Getting to Net Zero Energy: Passive House vs Energy Star
There is a lot of talk about net zero energy (NZE) houses. Clearly that is the goal if we are to live sustainably. But it is a difficult goal to achieve, even with a Passive House. The reason is that even though we may cut our heating and cooling costs by 90% with a Passive House, we still use a significant amount of energy on hot water, lighting, appliances, electronics and other auxilliary loads. The two charts below sum up where the energy goes in a typical house and in a Passive House:
Notice the percentage of energy that now goes to making hot water in a Passive House. Suddenly, solar hot water makes a lot of sense. In this project we have made the house solar-hot-water-ready by providing a solar heat exchanger in the hot water storage tank and lines to the roof for later hook-up by the owners. We did not provide the solar panels because the owner can use federal, state and local incentives to get those panels at 30 cents on the dollar, where we would have to pay the full price.
Getting to NZE: Passive House vs Energy Star
As an exercise, I looked at what it would require for our house to reach NZE and generate with solar panels as much energy as it uses from the grid. For these purposes I considered site energy not source energy. I then did the same exercise looking at a hypothetical identical house built to the Energy Star standard. In both cases to keep the calculations simple, I assumed all the energy to be generated by photovoltaics, though in fact you would want to generate your hot water energy from solar thermal panels. Finally, I calculated the cost of the solar panels without assuming any government rebates or tax credits. The results are listed below.