Solar yield calculator

[fredrussell]

I googled this and unsurprisingly what came up where loads of ‘panels on house roof’ types of businesses. They all want your email, address and/or gullibility factor before they give you a figure.

Anyone found a yield calculator for smaller (boats and campers) installations. I realise there’s loads of variables but the three main ones I would expect to see are panel size, latitude and time of year. I would have thought angle of incidence, amount of cloud cover, time of day, etc would have to be ignored and all those values treated as optimal. That is to say, the calculation would be described as “with a panel perpendicular to sun, with sun at highest point of the day, and on a fully sunny day, a fully functional panel of this size will create this many watts/amps/whatever.

So. Anyone found such a calculator?

 

[fredrussell]

Hmm, that’s a no then!

I’ll do some more googling - can’t help thinking it should be do-able.

 

[Plum]

I googled this and unsurprisingly what came up where loads of ‘panels on house roof’ types of businesses. They all want your email, address and/or gullibility factor before they give you a figure.

Anyone found a yield calculator for smaller (boats and campers) installations. I realise there’s loads of variables but the three main ones I would expect to see are panel size, latitude and time of year. I would have thought angle of incidence, amount of cloud cover, time of day, etc would have to be ignored and all those values treated as optimal. That is to say, the calculation would be described as “with a panel perpendicular to sun, with sun at highest point of the day, and on a fully sunny day, a fully functional panel of this size will create this many watts/amps/whatever.

So. Anyone found such a calculator?

It is a while since I did a calculation for a boat but I used this one MPPT Calculator - Victron Energy
and recall I used a factor found on the internet to allow for a horizontal panel

 

[fredrussell]

Cheers. I was more looking for a rule of thumb re latitude and time of year effects on output of a panel. I’m surprised not to have found anything yet - I’ve really lost confidence in Altavista these days.

 

[andsarkit]

Too many variables but based on my south facing 12 year old panels on the house roof and scaling down to a 100w panel you couild expect the following as a maximum for south Devon:
Summer average 25Ah per day
Winter average 5Ah per day

Reduce for horizontal fitting, orientation to south and shading. More modern panels could also be more efficient so more output for the same sized panel and maybe better in overcast light but a 100w panel is still a 100w panel . A good MPPT controller will also give you a small gain in efficiency.

 

[AntarcticPilot]

There are certainly maps of expected solar output - these are for rooftop panels. They take into account latitude and climate variables such as expected cloud free days

 

[andsarkit]

There are certainly maps of expected solar output - these are for rooftop panels. They take into account latitude and climate variables such as expected cloud free days

The last map there seems to work for me. I get an annual 4000kWh from just under 4kW of panels. If you are calculating for a boat you need the take into account the 5 fold difference between summer and winter depending on what you want to supply and the time of year.

 

[Malish]

The last map there seems to work for me. I get an annual 4000kWh from just under 4kW of panels. If you are calculating for a boat you need the take into account the 5 fold difference between summer and winter depending on what you want to supply and the time of year.

and the cleanliness of the panels surface

 

[Mistroma]

I've used PVGIS for years to estimate solar for boat and house. Works very well. Just pick location by zooming in on map. Enter direction roof faces and angle. I'll dig out a link.

I just enter 0 degrees for boat use as panels mostly lie flat and azimuth is pretty irrelevant in that situation so anything will work. However, you can get much more in winter in a yard by angling the panels and adjusting orientation. PVGIS will tell you the optimum for that if you select "Optimize". I used to put results into Excel and scale for panels on the boat (i.e. Enter 1kW in PVGIS and scale in Excel). I found average daily kWh for each month to be most useful when cruising. I haven't used it for ages after modelling home and current cruising area.

JRC Photovoltaic Geographical Information System (PVGIS) - European Commission

 

[fredrussell]

Aha! That’s more like it Mistroma - I’ll have a go on it and see what’s what. Cheers!

 

[jdc]

I use this site at home to charge the battery 'wall' at the cheap night rate if the solar generation next day is going to be low, but on the boat I look at Windy: one of the layers is called Solar power and it displays W/m².

Both are based on the EU PVGIS models, but then apply weather forecast data (presumably a function of cloud density at various heights) to attempt a short term forecast rather than an 'average for the time of year'.