. Sound like a very similar situation to yours.

Roger

When you make the evaluation of "a little far away to trench power to", you need to consider both the initial cost of the off grid PV system and the fact that you will be paying two to ten times the cost of grid power per kWh for as long as you are using the system.

For a very small power load (essentially lighting and phone charging only) it may still make economic sense.

NCTinkerer · August 2015

For us, it isn't so much to save money, not even in the long run. We just wanted to have a little fun with solar panels. I'm sure we could buy a whole lot of kWh for the cost of the solar panel system but what fun would that be.

Roger Thoms · August 2015

inetdog wrote: »

When you make the evaluation of "a little far away to trench power to", you need to consider both the initial cost of the off grid PV system and the fact that you will be paying two to ten times the cost of grid power per kWh for as long as you are using the system.

For a very small power load (essentially lighting and phone charging only) it may still make economic sense.

Absolutely. In our case there are several factors at play. First, I replaced a smaller system and am using the old equipment for the "guest house". I bought the SureSine after hooking our old Trace 800w MSW inverter up reverse polarity and frying it. Long story, but it's safe to say I won't make that mistake again. Second, is the fact that our landscaping is natural high desert and I always think long and hard about disturbing it. The other consideration was fact that building is roughly 400' from the new system and that I made no accommodations for running power out to that building.

For us it makes sense, especially considering that there isn't grid power any where near us.

Roger

NCTinkerer · August 2015

inetdog wrote: »

...you need to consider both the initial cost of the off grid PV system and the fact that you will be paying two to ten times the cost of grid power per kWh for as long as you are using the system....

Are you saying that after the initial PV system is paid for that each kWh afterward will cost 2-10 times the cost of grid power? Is this the cost of battery replacement averaged out over several years? I'm confused.

lkruper · August 2015

NCTinkerer wrote: »

Are you saying that after the initial PV system is paid for that each kWh afterward will cost 2-10 times the cost of grid power? Is this the cost of battery replacement averaged out over several years? I'm confused.

I think it is more complicated than that. It is true that some solar panels have long warranties, but if that company is no longer in business, then you self-warranty them. If squirrels eat your wiring, who pays for it? But more worrisome than that is that the electronics don't have the same long warranty as the panels. What is the cost of the 25 year extended warranty for charge controllers and inverters? They aren't available for a reason.

That being said, I think one could probably break even if one only considered the cost of battery replacement, especially at the higher tiers. Lets take a very small system with two Sam's club 6v 225 AH batteries, cycled to 50% DOD for the 1 year warranty.

2 X $85 + $15 core = $200 * 1.08 tax = $216
Daily usage = 112.5 * 0.90 inverter inefficiency = 101.25 AH
101.25 * 120v = 12150w = 12.15 kw
12,15 kW * 365 = 4434.75 kw / year
$216 / 4434.75 kw = 4.8 cents per kw

First year expenses:
Manual Transfer Switch - $400
Install of Switch - $350
Generator - $550

Note: the above are my current to date expenses for my cabin.

Battery Charger - $99
2 300w Solar Panels - $600
Charge Controller = $150
Inverter - $300
Batteries - $216
Cable and connectors - ?
Fuses - ?
Mounting Hardware?
Labor?

$2665
- 216
=====
$2449

Lets take 12 cents per kwh - 4.8 = 7.2 cents savings per kw
This system can make 4434.75 kw per year
4434.75 * 7.2 cents = $319.30 savings in the first year.
It takes 8.3 years to pay for everything but the batteries.
Now lets pay for the batteries at $216 per year for 8.3 years = $1802

So lets add $1802 + 2449 for total cost to break even = $4251.82
$4251,82 / $319.30 = 13.32 years for break even

But now need 5 more years of batteries = $1080
Total now needed to break even = $5333
5333 / 319 savings is now 16.71 years to break even.

Or have we really broken even?

Need to add 3 X $216 in batteries!

But my generator did not last 17 years. Neither did my inverter or charger controller
or my battery charger. They all had at best 3-5 year warranties.

And note that I did not include labor or hardware.

Check my math

###
Lets try an easier way. $319 in yearly savings - $216 in annual battery cost = $100 savings
$2449 in initial cost / $100 per year = break even in 25 years.

Now the panels are out of warranty too.
Needed to replace the generator how many times?
Did the electronics last 25 years?
How much could you have made investing $2500 in 25 year T-bills?

