PVT and HVAC: Integrating PV with solar thermal
1) Any recommendations for a combined PV and solar thermal solution for a single family residence? (i.e. solar thermal panels that integrate with PV to cool the PV panels and collect thermal energy for water heating and home heating and cooling). We’re familiar with SunDrum, PVTSolar, and SolarWall (though they seem to focus on commercial installations). Anyone know of any others or have particular recommendations for these?
2) Assuming we had a large PVT array, how could we most efficiently use excess thermal energy beyond what’s needed for water heating for home heating and cooling? Our current plan is to use a mini-split air source heat pump and heat recovery ventilation system powered by a PV array on an unobstructed south-facing roof. We plan to use solar thermal for domestic hot water, and have a southeast facing roof available for that purpose, but would prefer an integrated solution. We also hope to find a way to make the ASHP system more efficient, or replace it with an alternative system that would work the same way (refrigerant pipes to quiet indoor units) at less cost and higher efficiency…
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Replies
Karen,
1. Here's another company that sells a system that combines PV and solar thermal:
Dawn Solar Systems, Inc.
183 Route 125, Unit A-7
Brentwood, NH 03833
800-803-1476
http://www.dawnsolar.com
2. I don't recommend such systems. They provide less hot water per square foot than a conventional solar thermal system, and the hot water reaches a lower temperature than a conventional solar thermal system. Moreover, maintenance and repairs are a nightmare. Trust me, if you have a plumbing leak, you don't want to have to hassle with your PV modules at the same time that you are hassling with your solar thermal tubing.
It's kind of like having a combination TV-VCR-DVD player. If one of the elements conks out, you have to send the whole unit in for repairs, or throw the whole piece of equipment in the trashcan.
2. It's unlikely that a system installed on a residential roof will be producing any extra usable solar-heated hot water. It's far more likely that, during certain seasons of the year, you won't have enough hot water. However, the traditional solution to "too much solar hot water" is a dump loop. Options include routing the water to a swimming pool, or routing the water to your garage slab.
I agree with Martin, none of the combined systems have good enough thermal performance to be worth the bother, or the high cost.
Dawn Solar is intriguing because it's a good looking BIPVT system (Building Integrated PVT). But it's an unglazed thermal panel that collects almost no energy on cold days. That's disappointing, because the original NREL study that proposed the design showed a lot of promise for warmer climates.
If the dump loop is put into the ground under or around a house, and wing insulation is put around the house, the extra heat can warm up the ground there. Seasonal heat storage works best with a large area building, such as a warehouse, but can be used with a residence. It won't bring the house up to comfortable temperatures unless the building is designed for it, but does cut the heat bill.