How much Solar energy with only vertically or horizontally mounted solar panels?

Hedges

I See Electromagnetic Fields!
I plan to use a 48 V battery system, as I need to store about 10 to 20 kWh of solar energy.

What is your planned usage, that makes it necessary to have any battery at all?

Batteries can hold power to be used when the grid is down, and they can hold power from PV to use instead of from grid at another time. But, most batteries cost more per kWh than utility rates, meaning you lose money rather than saving money when drawing power from a battery rather than from the grid. Some batteries (DIY LiFePO4 and off-brand or recycled batteries) do appear to be cheaper than grid power.

PV, at least if installed DIY with your own labor, costs a fraction as much per kWh as grid power (in some areas such as California.) In other parts of the country cost is similar. It can be cheaper to install PV with zero-export and waste as much as 2/3 of production, only using 1/3 of PV production when you happen to have loads. That can save money compared to just buying from grid, and also compared to storing the unused power in battery for later.
 
Since you're mixing panels, you will likely need an MPPT for each panel type due to the fact that the 2S 400W will likely have different Vmp than the 2S 240W.
Yes, I was a little bit puzzle about the different panels size, and I was thinking to ask about later, but you immediately spotted it !!!
I was interested evaluating the maximum power I could get, than looking at technical issues.
I could use smaller panels on the roof too, to make it simple.
The larger panels could be also used on the side walls, there will be so shading issue, but it was just that
I prefer having more space all around the panels, especially on the bottom to make it easy when the roof cover get replaced.

Honestly, looking at the numbers, it seems that I would not need to build this smaller unit.
For the larger unit, you're just dealing with so much potential wattage, you may need 2X controllers; however, since your arrays will never see maximum output, one might suffice:

2400*3 / 48 = 150a - few charge controllers offer over 100A.
You are right, the east and west panels would not work at the same time, so it's more like a 12 panels than a 16 panels.
A single MPPT would be simple and cheaper, especially since I will have also about 200 to 300 ft of wires.

Speaking about wires, I wonder if I could stay with some stranded copper AWG 2, or if I need something bigger for such longer transmission line?

I cannot find any DC information for voltage higher to 48 V. Do you have any web site providing calculation tool for solar applications?
 
Last edited:

sunshine_eggo

Happy Breffast!
Discussed wiring/voltage drop on the first page and how to calculate it:


2awg is overkill. I'm assuming you will have a long run from the panels to the MPPT, i.e., 200-300ft.

I'm also assuming the wire between the battery and MPPT is relatively short, ~10 ft or less. In that case, you merely need to size it for the current. 2awg MIGHT suffice if it's rated for it, but you'd want to run the numbers with the calculator.
 
What is your planned usage, that makes it necessary to have any battery at all?

Batteries can hold power to be used when the grid is down, and they can hold power from PV to use instead of from grid at another time. But, most batteries cost more per kWh than utility rates, meaning you lose money rather than saving money when drawing power from a battery rather than from the grid. Some batteries (DIY LiFePO4 and off-brand or recycled batteries) do appear to be cheaper than grid power.

PV, at least if installed DIY with your own labor, costs a fraction as much per kWh as grid power (in some areas such as California.) In other parts of the country cost is similar. It can be cheaper to install PV with zero-export and waste as much as 2/3 of production, only using 1/3 of PV production when you happen to have loads. That can save money compared to just buying from grid, and also compared to storing the unused power in battery for later.
This solar project purpose is to power lighting in a residential building.
The electricity billing is based on a Tier base, where each Tier allowance, for this particular location, is 8 Kwh per day.

The first Tier is cheaper, the next three Tiers cost more, and over four Tiers "you go to jail" and pay penalties, like at least $.50 kWh plus taxes...
The building is already in the Red, so I try to lower the consumption, first by converting to LED the ballast fluorescent neon and so on.
The consumption during the day light, is 300 Wh and at night (about 6pm to 8 am) the current consumption is 1 kWh, but I try to lower it.

The electrical company however, starts to incite users to lower consumption during peak hours.
So you get basically two unlimited flat rates, similar to the EV (Electrical Vehicle) night rate, and I believe it's a 4 pm to midnight plan.
I already considered switching to this new plan, but the difference of rate was not that great, not like an EV night rate.

However you are right, depending of your billing kWh rate, the extra cost of a battery
might not worthwhile if most of consumption is when you get solar power directly.

I would certainly review the full solar project, considering that I have some surplus unused during the summer,
so I could try to make it more cost effective, by reducing as much as possible the numbers of solar panels and the battery capacity,
while having some electricity billing in Winter (December and January) to compensate the size reduction of the solar system.

