3 ms·

Presumably that’s a 9kWp system, with peak potential on a good day to generate 9kW at the optimal time of the day Is there any way to work out how many kWh suc

Presumably that’s a 9kWp system, with peak potential on a good day to generate 9kW at the optimal time of the day Is there any way to work out how many kWh such a system would tend to generate for a given latitude throughout the year? If I wanted to charge a 10kWh battery once a day for 12 months what kWp system would I need. What would it produce in June vs December etc.

devonkim 4y ago
There’s websites to calculate it based upon satellite photos of your roof alone (what the installer and system designers did for me along with permitting that would have taken me far too much time / effort). Your panel type, inverter, etc. all matter as well. A meter to determine your electricity usage throughout the year is good to have as well although I didn’t do that before I installed my system and expected to try to size a battery backup system only once I had sufficient data. But basically so far my house is pretty much a dud in terms of ROI for any more modernization efforts without tearing it down basically and this is what I’ve been thinking about a lot more than the usual trend of renewables and such. Old homes in the US are really, really, really hard to retrofit remotely economically and are burdens upon the energy grid and infrastructure throughout the lifetime of the structures. The costs fall disproportionately upon our population that can least afford it as well and subsidies are laughably minuscule and mostly taken by more affluent homeowners in practice.
mindslight 4y ago
https://pvwatts.nrel.gov/ https://pvwatts.nrel.gov/ The main issues are cloudy days, and angle of the sun. Do you still want to fully charge that battery on cloudy days? If not, then you need to size the battery based on how many cloudy days in a row you can tolerate before needing to cut back on energy use. The angle of the sun affects the number of hours of sunlight in the day, as well as the angle of incidence to the panel (and you can adjust the panel angle). The default is to angle your panels equal to your latitude. If you angle them more horizontal, you will have more summer generation. If you angle them more vertical, you will have more winter generation. Which is your design constraint - heating or air conditioning loads? You can also use adjustable mounts that can be changed over the year. When I ran this for myself, adjusting the panels a few times a year would only net me a negligible amount of additional generation. There's so much we take for granted with the grid abstraction. Net metering was a huge subsidy to drive adoption of solar, but ultimately if you want a truly independent setup you need to think like an off gridder. The hard truth is that you're probably better off designing for the 95% or whatever common case, and falling back to a gas generator for the few times conditions are worse.
moepstar 4y ago
PVGis does that: https://joint-research-centre.ec.europa.eu/pvgis-photovoltaic-geographical-information-system_en https://joint-research-centre.ec.europa.eu/pvgis-photovoltai... https://re.jrc.ec.europa.eu/pvg_tools/en/ https://re.jrc.ec.europa.eu/pvg_tools/en/

devonkim 4y ago

There’s websites to calculate it based upon satellite photos of your roof alone (what the installer and system designers did for me along with permitting that would have taken me far too much time / effort). Your panel type, inverter, etc. all matter as well. A meter to determine your electricity usage throughout the year is good to have as well although I didn’t do that before I installed my system and expected to try to size a battery backup system only once I had sufficient data. But basically so far my house is pretty much a dud in terms of ROI for any more modernization efforts without tearing it down basically and this is what I’ve been thinking about a lot more than the usual trend of renewables and such. Old homes in the US are really, really, really hard to retrofit remotely economically and are burdens upon the energy grid and infrastructure throughout the lifetime of the structures. The costs fall disproportionately upon our population that can least afford it as well and subsidies are laughably minuscule and mostly taken by more affluent homeowners in practice.

mindslight 4y ago

https://pvwatts.nrel.gov/ https://pvwatts.nrel.gov/ The main issues are cloudy days, and angle of the sun. Do you still want to fully charge that battery on cloudy days? If not, then you need to size the battery based on how many cloudy days in a row you can tolerate before needing to cut back on energy use. The angle of the sun affects the number of hours of sunlight in the day, as well as the angle of incidence to the panel (and you can adjust the panel angle). The default is to angle your panels equal to your latitude. If you angle them more horizontal, you will have more summer generation. If you angle them more vertical, you will have more winter generation. Which is your design constraint - heating or air conditioning loads? You can also use adjustable mounts that can be changed over the year. When I ran this for myself, adjusting the panels a few times a year would only net me a negligible amount of additional generation. There's so much we take for granted with the grid abstraction. Net metering was a huge subsidy to drive adoption of solar, but ultimately if you want a truly independent setup you need to think like an off gridder. The hard truth is that you're probably better off designing for the 95% or whatever common case, and falling back to a gas generator for the few times conditions are worse.

moepstar 4y ago

PVGis does that: https://joint-research-centre.ec.europa.eu/pvgis-photovoltaic-geographical-information-system_en https://joint-research-centre.ec.europa.eu/pvgis-photovoltai... https://re.jrc.ec.europa.eu/pvg_tools/en/ https://re.jrc.ec.europa.eu/pvg_tools/en/