Small Off Grid Job

[Chris Crawford]

We have been electrical contractors for a long time in Hawaii and are just getting into solar voltaic (this is our first job). I have a customer with a 1 bedroom house, all gas appliances, that wants solar voltaic + a 600W windmill to power lights and plugs via a battery bank and invertor off the grid. He already bought a SunForce 600W wind turbine and built his own little shed for the batteries that is about 4' x 8' with an 8' x 12' roof, located about 140' from the house. He wants us to put solar panels on the roof of the shed and install a battery bank and invertor to supply power for his house. I am thinking we could at best get 4 panels on the roof of the shed to produce about 1200 watts + the 600 from the windmill would be 1800W. Is that enough for his situation (it is a windy area with lots of direct sun) and what brand of equipment would you recommend (panels, invertor, and batteries)? Your input would be appreciated. Thanks

 

[jaggedben]

It's impossible to say whether this is feasible without knowing both the client's maximum electrical load and his overall electrical energy consumption. Also, while the solar resource can be estimated with databases and shading factors, wind resource varies on a very, very local scale and would probably require installing measurement instrumentation for at least a year to accurately forecast. The customer also ought to provide some answers to questions like: "How important is it that there be power most or all of the time?" "How much personal investment is he willing to put into battery maintenance?" And so on...

I would start with reading some entry level guides on off-grid systems. There's also the Wind-Sun forum, where you'll probably get a lot more feedback on offgrid systems.

 

[ggunn]

We have been electrical contractors for a long time in Hawaii and are just getting into solar voltaic (this is our first job). I have a customer with a 1 bedroom house, all gas appliances, that wants solar voltaic + a 600W windmill to power lights and plugs via a battery bank and invertor off the grid. He already bought a SunForce 600W wind turbine and built his own little shed for the batteries that is about 4' x 8' with an 8' x 12' roof, located about 140' from the house. He wants us to put solar panels on the roof of the shed and install a battery bank and invertor to supply power for his house. I am thinking we could at best get 4 panels on the roof of the shed to produce about 1200 watts + the 600 from the windmill would be 1800W. Is that enough for his situation (it is a windy area with lots of direct sun) and what brand of equipment would you recommend (panels, invertor, and batteries)? Your input would be appreciated. Thanks

What Ben said. Anyone who buys renewable energy gear first and then asks if it is enough to power his off grid house is working the problem backwards. It is imperative that you start with detailed energy consumption numbers and work out how much battery capacity it will take to serve the need, taking into account maximum discharge of the batteries so that they will last an acceptable amount of time (number of discharges) and the acceptable time of autonomy where no energy will be available from sun or wind. Then you determine how much solar and/or wind energy capture will be needed to keep the batteries charged. After that you do your research on what hardware you need to acquire to accomplish that capture.

And a note on wind... Wind resources, as Ben pointed out, are very hard to predict for a given area. The usual advice is to conduct a wind study with an anemometer and data recording gear for at least a year before plunking down any cash on a wind turbine. Also, with small wind particularly, one must be very careful when buying hardware; there is a lot of gear for sale out there which will not deliver the goods. Unscrupulous manufacturers take advantage of the unpredictability of wind resources to just throw junk out there for sale that wouldn't work even in ideal conditions. Caveat emptor.