Solar wasted watts/volts

[starcraft69]

I am curious what happens to the watts /volts when your system is fully charged and you have no demand? Were does the extra power go?

[Almot]

Hopefully good things won't get wasted.

I didn't notice any mention of controller, only that it will be MPPT. There is no such thing as "too much solar", your main concern should be the controller size.

Solar planning steps: 1. estimate or measure your daily consumption -> 2. estimate how much panel wattage you need -> 3. choose controller size suitable for a given array.

On the step 2 you might want to add 30-50% if possible. 24V panels are same size 65" by 40", be it 200W or 260W. Panels are cheap, and the price difference btw 30A and 40A MPPT like Tracer EP is insignificant.

[starcraft69]

Thanks all for the good advice.

[ktmrfs]

starcraft69 wrote:
I am curious what happens to the watts /volts when your system is fully charged and you have no demand? Were does the extra power go?

there is no "extra" power. the panel supplies the power needed up to it's output limit. No different than a battery when you don't draw power it doesn't supply any power.

[Almot]

There are calculators to estimate the output of 400W panel. Here is one that I used when planning my system https://pvwatts.nrel.gov/ but right now it doesn't seem to work, can't enter any city.
These calculators are based on historical data on solar radiation and weather for the last few decades, so they are as accurate as can be. Minor drawback is that they are meant for solar homes and provide data in KWH/month. Easy enough to multiply by 1,000 and divide by 12.7 and by 30.5, to get a daily AH data.

So, - run the numbers. If it comes short of needed 127 AH (and if this is really your average draw), getting more battery capacity will help to make it through some bad weather spell.

There might be 9 hours of daylight, but there are also mountains, trees, clouds, rain and low sun early and late in the day. Leave yourself a safety margin. I often hear a suggestion to add 50% to estimated solar harvest that you think you need, - and agree with this.

[Almot]

MW = MicroWave, in offgrid-related talks. At least, in this corner of the wide wobbly web. Frequent readers usually know.

[mike-s]

Almot wrote:
Another option would be to limit your MW use when on solar.

Avoiding megawatt usage with TT solar is always advisable.

[Boon_Docker]

starcraft69 wrote:

BFL13 wrote:

starcraft69 wrote:
Ok forget the hot water part If i put a over size system in how does the system dissipate the extra power being generated?

It is not being generated. Like you only get water if you turn on the tap.

Aside, there is a discussion of "over-panelling" for your controller's rating (with MPPT only--don't do it with PWM) on ISTR Morningstar's website. In the shoulder hours you get more amps with the extra panelling and those amps are still less than controller rating. Your controller cuts off the amps at its limit so you lose some mid-day AH, but you gain over the whole day averaged out for your AH haul.

So some over-panelling with MPPT is good, but within reason of course.

Next you will ask what happens with the extra amps the controller cuts off at its limit and can't use? 🙂

Thank you for the strait forward answer? Yes i do plan on a MPPT controller and was looking at a bit oversize in panels.

Using Go power calculator we use about 126.7 Amphrs a day in winter running furnace. summer much less. I currently have 2 6v GC batteries = 220 Amphrs. I plan on putting 300-400 watts 24v+ panels of solar and add 2 mor 6v batts

I don't think you would have a problem on a sunny day harvesting 127 AH with 400 watts @ 24v and an MPPT controller in the winter.
You will get 8-9 hours of sun daily which would work out to only about 16 amps that the panels/controller would need to generate.

[BFL13]

OP says:
"Using Go power calculator we use about 126.7 Amphrs a day in winter running furnace. summer much less. I currently have 2 6v GC batteries = 220 Amphrs. I plan on putting 300-400 watts 24v+ panels of solar and add 2 mor 6v batts "

That computes. At 35F out, we used about 110 AH in the 5er for furnace alone, and our usual 70AH on top of that. 180AH per day off grid and no solar in the winter cloudy sky and short daylight times--more lights on for longer too.

I found it worked better in those conditions to have 6 batteries instead of the usual four. However in CA, you might get solar in the winter when it is cold, where we did not, so maybe 4 batts would do, and the solar would do something for you.