I was also considering make use of the surplus, after getting the battery fully charged, to heat some water or charge an EV,
but I would then need to get a 240 V inverter, unless I can find an inverter able to switch the output to different voltages,
or use two 120 V inverters and put them in parallel or in series depending on the load.

I will also review the billing rate calculation, so I will check if I should better use only the stored solar energy during the peak hours,
and switch back to the grid thereafter in the middle of the night.

Something I have also to consider is that we experience some outages, especially during the summer to avoid wildfires
on windy days, so the building becomes like a big underground in the middle of the day. There are some emergency
lighting in the hallways but those use small 6 V batteries and don't last more than an hour,
and those batteries need to be regularly replaced even when they have never been used.
 
Last edited:
Discussed wiring/voltage drop on the first page and how to calculate it:


2awg is overkill. I'm assuming you will have a long run from the panels to the MPPT, i.e., 200-300ft.

I'm also assuming the wire between the battery and MPPT is relatively short, ~10 ft or less. In that case, you merely need to size it for the current. 2awg MIGHT suffice if it's rated for it, but you'd want to run the numbers with the calculator.
Thank you for the reminder, I apology, I should review again this full thread,
as I noticed that I sometime asked you about something you already mentioned.

There is also this site Build My Own Cabin where I found a compilation of various content,
and in particular a very handy and quite elaborated Voltage Drop Calculator,
but I was wondering if DC voltage would require specific wires calculations.
 
Roof eaves normally overhang walls a couple feet, so wall mounted panels need to be enough below the eaves to avoid shading until angle of sun is such that you don't mind having power production cut off.
Thank you for this concern, but there is no shading issue because the panels
will be installed on top of a flat roof and bolted again the walls of an utility room.

The utility room is built on top of the stairways, and the roof of the utility room also has a flat roof with no overhanging.
This type of utility room is a typical option made at construction time, to allow adding an extra floor or a penthouse.
 
Last edited:

Hedges

I See Electromagnetic Fields!
Consider a zero-export system to deliver some or all of consumption while the sun shines. Or net-metering, whichever looks better in terms of hassle and possible mandatory change of rate schedule.

Later in the day it won't keep up with consumption. My peak time is now 4:00 to 9:00 PM, so of course sun is low (used to be Noon to 6:00 PM.)

Possibly this would reduce consumption enough to avoid the higher tiers of billing, and no (big) batteries. At night you would have all illumination coming from grid. Battery backup for a decent amount of emergency lights could cover occasional power failure, maybe using AGM.
 

Hedges

I See Electromagnetic Fields!
You mean 300W (over 8 to 12 hours daylight, 2400 to 3600 Wh), and 1kW (over 16 or 12 hours night, 16kWh or 12kWh)?

A zero-export grid-tie system size for 300W would be pretty small. A couple panels, and there are some cheap inverters. Hardly worth the trouble. A grid-tie inverter that us UL-1741 listed and does do backfeed of grid is something you might get away with and not have utility notice.

An average of 15 kWh/day drawn from grid

About electricity cost, we have a billing based on quota of 8 kWh per day.
So the first quota is about $.20 to $.25 per kWh.
The next three quotas are in the $.30 to $.40 per kWh.
Above four quotas, or 24 kWh per day, the cost is around $.50 per kWh.
The building is always over the four quotas, thus the idea to install some solar panels.
There is about $200 a month cost for the monthly lighting.
I plan to build a full solar system for about $4k (?)

About $0.35/kWh for nighttime draw, $5/day $150/month $1800/year. OK, $200 actual.
The alternate rate schedule with low price at night may save you money, but lighting between 4:00 and 9:00 PM (peak time) and 3:00 to 4:00 & 9:00 to Midnight (one of the schedules) will cost more. GT PV would help in the afternoon until sun gets low, especially with panels aimed SW.

My cost estimate for batteries (cycled until wear-out) is:

$0.50/kWh AGM
$0.50 name-brand lithium
$0.25 FLA
$0.05 DIY LiFePO4
($0.05 to $0.20 for various recycled and off-brand batteries. Some even lower.)

A 48V 14kWh DIY LiFePO4 battery might cost around $2000 or so. If it does last 10 years, 3500 cycles, then you have saved a significant amount compared to utility rates.
Life tests of commercial batteries had only 5% of them reach expected cycle life without failure. I'd say don't count on DIY LiFePO4 lasting more than 25% of anticipated life (so 2.5 years for $0.20/kWh) which may be slightly better than break even. It may still do 5 to 10 years, in which case you come out ahead. So long as failures are BMS and cells are undamaged, you can DIY repair and are more likely to get the payback.

