solar for part load bill reduction

[nota]

I am thinking of a cheap way to reduce the el bill by adding some solar panels
for a part load daytime only solar

but not going whole hog on total rate system esp the batterys
as that may not be affordable and el corpRATS doNOT pay much for the power you send back anyway to justify the costs

if I add 3300 watts of solar [10 panels] at about $165 each on c-list now locally
and plan a daytime only power production

how much of the 3300w is loss in the conversion in the ac/dc controller wires ect
or how much power out of 10 panels in ac 220v to the house load = bill reduction
and ballpark guess at extra costs wire connectors and ac/dc box to get 220v ac

idea is just to cut daytime power use by the air cond unit my biggest draw
maybe add battery system and more panels if future costs go down esp LI-po battery

[bleucamaro]

The solar install companies have calculators that will tell you how to size the system for your needs. They factor in your location, exposure to sun, inclination angle of the panels, panel performance, etc.

They take that data and build a cost model to compare against your current electrical bill.

I'd suggest calling a couple of them to bid it and get a better idea if it's a worthwhile endeavor.

keep in mind, the cost isn't just the panels, it's the inverter, the net-meter, the shut-off, the engineering for modifying your roof, & the permitting.

Also, that 3300w you're looking for is a peak number, similar to a peak horsepower. you will rarely, if ever see that much output.

[wilnj]

It seems like OP doesn’t care to sell it back so he wouldn’t need the net meter. He just wants his own source so he’s pulling less off the grid during peak daytime loads.

But I would be curious about what kind of safeties would be required to protect anyone upstream.

I assume that part of the installation includes isolation to prevent power from going back onto the grid if the grid is down for some reason.


Sent from my iPhone using Tapatalk

[LWJ]

Probably work fine. I'm in Oregon. We heat/cool half our home with electricity. We have dropped monthly costs significantly with 16 panels.

Not a lot of sun in the winter. Still works fine on a 365 basis.

[Zeke]

Originally Posted by bleucamaro

The solar install companies have calculators that will tell you how to size the system for your needs. They factor in your location, exposure to sun, inclination angle of the panels, panel performance, etc.

They take that data and build a cost model to compare against your current electrical bill.

I'd suggest calling a couple of them to bid it and get a better idea if it's a worthwhile endeavor.

keep in mind, the cost isn't just the panels, it's the inverter, the net-meter, the shut-off, the engineering for modifying your roof, & the permitting.

Also, that 3300w you're looking for is a peak number, similar to a peak horsepower. you will rarely, if ever see that much output.

Originally Posted by wilnj

It seems like OP doesn’t care to sell it back so he wouldn’t need the net meter. He just wants his own source so he’s pulling less off the grid during peak daytime loads.

But I would be curious about what kind of safeties would be required to protect anyone upstream.

I assume that part of the installation includes isolation to prevent power from going back onto the grid if the grid is down for some reason.

I like where this is going. The only thing I see as a precaution is what happens if there is more power produced than is being drawn (clear summer day and no one home) and the cut off protection. I assume there is an auto switch for that like when using a generator (there is).

The reason for 'selling' excess power back to the grid is so excess power has a place to go when not being used at the home. There needs to be a battery and some way to buffer the production of power when 'off grid'. There are hybrid solar power systems but what you propose ain't one of them. It's not going to be as simple as you think. Read this for some enlightenment.

Not my area of expertise but I'm real leery of the solar installation companies.

[red-beard]

Originally Posted by nota

I am thinking of a cheap way to reduce the el bill by adding some solar panels
for a part load daytime only solar

but not going whole hog on total rate system esp the batterys
as that may not be affordable and el corpRATS doNOT pay much for the power you send back anyway to justify the costs

if I add 3300 watts of solar [10 panels] at about $165 each on c-list now locally
and plan a daytime only power production

how much of the 3300w is loss in the conversion in the ac/dc controller wires ect
or how much power out of 10 panels in ac 220v to the house load = bill reduction
and ballpark guess at extra costs wire connectors and ac/dc box to get 220v ac

idea is just to cut daytime power use by the air cond unit my biggest draw
maybe add battery system and more panels if future costs go down esp LI-po battery

What is your zip-code? Will the panels face south? Of not, which direction? What will be the angle of the solar panels?

First thing to understand is all electricity is fungible.

Most people are not using a lot of power all the time. The Air conditioner will only be on 20-60% of the time. So during the time the AC is running, the you are reducing your actual power company demand. In between, unless you have lots of other continuous loads, you will be selling power.

How does your electric provider calculate "NET POWER"? Most have 2 meters. One that shows all power that comes in and the other all power going out to the utility. They CHARGE you for all power on one, and pay you the going rate for the power exported.

Battery system do allow you to "net meter" yourself. But you have to have the right kind of system. Adding batteries after installing is possible but more difficult and more costly.