Even so, IMO, consider going to 6 batts even with the additional solar as planned. the solar will still be useful in the summer with less furnace time, and you can leave the extra two batts at home on a maintenance charger till the following winter.

It seems you don't use much inverter power, which we do, so that might make the diff too. But then you might "discover" that a 2000w inverter can run the microwave, and then you are on the slippery slope! 🙂 BTDT, would not go back to without either!

[jharrell]

The power from the sun hits the panels either way, if there is a load on the panels some of that power is converted into electricity, about 20% if your lucky with modern panels, the rest heats up the panels or is reflected back just like your roof. If there is no load all of the suns power turns into heat or is reflected and your panel is just a very expensive piece of roofing.

Just imagine if we had 80 or 90% efficient panels not only would we be getting amazing power they would act like amazing insulation too keeping your roof cool.

[Almot]

starcraft69 wrote:
Yes i do plan on a MPPT controller and was looking at a bit oversize in panels.

Using Go power calculator we use about 126.7 Amphrs a day in winter running furnace. summer much less. I currently have 2 6v GC batteries = 220 Amphrs. I plan on putting 300-400 watts 24v+ panels of solar and add 2 mor 6v batts

400W flat install won't get you 127 AH in winter.

To reduce the AH draw, get a catalytic heater - just don't tell anybody on this forum 😉 ... Another option would be to limit your MW use when on solar.

I would also suggest buying some $15 AH-meter on Ebay and measure your actual use, rather than rely on calculators.

There is Bogart PWM 30A controller that allows over-paneling up to - don't remember, 600W maybe. Normally with 30A PWM you would want to limit panels wattage to ~400W, and with 30A MPPT to ~500W.
One little problem with Bogart - you have to buy their battery monitor as well, or this controller won't work as it should.

[red31]

starcraft69 wrote:
I am curious what happens to the watts /volts when your system is fully charged and you have no demand? Were does the extra power go?

The controller disconnects from the panels therefore the panels do not make power when disconnected. During the connected times they make full power of the conditions at the time.

https://www.youtube.com/watch?v=QqxI-l5a6d4

[Lwiddis]

BLF shaves in the morning? Never noticed.

[mike-s]

jolooote wrote:
SOooo...if I run my generator but use no electric...than according to you...the generator uses no GAS??? lol.

It uses no gas to generate electricity. It does use gas to run the engine and spin things. Use electricity from it, and it will use even more gas.

[2oldman]

jolooote wrote:
SOooo...if I run my generator but use no electric...than (sic) according to you...the generator uses no GAS???

That's a very strange and illogical conclusion. A generator needs gas (energy) to move mechanical parts regardless of the electrical load.

[Chum_lee]

jolooote wrote:
SOooo...if I run my generator but use no electric...than according to you...the generator uses no GAS??? lol. Have you ever wondered why, as our electric usage in our homes and businesses gets more efficient using less Watts, our electric bill gets more expensive? The power generator (Power Company) must generate the POWER regardless of whether or not its used. As for u'r local Power Co. they have the same cost of production but less income as less power being not used is also Not paid for. As for we campers, we are the producers and always must pay for it. lol

IMO, the above post is nothing more than silly nonsense. The generator for your RV is governed. Read the fuel consumption specs. So are the power companies generating plants whether they are powered by coal, oil, gas, water, nuclear, wind, or, whatever. If you live on planet earth, chances are your power company charges you by the kilowatt-hour. Whatever rate in $$/kwh they charge you may vary by usage, it might not. That depends your your specific circumstance.

It's true that the poco's generating plants take a while to throttle up and/or down, but, they can change their generating capacity should they choose to do so. Usually power companies have multiple generators at each facility which may or may not be online at any given time. Often they run at maximum capacity because it's more efficient and they sell excess power generated through the grid to other areas. It's true that the poco's "FIXED COSTS" generally don't change once the generating plant is built, but, their "FUEL COSTS" certainly do if they choose to operate at less than capacity. Many poco's have whats called "Peaker Plants" which are small versatile generating stations to handle times of peak high demand so they don't have to buy overpriced power off the grid from gouger companies like Enron. (now deceased)

Chum lee