Bragging About My Solar Harvest

Re: Bragging About My Solar Harvest

Well, it was explained to you incorrectly.

A kilowatt is 1000 watts. A kilowatt HOUR the consumption (or production) of 1000 watts for one hour. So, while a 1000 watt generator might produce 1000 watts, if you plug in 10, 100 watt light bulbs that would be a 1 kw load, burn them for 1 hour and you will use 1 kilowatt hour.

So your 2000 watts of panel will never, under any circumstances produce 12 kw, but it might produce 12 kwh over a 6 hour period. The amount of power used or produced is only relevant with a time component, hence kilowatt HOUR.

I might add, as a moderator, that you should consider your tone a bit. People here are more than willing to share their knowledge with everyone, and most strive for accuracy. And by the way,, you don't "charge panels" you either feed loads (or grid) or you charge batteries.

You should also realize that PV panels will often produce more than rated output in cold conditions, and output is often further increased with reflection off of snow. Edge of cloud events can increase this even further.

As for the size and capacity of an off grid system, one ideally designs for average rather than best or worse case situations. The general rule of thumb that I use is the 50%X4 rule. That is take the name plate rating of the PV (in your case 2000) divide that in half to account for all cumulative system loses, then multiply that number by 4 to represent the average number of hours of good sun one might reasonably expect on a daily basis over the course of the year.

2000/2=1000X4=4 kwh/day.

On might on a perfect day double or triple that, but one certainly can't count on that as an average. Some local adjustment might be in order, but seldom more than ~ 6 hours over the course of the year. As an FYI, we live off grid with ~ 400 watts of PV. On average, we use ~600 watthours/day. On an ideal day we can generate as much as 1.5- 2 kwh. Over the course of the year, cold weather, cloudy days, it averages out to just about my 400/2=200X4=800 watthours/day.

Tony

Re: Bragging About My Solar Harvest

WE GET 350 Days of Sun a year!!! Two days of clouds just let's my system flex it's muscle and make the energy I normally don't need.

Like I said, adjustments for local variance is always in order. The fact that you get 350 days of good sun is certainly an adjustment factor to consider. As with all rules of thumb, that is what they are,, rules of thumb.

Quite frankly, on an annual basis your harvest may not be any better than an northern neighbour. Remember, in the far north, folks can get more than 18 hours of day light, and depending on local weather variance, can more than make up for 6 hours in the winter. Also, in the winter, shorter days tend to come with colder temps increasing PV output, as well as an increase due to reflection off of snow and ice. My average works out just about the same winter and summer, as some of my summer harvest gets lost due to some shading issues, while my winter harvest is better due to the above factors.

I am happy for your harvest.

Icarus

PS

You can't charge your panels without a generator..

From you post #3,, just a bit nit-picky tonight.

Re: Bragging About My Solar Harvest

I have yet to read any article that really tells what panel output can be expected anyway.

The test conditions are using 1000 watts/m2 - which virtually never happens at

The second set of conditions shown on a panel rating are using 800 watts/m2

In the winter few locations (except sunny Arizona and southern CA) see the 800 figure.

Here we are only now getting close. Two days with a 5 minute reading over 800 watts/m2 last month and a month average of 2.97 kW/m2/day. It seems like about 85% of the daily kW received are in the window where the panels can utilize them).

At my location - NASA shows an annual average insolation of 5,07 watts/m2.

In June, which seems to be our best month, the average daily insolation (last year) was 8.38 kW/m2/day. I record the hourly average insolation (DNR), daily total insolation and UV readings plus high momentary insolation for the day.

If a panel is 10% efficient (and that has to be 10% of available sun otherwise it makes no sense) and you have a 100 watt panel -

On a day with an insolation total of 2.97 kW/m2/day and considering 85% of that usable there would be 2.52 kW/m2/day of useful available sun. 10% of would be 252 watts.

Whether the panel is 100 watts or 300 watts you can't get more than that from the math. The 100 or 300 watts would be a maximum only I guess.

This does not seem to tally well with what people report and too many people tell a similar story so it is not possible to doubt them.

Trying to figure out the 'rest of the story'.

Russ

Re: Bragging About My Solar Harvest

And it is good when you can load shift during peak hours like you did. It saves 10-20% loss while charging the batteries. But it is a loss that does exist and needs to be included like they do here.

Re: Bragging About My Solar Harvest

Derik:
My bad for giving you a technical nerd response.
I applaud you for your power production. Isn't it great!
We need to celebrate this stuff more. Throw a party - have a cold one on me!

Re: Bragging About My Solar Harvest

From my Davis weather station which seems to come close to the NASA 10 year averages - we saw 1000 watts/m2 for one hour average last May.

The daily average for the month was 6.370 kW/m2/day.

Today it was 2.824 kW/m2 for the day. The high reading for an hour was 544 watts/m2.

The panel output would have to be different.

Understand the temp affect no problem - straight math and simple at that.

Re: Bragging About My Solar Harvest

Congrats on your system performance Derik! We often get some really good production on sunny winter days too; Sun+ Snow+ Cold= lots of PV generation. I also wanted to reiterate that there are indeed some very knowledgeable and very helpful folks here, some here are even BOTH at the same time :-) While it's easy to find flaws in any rule of thumb, bear in mind that most of the suggestions you'll find here are based on pretty well informed people. There's no way that you or anyone else should ever trust 100% what you read on the net, but all in all I've found that I always leave here having learned something new and/or having some new ideas on how to optimize life off the grid. In short, stick around, take what you see with a grain of salt, but don't discount the ideas and suggestions put forth ... I can guarantee you'll end up far more informed and equipped to deal with any issues if/when they do pop up in your system.
Cheers.