Project: Auxiliary solar heating

I've mentioned this before, but here up north solar isn't exactly greatest energy source, no matter how much environmental nuts try to push it. Summers do offer lots of sun, but winters, when the power need is at its peak, the production is pretty much zero. Days are short and sun is very low at the horizon, at northernmost part of the country sun doesn't rise at all! Good luck with solar panels under these conditions.

I've also mentioned that I have this summer cottage with running water and grid power, and keeping it warn (due to water supply) is somewhat expensive. I'd love to reduce that expense a bit.

So I came up with auxiliary heating /power supply idea with some solar panels, say 6 or 7 250-watt panels, bringing DC voltage up to 220v or so (with variations up and down, depending on load and supply).

So the basic idea was controller box where can can measure incoming voltage and control loads - that is, resistive heaters and auxiliary DC/AC inverter that is not connected to main grid (used for other power needs, like fridge, in summers).

Say, four to six channels, each with varying sized heaters (for example 800w, 200w, 100w, 50w), that are toggled separately on depending on voltage and current supplied by panels, and with a user input power can be supplied to DC/AC inverter.

During the darkest part of the winter the production will be next to nothing, but by the time the days start to get longer (or shorter, during the fall) there still will be plenty of sun to supplement normal heating and hopefully cut down the cost of grid power.

Whether this will really ever be economical is separate issue. Panels aren't too expensive, less than 1000€ total (taxes included), and the controller box isn't too expensive either - PCB and parts will be make around 100€ total. Heaters will be another few hundred euros. Most expensive part is the DC/AC inverter to run equipment that expects normal 220v AC grid power, but that won't be used for heating anyway so it's kind of a extra. And since there will be no batteries and no grid-tie, there really aren't any other major costs.

This of course completely excludes all the labor needed to actually design and build the system, but then again, this is a hobby project (at least right now) so that doesn't really count. Being hobby project doesn't mean that I don't take this seriously though - there are large current at high voltages involved, so I am taking the safety of the design very seriously indeed.

Let's see what I can cook up here...