If you can get a decent net-metering plan and put in a 3kW to 4kW GT PV system (about $3000 to $5000 for hardware, DIY installation labor), that will be better than batteries (store power in accounting of the utility bill.) My minimum connect fee is about $12, so $144/year, $1440 over a decade (ignoring future rate changes.) That's cheaper than a battery.

From your experience, would there be any advantage to install the solar inverters near the solar panels,
instead of in the basement where the batteries and inverter will be located?

If PV voltage is higher than AC voltage, then IR losses are less with a long run of DC from PV.
I prefer the long run in PV DC, because voltage drop doesn't cause any issues other than percentage of power lost.
A long run in either DC between SCC and battery or in AC can shift voltage out of spec and cause things to shut off.
 

12VoltInstalls

Solar Addict
Life tests of commercial batteries had only 5% of them reach expected cycle life without failure. I'd say don't count on DIY LiFePO4 lasting more than 25% of anticipated life (so 2.5 years for $0.20/kWh) which may be slightly better than break even. It may still do 5 to 10 years, in which case you come out ahead.
That is an astounding statement right there.
 

Hedges

I See Electromagnetic Fields!
That is an astounding statement right there.

Here's the reason for my statement:

 

SolarPrep

Solar Enthusiast
What is your planned usage, that makes it necessary to have any battery at all?

Batteries can hold power to be used when the grid is down, and they can hold power from PV to use instead of from grid at another time. But, most batteries cost more per kWh than utility rates, meaning you lose money rather than saving money when drawing power from a battery rather than from the grid. Some batteries (DIY LiFePO4 and off-brand or recycled batteries) do appear to be cheaper than grid power.

PV, at least if installed DIY with your own labor, costs a fraction as much per kWh as grid power (in some areas such as California.) In other parts of the country cost is similar. It can be cheaper to install PV with zero-export and waste as much as 2/3 of production, only using 1/3 of PV production when you happen to have loads. That can save money compared to just buying from grid, and also compared to storing the unused power in battery for later.
There are many valid reasons to buy batteries, and they don't all have to be based on an economic payback analysis. For example, preparedness in storms or disasters, avoiding the deductible that is applied to your claim for loss of things such as food, not having your boiler freeze and break when it is minus 30f, etc. A friend of mine just lost 2 freezers and a Sub Zero fridge full of food when they were out of State visiting a dying relative. Their insurance isn't covering the lost food, or the damage to the units from blood leaking out of meat.

A huge storm last year knocked out all power for weeks. No gas was available for generators, unless you were able to drive 75 miles to find some, and managed to not get flat tires from all the metal scraps littering the roads. If you couldn't take time off work, you wouldn't even have that option.

The infrastructure of this country is so bad that many locations have frequent power outages. Other than just the inconvenience of the outages, the resulting power variations are hard on equipment. Last, but not least, doing a grid tied/sell back agreement varies in complexity depending on where you are. When I'm located the utility makes you jump through hoops, and adds a lot of extra cost to any system. I'm penciling that out right now, and it appears ground mount is cheaper, and the savings could be applied to batteries or better equipment.

The traditional response to my statement would be that a generator is the way to go, and cheaper than batteries. In most cases that is probably accurate. But just wait until you are involved in one of these super storms that seems to happen way too often now, there is no gas, no stores open, no internet for 5-6 weeks, no repair parts on the shelf, and your generator has been sitting with gas that is now all gummed up and it won't start. Or, it is stolen by someone that can hear it from 4 blocks away. Our local Humane Society had their new generator stolen the first night, by some dirt bag who felt is was okay to leave a hundred animals with no cooling in the middle of August.
 

12VoltInstalls

Solar Addict
Here's the reason for my statement:

I remember that thread.

Oddly, with my recent upgrade purchases I’ll be installing next week (800W, 102+/- volts) I was seriously considering some LiFePo 12V that are parallel compatible (us$2000 for ~400Ah on those SOKs iirc?) which is about $1300 more than replacing all my (still good) walmartha lead acids that are at least three years of life to perhaps five years or more (I’ll have to wait to find out).

FWIW those walmartha batteries have been $67-$72 for years but are now ~$90 recently. So while the difference is closing, I’m not 100% sold on LiFePo yet; the product is still maturing in my opinion.
 