###

Photowhit · August 2015

lkruper wrote: »

2 X $85 + $15 core = $200 * 1.08 tax = $216
Daily usage = 112.5 * 0.90 inverter inefficiency = 101.25 AH
101.25 * 120v = 12150w = 12.15 kw
12,15 kW * 365 = 4434.75 kw / year
$216 / 4434.75 kw = 4.8 cents per kw

OOPS! Drawn to 50% or 112.5 Amps is correct, but that 112.5 amps is at 12 volts so Amps X Volts = watts or 112.5 x 12 = 1350 still have inverter inefficiency so X .90(most small inverters are less than 90%) = 1.215 Kw of stored power off by a factor of 10...

So make that 48 cents a Kwh, just for the batteries! Of course the batteries should last 4-5 years. Likely not that long if expected to be drawn down 50% every day...

You likely will get to use some energy after the batteries are full, if you are working on a system, try to run loads during the day. Charge the lawn mower during the day, no reason to store the energy only to transfer to another battery at night!

While a very few laptops may have problems with modified sine wave inverters, most will not, 99% of those car laptop inverters are MSW! I've run at least a dozen off MSW mostly older ones back in the XP days, I had one tha blew an inverter for the screen(laptop's inverter) which might have had a chance of being from running off MSW but unlikely IMHO.

lkruper · August 2015

Photowhit wrote: »

OOPS! Drawn to 50% or 112.5 Amps is correct, but that 112.5 amps is at 12 volts so Amps X Volts = watts or 112.5 x 12 = 1350 still have inverter inefficiency so X .90(most small inverters are less than 90%) = 1.215 Kw of stored power off by a factor of 10...

So make that 48 cents a Kwh, just for the batteries! Of course the batteries should last 4-5 years. Likely not that long if expected to be drawn down 50% every day...

You likely will get to use some energy after the batteries are full, if you are working on a system, try to run loads during the day. Charge the lawn mower during the day, no reason to store the energy only to transfer to another battery at night!

While a very few laptops may have problems with modified sine wave inverters, most will not, 99% of those car laptop inverters are MSW! I've run at least a dozen off MSW mostly older ones back in the XP days, I had one tha blew an inverter for the screen(laptop's inverter) which might have had a chance of being from running off MSW but unlikely IMHO.

Thanks ... I thought that 4.8 seemed way too good. Rooky mistake! You think a Sam's club battery could last 4-5 years?

Photowhit · August 2015

Mine did, 4 setup originally in a 12 volt system with minimal loads for the 1st year, then in a 24 volt system which was run down to 50% or less each hot summer day, running a window a/c, light loads spring and most of fall, though no backup so some times ran 50% or less in the fall/winter. Had a small fridge most of the time as well.

NCTinkerer · August 2015

As soon as I get the Kill a Watt meter, I'll be better prepared to estimate the power usage in my son's shed.
In the meantime, did I ask a taboo question when I asked for the names of companies that make solar equipment that have proven to be solid values?

I don't want to buy something, have it die an early death, then find out that everyone else knew it was junk.

Photowhit · August 2015

Mostly good stuff out there if you stick to items found at Arizona Wind and Sun, our sponsor. In some aspects you get what you pay for... That said solar panels are pretty simple and generally long lasting, in fact 2 of the three 'problem' panels in the past were very popular, well though of brands.

I've used;
Pulse/Trace/Xantrex/Schnieder (one company purchased by a company that changed names a couple times)
Specialty Concepts(2 units)
Trace
Midnite

Charge controllers and found them all very good, none died a natural death, in fact only the Pulse/Trace died at all due to a Japanese beetle across a FET (I think, beetle infested), and I guess a Specialty Concepts small unit, but it had contacts and spent the last 3 years of it's life in salt air on a pontoon boat very good service indeed!

Good reports on Outback, Morninstar and At least the older C series Xantrex, some iffy reports of their new CC's but likely bugs being worked out.

I've had good service from Prosine(Xantrex/Schnieder) inverter only inverters, I've had both 1000watt and 1800 watt units, had the fan go out on one, some how popped the internal fuse on another, 5 units, 20 years service between house and cabin. I have an ExelTech 1000 watt inverter that I might fall in love with, they are reported to have very low failure rates, American made, and I keep reading reports of people over loading them by 30-50% and they clip the wave form(?) and continue to power everything... I've only had mine a year and have been too sick (Shingles) or been too hot to use it much this year, it's setup for my outside/yard use.

I think most people here have had bad or heard bad experiences with Aims inverters, perhaps the one Brand I might suggest staying away from, though we had a fellow use a 6000watt(?) to run most of an office space for a couple years on an Aims Professional unit (some added name like that, likely to separate it from most of the 'junk' they sell)

Might stay away from Apollo, keep hearing reports of them closing their doors...

Beginner's Brain Freeze

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