Solar panels will produce in your area (South of Miami) about 5.4kWh/kW, or about 17.8kWh each day on average. More in the summer, less in the winter.

[ckelly78z]

The other part of this equation is the need to reduce your power usage during the day. Are there rooms that you could posibly not have to cool in the house ? Is someone home at all times that needs 70* air temps, or could you raise the temps during the night/mornings, and only cool while you are active in the house ? Is it more $$ efficient to upgrade your A/C unit, than it is to buy solar panels/install/other required infrastructure ?

[nota]

Originally Posted by red-beard

What is your zip-code? Will the panels face south? Of not, which direction? What will be the angle of the solar panels?

First thing to understand is all electricity is fungible.

Most people are not using a lot of power all the time. The Air conditioner will only be on 20-60% of the time. So during the time the AC is running, the you are reducing your actual power company demand. In between, unless you have lots of other continuous loads, you will be selling power.

How does your electric provider calculate "NET POWER"? Most have 2 meters. One that shows all power that comes in and the other all power going out to the utility. They CHARGE you for all power on one, and pay you the going rate for the power exported.

Battery system do allow you to "net meter" yourself. But you have to have the right kind of system. Adding batteries after installing is possible but more difficult and more costly.

Solar panels will produce in your area (South of Miami) about 5.4kWh/kW, or about 17.8kWh each day on average. More in the summer, less in the winter.

zip 33189
yes south by south east
just cut way back my royal poncie huge tree to clear the house/roof miss the shade
air cond runs all summer feb to nov this year/last
so only time low load is cold snap as we are both retired and home a lot
mini bill is about 140 in winter and 300+ in summer
would like to cut the bill 80-100 off summer peak maybe will be less in winter

in pre-plan stage trying to understand the other then solar panel costs
like an ac/dc unit and other switch gear wire connectors and what else I need
do NOT want at this time to get loans or big all power set up
just $1650 for 10 panels +x$ +y$ and +z$ for a guess at total cost ?
do it my self except for final hook up
and current in ac amps avg at 220v ? ie bill savings amount

[red-beard]

Originally Posted by Zeke

I like where this is going. The only thing I see as a precaution is what happens if there is more power produced than is being drawn (clear summer day and no one home) and the cut off protection. I assume there is an auto switch for that like when using a generator (there is).

The reason for 'selling' excess power back to the grid is so excess power has a place to go when not being used at the home. There needs to be a battery and some way to buffer the production of power when 'off grid'. There are hybrid solar power systems but what you propose ain't one of them. It's not going to be as simple as you think. Read this for some enlightenment.

Not my area of expertise but I'm real leery of the solar installation companies.

The standard "Grid-Tied" systems are setup to flow any excess out to the grid. They have no storage and most cannot modulate the power. And they also need a voltage/frequency signal from the utility to work. They are designed to shutdown if the power goes out.

Grid-Interactive systems have batteries. They also use charge controllers to collect the solar power and keep it DC. Depending on the manufacturer and the programming options, you can set up to sell excess, store excess, never sell. But these systems are more sophisticated and they include batteries.

Batteries have a finite life. After so many charge-discharge cycles, they stop working. And the number of cycles will depend on how deeply you discharge the batteries.

Li-Ion (NCA is most common) are terrible for storage. They are good for about 1000 cycles. I have special lead-acid types that allow 60-70% usable capacity and have 2600-3000 cycles. LiFePo4 are "the best", but they are expensive. They will last 7000-10000 cycles, which on a daily charge/discharge is 20 years.

I calculate the storage cost by taking the cost and dividing it by the (#expected discharge cycles * usable storage * the round trip efficiency).

If a 1.2kWh battery has a 1.0kW usable range and lasts 10000 cycles and has a 93% efficiency and costs $1K, then the battery charge/discharge cost is 10.8 cents/kWh.

If a 2.4kWh battery has a 1.44kW usable range and lasts 3000 cycles and has a 90% efficiency and costs $550K, then the battery charge/discharge cost is 14.1 cents/kWh.

And this is JUST for the battery storage. It does not price in the cost of the solar equipment. For most of us, that is more than we pay for electricity. So self storage, unless you are paying over 20 cents per kWh (California/Hawaii/Puerto Rico) it doesn't make sense.

What we sell is Hybrid Solar: Solar PV plus battery backup, backed up by a generator. It operates like a grid-tied system, except when the power is out. The batteries are kept full are are for short term power outages. During the day, the solar helps to supply power. At night, it is all battery. If you are short of power while the utility is out, the generator can supplement. It power the house and recharges batteries when the batteries reach a defined point. Once the batteries are recharged, the generator shuts off.

[1990C4S]

Originally Posted by red-beard

If a 2.4kWh battery has a 1.44kW usable range and lasts 3000 cycles and has a 90% efficiency and costs $550K, then the battery charge/discharge cost is 14.1 cents/kWh.