Hedges

I See Electromagnetic Fields!
There are many valid reasons to buy batteries, and they don't all have to be based on an economic payback analysis. For example, preparedness in storms or disasters, avoiding the deductible that is applied to your claim for loss of things such as food, not having your boiler freeze and break when it is minus 30f, etc.

I wanted to accomplish that without a huge outlay for batteries.
My usable battery capacity is approximately same as PV size (would charge at 1C if I let it), which happens to be just enough to make it through the night if I shut off a number of unnecessary loads. (Automatic switching or proper allocation to a critical loads panel would do that.)
I've programmed it to charge batteries at 0.2C, and all the rest of the PV capacity powers AC to the house during daylight hours (or is curtailed if not needed when operating off-grid.)
I was able to run A/C during power failures. If smoke or clouds reduced production by as much as 60%, maybe 80%, could still power refrigerators during the day and recharge batteries to power the at night.
It might not always meet the need. Because this is grid-backup, chances of being without power and without enough sun at the same time are reduced.
 
You mean 300W (over 8 to 12 hours daylight, 2400 to 3600 Wh), and 1kW (over 16 or 12 hours night, 16kWh or 12kWh)?

A zero-export grid-tie system size for 300W would be pretty small. A couple panels, and there are some cheap inverters. Hardly worth the trouble. A grid-tie inverter that us UL-1741 listed and does do backfeed of grid is something you might get away with and not have utility notice.

An average of 15 kWh/day drawn from grid
This correct, the current lighting consumption is between about 15.8 kWh and 18.4 kWh a day,
however I am also upgrading to LED to lower the consumption. To give you some perspective,
the billing rate is based by Tiers of 8 kWh a day, so the consuption is already about two Tiers,
and the rate for each Tier increases with usage, similarly any drop of consumption can be noticeable.

The lighting system is independent from the other utilities, in partcular from the service plugs.
(Well except one plug that was used to vacuum one of the hallways, and I had to fix this.)
So the Solar system can be easilly keept off grid and this simpler than to have to deal with any Grid-Tied meters and subscriptions.

Note: The Solar system can be used as an emergency backup, so I wonder how a GT is designed in case of an outage?
I imagine that Smart meters must be designed to avoid any Solar production getting sent back to the grid in this situation.

About $0.35/kWh for nighttime draw, $5/day $150/month $1800/year. OK, $200 actual.
The alternate rate schedule with low price at night may save you money, but lighting between 4:00 and 9:00 PM (peak time) and 3:00 to 4:00 & 9:00 to Midnight (one of the schedules) will cost more. GT PV would help in the afternoon until sun gets low, especially with panels aimed SW.
If there is any surplus available, well a GT could have some advantages, but surplus could be used locally, like heating hot water.
I might then consider adding some heat pumps, since the natural gas used for getting the hot water is also based on Tiers....

A 48V 14kWh DIY LiFePO4 battery might cost around $2000 or so. If it does last 10 years, 3500 cycles, then you have saved a significant amount compared to utility rates.
Life tests of commercial batteries had only 5% of them reach expected cycle life without failure. I'd say don't count on DIY LiFePO4 lasting more than 25% of anticipated life (so 2.5 years for $0.20/kWh) which may be slightly better than break even. It may still do 5 to 10 years, in which case you come out ahead. So long as failures are BMS and cells are undamaged, you can DIY repair and are more likely to get the payback.
I am currently evaluating various 48 V batteries, mostly based on 280 Ah (or 310 Ah), so using 3.2 V Cell, I should get
about 14.3 kWh (or 15.9 kWh), but I plan to discharge from 100% to 20%, about 225 Ah (or 248 Ah),
or from 3.65 V to (80 % of 3.65 V - 2.5 V cut off) = 2.73 V, to avoid too much degradation.
About ambient temperature, in San Francisco it is not be very common to reach 50 F or 10 C, especially inside a building.

Using a 80% discharge, there should be about 11.5 kWh (or 12.7 kWh) available. This might be a little bit short in winter,
since the night consumption would increase to reach a total of 18.4 kWh a day, but I cannot see too much any other battery
combination unless I have to double the capacity. However a larger battery capacity would allow getting
a depth of discharge (DoD) lesser than 0.6 C which could improve the lifespan of the battery cells.

Load is (1 kW / 48 V) = 21 A, so for a 280 Ah battery, the discharge rate of 0.07 C is well below the typical 1 C discharging.
About charging, since full capacity is (3.2 V x 16) = 51.20 Volts x 280 Ah = 14.336 Wh, and considering a 20 % of various conversion
and transport losses, a Solar production of 17.2 kWh would be required which is possible even in winter
when the expected production from the 18 PV system is still 19 kWh. But a full charge of 100% would be also much slower,
but sufficient to fully charge the battery, especially if the battery was only discharged to 20%.
 
Last edited:

Hedges

I See Electromagnetic Fields!
Note: The Solar system can be used as an emergency backup, so I wonder how a GT is designed in case of an outage?
I imagine that Smart meters must be designed to avoid any Solar production getting sent back to the grid in this situation.

GT inverter simply shuts off in case of outage. UL-1741 features makes absolutely certain it shuts off, regardless of what loads (neighbor's house, etc.) remain connected if grid disconnects.

Smart meters don't prevent backfeed, just tattle on you so utility becomes aware.

A few GT inverters have manually enabled off-grid backup feature (Sunny Boy "Secure Power", up to 2000W 120V direct from PV)
Some hybrid GT inverters offer zero-export with current transformers around utility feed, and offer battery and batteryless backup of downstream loads.

If there is any surplus available, well a GT could have some advantages, but surplus could be used locally, like heating hot water.
I might then consider adding some heat pumps, since the natural gas used for getting the hot water is also based on Tiers....

Using surplus from an off-grid system for heating can be done, but is difficult. Easiest would be to have a heater enabled when battery reaches 95% SoC, turned off when battery draws back down to 85% SoC. More difficult to make and control a variable load consuming exactly the instantaneous surplus.

With grid-tie it is easiest, you get credited for production an charged for power used to heat. If zero-export you might be able to enable heater to avoid any curtailing of PV production, or to heat 100% from surplus PV, but detecting those points is difficult. Ideal might be a resistive heating element driven by a light dimmer controlled by a circuit monitoring current transformer. Adjust operation of dimmer to keep power import from grid slightly positive, e.g. 0.5A flowing in so zero-export doesn't curtail production. But that is a circuit and control-system project.

The reduced power consumption of heat pump might beat savings from continuously variable control of resistance heating. Some heat pumps (some mini-split) have variable speed compressors so adjusting their thermostat setting could make them variable loads. Don't think heat pump water heaters are variable.

GT PV may be cheap enough ($0.05/kWh) to just over-panel a zero-export system and use resistance heating of water.
 
Using surplus from an off-grid system for heating can be done, but is difficult. Easiest would be to have a heater enabled when battery reaches 95% SoC, turned off when battery draws back down to 85% SoC. More difficult to make and control a variable load consuming exactly the instantaneous surplus.

With grid-tie it is easiest, you get credited for production an charged for power used to heat. If zero-export you might be able to enable heater to avoid any curtailing of PV production, or to heat 100% from surplus PV, but detecting those points is difficult. Ideal might be a resistive heating element driven by a light dimmer controlled by a circuit monitoring current transformer. Adjust operation of dimmer to keep power import from grid slightly positive, e.g. 0.5A flowing in so zero-export doesn't curtail production. But that is a circuit and control-system project.

The reduced power consumption of heat pump might beat savings from continuously variable control of resistance heating. Some heat pumps (some mini-split) have variable speed compressors so adjusting their thermostat setting could make them variable loads. Don't think heat pump water heaters are variable.

GT PV may be cheap enough ($0.05/kWh) to just over-panel a zero-export system and use resistance heating of water.
I already implemented a system using a voltage controller to have the load connected to the grid
when the battery is charging or when the battery voltage is too low.

When the battery is fully charged, I can then redirect the Solar production, as long there is enough sun,
to an additional electric water tank heater, located between the hot water return loop and the main gas heater.

Those water tanks typically have two 240 V 18 A 4500 W heating elements, so an extra 240 V inverter would then be needed, but I would
connect only one element considering the cost of the inverter. For more than six months, I will have a lot of surplus so this additional
installation could potentialy be a good way to convert any surplus of solar energy, even after considering any conversions losses (like 20%).
 
Last edited:

littleharbor2

New Member
I'm curious why you don't think you can tilt your panels. I live in Northern Baja and have my array mounted on a flat roof and tilted @31 degrees. We have strong winds on a regular basis (up to 70 mph) and have even had a degrading hurricane pass over. I have built a cedar dog eared fence type structure to break up any wind that may want to lift my array. It has remained rock solid throughout all wind events. I basically don't even think about it any more.
 

Attachments

  • DSCN4732 (1).JPG
    DSCN4732 (1).JPG
    966.8 KB · Views: 2
Top