And this is JUST for the battery storage. It does not price in the cost of the solar equipment. For most of us, that is more than we pay for electricity. So self storage, unless you are paying over 20 cents per kWh (California/Hawaii/Puerto Rico) it doesn't make sense.

This seems like very sound advice. Cut your use by conservation, it's the best way in the long run.

[tadd]

I highly recommend looking at the micro inverter systems. That is where each panel has its own small inverter. Major advantages is that you are wiring for AC (DC is kept to the panel), and if you have shadows, it doesn't affect the whole system, just that single panel. Single panel replacement is easy as well as future upgrades since the panels don't need to be of the same spec. Lets you build out as you need to. Single inverters need to be scaled per the inverter requirements. Cannot add a panel at a time.

Big disadvantage is that the cost is higher as you are buying many small inverters vs one large one. Used to be a 20% premium, 6 years ago when I was looking, but I would bet the small inverters have dropped faster in price than the larger inverters.

[Zeke]

Numbers, numbers. I use over 3.5 kW/hr during the summer sometimes peaking a 5.0 and during the AC cycling, down to 1.0 to 1.5. Nothing happening .05. That's the draw that computers, TV's that are off, etc., take.

I don't see now nota can handle even half that fluctuation w/o spending some money he may never see a pay back from. I might, as you say RB, in SoCal but I'd get ripped off if I called out a solar company.

[Aerkuld]

You're probably going to see very little benefit from solar panels if your objective is just to take off some of your peak load. If you monitor your actual electricity usage through the day, you're probably going to find your normal usage is less that 1 kW at any given time. When your AC kicks in, or you're using a high drain appliance, that will jump up considerably. Almost certainly more than ten panels would generate.

You're probably better off seeing if your electricity supplier does net metering. I don't know what options they have, but here we have a very fair net metering agreement. If your supplier works like ours, all the time your panels are producing electricity in excess of your present consumption that is credited to your as a unit of electricity, not a dollar amount. When you use more electricity than your panels are producing the credit is used, then you start consuming electricity from the grid as normal. This is basically the power company working like a storage battery for you.


You are correct in saying that you really don't want to be producing so much electricity that you're selling it back to the power company. They pay you very little for any excess electricity you generate. However, size the system correctly and you should have a minimal bill.


Other things you'll need - an AC service disconnect, inverter, DC disconnect, mounts for the panels, and electrical metal conduit. Some systems run 'optimizers' on individual panels which allow each panel to work at it's full capability.

Another thing; When you look at inverters you generally try to size the inverter at, or slightly under the peak output of your panels, not greater than (unless you plan on expanding the system later). Reason being, the inverters work more efficiently the closer they run to capacity. Don't think that putting a 12kW inverter on a 3kW system is doing you any favors.


Red-beard knows what he's talking about when it comes to the technical bits . . .

[sammyg2]

LOL sometimes ya gotta spend a lot of money to save a little

[red-beard]

Here is my house yesterday. The graph is every 15 minutes. You really need to multiply by 4 to see my power usage (kW), since the numbers are energy (kWh) per 15 minutes. But it still gives you an idea of the consumption during the day.

You can see the short cycling of the AC once the temperature is reached.

At my house, we raise the temp at 6AM and then further raise it after 9AM. At 4PM we reduce the temp for return from work and then turn it cooler for overnight. By Midnight we start to see the short cycling.



Here is August 1st, 2018 to compare for a summer usage in a high temperature state.

[red-beard]

Originally Posted by nota

in pre-plan stage trying to understand the other then solar panel costs
like an ac/dc unit and other switch gear wire connectors and what else I need
do NOT want at this time to get loans or big all power set up
just $1650 for 10 panels +x$ +y$ and +z$ for a guess at total cost ?
do it my self except for final hook up
and current in ac amps avg at 220v ? ie bill savings amount

1. You need mounting hardware and to make sure roof will not leak
2. The easiest/cheapest method is a single string grid tied inverter
3. The current is fairly low on a single string (under 10 amps), but put in an external DC disconnect (30A with 15A fuses)
4. As long as you do not have a generator, the easiest connection is into a single 240V breaker in you panel.
5. You will need to contact the utility and tell them you are connecting
6. You will most likely need an inspection by the utility at the end.

[Baz]

What if you wanted to set up a solar panel system independent of your home - such as for a shop that doesn't have any electricity?

Would it generate enough power to run a small window unit or small mini-split system? Or fans...lights?

Sorry to take the thread off the main path a bit but I'm really uneducated about solar energy and have already learned a bit already from some of the posts.

I like the idea especially being in Florida, like Nota.

[red-beard]

That would be an off-grid system and would require batteries.

We build systems that run lights and small air conditioners. But...true off-grid requires a large battery bank.

[Baz]

Originally Posted by red-beard

That would be an off-grid system and would require batteries.

We build systems that run lights and small air conditioners. But...true off-grid requires a large battery bank.

OK thanks, James. Good info.